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This PDF file contains the front matter associated with SPIE Proceedings Volume 10964, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.
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The 10th International Conference on Information Optics and Photonics
We demonstrated the arbitrary pulse shaping for a high power, joules class, and multi-pass ring Nd: glass laser amplifier system with nanosecond pulses based on the direct calculation method. While the square pulse with pulse energy 0.9mj and FWHM (full width at half maximum) pulse width 6ns, a 0.9J at 1Hz high power laser pulse energy is generated, which has the ability to change the waveform arbitrarily based on the full fiber front end. The laser amplifier system consists of three parts: full fiber seeder, diode pumped Nd: glass regenerative amplifier, and multi-pass ring amplifier. With the help of direct calculation method based on the input-output model, the input pulse shape has been calculated and the output pulse shape has been compared to the target pulse shape, showing that the simulation and experiment is consistent. Some other interesting pulse shapes have been produced with pre-compensated inject pulse based on the calculation which shows great potential to be applied in high power laser amplifier system with a desired pulse shape.
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Optical fibers have long been the backbone of modern communication system. One way of extending the capability of optical fibers is to thin down the core sizes as microfiber which facilitates light-matter interaction through evanescent light. Among different microfiber based structure, the microfiber knot resonator (MKR) is a resonant structure which finds applications in lasing, filtering and optical switching [1-2]. Particularly, when the MKR structure is combined with functional two-dimensional materials, a large panel of devices can be achieved via the investigation of variations in resonance properties.
Here, a layered metal dichalcogenide semiconductor tin disulfide (SnS2), characterized with high intrinsic electron mobility and strong absorption in the visible light regime [3], is chosen to be coated onto MKR. The all-optical control of light functionality is demonstrated in MKR with SnS2 structure where the signal light power is controlled by the external violet pump power via the absorption property of SnS2. The device fabrication, characterization and obtained experimental results will be presented in the talk.
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In recent years, microscopic imaging technology is playing an increasingly important role in neurobiology, cell biology and microbiology. On the basis of high spatial resolution, if the field of view (FOV) is greatly improved and the time bandwidth is saved, microscopic imaging will play an important role in the research of the mechanism of neural circuit connection, increase imaging flux and provide the possibility for the digital storage of generous samples. Scanning imaging is now one of the major ways to increase FOV. However, the time bandwidth of traditional "walk-stop-shot" scanning mode is limited to the time-consuming signal transmission among the host computer, the host computer and the camera. This paper presents a microscopic imaging system for slice scanning by a distinctive "continuous scanning imaging mode", the camera exposures under continuous scanning motion. Based on FPGA, the location is obtained from the real-time decoding of the gratings signal, and the TTL signal controlling the camera is generated by the position comparator. And, 1) a pre-calibration strategy is adopted to ensure each sub FOV is within the depth of field, 2) a PID control algorithm based on piecewise interpolation is proposed to optimize the motion performance of the sample platform, 3) a fast iterative image restoration algorithm based on maximum a posteriori estimation is established to remove motion blur from a single image under high speed scanning motion. Finally, a 20mm x 15mm FOV (21722 x 17474 pixels) is scanned under the 20 times high NA objective lens less than 60s.
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Glucose detection by means of the photoacoustic spectroscopy was performed in this paper. A set of photoacoustic detection system of glucose based on pulsed laser induced ultrasonic detection was established. Based on the photoacoustic system, a series of photoacoustic detection experiments for glucoses with different concentrations were performed. The time-resolved photoacoustic signals and photoacoustic peak-to-peak values of glucose under the excitation wavelengths of pulsed laser from 1300nm-2300nm were obtained. In order to get the optimal absorption wavelengths of glucose, the difference spectrum of photoacoustic peak-to-peak values between the glucoses and the pure water were used. At the same time, the interval partial least square algorithm was used to get the optimal absorption wavelength regions. The integrated wavelength region was divided into 10-15 sub-regions. For each sub-region, the model of partial least square was established, and the cross-validation method was also used. Results show that the wavelength regions of 1350-1440nm and 1490-1550nm are the optimal characteristic wavelength region. The prediction models were established in the optimal wavelength regions, four components of the partial least square algorithm were used. In the chosen optimal wavelengths, the correction coefficient between the glucose predicted concentration and original concentration can reach 0.9879 and 0.9969, respectively, the root mean square error of cross validations (RMSECV) are about 12.5mg/dl and 6.2mg/dl, respectively, the concentration bias is about 0.0581mg/dl, and 2.09mg/dl, respectively.
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Reliability and characterization of 850 nm 50 Gbit/s PAM-4 vertical-cavity surface-emitting lasers (VCSELs) are presented. These VCSELs have demonstrated a threshold current of 0.8 mA and a slope efficiency of 0.95 W/A. The maximum optical output power of 9 mW is achieved at a thermal rollover current of 13.5 mA. The optical power is up to 5 mW and the -3dB bandwidth is in excess of 17 GHz at 25°C and 6 mA bias. The current density and power dissipation density are low to 15 kA/cm2 and 25.5 kJ/cm2 , respectively. The standard deviations of photoluminescence peak wavelength and Fabry-Perot cavity wavelength of epitaxial wafer are 0.75 nm and 2.2 nm, respectively. After 1500 h of the reliability study no degradation or failures of the 22 VCSELs are observed at 80°C in a heating chamber at a bias of 6 mA. Considering high optical absorption of DX center, the impurity doping concentration of 3 pairs of N-DBRs that were adjacent to active region are optimized. The additional SiO2 passivation layer not only can provide moisture resistance but also provide a photon lifetime tuning. The output power increases by optimizing thickness of SiO2 layer reducing power dissipation density. Single thin oxide aperture is employed by slowing down the oxidizing rate and improving temperature during a VCSEL oxidation process to thereby reduce stress concentration of an oxidation. Single thin oxide aperture may limit the -3dB bandwidth, but the modulation characteristics can be improved by adopting advanced modulation techniques such as 4-level pulse amplitude modulation (PAM-4).
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CO2 lasers often produce PMMA microchannels, as non-metallic materials have a strong absorption capability for mid and far infrared. Triangular cross-section microchannels have been fabricated by conventional methods, due to the Gaussian distribution of laser intensity. It cannot meet the requirements of microfluidic chips sometimes. In this paper, a multi-pass translational method is proposed, which based on the lateral heat-affected zone (HAZ) formed by single ablation, and multiple ablation with its width. This way not only produces a clean bottom like the static multi-pass method, but can modify the cross-sectional topography to produce a clean trapezoidal microchannel. Next, we evaluated the topography of microchannel by introducing the parameter "S", analyzing the variations in surface roughness and HAZ. All these indicate that the multi-pass translational method is a rapid and economic way of fabricating high quality trapezoidal microchannel on PMMA-based microfluidic devices.
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The influence of the alignment error in laser communication is analyzed. The link energy model with the position deviation at the image surface is established, and on the basis of this model, the spot deviation and the receiving optical axis deviation caused by the angular deviation of the optical axis are discussed and analyzed. Under the conditions of initial transceiver parameters, the link energy and the allowable maximum angle deviation with the distance of 0~2km are further calculated. The model formula of alignment error can be applied to analysis and discussion under the father distance. It has a theoretical guiding significance for the field laser communication test.
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The upconversion of an orbital angular momentum (OAM) carried light in communication band is preferable for building OAM-based upconversion optical communication networks. Here we experimentally study the behavior of OAM of communication band light in sum frequency generation process. The wavelength of the pump beam with sub-nanosecond pumping fields is 1064 nm and the communication band light is 1560 nm. Both beams are imprinted with OAM using vortex phase plates.The topological charges of the upconversion pulses at 632.5 nm are observed by a self-referenced interferometric technique. The OAM conserves in coupled nonlinear optical conversions is confirmed by counting the fringes in the interference intensity profile.The sum frequency generation is performed by using a periodically poled MgO-doped lithium niobate (PPLN) crystal under quasi-phase-matching conditions. We also gave analytical expressions for the upconversion of two OAM-carrying beams. The experimental results are well matched with the theoretical simulations.
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In this papers, the influence of the line-width of probe light on the phase noise of phase extracted based phase-sensitive optical time domain reflectometry (Φ-OTDR) is theoretical analyzed and experimentally investigated. Analysis indicates that broad line-width probe light suffers time varying wavelength drift and high level of laser phase noise, and thus guarantees high level phase noise of the Φ-OTDR. In distributed acoustic sensing along 500 m sensing fiber, the phase noise is evaluated for probe lights of different line-widths, and experimental results display that the phase noise increases as the line-width of probe light broadens.
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Light wave becomes extremely distorted when it passes through a turbid medium. Indeed, the inhomogeneity of scattering medium and the mode dispersion of multimode optical fiber (MMF) always distort the propagation of light waves since they divert the propagation direction and disorder the spatial relationship of rays from the object. This becomes a big challenge for the applications of biological tissues endoscopic imaging. To overcome this problem, many methods based on computational optical imaging schemes have been reported and such a research has become a hot topic in recent years. These methods include the computational ghost imaging, the digital phase conjugation, the speckle correlation, the wavefront shaping, and the optical transmission matrix, etc. In this paper, we report our recent works on computational optical imaging based on digital wavefront modulation, which might be useful for the applications of endoscopy. On one hand, we propose a round-trip imaging method based on the optical transmission matrix of scattering medium, where the light wave is distorted twice. The object is recovered directly from the distorted output wave, while no scanning is required during the imaging process; one the other hand, by modulating the amplitude instead of the phase of the incident light wavefront, we propose a high-speed binary amplitude-only modulation method to focus and scan light through an MMF based on the digital micro-mirror device (DMD). This method can also be extended to focus and scan light at multiple planes along the axial direction by just modifying the input wavefront accordingly.
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Utilizing the mechanism of cavity secondary resonance, we proposed a tunable hybrid optical filter combined band-pass spectral and low-pass noise filtering for femtosecond lasers. The experimental results shown that, by stabilizing the cavity length to different transmission peaks, the 3 dB bandwidths of the spectral filter can be tuned from 1.78 nm to 2.8 nm and the tunable cut-off frequency of the low-pass noise filter can be identified by their different attenuations which vary from 9.5 dB to 15.2 dB, of the relaxation oscillation in the laser relative intensity noise (RIN).
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Strong electromagnetic pulse (EMP) may lead to serious damage once it is coupled into the interior of the electronic system. As a kind of special electromagnetic medium, plasma has the ability of shielding strong EMP. Therefore, EMP protection technology based on the plasma is of pratical significance. The experimental setup of the interaction between the nuclear electromagnetic pulse (NEMP) and the plasma based on a one-layer cylindrical plasma array is built. Combined with the density distribution characteristics, the protection performance of the plasma array against the NEMP is studied. The results indicate that the protection performance of the plasma array against the TE polarization NEMP is better than that against the TM one. For both TE and TM polarization NEMP, the one-layer cylindrical plasma array can reduce the transmission pulse energy greatly and the energy attenuation is up to 10dB when the electron density is 8.5×1016 m-3.
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For the current photoelectric mixing technology, there are many problems such as small array size, high noise level and poor receiving stability. Combined with the idea of microwave photonic down-conversion technology, this paper proposes a new photoelectric mixing technology based on electro-optical modulation. Using high-resolution, low-cost, mature 2D sensors and electro-optical modulators to perform mixed-frequency demodulation at the optical level, not only overcomes the limitations of array size on image resolution, but also has the advantages of high energy utilization and high signal-to-noise ratio. A mathematics model was set up with the mixing efficiency and mixing signal-to-noise ratio as the key performance parameters. The influence of the operating point offset, modulation depth, and incident optical power on the performance parameters was analyzed. The results show that taking into account the mixing efficiency, IF signal amplitude and mixing signal-to-noise ratio, the electro-optic modulator works best when the modulation depth is at the maximum at the standard operating point, which are laying a theoretical foundation for the further research.
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Hyperspectral imaging typically produces huge data volume that demands enormous computational resources in terms of storage, computation and transmission, particularly when real-time processing is desired. In this paper, we study a lowcomplexity scheme for hyperspectral imaging completely bypassing high-complexity compression task. In this scheme, compressive hyperspectral data are acquired directly by a device similar to the single-pixel camera based on the principle of compressive sensing (CS). To decode the compressive data, we propose a flexible recovery strategy by taking advantage of the joint spatial-spectral correlation model of hyperspectral images. Moreover, a thorough investigation is analytically conducted on compressive hyperspectral data and we find that the compressive data still have strong spectral correlation. To make the recovery more accurate, an adaptive spectral band reordering algorithm is directly added to the compressive data before the reconstruction by making best use of spectral correlation. The real hyperspectral images are tested to demonstrate the feasibility and efficiency of the proposed algorithm. Experimental results indicate that the proposed recover algorithm can speed up the reconstruction process with reliable recovery quality.
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The output beams of a dispersion-compensated polarization Sagnac interferometer include not only ±1st-order beams but also beams of 0th and other orders. Consequently, the contrast of the interference fringes generated in a focal plane array (FPA) is reduced, which means the quality of the image and reconstructed polarization images is poor. In this study, multistage diffraction is investigated to determine the effect of non-ideal beams on imaging quality. After determining the beams that can cast onto the FPA, the intensity on the FPA is studied with consideration of multistage diffraction. Results show that the non-ideal beams can lead to a serious reduction in imaging quality. The experiment and simulation results indicate that the beams can reduce the ratio of the fringe amplitude to the background signal to 1/8 from the ideal 1/2. Therefore, methods that can attenuate or eliminate other diffracted beams should be adopted. This conclusion is applicable to other optical structures containing gratings, such as a spatial heterodyne spectrometer.
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We demonstrate a mode-locked all-polarization-maintaining figure-of-8 erbium-doped fiber laser, with a repetition rate of 20.38 MHz. The self-starting fiber laser is based on a structure of nonlinear amplifying loop mirror (NALM). The output pulse duration of this laser can be de-chirped to about 590 fs. Such all-fiber laser with a high repetition rate has the advantages of high stability and self-starting, which leads to many scientific applications.
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A novel scheme of cascaded symmetrically chirped long-period fiber gratings (CSCLPFG) is proposed in this paper. Two linearly chirped long-period fiber gratings with opposite chirp coefficients are concatenated without an in-between fiber. In this fiber Mach-Zehnder interferencer (MZI) configuration, the light of different wavelength experiences different propagation distance both in core and cladding due to the symmetrically chirped grating structure. As a result, the phase difference between core and cladding mode increases nonlinearly with wavelength, which gives rise to an increment of fringe spacing with wavelength and thus, a nonuniform fringe pattern in transmission spectrum. The fringe spacing increases with the decreasing slope of phase difference curve versus wavelength. A Fourier transform analysis of the nonuniform fringe shows that the frequency range is substantially enlarged by symmetrically chirping, as compared to the uniform fringe of the cascaded identically chirped gratings. The overall fringe frequency increases with the grating length, while the wavelength scope of the fringe envelope is dependent on both the length and the chirp. In addition, the fringe frequency can be further adjusted by inserting a separation fiber in between two gratings. The mode coupling mechanism and fringe characteristics are numerically investigated, which may provide a theoretical foundation for the potential applications of this fiber device in filtering and sensing areas.
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Based on the extended Huygens-Fresnel principle and the unified theory of polarization and coherence, the explicit expression of cross-spectral density matrix for partially coherent beams in far field is derived. Also, we investigate the polarization changes of beams travelling through anisotropic turbulence along the horizontal link when the source is isotropic and anisotropic in correlation. Simulation results show strong relevance between the polarization states of beams and the source correlation. The conditions for partially coherent beams to be less affected by turbulence are given.
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Laser surface texturing is an advanced technology which can effectively improve surface tribological properties and has been attracted wide attention. However, the large diameter micro-dimple cannot be finished by fixed-point pulse processing, and fewer researches about the effect of laser scanning strategy on large diameter micro-dimple texture have been reported. Therefore, the effect of laser scanning strategy on the morphology of large diameter micro-dimple texturing is discussed in this work. An experiment of micro-dimple texturing on the 40Cr steel temples is performed by using a nanosecond laser. The effect of laser scanning mode on the micro-dimple texture is investigated to determine a reasonable laser scanning mode. Meanwhile, the influence of scanning interval on the micro-dimple texture with different diameters is studied under the best scanning mode. Results show that the diameter of the micro-dimples which are processed by the fixed-point pulse is about 48.1μm, and the spiral scanning is the best scanning mode for the large diameter micro-dimple texture. For spiral scanning, with the increase of scanning interval, the diameter of micro-dimples increases slightly, while the depth of micro-dimples, the height and the width of craters decreases. In order to ensure that the micro-dimple texture has good formability, the scanning interval can be properly floated on the basis of 10μm, but the scanning interval should not be close to the diameter of micro-dimples processed by the fixed-point pulse.
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Target tracking is an important research in computer vision. It has wide applications in human-computer interaction, machine recognition and artificial intelligence. But most existing tracking methods can not calculate the target scale well, resulting in low tracking accuracy. Some scale adaptive algorithms calculate scale by multiple attempts, which greatly improves the computational complexity. For this problem, this paper proposed a new scale adaptive correlation filter tracking algorithm based on the autocorrelation matrix. The method is based on the circulant structure of tracking-bydetection with kernels(CSK). Firstly, the sample of each frame is constructed as a cyclic matrix, and the kernel recursive least square (KRLS) method is used to learn the classifier. FFT accelerates the convolution process and makes the tracking speed faster. Finally, calculate the autocorrelation matrix using the standard image of each frame during correlation filtering. And get the target scale through the mapping of features between autocorrelation matrix. The experimental results showed that our method can update target scale during real-time tracking and improve the tracking accuracy effectively. Comparing to other algorithms, our algorithm can quickly adapt target scale during tracking and perform better in accuracy and speed.
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Geiger-mode Avalanche Photo Diode(Gm-APD) Ladar is a probabilistic device outputting three dimensional(3D) images based on the multi-frame imaging statistics, which makes the 3D recovery algorithm one of the key techniques of imaging system. Besides, performance of algorithm plays a crucial role in improving recovery quality of 3D images. This paper researches three 3D algorithms based on histograms, containing peak-selecting algorithm, range-selecting algorithm and Gaussian fitting algorithm. Firstly, the triggered model of Gm-APD is analyzed based on the work timing sequence and imaging theory of Gm-APD Ladar. Meanwhile, the recovery principles of three algorithms are analyzed and clarified. Secondly, two evaluation criterions, average range error and accuracy of range recovery, are raised to evaluate range accuracy. Finally, range images are obtained with above three algorithms in statistics of different frames, based on original data obtained from 64 × 64 Gm-APD Ladar imaging experiment. With the three construction algorithms, the result shows that the range accuracy of recovery range images improves and converges to 0.2~0.3m with the increment of number of frames participating in the statistics, and the accuracy of range recovery can be up to 90%. In low frame numbers, the range accuracy of recovery range profile is worst with peak-selecting algorithm, and the average range error with rangeselecting algorithm performs best while accuracy of range recovery with Gaussian fitting algorithm is highest among all algorithms. The result has important guiding significance for the choice of recovery algorithm under different requests.
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A new type of dual-channel interference microscope for quantitative phase imaging of transparent microscopic object is presented in this paper, which is comprised of an ordinary unpolarized cube beam-splitter and a ready-made Fresnel bi-prism. For this proposed microscope, the cube beam-splitter is tilted in an unconventional way, and the incident beam is only incident to one half of the cube beam-splitter and it is parallel with the central semi-reflecting layer of the cube beam-splitter. Subsequently, two copies of incident beam are created, the transmission beam is the simply replica and the reflection beam is the mirror-reverted replica. Behind the cube beam-splitter, the Fresnel bi-prism is placed in alignment with the cube beam-splitter and used to deflect the two generated beams to encounter and form the off-axis interference. Based on this kind of off-axis interference mode, we only need to record one interferogram for phase retrieval. Using this method, when the sample is only irradiated by one half of the incident beam, we can only use a single digital camera to record two symmetrical interference channels with a relative π (rad) phase-shift in one interferogram simultaneously. In addition, because of using less ordinary off-the-shelf optical elements, our method is simple and easy to operate with low cost, and it may be applied to traditional inverted optical microscope. Experimental results show that this method is suitable for quantitative phase imaging of transparent microscopic object.
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By employing germanium up-doped and fluorine down-doped, a novel design of all solid trench-assisted 19-core fiber with nearly zero flattened dispersion, large mode area and single supermode transmission is proposed. Dispersion can be adjusted by combining mode coupling mechanism and low refractive index trench. By using this strategy, the a flattened dispersion of 5.28±0.52ps/(nm·km) within a wavelength range of 1430nm~1680nm, which covers whole S+C+L+U communication band and an effective mode area up to 288.2μm2 at 1.55μm are achieved simultaneously. The fiber we proposed here has all solid and structure which is easy to draw and applicable to current DWDM system.
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As a resolve to high complexity of user selection and different users with different requirements of QoS(Quality of Services) optimization of multi-user selection with criterion of SLNR based on QoS is proposed in this paper with maximization of SLNR(Signal-to-leakage and Noises Ratio) as standard and different settlements of scheduling for different kinds of users in MIMO (Multiple-input multiple-Output) system. The simulation compares this algorithm with round robin scheduling and leakage based user scheduling. The results show the proposed optimization is much better not only in channel capacity but also in throughput and BER (Bit error rate) than these two algorithms.
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In this paper, a novel fiber ring laser (FRL) is proposed and investigated based on modal interference. Through core-offset splicing technique, an in-fiber Mach-Zehnder interferometer (MZI) is fabricated based on thin-core fiber and single mode fibers. Its distribution of light filed is comprehensively analyzed by beam propagation method. The FRL is then setup, in which the fabricated MZI is used as a band-pass filter. The output of laser is controlled and optimized by accurately adjusting the state of polarization controller. The experimental results show that, the extinction ratio of lasing wavelength reaches 39.8 dB, and the line width is less than 0.1 nm. Moreover, the proposed FRL is applied in temperature sensing, and the tested sensitivity reaches 122.7 pm/°C with the linearity of 0.9982. In addition, by calculation, the amplitude noise and the spectrum resolution are 8.84×10-3 nm and 2.89×10-3 nm, respectively. Therefore the detection limit in this laser sensor is about 0.07°C, which is obviously higher than that in passive fiber optic sensor.
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The characteristics of Calamines has been firstly analyzed by terahertz time-domain spectroscopy. Results show that the main composition of the Calamine is calcite. And the terahertz absorption much relates with the particle size, sample thickness, as well as the proportion of polytetrafluorethylene mixed in the sample.
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As a traditional mineral medicine, Lapis Chloriti has attracted much attentions in recent years. Based on the components determined by the X-ray diffraction, the Lapis Chloriti were characterized by the terahertz time domain spectroscopy. Results show that the absorption of sample has positive correlation with concentration. The more mass with Lapis Chloriti, the more absorption. And the absorption becomes more intense with the particle size increasing. In addition, the absorption influenced by other factors are also compared and discussed.
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In-fiber modal interferometers have been widely used in the applications of biochemical sensing, mine safety and health monitoring of buildings. The temperature feature of sensors is one of the most important characteristics, but the studies are rarely reported under the condition of subzero temperature. In this paper, through core-mismatch fiber splicing method, three in-fiber Mach-Zehnder interferometers (MZIs) are fabricated based on single-mode fiber (SMF), erbium-doped fiber (EDF, with core diameter of 3.6 μm) and multimode fiber (MMF, with core diameter of 50 μm), respectively. Their interference patterns are investigated through beam propagation method and Fast Fourier Transform analysis. The comprehensive tests of temperature are then performed in the range from -40 to 0°C. The experimental results show that, in subzero temperature, the transmission spectrums of MZI sensors based on single mode fiber (SMF) and MMF are worsened in terms of fringe visibility and intensity. And the sensitivity of MMF-based structure is 68.8 pm/°C with a 12.3-dB deduction of fringe visibility. Comparatively, the EDF-based MZI presents ideal sensitivity due to negative gain-temperature feature. By calculation, the 124.7 pm/°C sensitivity is gained with the linearity of 0.9892. Moreover, 10-dB enhancement in intensity and over-20-dB fringe visibility are demonstrated, which indicates that the EDF-based sensor is potential and promising for the applications of cryogenic sensing.
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In a phase extraction based phase-sensitive optical time domain reflectometry (Φ-OTDR), external perturbation induced phase variation of Rayleigh backscattered light-wave (RBL) is obtained from time varying interference signal that is comprised of two RBLs with a spatial shift along the sensing fiber. In this paper, the phase of the interference signal in the phase extraction based Φ-OTDR is studied. Derivation is performed on the interference signal considering the interference of multiple RBL within probe pulse covered fiber section. Theoretical analysis and experimental results reveal that the phase of interference signal are wavelength independent while the intensity of interference signal are wavelength dependent.
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Intermodal Brillouin frequency shift and Brillouin gain spectrum in few-mode fibers are investigated by full vectorial finite element method, and the influences of pump power on the time delay and pulse broadening factor are also simulated. The simulation results show that Brillouin gain of intermodal stimulated Brillouin scattering varies with different modes pairs. Time delay increases with increasing of pump power. Pulse broadening factors decrease with the input signal pulse width but increase with the input pump power. Optimized results show that time delay of LP01 - LP01mode pair is 213.2ns, and the corresponding pulse broadening factors is 1.126.
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By rotating the half-wave plate, the variable communication bit rate between 5.12Gbps and 2.56Gbps has been verified at satellite-to-ground optical communication linkage, the communication link used Differential Phase Shift Keying(DPSK) modulation format and the wavelength is 1549.731nm. Without error correcting code and adaptive optics, an average bit error rate of 1.9E-9 was achieved while the link distance exceeded 1500km.
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Bioluminescence tomography (BLT) can reconstruct internal bioluminescent source from the surface measurements. However, multiple sources resolving of BLT is always a challenge. In this work, a comparative study on hybrid clustering algorithm, synchronization-based clustering algorithm and iterative self-organizing data analysis technique algorithm for multiple sources recognition of BLT is conducted. Simulation experiments on two and three sources reconstruction are demonstrated the performances of these three algorithms. The results show that the iterative selforganizing data analysis technique is more suitable for the closer multiple-targets and the other two algorithms are suitable for distant targets. Moreover, iterative self-organizing data analysis technique has the least computing time.
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In order to enhance the emission spectrum of plasma in laser induced breakdown spectroscopy (LIBS), magnetic fields with different intensities were applied around the plasma to investigate its enhancement. Adjust the laser energy to 60mJ, change the magnetic field strength, use the traditional LIBS, magnetic field enhanced LIBS (MF-LIBS) for laser-induced breakdown of pure copper samples, to obtain the spectral comparison of characteristic line of trace elements (Bi I 206.16 nm) under different constraints and analysis of its enhancement mechanism. The experimental results show that the magnetic field of 153mT will reduce the spectral intensity, the 20mT, 50mT, and 90mT magnetic fields will enhance the spectral intensity. The stronger the magnetic field, the better the spectral enhancement effect, but the enhancement effect of 20mt is not obvious. The Lorenz fitting coefficient of the line is the lowest when magnetic field is not applied, the fitting coefficient gradually increases at 153mT, 20mT, 50mT and 90mT magnetic fields, indicating that the line shape is closer to the Lorentz type. And the spectral line width are also larger and reaches the largest when the 90 mT magnetic field is applied.
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This paper reports a simple method of creating multifocal microlens arrays on silica glass. The method involves the multi-step femtosecond-laser exposures followed by a chemical wet-etching process on silica glass, which enable fabrication of multi-layers concentric microstructures with high-quality and smooth curved surfaces. The flexibility of the maskless process was demonstrated in tuning the shape and depth of the multilayer concave structures by the arrangements of the laser exposure energy and chemical etching time. In addition, microlenses with different layers were fabricated and the results revealed their high surface quality and good optical property in creating multi-focus.
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For tunable quantum well lasers, it has been a huge challenge all along how to achieve an ultra-wide tuning spectrum far exceeding the full width at half maximum (FWHM) of gain in a classic quantum well and the uniform power output for all tunable wavelengths of the laser under a fixed injection power, especially based on a single well structure. In this paper, we are reporting some amazing results from a special asymmetrical InGaAs quantum well structure, with which both incredibly extremely-wide and nearly uniform gain spectra are obtained with a fixed injection power. The excellent gain characteristics may make above dream come ture for the InGaAs-based tunable lasers. The formation of the structure is associated with the Indium-rich island effect. The analysis showed that the spectrally-tunable range from this special well structure could be up to 6 times as broad as the FWHM of gain in the classic InGaAs well and the gain spectrum with quasi-rectangular feature in transverse electric mode was obtained as well. It enables nearly identical power output over the total spectrally tunable range of the laser to be realized with a fixed optical injection power.
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We demonstrate a silicon Mach-Zehnder modulator with L-shaped PN junctions to improve the modulation efficiency. The L-shape doping profile of the PN junction is obtained through multiple ion implantations with proper dose and energy. The depletion region of the PN junction has a strong overlap with the waveguide optical mode, resulting in improved modulation efficiency. We optimize the doping conditions to get a balanced performance in terms of modulator efficiency, insertion loss, and bandwidth. The measurement of the fabricated modulator reveals that the π phase shift voltage is 2.6 V for a 3-mm-long modulation arm. The modulation efficiency thus is Vπ·Lπ = 0.78 V·cm. The static extinction ratio is about 30 dB. The on-chip insertion loss is around 8.1 dB at zero bias. The EE 3-dB bandwidth is beyond 30 GHz at -2 V DC bias. Modulation of 32 Gb/s on-off keying (OOK) and binary phase-shift keying (BPSK) signals is successfully achieved.
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Phase-shifting digital holography (PSDH) is considered as a promising imaging technique with wide application in optical storage, topography measurement and defect detection. The amplitude-only vortex lens is a kind of diffractive optical elements (DOEs) which can be used for focusing and imaging in a wide spectral region, such as coherent X-rays and terahertz wave. Here four-step PSDH with an amplitude-only vortex lens is proposed. Four frames of hologram can be recorded by rotating the vortex lens installed in the reference beam path. Both a 1951 U.S. air force resolution test target and a vortex focal spot are measured by four-step PSDH with vortex lens. The experimental results are in good agreement with the theoretical analysis and verify the validity of our proposed PSDH with vortex lens.
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In this talk, we first review the current status for 400GBASE client-side optics standard and multi-source agreement (MSA). We then compare different form factors for 400GE modules, like CFP8, OSFP and QSFP-DD. The essential techniques to implement 400GE, like pulse amplitude modulation (PAM4), forward error correction (FEC) and continuous time-domain linear equalizer (CTLE), are discussed. A 400GE physical interface card (PIC) in Juniper’s PTX5000 platform has been developed, conforming to latest IEEE802.3bs standard. To validate the PIC’s performance, a commercial optical network tester (ONT) and the PIC are optically interconnected through two CFP8-LR8 modules. The CFP8-LR8 module utilizes 8 optical wavelengths through coarse wavelength division multiplexing (CWDM). Each wavelength carries 50Gb/s PAM4 signal. The signal transmits through 10km single mode fiber (SMF). The ONT generates framed 400GE signal and sends it to PIC through the first CFP8 module. The PIC recovers the signal, performs an internal loopback, and sends 400GE signal back to the ONT through the second CFP8 module. The optical spectrum, eye diagram, receiver sensitivity, long time soaking results, and internal digital diagnosis monitoring (DDM) result are fully characterized. The pre-FEC bit error rate (BER) is well below the KP4 FEC threshold of 2.2e-4. After KP4 FEC, error-free performance over 30km SMF is achieved. In this way, we demonstrate both the inter-operation between the PIC and the ONT, as well as the inter-operation between two CFP8 modules. This demonstration represents the successful implementation of 400GE interface in the core IP/MPLS router.
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In this work, we propose a novel approach to generate high-quality optical millimeter-wave signals using frequency 12-tupling without an optical filter. The proposed approach is comprised of one dual parallel Mach- Zehnder modulators. The two sub-MZMs, biased at the maximum optical transmission point, which is only used for even-order optical harmonic generation, and introduces a phase shift on the optical output signal between the sub- MZMs. By properly adjusting the MZM biasing point, RF LO voltages and phases shift, sixth order optical sidebands only are generated which can result in 12-tupled mm-wave at the photo detector. Optical sideband suppression ratio (OSSR) higher than 37.65 dB and radio frequency spurious sideband suppression ratio (RFSSR) not less than 32.08 dB are achieved in this scheme. The performance of the signal in terms of OSSR and RFSSR is discussed, and the effects of non-ideal factors on OSSR and RFSSR are analyzed.
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In this paper, we investigate the effects of silver shell thickness on the pasmonic resonances in single layer concentric core-shell particles by Mie theory. The plasmonic resonance is shown to be strongly influenced by the changing of shell thickness which leads the changes of dipolar and high order extinction resonance wavelength shift properties. Theoretical calculations indicated plasmon hybridization and phase retardation play an important role to influence the shift direction. Furthermore, different environment and geometrical properties are also considered.
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In this paper, passively mode-locked all polarization-maintaining (PM) dispersion-managed erbium-doped figure-of-9 fiber oscillator based on a nonlinear amplifying loop mirror (NALM) is demonstrated. The figure-of-9 fiber laser can generate 25.7-nm chirped-pulse at a center wavelength of 1550 nm with a repetition of 46.6 MHz, a pulse energy of 0.2 nJ, and a chirped pulse width of 571 fs. The laser output is then amplified by pre-chirped managed nonlinear amplification setup to 5 nJ and further compressed down to 167 fs. Compared to previous studies, the laser presented here has advantages of all-fiber structure, no Kelly sideband and wider bandwidth.
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We proposed a high-Q in-plane channel drop filter using photonic crystal (PhC) cavities that are defined by an effective Aubry-André-Harper (AAH) bichromatic potential. The channel drop filter consists of AAH cavities and line-defect waveguides. Three-port structure with a wavelength-selective reflection cavity is applied. The parameters of the channel drop filter is analyzed by two-dimensional (2D) finite-difference-time-domain (FDTD) method. The simulation results are namely, the center wavelength of the filter being 1573.0 nm, and the insertion loss being smaller than 0.6 dB. The 3 dB bandwidth is 0.2 nm, and the loaded Q is up to 8×103. So the proposed device can be applied in a dense wavelength division multiplexing (DWDM) system with a 100 GHz channel spacing. Besides, the channel drop filter has a broad free spectral range (FSR) of around 250 nm, covering from 1350 nm to 1600 nm. The footprint of the channel drop filter unit is only 10 μm×20 μm.
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A single mode optical fiber with a rectangular hole is proposed. Power coupling characteristics of the optical fiber are analyzed and discussed using numerical method. Firstly, the coupling intensity from the fiber core to the rectangular hole is investigated in different distances between the fiber core and the rectangular hole and different refractive index of the rectangular hole. Secondly, the power complete conversion and transmission characteristics are also investigated in different distances between the fiber core and the rectangular hole and different refractive index of the rectangular hole. The results show that the coupling efficiency of the proposed optical fiber from the fiber core to the rectangular hole can nearly reach to 50%. The high coupling efficiency from the fiber core to the rectangular hole can be used to develop the high efficiency mode converters. Moreover, the results also show that the coupling efficiency is higher when the refractive index of the rectangular hole is bigger than the refractive index of the fiber core. So, the proposed optical fiber has the potential application value in high refractive index sensing.
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Mixed molybdenum tungsten disulphide (MoxW1-xS2), a new member of the transition metal dichalcogenides, has drawn much research attention in the photonic devices. In this work, we demonstrate a Q-switched Tm-doped fiber laser (TDF) using Mo0.8W0.2S2 polymer film as a saturable absorber (SA). Mo0.8W0.2S2 is obtained by microwave-assisted solvothermal method and its nanosheets are embedded into a polyvinyl alcohol (PVA) film. The film SA is sandwiched between two fiber connectors and is inserted into the all-fiber TDF laser cavity. The total cavity length of TDF is 30m and a 4 m Tmdoped fiber is used as the gain medium. The TDF is pumped by a multimode 793nm laser diode (LD). Use the polarization controller (PC) to change the polarization states, a relatively stable Q-switched pulse train are realized when the pump power up to 2.17 W. The output power of the oscillator increase from 4.4 mW to 7.3 mW with the pulse repetition rate from 11.9 kHz to 15.7 kHz. In addition, the shortest pulse duration of 11.7 μs generated with the pump power of 2.26W.
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To wavelength modulation SPR sensor, the measuring sensitivity of refractive index increases with wavelength. A broadband light source (700 nm~900 nm) with relative narrow bandwidth at long wavelength is selected, to measure the refractive index of surrounding medium by using SPR reflection power spectrums, in order to obtain relatively higher sensitivity and resolution. But the measuring range of refractive index is decreased by the reduction in bandwidth of light source. We propose a surface plasmon resonance sensor based on wavelength and angular combined modulations, in order to solve the mutual restriction of measuring range and sensitivity/ resolution, sectional measurement method is adopted, i.e. different incident angles are selected respectively, which will detect different measuring ranges of refractive index. Wavelength and angular combined SPR modulations can cover the whole measuring range of refractive index, and improve the measuring sensitivity and resolution simultaneously.
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Automatic evaluation of optical network service quality is a research hotspot in optical network operation and maintenance management. Based on the large alarm data of optical network, a evaluation method of optical network service quality based on FCM and rough set theory is proposed in this paper. First, the evaluation index is selected based on the classification statistics of alarm data; Secondly, adopt the FCM method to fuzzy clustering of raw data, and locate the fuzzy language item; Finally, extract the optical network service quality evaluation rule and establish system of the optical network service quality evaluation. The test shows that the accuracy of this method is 73% based on the 22 alarm samples in an optical network and the accuracy of the evaluation increases with the increase of the number of samples.
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It’s interesting that the artificial structure colors can be actively manipulated by external stimuli such as solvents, temperature, and mechanical force. In this paper, polarization state, the inherent characteristic of incident light, is used to control the structure color by a one-dimension metamaterial perfect absorber with polarized absorption peaks based on the stacked array. The nanostructure, consisting of two metal-dielectric pairs and a bottom metallic film, shows above 90% reflectivity from 652 nm to 750 nm (the red structure color) for TE and above 80% reflectivity from 584 nm to 635 nm (the orange structure color) for TM. Because our designed one-dimension absorber has the absorption peaks at 548 nm and 684 nm for TE and TM, respectively. So the polarization-controllable structure color gradually changes from red to orange when the polarization angles increase from 0° (TE) to 90° (TM). The underlying physical mechanisms of high absorptivity is explained by the electric and magnetic fields distribution.
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In this paper, we propose the low loss negative curvature fiber with circular internally tangent nested tube in elliptical cladding tubes. The leakage loss can be decreased because the elliptical cladding tubes have higher curvature at the core boundary compared to the circular cladding tubes. The circular nested tube in the elliptical cladding tubes provides an additional antiresonant reflection element to reach lower leakage loss. The simulation results show the negative curvature hollow core fiber in this paper has a low leakage loss in the spectral region from 1.3μm to 1.7μm. In particular, the leakage loss is 0.012dB/km at 1.55μm.
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The light scattering properties of a transparent spheroidal particle is investigated using defocused interferometric particle imaging. Based on optical transfer matrix theory, the out-of-focus images are simulated using Matlab. We found that the angular variation of a spheroidal particle exhibits isometric with angular variation of the speckle of out-of-focus image. The out-of-focus images of transparent spheroidal particles under different angle of rotation are experimentally acquired using interferometric particle imaging system. The experimental results showed agreement with the simulation results. Thus, we propose a method for obtaining the angular variation of a spheroidal particle using out-of-focus image.
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Here a refractometer with the liquid prism is proposed. It has a simple structure, low cost and a large measurable refractive index range. When the vertex angle of liquid prism is 30°, the measurable refractive index range is up to 1.00-3.86, while the common refractometers have only the measurable range of 1.30-1.70. The optical system of this refractometer is design, where the angle of field is 80° and the total length is 110mm. A linear array CCD is used as the image receiver. The design results show that MTF is 0.35 in the tangential surface and 0.55 in the sagittal surface at the Nyquist frequency of 70lp/mm and the full field. The MTF values of other fields are more than 0.6, and the maximum distortion is 0.37%.
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Using optical coherence tomography angiography, we measured blood flow from the vessels in the lateral wall in the mouse cochlea directly through bone in mice with and without sympathetic neuronal function. We present in vivo imaging of blood flow and mechanical vibration in mice subjected to 30 min of loud sound. Loud sound caused blood flow reduction. In mice with superior cervical ganglion ablation, the loud sound-induced reduction in blood flow was partially ameliorated. These results demonstrate that sympathetic innervation likely plays a role in the pathological decrease in blood flow observed in the lateral wall vessels in response to loud sound.
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In this paper, a new type of electrically controlled liquid-crystal microlens arrays (ECLCMAs) based on plane nonuniform spiral microcoils (PNSMs) is proposed. The microlens array is based on a nematic liquid-crystal material, which presents a special characteristics of optical anisotropy and birefringence, and is fabricated by common ultraviolet lithography and dry ICP etching process to form needed PNSMs pattern. In the ECLCMAs, a glass substrate precoated by a film of indium tin oxide (ITO) on both surfaces of substrate is adopted. The key center electrode for shaping each functioned LC cell is drilled using a laser etching and emery polishing process. Metallic indium particles are selected to connect the upper and lower ITO layers. The design can guarantee the continuity of the upper and lower plates and does not affect the electric and magnetic fields generated by spiral microcoils, which are utilized to drive LC film to present needed functions of further controlling and adjusting incident microbeam distribution, which is preprocessed by main objective lens system. After an AC voltage signal is applied across the microcoil, an effective electromagnetic field can be formed in LC cell so as to drive LC molecules to rotate and thus demonstrates an electrically tuning focus. The simulations show that the design of patterned PNSMs can be effectively used to form a sufficient electric and magnetic fields that are directly used to rotate LC molecules and thus form a gradient refractive index distribution for converging incident microbeams so as to show a higher controlling-light efficiency than that of traditional patterned microelectrodes. The proposed method laid a solid foundation for future smart ECLCMAs.
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In this study, a kind of electronically controlled liquid-crystal microlens array (LCMLA) with plane swing focus and tunable focal length instead of a commonly microlens array with a fixed focal length and then focus distribution for highresolution image acquisition, wavefront measurement, and distortion wavefront correction, is proposed. The LCMLA mainly consists of two glass substrates coated with a film of indium-tin-oxide (ITO) transparent material on one side. Each sub-unit top layer is composed of four sub-square electrodes, and the bottom layer is a circular electrode. The key technological steps in electrode fabrication contain an ultraviolet lithography, a dry etching (ICP etching), and final electron beam evaporation and overlay. The current LCMLA can be realized in three operating modes under external driving circuitry, including intensity image acquiring, wavefront measurement and distortion wavefront correction. The LCMLA is only in the image acquisition mode under the condition of no driving electrical signal. As the same driving electrical signals are applied onto the top four sub-electrodes of each sub-unit, the LCMLA is in the wavefront measurement mode. The LCMLA is in the key wavefront correction mode when different driving electrical signals are simultaneously applied onto the top four sub-electrodes of each sub-unit. Experiments show that the focal point of the LCMLA can be moved along the optical axis and over the focal plane by applying appropriate driving voltage signals.
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Liquid-crystal material demonstrates a special property of optical anisotropy. So far, it is widely used in many fields including flat panel displaying and other various optoelectronic devices. Electrically controlled liquid-crystal microlenses have presented some unique capabilities such as swinging focus over the focal plane and tuning focal length only by electrical signals applied over them. According to the typical electro-optical characteristics of nematic liquid-crystal materials, a liquid-crystal microlens array (LCMLA) with a featured zoned quasi-single-microhole electrode with more controlling area than the past microelectrode structure developed by us, which is applied by a multiplexed controlling signals according to an electrically scanning fashion, is proposed for realizing a new type of dual-mode imaging including one addressable wavefront measurement and correction through sensor array zoned by LCMLA, and another intensity image. Each sub-electrode in a quasi-single-microhole electrode can be individually driving and adjusting. So, two operations of adjusting focus and swinging focus can be achieved only by applying suitable voltage signals over each subelectrode. However, to successfully achieve a dynamic compensation of the aberrated wavefront measured so as to minimize target image distortion, hundreds of LC microlenses are needed for measuring and reconstructing wavefront corresponding to realtime image acquired. This will lead to a problem: a large number of conductive wires cannot be effectively arranged and connected to the LC microlens. In this paper, a LCMLA based on an electrically scanning approach is proposed. An "active matrix" for applying voltage signal over different structural unit is used so as to realize a active control of wavefront measurement and correction corresponding to a target image.
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The surface plasmon polaritons (SPPs) is an electromagnetic wave that can be stimulated and then propagates over the surface of the preshaped metallic nanostructures or the interface between the surface of the metallic nanostructures and the substrate media due to a strong coupling of incident light and the surface free-electrons moving on the metallic nanostructure surface with a featured micrometer scale. As shown, through SPPs, incident light energy can be localized effectively in a sub-wavelength region or space, and thus so-called light diffraction limit can be break through easily. Therefore, it has demonstrated a good prospects for developing advanced functioned materials or devices such as light absorbing materials, optical antennas, and optical information storage modules. In this paper, we propose a special metallic nanostructures, which can be used to absorb a certain band of incident light by converting them into a kind of local freeelectron oscillation, which means that SPPs can be generated and processed efficiently. As shown, the metallic nanostructures will present a lower reflectivity in the wavelength range, and through adjusting several key parameters such as the period of the metallic nanostructures, we can achieve an effective control of reflectivity because a valley of the reflectivity curve can be formed, which means a low reflectance at a specific wavelength band has been obtained.
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During the detection process of atmospheric laser absorption spectroscopy in open space, the useful signal may be submerged in the noise due to the inherent noise of the instrument and external environmental noise. In order to effectively improve the signal-to-noise ratio, a new method of cascaded stepwise singular value decomposition has been proposed. By constructing different matrices, the low-frequency noise and high-frequency noise are removed in stages. A laser absorption spectroscopy atmospheric detection system in open space has been established to experimentally verify. The results show that, compared with the traditional method, the signal-to-noise ratio of the spectral signal processed by the method of cascaded stepwise singular value decomposition is increased from 0.211 to 1.029, the standard deviation is also reduced by 1.927 times. It is proved that the proposed method can effectively remove noise and obtain high-quality laser absorption spectrum signal to improve gas detection accuracy, which has practical value.
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Tracking methods based on Correlation Filter have been constantly improved in tracking accuracy and robustness. However, it still challenged in background clutter, rotation changes and occlusion, the drift of the model was one of the main reasons. In this paper, we propose an online sample training method based on Gaussian Mixture Model. The maximum response value, obtained from the convolution of samples and filters, is used to judge the availability of the online samples, which is able to reduce the interference of wrong online samples. Then, through Gaussian Mixture Model, samples are classified to strengthen the diversity of the sample set, which can avoid model drift effectively. Besides, we also propose a model update criterion to enhance the stability of the tracker, and heighten the efficiency of calculation. This criterion is determined by changes of target in scale and displacement. We perform comprehensive experiments on three benchmarks: OTB100, VOT2016 and VOT-TIR2016. Comparing with other trackers, our tracker has better robustness in the condition of background clutter, rotation change and occlusion. Moreover, its speed also maintains real-time performance.
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Cornea is an important part of human eye refractive system. Corneal astigmatism axis, as a key parameter to evaluate the corneal topography, is directly related to visual diagnosis and treatment. In 1997, International Organization for Standardization published the first ISO standard for requirements of corneal parameter measurement. However, due to the limitation of processing and testing technology at that time, the standard of corneal astigmatism axis has been an unsolved technical problem. Research work on corneal astigmatism axis standard was carried out early in 2007 by China National Institute of Metrology. In this paper, first, measurement principle of corneal parameter is described. Then, corneal astigmatism axis standard based on toroidal surface is designed and manufactured, which consists of axial model eye, axial sleeve and measurement support. Axial model eye is a square cylinder whose front surface is toroidal and back surface is scrub plane, which is located in the square through hole of axial sleeve, and axial sleeve is located on the trapezoid groove of measurement support. Next, by accurate measurement and metrological calibration, four axes of 0°, 45°, 90° and 135° are achieved and axis uncertainty U=0.3° (k=2). Finally, measurement results show that the newly developed astigmatism axis standard can realize the evaluation of corneal parameter testing instruments well. Besides, design structure specified in ISO standard is found to be hard for accurately location and infeasible in practice. A proposal for revision of this international standard will be drafted and discussed on ISO meeting of 2019 held in America.
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In order to study the effect of the ratio of oxidizing agent to reducing agent on the performance of the trilead tetraoxide/ Teflon/magnesium (Pb3O4/PTFE/Mg) powder decoy compounding agent, 5 different pharmaceutical formulations are designed by maintaining constant oxidant formula and changing the ratio of oxidant agent and reducing agent. Then the mixed powder is pressed into a powder by a table press. The combustion process of the drug column was measured with an 8-14 micron infrared thermal imager, and the burning time, mass burning rate, radiation area, radiance, and radiation intensity of each sample were calculated. The results show that with the increase of the proportion of reducing agent, the burninging time of the sample becomes shorter and the mass burninging rate becomes larger. The maximum temperature of the flame increased with the proportion of reducing agent first and then decreased. When the ratio of oxidant agent to reducing agent is 1.5:1, the maximum temperature of sample combustion reaches a maximum of 1503°C. The radiance increases first and then decreases with increasing proportion of reducing agent, and When the ratio of oxidant agent to reducing agent is 1:1.5, the infrared radiance is the maximum, which is 2510 W·m-2·Sr-1.Radiation intensity increases as the proportion of reducing agent increases. It can be seen that in the 8-14 micron band, when the ratio of oxidant agent to reducing agent is 1:1.5, the radiation characteristics of the sample is best and the sample is the best one as infrared decoy.
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ROF is the technology that integrates optical communication and wireless communication. It not only possesses the characteristics of high speed and long distance in optical communication, but also has the characteristics of flexible in wireless communication. GFDM is one of 5G's alternative technologies for high-frequency millimeter waves. This paper proposes and verifies that in the GFDM-ROF system with MIMO, cascaded Turbo-STBC coding can improve the reliability of the entire system. We use Turbo code as the out-of-channel code, and STBC code as the intra-channel code. When using two transmitting antennas and four receiving antennas and the SNR is higher than 5 dB, the BER is below 10-6. Furthermore, based on this system, under high load communication conditions, we proposed an adaptive coding technology with excellent performance and it can reduce system load rapidly.
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When a beam of TM electromagnetic wave with a matched frequency to a periodic nano-pattern array shaped in a metallic film is incident upon the metal interface, the surface free-electrons of the metal film will be stimulated and thus oscillate collectively. The phenomenon above means that the incident electromagnetic waves and surface free-electrons are coupled effectively and then a mixed excitation mode of surface plasmon polaritons (SPPs) are generated and also spreaded over the metal-dielectric or metal-air interface. According to current researches, the surface waves originated from a strong surface free-electron oscillation can propagate along a interface only being a micrometer scaled distance. When the energy and momentum of incident electromagnetic wave are suitable, a SPPs can be guided and thus a part of electromagnetic energy can be converged onto the metal tip, thereby reducing the surface reflectivity of the electromagnetic waves because they are already concentrated or storaged into the periodic nano-pattern array shaped. In order to study the influence based on several factors including metal surface structures, nano-pattern array period, and electromagnetic wave incident angle, an optical frequency SPP device is designed. The device with a gold plating film is fabricated over a silicon substrate, and then the substrate is etched so as to shape a metal nano-pattern array. The structure is called a sub-wavelength gold structure (SWGS). A virtual model is established according to CST microwave studio. The finite element method is also used to simulate the electromagnetic characteristics of the SPPs. Simulations are carried out to obtain reflectance waveforms so as to explore the reflectivity changes of SWGS irradiated by nearinfrared waves under different conditions including metal surface structural characters, nano-pattern array period, and electromagnetic wave incidence angles.
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A two-stage phase noise compensation (PNC) algorithm is proposed based on the circular multilevel quadrature amplitude modulation (C-mQAM). In the first stage, a cost function to estimate the phase noise roughly is constructed, before which the received symbols are classified by their amplitudes and rotated. It can be approximated to a cosine function, and three test phases are required for the calculation of its parameters. Kalman filter (KF), utilized in the second stage, provides the final estimation of phase noise. The performance of the proposed algorithm is evaluated with two aspects of computational complexity and the combined linewidth symbol duration product (△v·Ts) tolerance. The results show that the proposed algorithm offers a low computational complexity and high △v·Ts tolerance compared to the blind phase search (BPS) algorithm and extemded Kalman filter (EKF) algorithm.
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We propose a new method to discuss the evolution of physical systems, which has an analytic form. And we systematically introduce this new method by the example of Jaynes-Cummings model without rotation wave approximation. Simultaneously, while we repeat previous work by our method, we also calculate it by adding the time growth factor to the initial state unfolded in the steady state which is based on Fock state and is obtained by solving the time-independent Schrodinger equation (in this article, the traditional method refers to this method). By comparing these two results, we find the drawback of our method and improve it. Finally, we show that our improved method need the smaller Fock space than the traditional method for physical systems with two-mode cavity field and put forward expectations for the follow-up study.
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We propose the electro-optic mode deflection devices based on annealed proton exchange (APE) waveguides in lithium niobate with microstructured electrodes. Two mode deflection devices with right-triangle-shaped electrodes (Device A) and isosceles-triangle-shaped electrodes (Device B) are investigated. Taking advantage of the refractive index prism array formed when applying an external voltage to the electrodes, the mode can be deflected. Beam smoothing can be achieved by applying alternating voltages. A∼1.28 μm beam deflection is obtained by applying a voltage (20 V) for Device A. For Device B, a 3.52 μm beam deflection is obtained by applying a -15 V voltage to the electrodes. Device B has a horn-shaped input waveguide which ensures that the output is a quasi-single mode. The mode quality of the deflection beam is also quantified by the CMOS camera. Smoothing the non-uniform density distribution of light beam is confirmed by averaging over 69 images taken by the CMOS camera with alternating voltage. These electro-optic mode deflection devices have potential applications in electro-optic sampling, high-speed optical switch, and beam smoothing of a high-power laser.
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We present a compact hybrid-integrated 4 × 25.78 Gb/s TOSA based on butt coupling between DFB-LDs and silica-PLC AWG multiplexer. To obtain a low cost TOSA, high-cost conventional hermetic ceramic metal box is replaced with nonhermetic metal box. Experimentally, we demonstrate that the TOSA could achieve error-free operation for a 10 km transmission at 25°C. The packaged CWDM TOSA, which is 15.8 mm × 7.0 mm × 6.0 mm in size, shows a side-mode suppression ratio of >40 dB, a 3-dB bandwidth of >18 GHz, and error-free transmission with an average optical output power of >0 dBm and dynamic extinction ratio of >4.0 dB at 25.78125 Gb/s over a 10-km single-mode fiber for all four lanes.
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In the future, with multiple services and large-capacity access network scenarios, the network load is often high but the bandwidth is limited. On the situation, based on the software-defined TDM-PON access network architecture and network traffic prediction-correction model, a dynamic bandwidth allocation algorithm is proposed. In the algorithm, a prediction model is used to predict traffic information and a correction mechanism is used to correct the prediction model. After analyzing the global information of the network, the algorithm provide corresponding bandwidth management policies based on business priorities according to different network load conditions. We compare this algorithm with IPACT algorithm, unused prediction algorithm and neural network prediction without correction. It proves that the algorithm guarantees the service quality requirements of different priority services when the bandwidth is limited and the network load is high, and it performs better in terms of average packet delay, bandwidth utilization, etc. Simulation shows, compared with the traditional strategy, the average packet delay is reduced by 70%, and the bandwidth utilization is increased by 19%.
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This type of sensor is manufactured by using the KF-FBT type fusion taper machine to uniformly pull the same single mode optical fiber. Double tapered section cascade type singles mode fiber. When the signal light passes through the concatenation fiber cone, the cladding mode is excited after passing through the first stage cone region. After a certain distance transmission, the second stage cone region interferes with the core mode. The change of the waveform is seen from the spectrometer. When the two cones are bent by 90, the article explores a double-cone-section cascading sensor that is easy to operate and easy to perform multi-point measurements from both theory and experiment. The spectral peak-to-valley contrast of the interference fringe is more obvious, and it can serve as a sensor head to test the ambient temperature. The sensor has a temperature sensitivity of 60 pm/°C.
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Lidar has been widely used in both military and civil applications. Its received optical signal undergoes considerable loss and disturbance from background noise, which limits its performance especially in bad weather or air conditions. A high-gain and frequency-selective amplifier for weak optical signal based on stimulated Brillouin scattering in single mode fiber is proposed, which is an excellent candidate for the signal enhancement in lidar system. The characteristics of the amplifier were studied numerically and experimentally. In experiment, a 430-nW (peak power) pulsed signal was amplified by 70 dB with a signal-noise ratio of 14 dB, which was in good agreement with theoretical result.
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Due to the properties of super-narrow focusing and super-resolution imaging, microsphere lens has attracted many attentions. In order to operate the microsphere lens freely, a microsphere holder is necessary to control its 3-D motions accurately. In this paper, a stable and practical microsphere holder is designed for microsphere lens scanning imaging. Furthermore, we numerically analyzed the influence of microsphere holder on the focusing properties of microsphere lens. With the reflections from the surface of microsphere holder, the wavefront in microsphere could be reconstructed through the interference between the incident light and reflection beams. At proper conditions, the curvature radius of incident wavefront in microsphere could be enlarged by the reflections beams, which could generate longer focal length of microsphere lens. Meanwhile, the width of focal spot is almost constant, which is as narrow as the one without microsphere holder. Therefore, the microsphere holder will almost not reduce the imaging resolution of microsphere lens, but enlarge its working distance obviously, which is significant for microsphere assisted far-field super-resolution imaging. Through the optimization of the opening angle and the material of microsphere holder, an ultra-long working distance of 6.5λ has been achieved by microsphere lens with a proper microsphere holder. This holder could be applied for microsphere assisted far-field super-resolution imaging due to its contribution on microsphere lens control and focal length increase from near-field to far-field, and extend the applications of microsphere assisted nano-imaging into more fields and more samples.
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We demonstrated a dual-wavelength Tm,Ho:LuLiF4 laser operating at 1895nm and 1950nm by adjusting the pitch angle of the output coupling mirror. With a X-type four-mirror cavity, a total output power of 575 mW is achieved at an incident pump power of 2.1 W, which corresponding slope efficiency is 27.95% and the threshold power is low to 110 mW. The dual-wavelength laser is very useful for the generation of coherent light source in terahertz band.
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The inhomogeneity of scattering media will distort the propagation of the waves, which is detrimental to the performance of optical imaging. Although various approaches have been proposed recently to overcome this problem, they are not suitable to image the rapid-movement objects as a long sequence of measurement steps are required. In this paper, based on the optical transmission matrix of the scattering medium, we show that the information of the object can be recovered directly from the distorted output optical field. Especially, our method is effective to the thick scattering medium. We predict it might have the potential application for real-time imaging.
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In this research, a color grating projection system is designed to effectively and flexibly display spatially sampled large size and high resolution color Fresnel hologram. The sampled color Fresnel hologram is placed in the image plane of projection system. The parameters of color grating are adjusted for 3D color display. Specifically, one effective scheme of spatially sampled color Fresnel hologram is used for reducing the data redundancy of computer generated Fresnel hologram while keeping a high resolution of reconstructed 3D image. A hologram with the size of 30mm×30mm at the resolution of 94208×94208 is calculated and optically reconstructed to verify the proposed display system.
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This paper presents a polarization insensitive infrared filter based on a liquid-crystal Fabry-Perot (LC-FP) developed for electrically tunable spectrum and performing high efficient imaging detection. Generally, the LC-FP filters are polarization sensitive optical devices, which means that filtering effect will be enormously influenced by ray polarization so as to lead to a low utilizing efficiency of incident energy. Therefore, it is of great significance to find an approach to improve or even solve the problem. The new type of infrared filter designed by us is mainly consists of a FP resonant cavity with a layer of zinc selenide (ZnSe) material as its substrate and a thin film of nano-aluminum (Al) material acting as its electrode and high-reflection mirror. Particularly, compared to the common filters, it has a multi-directional layer of ployimide (PI) film which can make the LC distributed along two mutually perpendicular directions so that the incident infrared light in different polarization orientations are able to be modulated. The experiment results indicate that the filter’s polarization insensitivity is substantially improved, thus it can work well in various polarized infrared radiations, and obviously will have a broader prospect of application.
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To further accelerate the calculations associated with point-cloud-based holograms, wavelet shrinkage-based superpositIon (WASABI) has been proposed. Wavelet shrinkage eliminates the small wavelet coefficient values of the light distribution emitted from a point cloud, resulting in an approximated light distribution calculated from a few representative wavelet coefficients. Although WASABI can accelerate the hologram calculations, the approximated light distribution tends to lose the high-frequency components. To address this issue, random sampling was applied to the light distribution.
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The intensity distribution of an initially plane wave incident on ceria in subsurface layer is calculated numerically with Finite-different time-domain (FDTD) solutions.The results show that the light intensity enhancement is caused by lens effect due to the high refractive index of ceria, and the surface damage characteristics of fused silica is very sensitive to location of ceria, ceria size and incident wavelength. The ceria located on the exit surface of fused silica generates electric field enhancements that are stronger than those on the entrance surface. The increasing of ceria size can lead to higher light intensity enhancement factor (LIEF) and the LIEFs can reach two orders of magnitude when the diameter of ceria is three times that of the incident wavelength. The light intensity enhancement caused by ceria with the same location and diameter decreases with the increasing of wavelength. As ceria on polished surfaces is randomly oriented, the probaility for large intensity enhancements to occur is high. The model may provide effective support for research on laser-induced damage and improvement of processing technology for fused silica.
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The slit spatial filter can be used in high-power laser system. The performance of two-lens slit spatial filter is described and discussed. The laser intensity at the slit edge and the peak intensity of the focal line with different F-numbers and the cut-off frequencies are compared with that of the traditional spatial filter. Simulation results show that the laser intensity at the slit edge and the peak intensity of the focal line are less two orders of magnitude than that of the traditional spatial filter. Besides, the vacuum degree required in the slit spatial filters is about 10-1Torr, which is less two orders of magnitude than that of the traditional spatial filter.
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Paint removal based thermal stress with high repetition pulse is considered in this paper. The temperature distribution of aluminum substrate and paint under laser irradiation is simulated and the thermal stress generated by thermal expansion is calculated. The adhesion force between the paint and the substrate was calculated according to adhesion formula. The conditions for the paint removal can be obtained by comparing the force of thermal stress and adhesion. At the scan speed of 5000 mm/s, the fiber laser with wavelength of 1064 nm, pulse width of 240 ns and frequency of 100 kHz is used to strip red paint from aluminum without any damage. And the stripping effect at the different output power is also taken into account.
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The electric and thermal effects of optical thin film irradiated by Gaussian-pulsed laser are simulated with finite element method (FEM) based on the software ANSYS. The electric field intensity distribution of HfO2/SiO2 high reflective (HR) film is investigated. The transient heat-conduction model of the film is established for the calculation of temperature field of optical thin film coating. Simulation results show that, multilayer films are more prone to damage than single film, and the upper layer of HfO2 layer in the spot center may easily be damaged.
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Infrared small target detection is one of the key techniques in infrared search and track system, and the essence of infrared small detection is background suppression and target enhancement. Inspired by that fact that phase spectrum is proved to be more effective to extract the salient areas than the amplitude spectrum of Fourier transform, a new infrared small target detection method based on phase spectrum of quaternion Fourier transform (PQFT) is proposed in this paper. First of all, four features including intensity, motion, gradients of horizontal and vertical directions are used to construct a quaternion of PQFT. Then, the target enhancement map that highlights the salient regions in the time domain is computed using the inverse PQFT. At last, the real target is directly segmented by an adaptive threshold. Both qualitative and quantitative experiments implemented on real infrared sequences evaluate the proposed method, and the results demonstrate that our method possesses more robustness and effectiveness in terms of background suppression and target enhancement when compared with other conventional methods.
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In this paper, the laser cleaning soil rust layer on the surface of ceramic artifacts by the way of ablation and thermal stress with infrared high-repetition pulse laser is carried out. A cleaning effect can be achieved with laser scanning 10 times at the speed of 480 mm/s and fluence of 795.7747 J/m2 near the ablation threshold. However, the external force is required to make the soil rust layer fallen off. In contrast, a better cleaning effect that the soil rust layer is directly peeled off under the effect of thermal stress without ablation at the contact surface and external force can be observed with the fluence of 1591.5494 J/m2 and laser scanning at 1 time. Furthermore, a two-layer structure model is built to analyze the mechanism of cleaning by thermal stress based on the heat conduction and thermal stress equation. The maximum peeling thermal stress at the contact surface is 2.854×107 N/m2, which is greater than the adhesion stress of 2.050×107 N/m2. This is in agreement with experiments.
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Reconstruction of the lost phase information in the complex optical field from a single-intensity measurement in the Fourier domain is often termed as phase retrieval. This method can be used in many fields, such as electron microscopy, wavefront sensing, astronomy and crystallography and so on. The classical phase retrieval methods use the two-intensity measurements recorded or single-intensity measurement recorded with some prior knowledge, which utilizes the Gerchberg-Saxton(GS)-like algorithm to iteratively recover the phase of the complex optical field. Aiming at the problem that the single-intensity phase retrieval method has poor reconstruction quality and low probability of successful recovery in practical application, an improved method is proposed in this paper—two-step phase retrieval algorithm from single-exposure measurement. Our proposed method divides the phase retrieval into two steps: first, the GS algorithm combined with prior knowledge is used to recover the amplitude information in the spatial domain from the single-spread Fourier spectrum, and then the classical GS algorithm using two-intensity measurements (one is recorded and the other is estimated from the first step) is used to recover the phase information of the complex optical field behind the coded aperture. Finally, the effectiveness of the proposed method is verified by numerical experiments. Compared with the single-intensity phase retrieval method, our proposed method can significantly improve the reconstruction quality and probability of successful recovery.
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Terahertz compressive holographic tomography has been one of the most investigated research topics ever since the generation of terahertz signals. The accuracy of the 3D reconstruction results are influenced by samples size directly. This paper mainly studies that different samples size influence the compressive sensing algorithm iteration number and sparse restriction parameters on the 2.52THz reconstruction results under Gaussian noise conditions. The best reconstruction parameters are given and compared with condition of no noise. This simulation study is possible benefit to the practical application.
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A four-order asymmetric Y-junctions mode (de)multiplexer ((de)MUX) was theoretically proposed for highly integrated on-chip mode-division systems. The high-order mode in the stem waveguide of asymmetric Y-junctions is designed to be separated from the lower-order mode and evolve into the fundamental mode in the narrow arm. Through the widths optimization of branch arms by effective index matching and beam propagation method, the footprint of four-order mode (de)MUX was controlled to be 140×7.1μm2. The calculated excess loss and crosstalk were less than 0.3 dB and -18 dB within the operation wavelength range from 1460 to 1660 nm, respectively. This scheme may be expanded to higherorder modes (de)MUX design.
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Light control-light characteristics of a micro fiber (MF) coated with tungsten disulfide (WS2) nanosheets is demonstrated in this paper. A device with WS2-coated MF has been fabricated, and the transmitted optical powers of the device are measured with 405 and 660 nm pump lasers. By tuning the pump lasers, we achieve the all light controllable sensing of WS2-coated MF over a broadband wavelength range from 1520 to 1620 nm, offering competitive sensities of 0.238 and 0.136 dB/mW for 405 and 660 nm pump lasers, respectively. In addition, The rise and fall times of the transient response to pump lasers are also measured. For the 405 nm laser, the rise and fall times of the transient response are 0.32s and 0.42s, respectively. For 660 nm laser, the response times toward the presence (removal) of the pump light transient response are 0.28s and 0.37s, respectively. Experimental results indicate that the device integrated with WS2 could hold promising potentials in photoelectric and photonic applications.
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Star sensor is a high accuracy sensitive instrument for attitude determination, and the optical system is an essential part of the star sensor. According to the user requirements and CODE V patent library, the optical lens of a star sensor with large relative aperture and wide-spectrum range is optimized. The final design consists of 8 spherical lenses. The focal length is 50mm, the relative aperture is 1/1.35, the field of view is 7° × 7° (the diagonal field is 9.9°), and the spectral range is 500nm to 800nm. The design results show the optical lens has good performance. The distortion is less than 1%, the energy concentration is more than 80%, and the MTF of all fields of view is close to each other. The energy concentration of the spot diagram on the off-axis field of view and the on-axis field of view remains basically the same. The optical system meets modern design requirements for the star sensors.
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Lichen sclerosus (LS) is a chronic inflammatory dermatosis that caused substarntial discomfort and morbidity. Early diagnosis and treatment can prevent the occurrence of squamous cell carcinoma (SCC). Multiphoton microscopy (MPM) has the potential as an effective, noninvasive diagnostic tool for tissues imaging at a molecular level. The technique has several advantages including deeper penetration depth and minimal photo-toxicity and photo-bleaching compared with other microscopy techniques. In this work, MPM was expand to histological investigations, differentiating LS lesion from normal skin by imaging unstained histological sections without hematoxylin and eosin (H and E) staining. Our results present that MPM has the ability to identify the characteristics of LS including the changes of hyperkeratotic epidermis, homogenized collagen, and inflammatory cell infiltration. These tissue architecture details are in perfect agreement with the corresponding H and E-stained images. In addition, the results of collagen content show significant difference in normal skin and LS. The studies indicate that the MPM technique not only has the ability comparable to the H and E-stained images to distinguish between normal tissue and LS, but also can provides more comprehensive diagnostic information for the pathologist. With the advent of the clinical portability of MPM, this technique has the potential to be a powerful tool for diagnosing LS and monitoring the treatment response in vivo.
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Based on the multiple scattering theory and effective medium theory, we demonstrate that flexibly molding the propagation of electromagnetic waves can be realized by designing magnetic metamaterials (MMs) with an array of ferrite rods. By calculating photonic band diagrams and effective constitutive parameters, it is shown that MMs can be used to achieve effective zero index with both the effective permittivity and permeability close to zero, a matched zeroindex material (MZIM). The transmitted Gaussian beam exhibit zero phase delay when it pass through the MZIM slabs with different thicknesses so that the spatial phase change of electromagnetic waves can be regulated, thereby realizing a diversity of electromagnetic wave-front modulation. In particular, the effective index of MMs can be tuned from negative to zero and to positive by controlling bias magnetic field (BMF), resulting in the switching of beam reflection and refraction. The working frequency of MZIM can also be tuned by controlling BMF, adding additional degree of freedom. Moreover, the gradient index MM can be realized by applying a gradient BMF, which can provide an additional parallel wave vector so that the direction of transmitted beam can be controlled more flexibly by controlling the gradient of BMF, which is more convenient for the designing electromagnetic devices.
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Measurement of the surface profiles of machined workpieces is becoming increasingly important to the progress of ultra-precision engineering. Optical non-contact probe is fit for measuring small, thin, soft parts, and it will not cause abrasion damage for the fragile surface of the workpiece. Astigmatic detection systems (ADS) based on the commercial digital versatile disk (DVD) optical pickup heads (OPH) are in widespread use for this purpose due to its well-established standards, high detection bandwidth, compact size, low cost and ease of use. Unfortunately, it has some serious drawbacks relating to issues concerning about dynamic characteristic, low stability and accuracy. In this paper, a high precision displacement measurement system was constructed with a modified DVD optical head by using differential astigmatism focus error detection. The proposed system is cost-effective to quickly accurately estimate and correct systematic errors of four quadrant detector (4QD). Moreover, based on replaceable micoscope objective and automatism testing system of 4QD, it can also detect the two-dimensional angular tilt of the object surface. Our experimental results demonstrated that the OPH showed about 8um measuring range and 20nm resolution.
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An ultra-stable microwave (USM) based on an ultra-stable laser (USL) and fiber optical frequency comb (OFC) is built at the National Institute of Metrology (NIM), China. The sum frequency of the carrier envelope offset frequency of FOFC and the beating frequency between the USL and FOFC is stabilized with an 100MHz microwave signal which is controlled by the H master. The error signal controls the pumping laser power through the pumping current and the cavity length by the piezoelectric transducer (PZT). Meanwhile, the error signal is send to the temperature control part of the optical resonant cavity for the long term stability. The stability of the USM is 1.33E-14 at 1s. The whole USM system is much robust, and can continuously running more than 30 days. This USM will be applied as the local oscillator for NIM5 Cs fountain to improve its short term stability.
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Atmospheric anisoplanatic effect is an important problem to be solved in telescope observation of space target imaging. Numerical simulation of atmospheric anisoplanatic imaging is the basis for studying the restoration of anisoplanatic images. Based on the propagation theory of light waves on the inhomogeneous turbulent path and multilayer phase screens distribution model, this paper establishes a theoretical model of atmospheric imaging for space targets under anisoplanatic conditions. The near-surface atmosphere can be divided into several stratifications of atmosphere at different altitudes. Find out the best phase screen distribution location for each atmospheric stratification, and use the multilayer phase screens at different altitudes to represent the atmospheric anisoplanatic effect. The phase change of the light wave emitted by each point on the space object through the atmosphere is represented by a phase screen, and the final phase size is the superposition of the phase of the light wave passing through the phase screens of each layer. A series of spatial target images are simulated by different layers of phase screens for anisoplanatic imaging, and combined with theoretical analysis to find the best phase screen position and the number of layers. The experimental results show that the three-layer phase screen can accurately simulate the atmospheric anisoplanatic imaging while maintaining the computational efficiency, and effectively reflect the changes of the point spread function (PSF) when the spatial position changes. The imaging results have no ringing and edge effects, and can accurately represent the influence of atmospheric anisoplanatic effect on atmospheric imaging.
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With 3D laser scanning technology, it is possible to record clear and abundant surface information of the measuring object, but it also contains a large amount of redundant information. Because of the complexity of measurement environment, the 3D data obtained by camera contains a large amount of noise, which increases the difficulties of 3D visualization, feature extraction and recognition. In this paper, classical 2D filtering algorithm and 3D spatial clustering are combined for applying to 3D point cloud, which can preserve as much detail as possible on the surface of measured object. Then, Non-Uniform Rational B-Splines (NURBS) surfaces are used for reconstructing the surface of the object from filtered point cloud. In order to reduce the computing time in the reconstruction process while reduce the losses of surface information of the object, a simplification algorithm for point cloud that can preserve the geometric features of the object surface is proposed. The proposed algorithm has explicit significance in surface reconstruction of point cloud with noise, feature extraction and recognition in the future work.
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The RGB-D camera can simultaneously acquire the color and depth information of the target surface, and has been widely used in 3D modeling, machine vision and other related fields. The traditional point cloud registration algorithm only considers the geometric information, it’s operating efficiency is low and the initial value requirement is high. This paper presents a new approach to align different frames point cloud obtained by RGB-D camera, which considers visual textures and geometric information simultaneously. Firstly, detect and match feature points on RGB images, and use RANSAC algorithm to eliminate the wrong matches. Then, convert the 2d matching pairs to 3d feature point cloud based on the depth camera model, and these point pairs without deep data are deleted. Finally, calculate the camera pose parameters by performing the iterative closest point(ICP) on feature point cloud, and apply the calculated pose parameters to the whole frame data. The experimental results show that, (1) In SIFT, SURF, and ORB feature point extraction operators, ORB has the best performance for point cloud registration. (2) The proposed algorithm has a high registration accuracy, the rotation and transform estimation error are less than 0.0097 and 4.2mm respectively. (3) The algorithm also significantly improves the convergence speed, only require 0.138 seconds, and it can meet the real-time processing requirements. (4) The algorithm is insensitive to the initial values and has strong robustness.
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Edge detection plays an important role in image pattern recognition. Because of the shortcomings of poor anti-noise and spurious edges by using traditional edge detection methods. A method of image edge detection based on Sparse Autoencoder neural work is proposed in this paper. This method uses Berkeley Segmentation data set to extract the highdimensional edge features of sample data by training the sparse autoencoder. Through the ZCA (Zero-phase Component Analysis) whitening treatment, the correlation between images is effectively reduced. The standard edge images are input into a Softmax classifier to train a classifier that can classify the edge features of each pixel. Last, the extracted features of each pixel sample are input into the trained Softmax classifier to classify the edge pixels to achieve edge detection. Experiments show that the algorithm has good noise immunity and certain application value.
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The segmented planar imaging method is a new imaging concept based on Van Cittert-Zernike theory that offers significantly reduced size, weight, and power consumption compared to a traditional imaging system and aims to realize high resolution imaging. In this paper, the segmented planar imaging detector (SPID) imaging process has been accurately modeled and quantitatively analyzed to image quality enhancement. The influences of the longest interferometer baseline and the spectral channel number of array wave-guide grating(AWG) on the imaging quality of the SPID have been analyzed. It is verified that the cut off spatial frequency and the resolution of the SPID system is determined by the longest interferometer baseline Bmax. The imaging process of different Bmax have been numerical simulated to evaluate the impact of longest interferometer baseline on the SPID system, and the reconstruction image shows that the imaging quality can be improved by increasing the longest interferometer baseline. Also, the numerical simulations of different number of spectral channels of AWG have been operated, and the results showed that the visibility of interference fringes and spatial frequency coverage points are increased with the increasing number of spectral channels. Therefore, the imaging quality improved with the increasing number of spectral channel of AWG. In conclusions, the research results will provide theoretical and technical supports for segmented planar integral optical imaging system development.
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Based on the multiple scattering theory and Mie theory, we have investigated two types of electromagnetic systems with broken symmetries, which are used to manipulate the propagation of electromagnetic waves. The former one is magnetic metamaterial made of an array of ferrite rods arranged either in periodic or non-periodic configurations, which bears the time-reversal-symmetry (TRS) breaking by applying a bias magnetic field. It can act as a perfect unidirectional absorber that can absorb the incident beam at a specified direction completely, while reflect nearly one half of the incident beam at the symmetrically opposite direction. The underlying physics lies in the excitation of magnetic surface plasmon that behaves differently for various incident directions. The phenomenon can also be understood by calculating the photonic band diagrams and effective constitutive parameters. The latter one is all-dielectric complex graded photonic crystal (GPC) consisting of dielectric rod dimers with a rotational gradient introduced layer by layer, which therefore breaks the spatial inversion symmetry of the system. The GPC is shown to split the incident beam into two separate ones, while for the light beam incident from opposite direction the focusing effect can be observed. The phenomenon can be interpreted by calculating the photonic band diagrams and iso-frequency curves. By tuning the gradient, the performance and the efficiency can be further controlled. The comparative study of configurations with two kinds of broken symmetries is significant for the understanding unidirectional wave propagation and the design of related electromagnetic devices.
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The sensing distance of the traditional phase-sensitive optical time domain reflectometry (Φ-OTDR) distributed optical fiber disturbance sensing system can only reach about 26 km. In order to increase the sensing distance without introducing the new technology and increasing the system cost, a method of processing the data by segmenting thresholds was proposed to increase the system sensing distance to 53.6 km. The locating accuracy is up to 20 m. Considering the impact of noise signal on the system's false alarm problem, a wavelet threshold denoising method based on empirical mode decomposition (EMD) is proposed. Experimental tests show that the method can significantly reduce the noise in the scattering signal and improve the alarm performance of the system.
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To study the performance and microstructure of TC17 thin-walled parts in shock wave and its reflection wave induced by laser, TC17 titanium alloy samples are processed using YAG laser with the wavelength of 1064 nm, pulse energy of 7J and pulse width of 15ns. Thus, its residual stress, microhardness and microstructure of overlapping shock with different thickness are obtained. The results show that with the thickness increasing, the front micro-hardness increases, and the reverse micro-hardness increases firstly and then decreases. The variation of residual stress with the thickness is consistent with the micro-hardness. The front residual stress maximum reaches -496.5MPa at the thickness of 5mm, and the reverse residual stress maximum reaches -171.1MPa at the thickness of 2mm. With the increase of thickness, the distribution of surface dislocations is more uniform, the grain refinement effect is more obvious, and the strengthening effect is the better. The causes of the variation of the double-sided residual stress field with the thickness are explained by theoretical analysis of the propagation and reflection of the shock wave in the material. The conclusions of this investigation have significance for the optimization of laser shock peening thin-wall workpieces.
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A high performance hollow fiber (HF) refractive index (RI) sensor utilizing Tamm plasmon polariton is proposed. The structure of the sensor is a HF with the one dimensional photonic crystal (1DPC)/metal multi-films coated on the inner surface of supporting tube. Theoretical analysis based on a ray transmission model is carried out to evaluate the performance of the designed sensor. Because the lights transmitted in the HF have much larger incident angles than those in the prism based sensors, the center wavelength of the 1DPC should shift to longer wavelength. The origin of multiple resonance dips in the transmission spectrum is investigated by calculating the electric field distribution in the 1DPC/metal structure. The variation of the RI detection range of the sensor with different bilayer period is also analyzed. The optimal bilayer period of the sensor for achieving the highest figure of merit (FOM) at different sensed RI is obtained. Compared to the convention HF surface plasmon resonance sensors which can only detect sensed medium with RI higher than that of the supporting tube material, the RI detection range of the proposed sensor is largely extended to 1.33-1.60 while the FOM is enhanced several times.
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The propagation properties of elliptically polarized light in one dimensional photonic crystal with a magneto-optical defect layer is studied. The one-dimensional photonic crystal is composed of GaAs (H) and Ta2O5 (L), the defect layer material is magneto-optical material Ce:YIG (M), and the structure model of one-dimensional photonic crystal with a magneto-optical defect layer is designed as (L/H)N/M/ (H/L)N. The propagation properties of elliptically polarized light is calculated numerically by using the 4 × 4 transfer matrix method, and the possibility in the polarization controller is discussed. The results shows that the polarization state of the elliptically polarized light is changed with the increase of applied magnetic field, when the center wavelength is 1550 nm, N=8 and the phase difference (φX-φY) of the incident elliptically polarized light is π/6 the transmittance of elliptical polarized light is decreased from 1 to 0.6404, and the phase difference (φX-φY) is increased from π/6 to 0.3565π; then, when the center wavelength is 1550 nm, the applied magnetic field remains unchanged and the N is changed from 1 to 9, the transmittance of the elliptical polarized light is decreased from 1 to 0.2343, and the phase difference (φX-φY) is increased from π/6 to 0.7363π.
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The accuracy of air target identification is of great significance for air defense operations and civilian management. A fine-grained recognition model of aerial target based on bilayer faster regions with convolution neural network (Faster R-CNN) with feedback is proposed in the paper. Faster R-CNN model is a typical target detection model based on deep learning. However, its ability to distinguish categories with subtle differences is not enough. In the proposed model, Faster R-CNN model is used for the first training to get a classification model and the clustering analysis of the classification result is used to get confused categories. Then the first training model is fine-tuned to retrain the confusing categories. The model is tested in the FGVC-Aircraft-2013b data set, and the average training accuracy is raised from 88.7% to 89.3%, the accuracy of the classification is raised from 88.98% to 91.21%, which shows that this model is effective in improving the fine-grained identification of air targets.
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