This PDF file contains the front matter associated with SPIE Proceedings Volume 11850, including the Title Page, Copyright information, and Table of Contents.

The performance of the imaging system under low light intensity will be affected by shot noise, and the shot noise will become stronger as the power of the light source decreases. Aiming at the impact of shot noise, this paper applies the principle of deep learning to low-light image enhancement. To improve the generalization ability of deep neural networks in different scenarios, a block matching solution based on BM3D is proposed to optimize the data of the Retinex network model. In the training process of the network, the consistency of the reflection component and the smoothness of the illumination component of the low-light image and the normallight image are used to constrain, without the need for real data of the reflection component and the illumination component. Experimental results show that this method can obtain a satisfactory low-light enhancement effect, and can significantly improve the reconstruction results of low-light images affected by noise.

Utilizing the single-photon detector, a direct-detection single-end Brillouin optical-fiber sensor is proposed and experimentally demonstrated for distributed temperature information measurement, which is an excellent candidate for the demodulation of frequency shift from Brillouin gain spectrum in conventional Brillouin schemes with coherent detection and frequency sweep. In our scheme, the ratio of the backscattered Rayleigh component and the Brillouin anti- Stokes signal is used to evaluate the ambient temperature along the fiber under test. Proof-of-concept experiments demonstrate 20dB dynamic range over 34km sensing fiber with a 0.96°C temperature error. In view of the good characteristics we achieved now, the photon-counting distributed Brillouin temperature sensor may be used in practical engineering fields such as smart grid.

Metasurface is a class of two-dimensional microstructure functional materials, which has an ability of modulating light in subwavelength region and becomes a hot topic during the last decade. An advantage of metasurfaces is their versatility by invoking the degrees of freedom of light field to achieve various functionalities. In this paper, we report methods of using the polarization and dispersion of light to achieve multifunctional metasurface devices, allowing the different degrees of freedom of light to carry independent phase profiles to achieve the polarization-dependent conversion of Bessel beams with different orders and numerical apertures as well as integrated optical tweezers-optical spanner metasurface. Also, the wavelength-controlled multifunctional metalens by introducing an improved genetic algorithm has been implemented. We envision our research are expected to be the potential candidates in multifunctional integrated optical devices.

Image fusion method is an algorithm that synthesizes images from different sources into a new image. The advantage of image fusion technology is that different image information presented by multi-source sensors can complement and improve each other to extract the effective information in the source image. It can also obtain a more effective and richer image with description information. According to the technical methods of image fusion, an improved image fusion method for fast non-downsampled contourlet transform (NSCT) was selected for handheld. The source infrared image and source low-light image collected by the observer were image fusion. In this method, the scale filter and the directional filter were convolved respectively in the composition of image decomposition and reconstruction to reduce the number of iterations of image decomposition and reconstruction, improve the efficiency of algorithm operation, and ensure that the system worked in real time.

A subwavelength nanocavity grating structure designed as a linear polarizer for application in infrared wavelength range with ultra-broadband bandwidth of 3-20 μm is proposed. The structure of the proposed linear polarizer consists of barium fluoride layer as dielectric antireflection layer and nano optical cavity formed by metal aluminum, zinc sulfide (ZnS) and metal aluminum that is prepared on zinc selenide (ZnSe) substrate. It is found that when the total thickness of cavity layer and metal layer is fixed, increasing the number of cavities can significantly improve the extinction ratio of the structure while the transmission of the polarized component remains almost unchanged. Theoretical simulation results show that a transmission of greater than 83% and an extinction ratio of greater than 53 dB in the whole 3-20 μm waveband can be obtained by optimizing the structure parameters with a period of grating of 600 nm and single nanocavity. The proposed cavity structure of the linear polarizer provides a new idea for the design and development of high-performance linear polarization devices.

We use commercial finite element simulation software COMSOL Multiphysics to simulate the generation and propagation of photothermal signals. The software is based on the finite element method, solving actual physical phenomena, through mathematical methods to solve partial differential equations to simulate real physical phenomena. Its advantages mainly include excellent computing performance and multi-field coupling ability, accurate numerical simulation results, and good calculation for various physical phenomena in various fields of scientific research. In the visualization research of breast cancer photothermal imaging in this paper. We mainly simulate the generation and transmission of breast cancer photothermal effect through two modules: light transmission module and biological heat transfer module. We use the simulation software COMSOL Multiphysics to develop a computer numerical simulation model composed of water, tumor, breast tissue, subcutaneous tissue, epithelial tissue and short pulse laser sources of different wavelengths. The model studied the propagation and heat transfer of laser at 633nm, 700nm, 752nm and 900nm in the human breast. The energy transfer from the water layer to the breast tissue is described by the diffusion equation or the Helmholtz equation. The temperature change of the breast tumor and each breast tissue is obtained by solving the biological heat transfer equation. The interaction of the short pulse laser with the breast model at different wavelengths was obtained.

Atomics magnetometers achieve remarkable accuracy, applying to production and scientific research. However, their size and bulk components make it difficult to achieve higher accuracy. We investigate the influence of the skew angle of the pump beam on the optical pumping rate in an atomic magnetometer. An analysis based on the Bloch equation is proposed to decrease evaluate optical errors in the process of production and assembly. When the incident angle is non-zero, the pumping rate has a projection in the direction of a static magnetic field. By establishing the pumping rate equation, the pumping rate of each position in the vapor cell in the direction of static magnetic field at different pump light skew angles is calculated in our study. The sensitivity was measured experimentally to demonstrate the simulation results. The results indicate that the optical pumping rate decreases as the amplitude of skew angle and propagation distance increasing which can be evaluated by one-dimensional distribution while the decay rate increases with the rise of the angle. The simulation values of the rubidium pumping rate, obtained with an incident angle of 0.5° , in the center of the vapor cell are reduced by 46%. The sensitivity decreases with the increasing skew angle similar to the attenuation trend of the optical pumping rate but not the same. Our work provides a reference for evaluating the optical error of atomic magnetometer which is useful for miniaturization design.

A THz hollow-core Bragg waveguide constructed by cascading waveguide units with supporting bridges on different air rings is proposed. The influence of the supporting bridges on the transmission loss of the waveguide is demonstrated numerically. Results show that the supporting bridges in the first air ring play the most important role on the transmission loss. By reasonably selecting the length ratio of the waveguide units, the waveguide transmission loss can be reduced to less than 0.5 dB/m in range from 0.572 to 0.62THz, and the loss of the proposed Bragg waveguide are close to those of the IHC Bragg waveguide.

Color rainbow holographic near-eye display with none-overlapping frequency components from color object has been proposed. The resolution, however, is low due to the very small bandwidth of object information used in the calculation. Numerical simulation methods for color rainbow hologram calculation and simulation that allow a certain overlap in the frequency domain is demonstrated in this study to improve the image quality of reconstructed image of color rainbow hologram. Through optical experiments, it has been proved that allowing higher recording bandwidth can improve the display quality.

In dynamic scene imaging, multi-sensor high dynamic range (HDR) fusion technology used to solve the ghosting problem of multi-exposure fusion based on camera aperture, and achieve high-quality HDR video imaging. Therefore, it has made significant progress in image capture and synthesis of HDR optical imaging. First, we introduce the development status of multi-sensor based on time bracketing and space bracketing. Then introduce the different method of multi-exposure image fusion, including aligning different exposures, rejecting misalignment information and patch-based optimization. Finally, discuss the key technical issues and development trends of this technology in HDR imaging technology.

For several years, Brillouin-based optical fiber sensors plays an important roles in the fields of distributed temperature and strain measurements in the real world. Among these sensors, the optical chirp chain (OCC) based Brillouin optical fiber sensor is a good candidate to realize ultrafast distributed sensing, which is of great importance to distinguish quickchanging events in practical applications. In this paper, the principle of OCC and the OCC based Brillouin optical timedomain analysis (BOTDA) sensing are introduced. In OCC-BOTDA, there are three types of spectral distortions, i.e. the back end distortion, the frequency lag of main peak and the frequency saltation distortion, which are influenced by the transient stimulated Brillouin scattering, are verified in the simulation and experiment in this paper and attributed to the rapid frequency sweeping.

A high resolution distributed dynamic strain sensing has been proposed and experimentally demonstrated based on the combination of Brillouin and Rayleigh scattering. The proposed scheme employs the same set of frequency-scanning optical pulses modulated through the frequency-agile technique for fast measurements. The Brillouin optical time domain analyzer (BOTDA) technology is used to provide absolute measurement benchmarks, while the phase-sensitive optical time domain reflectometer (φ-OTDR) technology is used to capture relative strain changes in details. Two groups of 100 Hz vibrations with different amplitude (300 nε and 250 nε) have been measured under two different absolute strains (1173.9 με and 525.3 Με), which allows for dynamic absolute strain measurement with a high resolution of 8.4 nε.

We proposed a multiplexing method of optical fiber Fabry-Perot interferometer (FPI) for multi-point refractive index (RI) sensing application. This method is based on the frequency modulated continuous wave (FMCW) interferometry, in which a series of FPIs are connected by fiber couplers as like the bus-structure. Due to the spatial difference among FPIs, the reflection signals from different FPIs can be separated in spatial domain by Fourier transform. Applying inverse Fourier transform, the interference spectra of every FPIs can be demodulated independently in wavelength domain. Three FPIs are multiplexed for verifying the multi-point RI sensing ability of the proposed method. The experimental results show that the proposed multiplexing method performs well in multi-point RI sensing applications. In the RI range of 1.3334~1.3410, the RI sensitivities of the multiplexed FPIs are as high as 1200 nm/RIU, and the RI measurement accuracies are as high as 5×10^-6 RIU. In addition, the sensing system can demodulate the interference spectrum from the reflected signal as low as 5 pW. When the light source power is 3.2 mW, the theoretical maximum multiplexing number is 8000. This work provides an efficient solution for multi-point RI sensing.

A dynamic distributed Brillouin optical fiber pressure sensor based on frequency agility technology is proposed, and the performance of dynamic and static pressure sensing is experimentally demonstrated. A set of frequency-agile pump pulse sequences with single pulse duration of 250 ns are generated by an arbitrary waveform generator. The interval of the frequency sweep pulse sequence is 30 μs, the maximum repetition frequency is 18.2 kHz, and the average is 64 times. Double-coated single-mode fiber (SMF) is used as the sensing fiber to enhance the pressure sensitivity of Brillouin frequency shift (BFS), which the outer coating diameter is 3000 μm. The BFS pressure sensitivity of -3.32 MHz/MPa is achieved in the pressure range of 0-24 MPa, which is about 4.5 times that of SMF. The measurement time of the proposed optical fiber pressure sensing system is only 3.52 ms. Furthermore, the dynamic pressure measurement experiment is carried out, and the continuous measurement of the dynamic range of 6-0 MPa is achieved, and the dynamic distributed pressure measurement ability of the sensing system is verified.

In this paper, we implemented diffraction tomography (DT) by using a continuous-wave (CW) terahertz (THz) source. An off-axis digital holographic interferometry was built to measure the complex amplitude distributions of the sample at various rotational angles. Based on the Rytov approximation, the three dimensional (3D) refractive index (RI) distribution of the polystyrene (PS) foam spheres was reconstructed by the filtered backpropagation (FBPP) algorithm. For enhancing the quality of the reconstructed RI tomograms, the auto-focusing algorithm was applied to correct the decentered error of the sample when placed on the rotation configuration. This study demonstrated that THz-DT can be applied to reconstruct the high-precision 3D RI distribution, which has extensive application prospects in 3D imaging and nondestructive testing.

During the stimulated Brillouin scattering in multimode fiber, the Brillouin gain of different mode of the signal beam is affected by the property of both the light modes and acoustic modes in waveguides. In our study, the stimulated Brillouin scattering process in two-mode fiber is investigated, both experimentally and numerically, based on the mode characteristics of light field and acoustics field. The results indicate that the Brillouin gain of corresponding combination of signal-pump modes is determined by the overlapping area of optics-acoustic mode fields.

In this paper, stress waves caused by laser pulses with three different temporal profile sets have been detected by using PVDF piezoelectric films. In the experiments, a solid target was irradiated by laser pulses in air. Firstly, the influence of laser pulse width on the stress wave’s pressure peak has been studied. The results show that the maximum pressure of the laser-induced stress wave will increase with increasing full width of laser pulse and there is a saturation width of the laser pulse. Then, the influence of laser pulse rise time on the stress waves’ pressure increasing process has been analyzed. The results show that a laser pulse with shorter rise time could produce the plasma as well as the stress wave, earlier. Earlier production time means that laser-induced stress wave has more time to improve its maximum pressure.

In order to realize high diffraction efficiency and high-quality imaging of liquid crystal-based Pancharatnam-Berry phase (P-B phase) lens at designed wavelength, the polarization holography method is utilized to expose the azo dye molecules and the mixture of liquid crystal molecules. Different from the usual method of spin-coating alignment materials and then spin-coating liquid crystals, this method is voltage tunable which does not require strict control of the spin-coating thickness of the liquid crystal in order to achieve the thickness of the half-wave plate. In addition to the advantages of high resolution and large aperture, the fabrication process of the liquid crystal based lens is greatly simplified. Experimental results show that clear images with diffraction-limited resolution can be obtained, and the diffraction efficiency is greater than 90%. This work provides the possibility for the wide application of P-B phase liquid crystal lenses, especially in the fields of 3-dimensional virtual reality (VR) and augmented reality (AR).

A metal-dielectric-metal nanopillar metasurfaces with variable three-dimensional sizes is proposed and experimentally demonstrated to achieve anomalous deflection at different angles with different phase gradients. Theoretical studies have shown that subwavelength nanopillar with different lengths, widths and heights on a glass substrate can achieve high amplitude response and complete 2π phase delay in the reflection field. Anomalous deflection metasurfaces with three phase gradients of π/2, π/4 or π/8 in supercell units composed of 4, 8, or 16 nanopillars of different sizes working at wavelength of 1550 nm are designed and investigated. Under linearly polarized normal incident beam, the anomalous deflection angles of the three phase gradients are, respectively, 23.97°, 12.21° and 5.87° with a reflection of 83%, which is consistent with the generalized Snell's theory. The negative refraction and total reflection phenomenon under the oblique incident beams are generated in the case of phase gradient of π/4, which are completely consistent with the numerical results. Using two-photon laser direct writing technology, a metasurface with π/2 phase gradient nanopillar was fabricated on a 170 μm thick borosilicate glass substrate. The anomalous deflection angle measured by infrared polarization detection is 24°, which is essentially the same as the designed value. The demonstrated work provides a new way for realizing artificial control of electromagnetic wave propagation in optical communication and other fields.

The beam quality factor (M² parameter) of output laser in a three-core and seven-core conventional photonic lantern excited by incoherent sources is analyzed based on analytical and numerical method. Theoretical results show that the limitation of output laser beam quality is M²=1.75 for a three-core photonic lantern and M²=2.70 for a seven-core photonic lantern. Both the mode evolution process and beam quality factors of these two kinds of photonic lanterns are verified by numerical calculations. It is shown that good beam quality of the theoretical limitations can be realized only if the adiabatic conditions are satisfied very well. These results are very meaningful for practical application of high brightness incoherent beam combining based on conventional photonic lanterns.

Irradiating experiments with a 532nm laser were conducted to investigate the effect of integration time on crosstalk line intensity for IT-CCD. Crosstalk lines were observed in all the experimental images with different integration times when laser power was high enough. Crosstalk line gray value was calculated by eliminating the impact of background light and main spot. Calculation results show that crosstalk line intensity is independence of integration time while proportional to laser power. According to the working principle of IT-CCD image sensor, the formation mechanism of crosstalk line is the quantitative overflow of stored charges from photodiode to vertical CCD in the process of vertical transfer. According to the working principle of electric shutter, the reason of the independence of integration time on crosstalk line intensity is that the period of shutter pulse is an invariant. This research enriches the knowledge of crosstalk effects for IT-CCD, and provides important support for deep searching the mechanism of laser jamming on CCD.

The microneedle array (MNA) is a painless, minimally invasive device composed of micrometer-sized and submillimeterheight needles, which is used to deliver drugs or extract signals. In this paper, we can use digital light processing (DLP) 3D printing technology to simply fabricate sharp MNAs (tip radius<6 μm) and good straightness (coefficient of determination R²>0.996) with adjustable size, then PDMS molds can be obtained by replicating MNAs through the soft imprinting process. Further, we proposed a UV imprinting method to produce microneedle molds rapidly and massively, by casting photosensitive resin in PDMS mold to transfer the MNAs microstructure. Based on the dissolvable MNAs fabricated by PDMS molds, we also conducted a skin penetration study to verify the functional capabilities of the MNAs in biomedicine.

Two types of fast Brillouin optical time-domain reflectometry (BOTDR) for dynamic strain measurements have been proposed and experimentally demonstrated based on the frequency-agile technology. Using the frequency-agile modulated reference wave, the spontaneous Brillouin gain spectrum (BGS) is fast scanned in the frequency domain. Then, the spontaneous BGS can be reconstructed in the time domain by employing the band-pass filter and envelope detection. The frequency-agile technology enables two fast frequency-modulation methods, optical frequency sweeping and optical chirp chain modulation. Based on these two methods, the proposed fast BOTDR allows for a distributed, one-end-access and dynamic strain measurements. Besides, the sensing performance is investigated with different experiment parameters. The dynamic strain with dozens of Hertz vibrating frequency is successfully measured for both fast BOTDR schemes, which shows the proposed fast BOTDR a bright prospect.

Here, we use a compact gas cavity based on anti-resonance hollow-core fiber (HCF) for trace gas detection. Since there are lots of characteristic absorption lines (P and R branch) of CO₂ molecule in 2 μm band, we used a self-made 2 μm fiber amplifier seeded by a precisely tunable narrow linewidth diode laser as the detection light source. The absorption characteristics of R(26), R(28), R(30) and R(32) at different CO₂ pressure are measured and analyzed. This work provides a potential cost-effective method for the high-precision detection of trace gas.

This paper proposes a D-type optical fiber local surface plasmon resonance biosensor based on graphene-gold nanowires-graphene sensitization. In this paper, the modal characteristics of three sensor models are analyzed by the full vector finite element method (FEM). Their simulation results are compared, which shows that the sensitivity of the sensor designed in this paper is better than that of the other two models. When the external refractive index is 1.33-1.40, the maximum sensitivity of the sensor designed is 7383.79 nm/RIU. The average sensitivity is 4136 nm/RIU.

The detection of ocean profile optical parameters is of great significance to ocean science. The existing ocean passive remote sensing systems mainly focus on the detection of surface parameters. If we want to obtain the ocean profile parameters in a big area, active remote sensing technology is necessary to adopted. The difficulty of ocean active remote sensing detection system lies in the strong reflection of the sea surface, and rapid attenuation of the laser energy under the surface. Therefore, the dynamic range of the signal can reach nearly five orders of magnitude. It’s a great challenge for the performance of the detection system that undertakes the role of photo-electric conversion. Only by fully simulating the performance of the detection system can we obtain the corresponding relationship between the returned optical signal and the output electrical signal, and ensure the reliability of the subsequent signal processing. In this paper, Hamamatsu multipixel Photon Counter is selected as the detector, and the return photo profile data is provided by Ocean University of China. The photoelectric conversion process is simulated both in digital and analog mode. Meanwhile, the influences of background light, after pulse, accumulation times, laser wavelength and detection area are also simulated and analyzed. The simulation results are in good agreement with the trend of the theoretical curve. The simulation system provides a basis for accurately evaluating the photoelectric conversion process of Ocean Lidar, and guarantees the authenticity of the subsequent signal processing system.

Since microcavity Kerr soliton combs have spectrum which can exceed one octave, high repetition rate and potential for on-chip integration, the dissipative Kerr soliton generation in microresonators has been widely studied in recent years. Although microcavity soliton combs have been demonstrated in microcavities of different materials and shapes, it is still challenging for soliton generation due to positive thermal effects. In this paper, a sol-gel processed SiO₂-CaF₂ hybrid toroid microresonator is numerically investigated. Based on the calculation and simulation model we developed, this CaF₂ coated SiO₂ microresonator may avoid thermal effects and thermo-mechanical oscillations. Compared to organic coatings for thermal compensation in previous studies, it is a more promising platform for soliton generation.

The atmospheric turbulence disturbs the phase fronts of orbital angular momentum (OAM) beams, which significantly affects the detection of beam modes. In this paper, we propose a method based on the convolutional neural network (CNN) to detect OAM modes in atmospheric turbulence. This method does not require a separate system to suppress the influence of atmospheric turbulence. The propagation of multimode OAM beams in atmospheric turbulence is simulated by setting several random phase screens in the transmission channel. We select three levels of atmospheric turbulence. In all these cases, the predicted error of the trained CNN is lower than 2 ×10^-5 , which indicates that our network can detect the mode distribution in multimode OAM beams efficiently and accurately. We believe that this approach for detecting OAM modes holds great promise for potential applications and will provide widespread benefits for many optical fields.

The interference results are associated with the force and temperature fluctuation in Taiji-1. To obtain the maximum effect of these noises, the coupling noise analysis of the force and temperature on the interferometer is discussed. First, the impact mechanism of force and temperature fluctuation is introduced. Then, the mechanical and optical simulation based on a simplified model are performed in turn to get the relationship between the noises and the interference results. The final relationship indicates that coupling effect of the force and temperature fluctuations on the interference is a superposition of the results from the situation with only force or temperature fluctuation, corresponding to the respective frequencies. Based on the relationship, the final amplitudes of interference results caused by the force and temperature fluctuation are 111pm@0.1Hz and 87.47pm@0.05Hz, respectively, when the corresponding noises are 50µN@0.1Hz and 1.7mK@0.05Hz in the proposed simplified model.

Based on the analysis of Talbot phase-locking theory of edge emitting semiconductor lasers, a method to obtain a single in-phase mode on a tapered laser chip is proposed. A phase-locked model with 1/2 Talbot spatial filter cavity for mode selection placed between 8 emitters on each facet is set up. Based on the mode coupling rate equation theory, the parallel coupling phase-locking conditions with different fill factors is analyzed. The results show that the stable parallel coupling phase lock can be achieved for 8 emitters with the pitch of 20 um, when the fill factor is set between 0.06 and 0.12, and the phase-locking time is about 3 ns. The supermode threshold gains are also calculated under different fill factors. In the phase-locked model, when the fill factor is approximately 0.1, the threshold gain difference between the in-phase mode and out-phase mode could reach the maximum, which is around 78cm^-1 . Therefore, single in-phase mode output of this novel laser with Talbot cavity becomes more robust. The simulation analysis provides a reliable theoretical support for the preparation of a coherent array laser with a single in-phase mode output.

For the collimation and focusing of supercontinuum, the divergence angle is an important parameter. In order to obtain the far-field beam divergence angle corresponding to multiple wavelengths of the supercontinuum in the wide spectrum range of 0.5-2.3μm, two types of cameras are used to collect the far-field spot image. The range covers the supercontinuum that PCF can generate. The relationship between the beam quality/divergence angle and the wavelength is summarized. The experimental values are in good agreement with the theoretical values. To the best of our knowledge, it is the first report to measure the divergence angle of supercontinuum in such a wide range of wavelength. The divergence angle of the supercontinuum after transmission through a section of passive optical fiber with a core diameter of 10μm was also measured. The results show that the divergence angle of supercontinuum variation with wavelength exhibits different characteristics for the 10μm core fiber and the PCF.

Recently, bio/chemical sensors are widely used in the fields of medical diagnostics, environmental monitoring, and food safety. Among them, reflection interference spectroscopy sensor has significant advantages in real-time, label-free and non-destructive detection. However, reflective interferometer sensors are mainly based on porous materials with a small variation range of the aperture size, and flow of the measured molecules is not smooth in the semi-closed nanopores, leading to the limited detection range, long response time and poor anti-interference ability. In this work, we experimentally demonstrate a real-time reflective interferometric optical sensing system based on the ordered nanowires/disordered porous Si hybrid structure. Combined with an optical fiber spectrometer and a microfluidic unit, our constructed sensor can realize the selective detection of glucose molecules. The peak shift of fast Fourier transform (FFT) spectrum can be up to 308.6 nm as the glucose concentration changes at 1 mol/L. The response time is about 80 s, and the linear range is from 2 mmol/L to 3 mol/L. The proposed hybrid structure is much superior in sensitivity and response time as compared to the sensors based on the double-layer porous Si, and can simultaneously realize the selective detection of both large and small molecules under reasonable design, while the sensors based on single layer of order Si nanowires or porous Si cannot. This work opens a pathway for label-free and selective sensing in the circumstances of mixed large and small molecules, which expands the functions and applications of reflective interference optical sensors.

Compared with traditional refraction and reflection elements, diffractive imaging elements can be used as the primary mirror in large-aperture space telescope systems due to their low surface density and loose surface tolerances. At the same time, the expansion of the aperture of diffractive imaging elements has become an important development trend. In order to explore the manufacturing method of large-aperture diffractive imaging element. This paper proposes to use holographic lens as the diffractive mirror, and enlarge the aperture of holographic lens through exposure mosaic technology. By deflecting light path and rotating the substrate, the distribution position of the Gaussian beam center of the interference light field is changed, and the aperture of the holographic lens is increased through multiple exposures and developments. The effect of splicing errors on the imaging of the holographic lens is analyzed. In the scheme, the exposed and developed area is used as the alignment basis. The splicing error is judged according to the moiré fringe formed by the light field and the developed area, the fringe acquisition and control system is used to collect the moiré. The interferometer measured the phase error at the splicing area of the sample to be about 0.1λ,and the splicing error satisfies the imaging requirements of the holographic lens. The results show that the holographic splicing scheme is feasible and the splicing accuracy is high, which provides a solid theoretical foundation and technical support for multiple exposures to produce larger-diameter holographic lenses.

The effect of the local error in the display module on the reconstructed image quality of the integral imaging system is analyzed. First, the geometric optics and the ray tracing theory are utilized to build the local error theoretical model based on the integral imaging principle by considering the optical axis transform and the pixel information dislocation. The simulation experiments are carried out to verify the validity of the above analysis. Experimental results show that the homologous points on EIs form two separate images. The separation distance depends on the local error, the size of the lenslet and the magnification ratio of the integral imaging system.

We explore the influence of cooling temperature on mode instability (MI) effect based a 2kW oscillator that can work stably at low temperature. The corresponding MI threshold of the oscillator is carefully measured with different operating temperatures of the Ytterbium-doped fiber (YDF) and laser diodes (LDs). It is found that whether decreasing the cooling temperature of the LDs or YDF, the MI threshold would rise, but decreasing the cooling temperature of the LDs has better effects. In our experiments, the MI threshold increases by 21.6%，from 1752W to 2130W when the operating temperature of the LDs changes from 25°C to 5°C due to the central wavelength of the LDs shifts from 976nm to 970nm, corresponding to a lower thermal load. In the process that only the cooling temperature of the YDF drops, although the increase is small, we have observed a rising trend of the laser MI threshold. This work can clarify the influence of cooling temperature on the laser thermal effect, which is conducive to perfecting the theoretical model of the MI effect of the fiber lasers.

Photonic crystals (PCs) are artificial micro-nano structures consisting of different materials periodically arranged. They can be divided into two categories: simple and compound PCs. They have broad application prospects in many fields such as micro-nano photonics and optoelectronic integration. Laser holography method is an important method for fabricating PCs. In this work, a theoretical study on the production of compound PCs by multi-beam holographic interferometry is carried out, and a four-beam configuration with a certain symmetry is designed to produce two-dimensional compound PCs. Simulations based on MATLAB program are in good agreement with the theoretical analysis. The evolution of the unitcell and contrast of the compound PC under different polarization combinations of a single beam and double beams are further studied. The results indicate that the polarization affects the unitcell of the PC sensitively. Under different polarization combinations, a variety of rich unitcell shapes of compound PCs such as elliptical-like rods and wave-like stripes are obtained. When all interfering beams are linearly polarized within the xoy plane, the compound PC has the best contrast. These above results hold promise for the design and fabrication of compound PCs with various unitcell shapes.

During the production and processing of the cavity surface of a semiconductor laser, micro-defects such as scratches, cracks and grooves will inevitably be caused to the cavity surface. The existence of micro-defects on the cavity surface will affect the distribution of the laser inside the cavity surface, causing the cavity surface temperature to rise sharply. When the temperature reaches the melting point of the cavity surface material, it will cause thermal fusion damage to the cavity surface. When the temperature reaches the vaporization point, microdefects on the surface of the cavity will cause further damage and expansion.In the summary and analysis of the interaction mechanism between laser and optical materials, the temperature distribution and damage expansion model of GaAs cavity surface were established based on the theory of heat conduction and deformation geometry.By comparing and analyzing the damage expansion induced by tapered microdefects with different depths and base radius, it is found that the depth of damage expansion is inversely proportional to the depth of the initial defect and directly proportional to the width of the initial defect.And it was found that the larger the surface area of the initial microdefects, the greater the damage expansion speed and depth.At the same time, by comparing the change rule of the dot center temperature with the damage expansion speed, it is found that the damage expansion speed caused by the microdefect is consistent with the rising speed of the point center temperature.

In this paper, first, we show the measuring results of 2D MoS₂ Raman spectra separately under the laser excitation of 532nm, 660nm, and 785nm. We confirmed that when the photon energy is close to the energy gap of the single layer MoS₂ (i.e. when using the 660nm laser wavelength), many Raman spectral peaks related to double resonance will appear. Through analysis, we actually can locate total 18 Raman spectral peaks under 660nm excitation, and we labeled the vibration origin of some Raman peaks. Then, we present the Raman spectra characteristics of 2D MoS₂ excited by the laser (532nm) with different polarization, where we did the measurements with the radially polarized light and azimuthally polarized light and the corresponding radial or azimuthal polarization analyzer. We analyzed the measuring results and found that the Raman spectra contributed by two different parts: one part comes from the light that still keeps the radial or azimuthal polarization, while the other part lost the original polarization.

Semiconductor laser is partially coherent beam, while the beam quality factor is based on fully coherent beam. The Wigner distribution function for partially coherent beam is used to analyze the semiconductor laser beam. The Wigner distribution function contains both spatial information and spatial frequency information in the phase space. A method for measuring the Wigner distribution function of semiconductor laser is reported. The intensity distribution of the beam caustics is measured by two focusing mirrors, and the Wigner distribution function of semiconductor laser is reconstructed. Based on the reconstructed Wigner distribution function, the light intensity of semiconductor laser is simulated. The simulated data are in good agreement with the experimental data. Through the properties of Wigner distribution function, the wavefront aberration and coherence of semiconductor laser are analyzed. The wavefront of semiconductor laser is symmetrically distributed around a point, and the wavefront on the left side of the laser diode array is larger than that on the right side. Due to the temperature difference of the laser chip, the coherence on both sides of the laser diode array is better than that in the middle of the laser diode array.

Micro-nano optical device based on the moiré imaging effect has been widely used in the visual security and anticounterfeiting due to the unique visual effect. However, the micro-pattern array in the state-of-art moiré imaging device is based on nanoimprint lithography and the gravure printing technique which cannot achieve multi-color effect. Even worse, the volatile organic compounds in the printing ink does harm to the environment and human health. Therefore, it is urgently needed to develop a moiré imaging device free of ink. In this paper, we propose to integrate the diffraction grating into the moiré imaging device. Grating MPA is formed by rasterizing the micro-pattern array layer, and combined with the microlens array to construct a moiré imaging device, which was a hybrid refraction-diffraction structure. In the experiment, a diffraction grating with a period of 2 μm and a cylindrical lens array with a focal length of 90 μm were integrated on both sides of a 50 μm thick film to realize the imaging device. A formula that can predict the intensity of diffraction dispersion is derived, and the colorful moiré image related to the orientation of the grating and the position of the light source is achieved, in which the color can cover the whole visible spectrum under different viewing angle.

To improve the life of semiconductor laser, the size of semiconductor laser resonator surface damage must be studied to determine the catastrophic degradation mechanism of semiconductor laser. In this paper, the light intensity distribution of the GaAs laser resonator surface with a wavelength of 980 nm is studied under the condition of a local heat source. In order to effectively describe the influence of resonator defects on the light intensity of semiconductor lasers, according to different sizes and types of defects, the cuboid defect model and the sphere defect model are set up. The internal light intensity distribution of different sizes of micro-defect resonator surface and non-defect resonator surface is compared and analyzed, and the light intensity increase multiple is used to evaluate the influence of defect size on light intensity. The results show that under the same parameters, the irregularity of the sphere defect leads to a greater intensity enhancement than that of the cuboid defect. The size of the micro-defects is the main mechanism that causes the intensity of the resonator surface to increase, and at the same time affects the damage propagation of the laser resonator surface. It can be quantitatively predicted that the maximum light intensity will be produced when the defect size (length, width and depth) is similar to the wavelength of the semiconductor laser.

The accurate prediction of spectral sensitivity of digital camera is essential for various aspects in color science, such as color correction, color rendering and color constancy. In this paper, a multi-objective optimization algorithm was proposed to estimate the spectral sensitivity of cameras. Multiple objective functions and Sine subspace based spectral sensitivity were employed in the proposed algorithm, in which excellent robustness and high smoothness were achieved. The performance of this algorithm was theoretically evaluated by multiple numerical simulation experiments, and was further compared with other algorithms in previous literatures based on the criteria of color aberration (δE), spectral recovery error (SE) and similarity between the estimated sensors and the measured ground truth (Vora). According to the numerical simulation results, the multi-objective algorithm can significantly improve the performance of the spectral sensitivity estimation, which may promote its various applications in the fields of color correction and illumination modeling between cameras.

An ultra-lightweight and compact diode-pumped solid-state laser has been developed targeting the applications of LiDAR in resource exploitation, environmental monitoring, etc. We have achieved Q-switched pulse energy of above 650 μJ at a central wavelength of 1534 nm with an optical conversion efficiency of 3.3% in the operating frequency range of 1-20 Hz at a peak pump power of 10 W. In our experiments, we used a 940-nm semiconductor laser to pump Er,Yb co-doped glass with a saturable absorber (Co:Spinel) to realize passive Q switching. Meanwhile, we have developed a theoretical model for this Er,Yb co-doped glass laser under pulsed pumping. This model was validated in both gain-switching and Q-switching scenarios, taking into account the presence of excited state absorption and up-conversion effects. The simulation results are in excellent agreement with the experimental ones.

Skin spectral reflectance is playing an increasingly important role in many fields, including medical diagnosis, computer graphics, cosmetics industry, and even social sciences. In this paper, we proposed an algorithm based on multispectral imaging to reconstruct the skin spectral reflectance. Polynomial regression model, the equi-Gaussian filters and the equienergy filters were employed in the proposed algorithm. The performance of the proposed algorithm was evaluated under different numbers of filters and noise based on the chromatic aberration (ΔE) under D65 light source, and compared with the other spectral reconstruction algorithms appeared in previous literatures. What’s more, the real human skin datasets were employed to reconstruct the skin spectrum, which made our research more practical. According to the reconstruction results of the real skin data set, the proposed algorithm leads to considerable improvements in comparison with other algorithms.

We introduce a method for detecting the topological charge of power-exponential-phase vortex beam(PEPVB) and its power-exponent parameter by using a Laguerre-Gaussian beam that interferes with a PEPVB. The intensity shows a unique flower pattern after interference. According to the number of petals l-l₀ and the topological charge of LG light l₀ , we can obtain the topological charge of the PEPVB 𝑙. One of the most significant characteristics of PEPVB is the petals in the interference pattern become narrower clockwise. Moreover, the angle of the largest petal Δφ gradually decreases with an increasing power-exponent parameter. By measuring the angle φ₁, φ₂, the value of the power-exponent parameter 𝑛 can be calculated.

Based on the cavity quantum electrodynamics (CQED), we propose two schemes for realization of basic quantum information processing tasks, i.e., constructing a quantum SWAP gate directly and preparation for entangled coherent states. In the present paper, we show that the quantum swap gates of photonic qubits can be implemented only by one step with a three-level Λ-type atom trapped in a bimodal optical cavity. The purpose for the direct construction of swap gates is to save a great many quantum resources in practical quantum information processing and reduce the number of required unitary operation. For the latter, we obtain the entangled coherent states via the large detuning interaction, in the process of the unitary evolution of dressed states. This scheme provides a suitable cavity QED to prepare quantum entanglement for researchers, and provides a wider horizon for the generation of quantum entanglement based on cavity QED, which, to some extent, possesses reference value and guiding effect in the experiment, and the quantum entanglement can be used for the potential application in the quantum information and quantum communication in the future.

For diode pump fiber laser, there’s potential to achieve high power quasi-CW output by applying overshoot pulse modulation to diode, meaning that applying several times of currents to the diode to attain remarkably higher power than rated value. In this paper, we first build up the physical modal of the quasi-CW fiber laser based on time-dependent rate equations and solve them with parallelizable bidirectional method for simulation. The result shows that for square wave pump with 1kHz frequency and 500μs duration, the output peak power is about 5.1kW with 2kW forward pump and 4kW backward pump. Applying overshoot pulse modulation to 3 diodes at 976nm to pump ytterbium-doped fiber oscillator, we obtain 500Hz, 1kHz frequency and 100, 200μs duration output, respectively. With 1kHz frequency and 200μs duration pump with an average power of 192W, the average output power is 192W with 60.8% optical efficiency at 1080nm, of which the M² beam quality is about 1.5. The output waveform shows good consistency of the pump diode with low delay between. It’s the very first time in the country to attain pulse fiber laser output by applying overshoot pulse modulation to diode to our acknowledgment.

The interference patterns between two vortex beams are systematically studied in experiment. Vortex beams with different topological charges (TCs) (±1, ±2, ±3) are generated by modulating the fundamental Gaussian beam with the spiral phase plate, and an improved Mach-Zehnder interferometer is built to study these different interference patterns. When two interference beams are both plane waves, off-axis interference produces fork-shaped interference patterns. The fork direction and the fork number in the fork-shaped patterns are related to the TCs and orientation relation of two vortex beams. When two LG_0l vortex beams with different curvature radii interferes coaxially, the interference pattern with a spiral structure is generated, the spiral direction and spiral leaves depend on the curvature radii and TCs of two interfered vortex beams. Coaxial interference of two vortex beams with the same curvature radius produces the spiral-shaped pattern with a petal-shaped (or wheel-shaped) structure (a composite vortex field).

In this paper, a real-time monitoring method of buoyancy material curing process based on cascaded fiber Bragg grating (FBG) sensors is proposed. The strain change of buoyancy material curing at different heights is monitored by embedding prestressed-cascaded FBGs in the mixture of hollow glass beads and epoxy resin. Meanwhile, the cascaded reference FBGs encapsulated in a capillary glass tube is used to monitor the temperature change of buoyancy material curing process. The experimental results show that the strain and temperature change trends at different heights are different during the entire process. The proposed method is practical in monitoring of the curing process of buoyancy materials.

This paper uses the measured atmospheric coherence length profile data of DCIM lidar to analyze the effect of different regularization parameter selection strategies on the inversion of atmospheric turbulence profile. The criterions of L-curve, generalized cross-validation(GCV), quasi-optimal are used respectively, The inversion results is evaluated by signal-tonoise ratio(SNR) and root mean square error(RMSE). The results show that the GCV criterion perform more stable for various measurements than L-curve and quasi-optimal criterion.

In this article, a mode converter based on irregularly distributed long period fiber gratings(LPGs) is proposed. The mode conversion characteristics of LP01 mode to LP02 mode are analyzed by beam propagation method. The effects of the cross-section shape and diameter of the gratings on the mode conversion efficiency and bandwidth are analyzed. Mode conversion bandwidth between the LP01 mode and the LP02 mode is found strongly dependent on the interaction between the mode fields and the LPG section.

In order to study the phenomenon of spallation in titanium alloy under nanosecond laser shock, and on the basis of analyzing the advantages of laser shock forming technology and the relevant domestic and foreign research status, this paper conducts numerical simulation and experimental research on laser shock forming of titanium alloy sheet, systematically studies the effect of different laser energy and impact times on laser shock forming effect, and the deformation law of TC4 titanium alloy material in the process of laser shock forming are analyzed. The simulation model analyzes the deformation of the target material based on the target displacement cloud map at different times. In addition, the laser shock experiment verifies the correctness of the simulation results with experimental data. The results show that under the single-variable method, as the energy gradually grows, the target shape variable also increases. As the number of impacts increases, the target deformation gradually increases until cracks appear. These results provide a basis for setting laser parameters and selecting targets when nanosecond laser strikes the TC4 target.

We developed a distributed refractive index (RI) sensor based on high performance optical frequency-domain reflectometry (OFDR) by simply bending a piece of standard single mode fiber (SMF) in a U shape. In the U-bent region, cladding modes are excited, which can reach to the boundary of the SMF to sense external RI variation. The cladding modes are then coupled back to the core mode and interfere with the fundamental mode. Thus, the fundamental mode can carry the varied RI information, and distributed index sensing is achieved by measuring the wavelength shifts of the local Rayleigh backscattered spectra. Thanks to the high signal SNR of OFDR, that compensating the bending induced loss, the proposed sensor can be bent in a small bending radius so that a high sensitivity of RI could be achieved. In the experiment, index sensitivity of 39.08 nm/RIU is achieved by imposing a bending radius of 4 mm, when the RI ranges from 1.3330 to 1.3773. Additionally, the proposed sensor maintains buffer coating intact, which boosts its practicability and application flexibility.