A significant improvement to the recently introduced complex screen (CS) method for generating partially coherent Schell-model sources is presented. The method, called the modified phase screen (MPS) technique, applies a deterministic amplitude and the phase portion of a CS to an initially coherent light source using a single phase-only spatial light modulator. The MPS technique, unlike the CS approach from which it is derived, does not produce a fully developed speckle pattern in the source plane, and therefore converges faster and more uniformly to the desired partially coherent source. The analytical development of the MPS method is presented. Experimental results of a Bessel-Gaussian-correlated Schell-model source, generated using the CS and MPS approaches, are compared to demonstrate the validity and utility of the MPS technique.

Visible-light communication (VLC) is license free and electromagnetic-interference free; it thus can be deployed in radio-frequency forbidden areas. The light-emitting diode (LED) system providing simultaneously lighting, VLC, and positioning is highly desirable for providing real-time tracking, monitoring, and navigating with very little extra cost. We propose and demonstrate a multiple-input multiple-output (MIMO) VLC-positioning system using white-light LEDs. Our scheme is based on MIMO to provide both position and VLC. Experimental results show that the proposed MIMO VLC system can achieve a bit-error rate of 10⁻¹⁰, while the positioning errors are within 1 cm. Numerical analyses are also performed, showing the positioning error can be measured within 1 cm. Further analysis of tilting angle of the receiver is also presented.

Parallel-coupled dual racetrack silicon microresonator structures are fabricated and characterized. With an integrated Mach–Zehnder interferometer, the full information of amplitude and phase of the structure is obtained experimentally. The spectral characteristics of the amplitude and phase are shown to be in reasonable agreement with simulation results, considering possible small structure variations in fabrication. The structure is potentially useful for developing modulators for advanced modulation formats.

Two texture metrics based on gray level co‐occurrence error (GLCE) are used to predict probability of detection and mean search time. The two texture metrics are local clutter metrics and are based on the statistics of GLCE probability distributions. The degree of correlation between various clutter metrics and the target detection performance of the nine military vehicles in complex natural scenes found in the Search_2 dataset are presented. Comparison is also made between four other common clutter metrics found in the literature: root sum of squares, Doyle, statistical variance, and target structure similarity. The experimental results show that the GLCE energy metric is a better predictor of target detection performance when searching for targets in natural scenes than the other clutter metrics studied.

We designed and developed a system to project video scenes in the near‐infrared (NIR) band based on digital micromirror devices (DMD) and digital signal processors (DSP). The system deals with the integration and interfacing of different embedded systems both in the field of digital light processing (DLP) and digital signal processing. On the DLP side, we integrated DMD, NIR light source, and projection optics. The input video source for the dynamic scene was generated using a DSP, where we designed and implemented a fast video‐retrieval algorithm. The proposed system can be used for testing and design of equipments operating in the NIR band. The system is tested for projecting NIR video at different projection distances using different driving powers of the NIR laser source, and it operated correctly and was capable of producing high frame rate of 180 frames per second (fps) without delay or distortion when viewed by an NIR camera.

An all‐fiber pulsed coherent Doppler LIDAR (CDL) system is described. It uses a fiber laser as a light source at a 1.54‐μm wavelength, producing 200  μJ pulses at 10 kHz. The local oscillator signal is mixed with the backscattered light (of different frequency) in the fiber. The atmospheric wind speed is determined through the fast Fourier transform applied to the difference frequency signal acquired by an analog‐to‐digital converter card. This system was used to measure the atmospheric wind above the upper‐air meteorological observatory in Rongcheng (37.10°N, 122.25°E) of China between January 7 and 19, 2015. The CDL data are compared with sounding‐ and pilot‐balloon measurements to assess the CDL performance. The results show that the correlation coefficient of the different wind‐speed measurements is 0.93 and their discrepancy 0.64  m/s; the correlation coefficient for wind‐direction values is 0.92 and their discrepancy 5.8 deg. A time serial of the wind field, which benefits the understanding of atmospheric dynamics, is presented after the comparisons between data from CDL and balloons. The CDL system has a compact structure and demonstrates good stability, reliability, and a potential for application to wind‐field measurements in the atmospheric boundary layer.

Visual discomfort is a common problem in three-dimensional (3D) videos, and this issue is the subject of many current studies. Among the methods to overcome visual discomfort presented in current research, parallax adjustment methods provide little guidance in determining the condition for parallax control. We propose a parallax adjustment based on the effects of parallax distribution and cross talk on visual comfort, where the visual comfort level is used as the adjustment parameter, in parallax-barrier-type autostereoscopic 3D displays. We use the horizontal image shift method for parallax adjustment to enhance visual comfort. The speeded-up robust feature is used to estimate the parallax distribution of 3D sequences, and the required amount for parallax control is chosen based on the predefined effect of parallax distribution and cross talk on visual comfort. To evaluate the performance of the proposed method, we used commercial 3D equipment with various intrinsic cross-talk levels. Subjective tests were conducted at the fixed optimal viewing distance for each piece of equipment. The results show that comfortable videos were generated based on the proposed parallax adjustment method.

The pixels of a retina-like sensor are arranged in concentric rings, and the output image is given in log-polar coordinates. Thus, additional residual errors will not be produced when the output image is rotated. Therefore, retina-like sensors have obvious advantages and many prospects for applications in the fields of image rotation and rapid image rotation-elimination. In this study, a theory concerning the image rotation of a retina-like sensor is proposed, and a solution based on the theory is presented and realized for eliminating image rotation caused by camera rotation. The camera rotation angle is obtained using a microelectromechanical systems digital accelerometer and gyroscope; only the readout sequence of each row from static random-access memory must be changed to achieve image rotation-elimination. Several image rotation-elimination experiments have been performed which show that the proposed solution is simple, accurate, and rapid. This rapid image rotation-elimination method can be used in fields that require higher image rotation-elimination processing speeds.

This paper presents an algorithm for target detection and tracking by fusion of multispectral imagery. In all spectral bands, we build a background model of the pixel intensities using a Gaussian mixture model, and pixels not belonging to the model are classified as foreground pixels. Foreground pixels from the spectral bands are weighted and summed into a single foreground map and filtered to give the fused foreground map. Foreground pixels are grouped into target candidates and associated with targets from a tracking database by matching features from the scale-invariant feature transform. The performance of our algorithm was evaluated with a synthetically generated data set of visible, near-infrared, midwave infrared, and long-wave infrared video sequences. With a fused combination of the spectral bands, the proposed algorithm lowers the false alarm rate while maintaining high detection rates. All 12 vehicles were tracked throughout the sequence, with one instance of a lost track that was later recovered.

A shape descriptor and a complete shape-based recognition system using slice images as geometric feature descriptor for ladar range images are introduced. A slice image is a two-dimensional image generated by three-dimensional Hough transform and the corresponding mathematical transformation. The system consists of two processes, the model library construction and recognition. In the model library construction process, a series of range images are obtained after the model object is sampled at preset attitude angles. Then, all the range images are converted into slice images. The number of slice images is reduced by clustering analysis and finding a representation to reduce the size of the model library. In the recognition process, the slice image of the scene is compared with the slice image in the model library. The recognition results depend on the comparison. Simulated ladar range images are used to analyze the recognition and misjudgment rates, and comparison between the slice image representation method and moment invariants representation method is performed. The experimental results show that whether in conditions without noise or with ladar noise, the system has a high recognition rate and low misjudgment rate. The comparison experiment demonstrates that the slice image has better representation ability than moment invariants.

As one branch of stereo matching, video stereo matching becomes more and more significant in computer vision applications. The conventional stereo matching methods for static images would cause flicker-frames and worse matching results. We propose a joint motion-based square step (JMSS) method for stereo video matching. The motion vector is introduced as one component in the support region building for the raw cost aggregation. Then we aggregate the raw cost along two directions in the support region. Finally, the winner-take-all strategy determines the best disparity under our hypothesis. Experimental results show that the JMSS method not only outperforms other state-of-the-art stereo matching methods on test sequences with abundant movements, but also performs well in some real-world scenes with fixed and moving stereo cameras, respectively, in particular under some extreme conditions of real stereo visions. Additionally, the proposed JMSS method can be implemented in real time, which is superior to other state-of-the-art methods. The time efficiency is also a very important consideration in our algorithm design.

Based on the techniques of laser microdrilling and solvent reflow, this study reports on a straightforward approach for fabricating plastic microlens arrays (MLAs). First, we use the ArF excimer laser to drill microholes on a polymethylmethacrylate plate for defining the lens number, initial depth, and diameter. The propylene glycol monomethyl ether acetate solvent is then employed to regulate the surface profile that leads to a resulting negative (concave) MLA. The corresponding positive (convex), polydimethyl-siloxane MLA is obtained by the soft-replica-molding technique. Through varying the pattern size and period on the mask and the light intensity for laser drilling and regulating the solvent in the reflow process, we exhibit the feasibility of making MLAs with various sizes and shapes. By modifying the laser ablation step to drill two microholes with different diameters and depths at two levels, we fabricate a bifocal microlens. The obtained microlenses have excellent surface and optical properties: surface roughness down to several nanometers and focal lengths varying from hundreds to thousands of micrometers. This approach is flexible for constructing microlenses with various sizes and shapes and can fabricate MLAs with a high fill factor.

A necessity exists for the protection of people and their property against the unauthorized use of photoelectric devices. The retroreflection of optical systems can be utilized to detect and recognize photoelectric devices. The reduction of false alarms and processing speed are two crucial issues, particularly for interior applications involving complex scenes. Here, we propose a local texture criterion that determines the local maximum and local continuity of the reflections. A comprehensive evaluation method that combines a modified shape criterion and the local texture criterion to improve the recognition probability is also presented. A searching strategy for scanning and locating the target candidates with reduced time cost was used in laboratory experiments performed at operating distances of 2.2, 3.2, and 4.2 m with the presence of disturbing objects. The results demonstrated the practicability of the proposed method, its superior recognition probability over that of single-criterion methods, and its enhanced average processing speed in comparison with existing methods.

We present a method to reconstruct the three-dimensional (3-D) Tang Dynasty building model from raw point clouds. Different from previous building modeling techniques, our method is developed for the Tang Dynasty building which does not exhibit planar primitives, facades, and repetitive structural elements as residential low- or high-rise buildings. The proposed method utilizes the structural property of the Tang Dynasty building to process the original point clouds. First, the raw point clouds are sliced into many parallel layers to generate a top-bottom hierarchical structure, and each layer is resampled to achieve a subset purification of 3-D point clouds. In addition, a series of different building components of the building are recognized by clustering these purifications of 3-D point clouds. In particular, we get the tree-structured topology of these different building components during slicing and clustering. Second, different solutions are explored to reconstruct its 3-D model for different building components. The overall model of building can be gotten based on the building components and tree-structured topology. Experimental results demonstrate that the proposed method is more efficient for generating a high realistic 3-D model of the Tang Dynasty building.

The notion of modulating an aircraft’s infrared (IR) signatures based on the anisotropic emission behavior of aircraft skin is proposed. The integrated IR transmission model from aircraft to detector is established by the matrices. IR signature azimuthal profiles and gray-level images are used to evaluate the effectiveness of the IR modulation technique. The results show that as the hemispherical emissivity remains constant, changing the angular emission behavior of aircraft skin can modulate the directionality and contrast characteristics of IR signatures.

We investigate the Fraunhofer diffraction of a Laguerre–Gaussian (LG) beam incident on a dynamic superposed dual-triangular aperture. The evolution of the diffraction pattern from this aperture is analyzed experimentally and theoretically. A special aperture, called the hex-star triangular aperture, demonstrates interesting diffraction patterns. Further, the diffraction properties of integer, half-integer, and fractional orders of topological charges at the Fraunhofer zone are studied by using the hex-star triangular aperture. This study can provide additional information to enhance the understanding of the diffraction properties of the LG beam transmitted through a complex aperture.

We develop an algorithm based on a subspace model to detect anomalies in a hyperspectral image. The anomaly detector is based on the Mahalanobis distance of a residual from a pixel that is partitioned nonuniformly according to the groups in the spectral components in the pixel. The main background is removed from the pixel by predicting linear combinations of each subset of the partitioned pixel with linear combinations of the main background. The residual is defined to be the difference between the linear combinations of each subset of the partitioned pixel and the linear combinations of the main background. The anomaly detector is designed for anomalies that can be best detected in the residual of the pixel. Experimental results using two real hyperspectral images and a simulated dataset show that the anomaly detector outperforms conventional anomaly detectors.

We propose and demonstrate an optical component that overcomes critical limitations in our previously demonstrated high-speed multispectral videography—a method in which an array of periscopes placed in a prism-based spectral shaper is used to achieve snapshot multispectral imaging with the frame rate only limited by that of an image-recording sensor. The demonstrated optical component consists of a slicing mirror incorporated into a 4f-relaying lens system that we refer to as a spectrum slicer (SS). With its simple design, we can easily increase the number of spectral channels without adding fabrication complexity while preserving the capability of high-speed multispectral videography. We present a theoretical framework for the SS and its experimental utility to spectral imaging by showing real-time monitoring of a dynamic colorful event through five different visible windows.

A laser Doppler velocimeter (LDV) for measuring two-dimensional components of velocity vectors based on optical quadrature detection is presented. The LDV uses a simple structure without frequency shifting or multiple wavelengths. In this LDV, the scattered light is monitored in different directions with two detection blocks. In each block, two PDs are used and a 90-deg phase shift is applied to one of the reference beams to detect the absolute value and sign of the beat frequency. We performed an experiment for measuring two-dimensional velocity vectors using a setup introducing orthogonal polarized beams for optical quadrature detection. The experimental results indicate that two-dimensional velocity vectors can be successfully estimated using the proposed method.

Studies for representing three-dimensional (3-D) objects are an important subject in different fields, such as computer vision, data compression, creation of virtual scenes, and others. Any surface can be seen as a 3-D object and studied as such. 3-D voxel-based surfaces are described using a 3-D tree structure known as an enclosing tree. A modified version of this structure is used to describe the surface. In order to describe the surfaces, we used the enclosing trees that are represented via the orthogonal direction change chain code. The representation obtained is compared with the original to verify if proper data compression is achieved.

A framing camera with high temporal and spatial resolution is demonstrated using pulse-dilation technology and a magnetic lens. The magnetic field of the magnetic lens is simulated using LORENTZ-3EM software, and the magnetic field distribution on-axis is similar to a Gaussian function. The temporal and spatial resolutions of the instrument are measured using light at the wavelength of 266 nm from a frequency tripled femtosecond laser. The measured exposure time of this camera is ∼11  ps, and the spatial resolution is better than 100  μm.

Scan imaging systems rely on the rotation of a mirror to scan an image. The rotation in the resulting image must be compensated to prevent information loss. Satisfactory performance of an imaging system is difficult to achieve when employing the methods of mechanical transmission and unilateral tracking control, especially when the system suffers from nonlinear factors, disturbances, and dynamic uncertainties. This paper proposes a compensation method based on bilateral control derived from the field of haptic robots. A two-loop disturbance observer was designed to guarantee that the dynamic characteristics of the motor are close to those of the nominal model. The controllers were designed on the basis of the small gain theorem. Experiments were conducted for a comparison with the traditional unilateral control-based compensation. The comparison showed a reduction of 99.83% in the L₂ norm of error, which validates the method. The proposed method improves the accuracy of compensation for rotation in imaging, and demonstrates that bilateral control has feasibility for application in various fields, including photogrammetry.

Erythrocyte morphology is an important factor in disease diagnosis, however, traditional setups as microscopes and cytometers cannot provide enough quantitative information of cellular morphology for in-depth statistics and analysis. In order to capture variations of erythrocytes affected by metal ions, quantitative interferometric microscopy (QIM) is applied to monitor their morphology changes. Combined with phase retrieval and cell recognition, erythrocyte phase images, as well as phase area and volume, can be accurately and automatically obtained. The research proves that QIM is an effective tool in cellular observation and measurement.

This paper describes a relatively general method based on finite-difference time-domain for modeling the scattering loss of silicon nano-optical waveguides as well as quality factor Q of the waveguide resonators. This paper explains how the surface roughness affects the performance of silicon-on-insulator optical ring resonators. Furthermore, the model we built in this paper was also employed to design and optimize the structure of an optical resonator and a good match was found between calculated and measured data. Also, our results were compared with those obtained by other approaches, again proving that the model worked well.

The intensity distributions of some light sources have the rotationally symmetric property. We propose a method to design freeform optics by sampling the source intensity distribution nonuniformly in a modified double‐pole coordinate system to satisfy the circular emission pattern of the light source. We can greatly improve the smoothness of the designed freeform surfaces and maximize the collection efficiency. We demonstrate the design method with two freeform illumination lenses: one for the light from the multimode filter and the other for the light emitting diode with a hemisphere emitting solid angle. We also demonstrate that the nonuniform sampling algorithm has significant advantages for designing freeform reflectors with superlarge collection angle.

Multilayered transparent composites having laminates with polymer interlayers and backing sheets are commonly used in a wide range of applications where visibility, transparency, impact resistance, and safety are essential. Manufacturing flaws or damage during operation can seriously compromise both safety and performance. Most fabrication defects are not discernible until after the entire multilayered transparent composite assembly has been completed, and in-the-field inspection for damage is a problem not yet solved. A robust and reliable nondestructive evaluation (NDE) technique is needed to evaluate structural integrity and identify defects that result from manufacturing issues as well as in-service damage arising from extreme environmental conditions in addition to normal mechanical and thermal loads. Current optical techniques have limited applicability for NDE of such structures. This work presents a technique that employs a modified interferometer utilizing a laser diode or femtosecond fiber laser source to acquire in situ defect depth location inside a thin or thick multilayered transparent composite, respectively. The technique successfully located various defects inside examined composites. The results show great potential of the technique for defect detection, location, and identification in multilayered transparent composites.

An optical encryption method based on compressive ghost imaging (CGI) with double random-phase encoding (DRPE), named DRPE-CGI, is proposed. The information is first encrypted by the sender with DRPE, the DRPE-coded image is encrypted by the system of computational ghost imaging with a secret key. The key of N random-phase vectors is generated by the sender and will be shared with the receiver who is the authorized user. The receiver decrypts the DRPE-coded image with the key, with the aid of CGI and a compressive sensing technique, and then reconstructs the original information by the technique of DRPE-decoding. The experiments suggest that cryptanalysts cannot get any useful information about the original image even if they eavesdrop 60% of the key at a given time, so the security of DRPE-CGI is higher than that of the security of conventional ghost imaging. Furthermore, this method can reduce 40% of the information quantity compared with ghost imaging while the qualities of reconstructing the information are the same. It can also improve the quality of the reconstructed plaintext information compared with DRPE-GI with the same sampling times. This technique can be immediately applied to encryption and data storage with the advantages of high security, fast transmission, and high quality of reconstructed information.

Volume holographic gratings have been used in waveguide displays to implement full-color three-dimensional imaging. Among these, multiplexing gratings are advanced in low energy losses and simple manufacture technologies when used as couplers of color hologram waveguides. A multiplexing holographic grating is designed to realize a uniform red, green, and blue diffraction efficiency and eliminate stray light to the largest extent. Results indicate that the red, green, and blue light incident normal to the grating could be successfully in-coupled into the planar waveguide for total internal reflection with high peak diffraction efficiency, similar energy output, and little stray light. We also analyze the effect of the technical tolerance, including gating thickness, index modulation, grating period, slanted angle, and incident angle. This analysis could help to minimize the optical system and improve the color image quality of waveguide displays.

The influence of organic contamination (rubber outgassing) on the transmittance of the SiO₂ sol‐gel antireflection (AR) film and laser‐induced damage threshold (LIDT) at 355 nm for 3ω AR film and at 1064 nm for 1ω AR film is studied. The correlation between the contamination time and the transmittance loss/LIDT of 1ω/3ω AR film is also investigated both in atmospheric and vacuum environments. The results show that the transmittance loss increases with increasing contamination time, and the LIDT decreases with increasing contamination time for both in atmospheric and vacuum environments. In addition, the resistance against contamination of the 1ω film is stronger than 3ω film, and the contamination is more serious in vacuum than in an atmosphere environment for the same contamination time. Meanwhile, the damage mechanism is also discussed. It indicated that both the porous structure and photo‐thermal absorption contribute to the decreasing LIDT of the sol‐gel AR film.

A modulation format of differential pulse amplitude modulation in visible light communication using a single transmitter module composed of multiple semiconductor light‐emitting diode (LED) chips is proposed and experimentally demonstrated. Precoded different nonreturn‐zero on–off‐keying signals were assigned to each LED chip, and linearly overlapped signals were detected by a single photodiode. In this demonstration, pre‐equalization and optical filtering were applied to compensate the modulation bandwidth limitation and nonlinearity of the light source. Data rate up to 200  Mbit/s with less than 7.8×10−⁵ bit error rate was verified by experiment using the proposed modulation method.

The performances of satellite‐to‐ground downlink optical communications over Gamma–Gamma distributed turbulence are studied for a multiple‐aperture receiver system. Equal gain‐combining (EGC) and selection‐combining (SC) techniques are considered as practical schemes to mitigate the atmospheric turbulence under thermal‐noise‐limited conditions. Bit‐error rate (BER) performances for on‐off keying‐modulated direct detection and outage probabilities are analyzed and compared for SC diversity receptions using analytical results and for EGC diversity receptions through an approximation method. To show the net diversity gain of a multiple‐aperture receiver system, BER performances and outage probabilities of EGC and SC receiver systems are compared with a single monolithic‐aperture receiver system with the same total aperture area (same average total incident optical power) for satellite‐to‐ground downlink optical communications. All the numerical results are also verified by Monte‐Carlo simulations.

A frequency-doubling optoelectronic oscillator (OEO) using two cascaded modulators based on destructive interference is proposed and experimentally demonstrated. In the proposed system, we utilize a cascaded modulator including a phase modulator and an intensity modulator, which implements a carrier-suppressed double-sideband modulation based on destructive interference to generate a frequency-doubled microwave signal. Meanwhile, the phase modulator is connected by a chirp fiber Bragg grating in the loop, which forms a microwave photonic filter to select the fundamental frequency signal in the OEO loop. As a result, a frequency-doubled microwave signal at 17.9 and 20.5 GHz is generated, respectively. The phase noises and the long-term stability of the generated microwave signals are also investigated.

We proposed and demonstrated a centrally controlled and self-healing wavelength division multiplexing passive optical network with colorless optical network units (ONUs) based on optical carrier suppression technique. By switching the affected data in the OCS signal sideband to an alternate protection path, only one optical switch is provisioned at the optical line terminal, which is controlled by a logic control circuit upon monitoring of power outage on the working path. The proposed scheme can reliably protect against both distribution and feeder fiber failures. Moreover, gain-saturated reflective semiconductor optical amplifiers are used as colorless transmitters in ONUs. The protection scheme feasibility and system performances are experimentally verified with 10  Gb/s downstream and 1.25  Gb/s upstream data in both working and protection modes. The protection switching time was measured to be around 1 ms.

Fabrication of grating structures on surfaces of wide-bandgap semiconductors, namely silicon carbide (SiC) and gallium nitride (GaN), was achieved using a femtosecond laser and a phase mask. The phase mask was used to produce stable interference patterns from the focused femtosecond laser to form the grating structures on the bulk materials. The effects of the irradiation power and time on the Bragg grating morphology that was formed on the SiC surface were studied. By optimizing the fabrication parameters, we successfully produced grating structures with uniform periods of 1.07  μm on SiC and GaN. The threshold powers necessary for grating structure formation on wide-bandgap semiconductors were investigated. It was found that the threshold powers for SiC and GaN were much smaller than those for silica glass. The reason for this difference is that the absorption of the incident laser light in SiC and GaN is a lower-order nonlinear absorption process compared to that in silica glass.

A self-starting optoelectronic oscillator that employs a diverging time lens and a Mach–Zehnder modulator (MZM) in a fiber-extended cavity to generate a multiwavelength ultrashort pulse train is demonstrated. The switching window formed by the MZM is narrowed by the use of a diverging time lens, which is a phase modulator in our study. A wavelength assignment scheme is deployed to simultaneously suppress the pedestals of pulses on different wavelengths. A detailed analysis is given, and the results are presented by experiment. We have generated 25 GHz optical pulses simultaneously on four wavelengths as a proof-of-concept demonstration. The pulse width of the optical pulse, the phase noise, and the timing jitter performance of the generated microwave signal are experimentally measured.

We report a high-resolution optical refractometer based on the long-period grating Michelson interferometer. The interferometer phase shift depends on the refractive index that surrounds the fiber probe. A cross-correlation signal-processing method is used to demodulate the interferometer phase shift. Experimental results show that a resolution of 3×10⁻⁶   refractive  index  unit (RIU) can be obtained using this cross-correlation signal processing method. In addition, a measurement sensitivity up to 3×10³  deg/RIU is showed as the surrounding refractive index changing from 1.33 to 1.42. Such high-resolution and low-cost optical refractometers would find more applications in chemical or biochemical sensing fields.

The relationships among macro-bending loss, power of the 1500-nm amplified spontaneous emission (ASE), gain, and noise figure of an erbium-gallium co-doped silica fiber amplifier are investigated and explained. The dependence of macro-bending loss on different bending radii is examined. Using different fiber lengths and bending radii, the effects of macro-bending on ASE, gain, and noise figure are analyzed in comparison to an unbent fiber. The ASE power changes because macro-bending alters the number of Er³⁺ ions in the ⁴I_13/2 level that decay to the ⁴I_15/2 level emitting photons of shorter and longer wavelengths. The trade-off relationship that exists between the change in the ASE power and signal loss, where both result from macro-bending, explains the gain change. Fiber length also affects the changes in the ASE power and gain. Noise figure in the longer-wavelength region increases. In the shorter-wavelength region, for a long fiber, the noise figure improves only slightly. For a short fiber, it worsens due to gain decrement. The findings from this study explain the reason for gain improvement upon suppressing either a competing or a noncompeting ASE via filters or macro-bending in other rare-earth-doped fibers.

Hierarchical control architecture is designed for software-defined multidomain optical networks (SD-MDONs), and a unified service logic processing model (USLPM) is first proposed for various applications. USLPM-based virtual optical network (VON) provisioning process is designed, and two VON mapping algorithms are proposed: random node selection and per controller computation (RNS&PCC) and balanced node selection and hierarchical controller computation (BNS&HCC). Then an SD-MDON testbed is built with OpenFlow extension in order to support optical transport equipment. Finally, VON provisioning service is experimentally demonstrated on the testbed along with performance verification.

We present the investigation of a synchronously pumped optical parametric oscillator (SPOPO) based on beta barium borate (BBO) nonlinear crystal with broadband complementary chirped mirror pairs (CMPs). Three SPOPO cavity configurations with slightly different intracavity dispersion were explored. Dispersion properties of cavity mirrors were characterized using a white light interferometer and found to be the key factor determining the gap-free tuning range as well as simultaneous multiwavelength generation. The SPOPO is pumped by the second harmonic of a Yb:KGW oscillator and provides signal pulses tunable over a spectral range from 625 to 980 nm. Signal pulse duration ranges from 102 to 268 fs in various intracavity dispersion regimes. In addition, signal beam power in excess of 500 mW is demonstrated, corresponding to 27% conversion efficiency from pump to signal wave.

This study evaluated a directly modulated distributed feedback (DFB) laser diode (LD) for cable TV systems with respect to carrier-to-nonlinear distortion of LDs. The second-order distortion-to-carrier ratio is found to be proportional to that of the second-order coefficient-to-first-order coefficient of the DFB laser diode driving current and to the optical modulation index (OMI). Furthermore, the third-order distortion-to-carrier ratio is proportional to that of the third-order coefficient-to-first-order coefficient of the DFB laser diode driving current, and to the OMI².

We fabricated a fiber laser that uses a thin semiconductor layer surrounding the glass core as the gain medium. This is a completely new type of laser. The In₂Te₃ semiconductor layer is about 15-nm thick. The fiber laser has a core diameter of 14.2  μm, an outside diameter of 126  μm, and it is 25-mm long. The laser mirrors consist of a thick vacuum-deposited aluminum layer at one end and a thin semitransparent aluminum layer deposited at the other end of the fiber. The laser is pumped from the side with either light from a halogen tungsten incandescent lamp or a blue light emitting diode flash light. Both the In₂Te₃ gain medium and the aluminum mirrors have a wide bandwidth. Therefore, the output spectrum consists of a pedestal from a wavelength of about 454 to 623 nm with several peaks. There is a main peak at 545 nm. The main peak has an amplitude of 16.5 dB above the noise level of −73  dB.

We report on diode-end-pumped a-cut Nd:YLF laser on ⁴F_3/2→⁴I_11/2 transition. In a free-running regime, using an output coupler with a radius of curvature of 1000 mm, we obtain dual-wavelength laser operation at both π-polarized 1047 nm and σ-polarized 1053 nm with maximum output power of about 1.25 W and the highest slope efficiency of about 50.9% at pump power of 5.77 W at room temperature, for the first time to our knowledge. Furthermore, using a 0.1-mm glass plate as a wavelength selector, a dual-wavelength laser at 1047 and 1072 nm can also be yielded with the maximum output power of 0.34 W, which has not been reported before.

Semiconductor saturable absorber mirror (SESAM) mode locked Yb doped ultrafast lasers have been widely used in industrial applications. High laser stability against environment change and delivery process are required for industrial laser systems. A double Z-type ultrafast laser cavity was demonstrated experimentally and theoretically. Compared with the conventional Z-type cavity, this double Z-type cavity SESAM mode locked laser is less sensitive to misalignment and can tolerate more arm length changes while still staying cw mode locking.

This study proposes an optical sensor based on a refractometer integrating a bend waveguide and a trench structure. The optical sensor is a planar lightwave circuit device involving a bend waveguide with maximum optical loss. A trench structure was aligned with the partially exposed core layer’s sidewall of the bend waveguide, providing a quantitative measurement condition. The insertion losses of the proposed 1×2 single-mode optical splitter-type sensor were 4.38 and 8.67 dB for the reference waveguide and sensing waveguide, respectively, at a wavelength of 1550 nm. The optical loss of the sensing waveguide depends on the change in the refractive index of the material in contact with the trench, but the reference waveguide had stable optical propagating characteristics regardless of the variations of the refractive index.

Issues associated with the development and exploitation of infrared (IR) and terahertz (THz) radiation detectors based on a narrow-gap “HgCdTe” semiconductor have been discussed. This mercury–cadmium–telluride (MCT) semiconductor can be applied for two-color detector operation in IR and sub-THz spectral ranges. Two-color uncooled and cooled down to 78 K narrow-gap MCT semiconductor thin layers grown using the liquid phase epitaxy or molecular beam epitaxy methods on high-resistive “CdZnTe” or “GaAs” substrates, with bow-type antennas, have been considered both as sub-THz direct detection bolometers and 3 to 10  μm IR photoconductors. Their room temperature noise equivalent power at the frequency ν≈140  GHz and signal-to-noise ratio at the spectral sensitivity maximum under monochromatic (spectral resolution ∼0.1  μm) globar illumination reached the following values; ∼4.5×10−¹⁰  W/Hz^1/2 and ∼50, respectively. Aspheric lenses used for obtaining the images in the sub-THz spectral region were designed and manufactured. With these detectors, about 140 and 270 GHz imaging data have been demonstrated.

Pyramidal silicon nanospikes, termed black-Si (b-Si), with controlled height of 0.2 to 1  μm, were fabricated by plasma etching over 3-in wafers and were shown to act as variable density filters in a wide range of the IR spectrum 2.5 to 20  μm, with transmission and its spectral gradient dependent on the height of the spikes. Such variable density IR filters can be utilized for imaging and monitoring applications. Narrow IR notch filters were realized with gold mesh arrays on Si wafers prospective for applications in surface-enhanced IR absorption sensing and “cold materials” for heat radiation into atmospheric IR transmission window. Both types of filters for IR: spectrally variable and notch are made by simple fabrication methods.

High-performance wavelength-selective infrared (IR) sensors require small pixel structures, a low-thermal mass, and operation in the middle-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) regions for multicolor IR imaging. All-metal-based mushroom plasmonic metamaterial absorbers (MPMAs) were investigated theoretically and were designed to enhance the performance of wavelength-selective uncooled IR sensors. All components of the MPMAs are based on thin layers of metals such as Au without oxide insulators for increased absorption. The absorption properties of the MPMAs were investigated by rigorous coupled-wave analysis. Strong wavelength-selective absorption is realized over a wide range of MWIR and LWIR wavelengths by the plasmonic resonance of the micropatch and the narrow-gap resonance, without disturbance from the intrinsic absorption of oxide insulators. The absorption wavelength is defined mainly by the micropatch size and is longer than its period. The metal post width has less impact on the absorption properties and can maintain single-mode operation. Through-holes can be formed on the plate area to reduce the thermal mass. A small pixel size with reduced thermal mass and wideband single-mode operation can be realized using all-metal-based MPMAs.

Betatron radiation from the transverse oscillation of laser-wakefield accelerated electrons is very promising for a wide range of applications. Currently, the main limitation of this radiation source is the x-ray photon yield. We present our recent progress in achieving higher photon flux using a clustering gas target instead of the normal gas jet, leading to a 10-fold enhancement. Moreover, we observed monoenergetic electron beams and bright x-rays simultaneously, an occurrence which is considered contradictory, and succeeded in using the betatron radiation as a probe in the evolution of bubble dynamics. These breakthroughs are of great significance for pushing the use of betatron radiation source toward new applications.

A combined scheme using the light source of a reflective semiconductor optical amplifier (RSOA) and an optical signal processing unit (OSPU) based on the compact TO-can package is fabricated and characterized for a fiber Bragg grating (FBG) sensing system. Due to the optical feedback behavior from the FBG sensor, the RSOA is self-injection locked and lasing occurs at the Bragg wavelength. Using the wavelength-dependent filter method, all of the components in the OSPU are compactly integrated on the TO-can package with a height of 17.6 mm and diameter of 6.0 mm. The wavelength demodulating output signals are based on the optical power difference, depending only on the wavelengths without the effect of input optical power variations. The sensitivity of the output signal to temperature shows 0.026  dB/°C. The entire FBG sensing system has an excellent linear response to temperatures controlled with an accuracy of ±0.3°C.

A narrowband terahertz (THz) filter based on metal–dielectric–metal structure with a circular loop array patterned on metallic films was proposed. The transmission properties in the THz range of the structure were experimentally and theoretically analyzed. The structure’s transmission spectrum has two narrow bands of which band 1 in the lower frequency range was dominated by the transmission mode due to localized plasmon polaritons and band 2 in the higher frequency range was dominated by propagated plasmon polaritons mode and guided mode. Both band 1 and band 2 have high Q-factors. By designing an asymmetry periodic constant in orthogonal directions, band 2 exhibits potentials as a narrowband polarizer. Furthermore, the transmittance of band 2 can be promoted to 100% by laterally shifting the metallic arrays.