I spent some time growing up in one of the poorest counties in Georgia. My sister is now an attorney in a tri-county area not too far from Savannah. Before she went into her own practice, she was the county prosecutor. I always wondered about appeals and, in particular, about one old famous case in the county that some of the old timers still swear is true.

A high-efficiency narrow-band 2000 nm Tm:YAG ceramic laser that combines the advantages of in-band pumping at 1617 nm and volume Bragg grating for wavelength selection was demonstrated. Using an output coupler with 10% transmission, a maximum output power of 1.64 W was obtained at 1999.9 nm under 4.56 W of incident pump power, corresponding to a slope efficiency of 50% with respect to the incident pump power. To the best of our knowledge, this is the highest slope efficiency achieved for 2000 nm Tm:YAG lasers so far.

Color remapping can give multispectral imagery a realistic appearance. We assessed the practical value of this technique in two observer experiments using monochrome intensified (II) and long-wave infrared (IR) imagery, and color daylight (REF) and fused multispectral (CF) imagery. First, we investigated the amount of detail observers perceive in a short timespan. REF and CF imagery yielded the highest precision and recall measures, while II and IR imagery yielded significantly lower values. This suggests that observers have more difficulty in extracting information from monochrome than from color imagery. Next, we measured eye fixations during free image exploration. Although the overall fixation behavior was similar across image modalities, the order in which certain details were fixated varied. Persons and vehicles were typically fixated first in REF, CF, and IR imagery, while they were fixated later in II imagery. In some cases, color remapping II imagery and fusion with IR imagery restored the fixation order of these image details. We conclude that color remapping can yield enhanced scene perception compared to conventional monochrome nighttime imagery, and may be deployed to tune multispectral image representations such that the resulting fixation behavior resembles the fixation behavior corresponding to daylight color imagery.

Directional empirical mode decomposition (DEMD) has recently been proposed to make empirical mode decomposition suitable for the processing of texture analysis. Using DEMD, samples are decomposed into a series of images, referred to as two-dimensional intrinsic mode functions (2-D IMFs), from finer to large scale. A DEMD-based (2-D) ² linear discriminant analysis (LDA) for palm vein recognition is proposed. The proposed method progresses through three steps: (i) a set of 2-D IMF features of various scale and orientation are extracted using DEMD, (ii) the (2-D) ² LDA method is then applied to reduce the dimensionality of the feature space in both the row and column directions, and (iii) the nearest neighbor classifier is used for classification. We also propose two strategies for using the set of 2-D IMF features: ensemble DEMD vein representation (EDVR) and multichannel DEMD vein representation (MDVR). In experiments using palm vein databases, the proposed MDVR-based (2-D) ² LDA method achieved recognition accuracy of 99.73%, thereby demonstrating its feasibility for palm vein recognition.

The reflection of the sunlight over the sea surface is called glitter pattern. In previous works where the one-dimensional case was analyzed, the glitter function was mathematically described by a rect function. This rect function has proven to be a very good representation of the glitter pattern. A Gaussian glitter function is used like a first approximation to the rect function. The statistical relationship between the variance and the correlation function of the intensities of the image, the glitter pattern, and the variance of the sea surface slopes are obtained and analyzed. The analytical solutions for these relationships are given by different equations; however, the graphic representations are very similar.

An analytical model for the electro-thermal feedback effect in a microbolometer infrared focal plane array is presented. The presented model is the integrated optical-electro-thermal model, in which the electro-thermal feedback effect incorporated with the response of incident IR can be described. In addition, since the model is based on physics, the model parameters also have their own physical meaning. This analytical model can be easily utilized to describe the temperature increase caused by the applied heat sources and has a unique feature describing capability of optical-electro-thermal analysis in a quasi-steady-state, which can hardly be performed with thermal analysis tools based on the finite element method. The model shows that the temperature of the microbolometer in this study can be increased 7.1% to 18.6% more by the electro-thermal feedback effect.

The presented linear mode avalanche photodiode (APD) uses the standard layers and process steps available in the 0.35-μ m Si bulk CMOS process. Due to a low-doped epitaxial layer with a resistivity of 664  Ω cm , a deep intrinsic zone is realized to enable a large depleted absorption region at already moderate bias voltages and therefore ensures a high low-voltage responsivity. In combination with avalanche gain at high bias voltages, this leads to an overall responsivity of 1.7×10 ⁵   A/W at 1.1 nW optical input power and 670-nm wavelength. The maximum achieved avalanche gain was 4.94×10 ⁵ . The maximum −3  dB frequency of 700 MHz was measured at a reverse bias voltage of 30 V and an optical input power of 14.7 μ W.

Range-gated active imaging has significantly been improved in the recent past. Due to constraints imposed by the different types of sensors, systems using laser diodes as illumination sources are working in “accumulation” mode and systems using solid-state lasers are working in “flash” mode. Consequently, the type of source (diode or solid-state laser) gives basic differences in the behavior of the two types of systems. We systematically investigated the theoretical and practical differences between the two modes to point out their advantages and weaknesses. Parameters such as image quality, sensitivity to day light or stray light, fog penetration capacity, sensitivity to turbulence, and laser safety are examined. For comparative experimental purposes, we have built a range-gated active imaging system that allows the investigation of both illumination methods on the same sensor. We have carried out precise comparative studies between the two acquisition methods. Some differences are pointed out that have to be taken into account when designing a range-gated active imaging system in function of the desired performances. In particular, this work will help to design a new range-gated underwater active imaging system.

Recently, a new strategy to achieve high-operating temperature (HOT) infrared photodetectors to include cascade devices and alternate materials such as type-II superlattices has been observed. Another method to reduce dark current is related to the limitation of the volume of detector material via a concept of a photon-trapping detector. The performance of an innovative HOT detector designing so-called interband (IB) cascade type-II MWIR InAs/GaSb superlattice detectors is presented. Detailed analysis of the detector’s performance (such as dark current, RA product, current responsivity, and response time) versus bias voltage and operating temperatures (220 to 400 K) is performed, pointing out the optimal working conditions. At the present stage of technology, the experimentally measured R₀A values of the IB cascade type-II superlattice detectors at room temperature are higher than those predicted for HgCdTe photodiodes. It is shown that these HOT detectors have emerged as the competitors of HgCdTe photodetectors.

An instantaneous three-dimensional imaging technique using a chirped supercontinuum and an ultrafast optical Kerr gate, in which a sapphire plate and a TeO ₂ -ZnO-Na ₂ O oxide glass were used to generate the chirped supercontinuum and the ultrafast optical Kerr gate, respectively, is demonstrated. This technique is applicable to ultrafast shape measurement, such as shape imaging of moving objects, or imaging of laser-induced refractive index changes in transparent media.

The potential benefits of real-time, or near-real-time, image processing hardware to correct for turbulence-induced image defects for long-range surveillance and weapons targeting are sufficient to motivate significant resource commitment to their development. Quantitative comparisons between potential candidates are necessary to decide on a preferred processing algorithm. We begin by comparing the mean-square-error (MSE) performance of speckle imaging (SI) methods and multiframe blind deconvolution (MFBD), applied to long-path horizontal imaging of a static scene under anisoplanatic seeing conditions. Both methods are used to reconstruct a scene from three sets of 1000 simulated images featuring low, moderate, and severe turbulence-induced aberrations. The comparison shows that SI techniques can reduce the MSE up to 47%, using 15 input frames under daytime conditions. The MFBD method provides up to 40% improvement in MSE under the same conditions. The performance comparison is repeated under three diminishing light conditions, 30, 15, 8 photons per pixel on average, where improvements of up to 39% can be achieved using SI methods with 25 input frames, and up to 38% for the MFBD method using 150 input frames. The MFBD estimator is applied to three sets of field data and representative results presented. Finally, the performance of a hybrid bispectrum-MFBD estimator that uses a rapid bispectrum estimate as the starting point for the MFBD image reconstruction algorithm is examined.

This paper presents a Kinect–stereo camera fusion system that significantly improves the accuracy of depth map acquisition. The typical Kinect depth map suffers from missing depth values and errors, resulting from a single Kinect input. To ameliorate such problems, the proposed system couples a Kinect with a stereo RGB camera to provide an additional disparity map. Kinect depth map and the disparity map are efficiently fused in real time by exploiting a spatiotemporal Markov random field framework on a graphics processing unit. An efficient temporal data cost is proposed to maintain the temporal coherency between frames. We demonstrate the performance of the proposed system on challenging real-world examples. Experimental results confirm that the proposed system is robust and accurate in depth video acquisition.

A fast and simple solution is proposed to wavefront sensing for laser beams with spatial smoothly varying intensity, where Shack–Hartmann wavefront sensor and the modified Fourier domain centroiding algorithm are applied. Detailed analysis has been conducted to Fourier domain centroiding, simplifying the origin double-frame method to work with merely single frame, and revealing its interesting property of robustness to nonuniform intensity perturbation. The key parameter is also analyzed to optimize the algorithm’s performance. Numerical simulations demonstrate that the proposed method outperforms the center of gravity algorithm, with an average phase error reduction up to approximately one order in root mean square. Application of the proposed method in joint amplitude–phase compensation system is also verified by simulation with practical models and parameters. The modified Fourier domain centroiding is promising to enhance real-time actual wavefront measurement for adaptive optics in high-power lasers, such as joint amplitude–phase compensation.

Single-exposure generalized phase-shifting digital holography enables one to remove the zeroth-order and conjugate terms from the single hologram. For the phase-shifting, a random-complex-amplitude encoded wave is used as the reference wave. This encoded wave can be made by a commercially available element. Selective calculation is proposed for the improvement of reconstructed images in single-exposure generalized phase-shifting digital holography. Three calculations are used as a function of the complex amplitude quantities of the reference wave on the each pixel of the image sensor. The selective calculation improves the quality of the reconstructed image compared with applying only one of the three calculations to the hologram. The derivation of the three calculations and the reason why the number of calculations is three are presented. A parameter is defined and used to select the appropriate calculation from the three calculations. Relationships between the proposed method and the previous method for the improvement of the reconstructed images in single-exposure generalized phase-shifting digital holography are discussed. Two kinds of experimental results are given to confirm the effectiveness of the proposed method. One shows the dependence on the speckle size of the reference wave. The other shows the feasibility to dynamic phenomena.

Phase unwrapping is a key problem of phase-shifting profilometry vision measurement for complex object surface shapes. The simple path-following phase unwrapping algorithm is fast but has serious unwrapping error for complex shapes. The Goldstein+flood phase unwrapping algorithm can handle some complex shape object measurement; however, it is time consuming. We propose a fast phase unwrapping algorithm based on region partition according to a quality map of wrapped phase. In this algorithm, wrapped phase image is divided into several regions using partition thresholds, which are determined according to histogram of quality value. Each region is unwrapped by using a simple path-following phase algorithm and several groups with different priorities are generated. These groups are merged according to their priorities from high to low order and a final absolute phase is obtained. The proposed method is applied to wrapped phase images of three objects with and without noise. Experiments show that the proposed method is much faster, more accurate, and robust to noise than the Goldstein+flood algorithm in unwrapping complex phase image.

Spatial heterodyne interferometry (SHI) is a technique based on Fourier transform spectroscopy. As such, many of the benefits, such as high spectral resolving power, can be realized. Furthermore, unlike a Fourier transform spectrometer, an SHI is able to minimize the number of required samples for a given resolving power and spectral range. The calibration and detailed modeling of a polarization spatial heterodyne interferometer (PSHI) are detailed. Unlike our original first-order ray tracing model, the new model is based on the Jones matrix formalism. Using this improved model, we explore the nonideal aspects of the PSHI, including interference effects caused by retardance errors in the polarization grating and quarter wave plate. To minimize the influence of these errors, a calibration procedure is described based on a linear operator theory. Finally, the Jones matrix model and calibration procedure are validated through a series of simulations and experiments.

Annular subaperture stitching interferometry (ASSI) is increasingly used for precision metrology of aspheric surfaces. The stitching model is a critical factor for stitching algorithms in ASSI. An optimized stitching model is proposed, which describes the alignment errors of adjacent subapertures based on an off-axis model and wave aberration theory. To keep the stitching errors from transmitting and accumulating, a simultaneous optimization algorithm is presented. The residual difference of overlapped regions of adjacent subapertures is utilized to evaluate the stitching accuracy. Finally, the comparative numerical simulations and experiments are carried out. It shows that the optimized stitching model has a better performance and validity.

An approach for the measurement of surface displacement fields in three dimensions is presented based on the combination of two-dimensional digital image correlation with fringe projection. Only a single RGB image is required at each deformation state, thereby allowing real-time data acquisition, which is achieved using red speckle and projected blue fringes that are captured in the single image and separated using a Bayer filter. The approach allows both a perpendicular alignment relative to a flat reference surface and self-calibration, i.e., no calibration object is employed. The minimum measurement uncertainty of such a system is found to be 0.0083±0.00239 and 0.0238±0.0068 mm, respectively, for the in-plane and out-of-plane displacements. The potential of the approach is demonstrated for an elastic membrane undergoing large (5 to 20 mm) applied out-of-plane displacements, and the results show no significant difference (<1%) in the measured in-plane displacement fields compared with a commercially available system for stereoscopic digital image correlation.

Both radially polarized (RP) and radially polarized vortex (RPV) beams are generated by an experimental setup with one phase-only liquid crystal spatial light modulator which efficiently modulates the phase retardation distributions of input beam by twice reflections. The polarizing properties and double-slit interference of both RP and RPV beams are investigated in detail. Misplacement and tilt appear in double-slit interference fringes of both RP beams and RPV beams in simulations and experiments. The fringe tilt number F in the intermediate region is proportional to the topological charge l of RPV beams with the approximate relation F_s(l)=0.8125l in simulations and F_e(l)=0.8182l in experiments. The double-slit interference method can be utilized to determine and analyze the topological charge of the beams.

An improved structure for the optical coherence tomography (OCT) scheme based on a 4×4 fiber coupler for simultaneously measuring the refractive index and thickness of optical samples is presented. The proposed structure incorporates the optical path length difference of interference light and is used to calculate the refractive index and thickness of an unknown sample without any prior knowledge of the sample parameters. Two methods (time-domain and Fourier-domain OCT) of obtaining information about an unknown sample are proposed, and a high-speed high-resolution OCT system was developed.

The measurement accuracy of phase shifting shadow moiré is affected by both the spatially nonuniform phase shift error and random phase shift error. Substantial work has been done to overcome this difficulty, but few works can deal with the two error sources simultaneously. In the presented paper, we describe a solution that can compensate for the two error sources at the same time. In our method, a binocular stereovision system is integrated into a shadow moiré configuration to calibrate the setting parameters. Thus, a precise measurement setup is built. Then, we developed an iterative least-squares algorithm to analyze the acquired three fringe patterns. The proposed algorithm can extract the measurement phase without nonuniform phase shift error. On the other hand, it can compensate the random phase shift error by calibrating the distance of grating translation using the least-squares fitting in spatial. Optical experiments show that the proposed method can effectively minimize the phase-shift error and that it possesses a superior performance than the existing typical phase shifting algorithm.

The application of laser ultrasound for nondestructive testing of carbon fiber–reinforced plastics (CFRP) and carbon fiber–reinforced thermoplastics (CFRTP) is shown. Laser-generated excitation creates a three-dimensional, thermoelastic zone which emits ultrasound waves during expansion and contraction. In order not to exceed the damage threshold of the material to be tested usually only a low-energy density and therefore a weak excitation of ultrasound waves can be achieved. For instance, the use of a YAG laser type with a wavelength around 1 μm leads to a very low absorption in the matrix of CFRP while the absorption in the fibers is very high. As a consequence the excitation is often destructive. To solve this problem, we describe the successful introduction of a spatial light modulator to laser ultrasound allowing for tailored spatial energy distributions for efficient nondestructive excitation of ultrasound waves within CFRP or CFRTP.

We propose a position determination sensor based on a dual-wavelength Sagnac interferometer. With the wavelength division multiplexing technology, the system has a unique feature of Rayleigh backscatter rejection. The obtained results prove that this new configuration can reduce the scatter noise. The location result is more accurate and the monitoring range is increased.

An improved analysis of optical turbulence effects on short-exposure passive (SE) imaging is described, resulting in a new analytic expression for the SE modulation transfer function (MTF). This analysis expands on a 2011 study that examined characteristics of a tilt-phase component discovered in the standard theory of SE turbulence effects characterization. The analysis introduces an improved integration technique and a reformulated phase structure function, facilitating computation of a 38,007 element database of MTF results at low- to high-angular frequencies covering a wide range of diffraction and turbulence conditions. Analysis of this database is described, yielding a new analytic SE MTF, accurate to a root-mean-square error of 0.000218 versus the database. Comparisons show that the new expression is well correlated to an alternative computationally intensive method, and it is a factor 29 to 64 improvement over prior analytic expressions. Limits of applicability of the approach for incoherent imaging are also discussed. The low-computational cost of the new method is suitable for systems performance modeling of turbulence impacts, including path-varying turbulence scenarios.

We report the results of Raman measurements on some common military explosives and explosives precursors deposited on clothing fabrics, both synthetic and natural, in concentration comparable to those obtained from a single fingerprint or mixed with similar harmless substances to detect illegal compounds for smuggling activities. Raman spectra were obtained using an integrated portable Raman system equipped with an optical microscope and a 785-nm laser in an analysis of <1  min . The spectral features of each illicit substance have been identified and distinguished from those belonging to the substrate fabric or from the interfering compound. Our results show that the application of Raman spectroscopy (RS) with a microscope-based portable apparatus can provide interpretable Raman spectra for a fast, in-situ analysis, directly from explosive particles of some μm ³ , despite the contribution of the substrate, leaving the sample completely unaltered for further, more specific, and propedeutic laboratory analysis. We also show how the RS is suitable for detecting illegal compounds mixed with harmless substances for smuggling purposes or for counterfeiting activities.

For certain applications, total internal reflection (TIR) lenses are potentially more effective compared with refractive lenses and reflection mirrors since they permit more light power to go through the optical system. The efficiency of such lenses becomes even more prominent for miniature systems application where light absorption has negligible effect compared with the reflection losses at the interfaces. However, at such scales, the effect of Goos-Hänchen shift that associates the TIR should be accounted for in order to design a proper surface profile of the TIR lenses. It has been shown that a useful design that determines the total internal reflective surface profile can be obtained by solving an ordinary differential equation; such results facilitate realizing effective macro- and micro-scale lenses that are highly useful in integrated optics circuits and miniature optical systems.

An asymmetric negative-zero-positive index metamaterial (NZPIM) waveguide with two different Dirac points (DPs) operating in the terahertz (THz) regime is proposed. Its propagating characteristics are investigated by using the graphical method. Due to the linear dispersion near the DPs, the asymmetric NZPIM waveguide exhibits unique properties of guided modes, which are different from that in conventional waveguide but similar to that of electron waves in graphene waveguides. It is shown that the guided mode properties can be tuned by adjusting the incident angular frequency. In addition, the properties of surface-guided modes are also discussed. Our work may have potential applications in THz functional devices as well as reference value in investigating the guided modes of electrons in graphene waveguides.

White light-emitting diodes (LEDs) are predicted to be widely used in domestic applications in the future, because they are becoming widespread in commercial lighting applications. The ability of LEDs to be modulated at high speeds offers the possibility of using them as sources for communication instead of illumination. The growing interest in using these devices for both illumination and communication requires attention to combine this technology with modern lighting layouts. A dual-function system is applied to three models of modern lighting layouts: the hybrid corner lighting layout (HCLL), the hybrid wall lighting layout (HWLL), and the hybrid edge lighting layout (HELL). Based on the analysis, the relationship between the space adversity and the signal-to-noise ratio (SNR) performance is demonstrated for each model. The key factor that affects the SNR performance of visible light communication is the reliance on the design parameter that is related to the number and position of LED lights. The model of HWLL is chosen as the best layout, since 61% of the office area is considered as an excellent communication area and the difference between the area classification, Δp, is 22%. Thus, this system is applicable to modern lighting layouts.

A color holographic display method is proposed. It uses a spatial light modulator with a synthetic computer-generated hologram, which includes red, green, and blue three monochromatic scenes’ information. We calculate three holograms corresponding to red, green, and blue, and then generate a color hologram according to the law of sampling. A filter owning the pixel structure is designed so that white light emitting diode can be used as reconstructed light. We numerically evaluate the image quality of color-reconstructed images and compare the quality of color-reconstructed images with that of reconstructed color images using another color holographic projection method. The experimental results verify the feasibility of the method.

Indoor positioning has become an attractive research topic within the past two decades. However, no satisfying solution has been found with consideration of both accuracy and system complexity. Recently, research on visible light communications (VLC) offer new opportunities in realizing accurate indoor positioning with relatively simple system configuration. An indoor positioning system based on VLC technology is introduced, with no synchronization requirement on the transmitters. Simulation results show that, with over 95% confidence, the target receiver can be located with an accuracy of 5.9 cm, assuming indirect sunlight exposure and proper installation of light-emitting diode bulbs.

An analytical solution of the generalized nonlinear Schrodinger equation which is implemented with fiber laser applications has been presented. The solution based on the exp-function method which is depending on time, space and small perturbations has been found. This solution was used to test the behavior and study the propagation characteristics of laser pulses and compared with some of the researches in the same field and the nonlinear effects as gain dispersion, second anomalous group velocity dispersion, self phase modulation, and frequency are investigated. The net results are that the parabolic pulse growth after [i]z=4  m , and generate a periodic pulse train, the power of pulse is increased with increasing the length of fiber laser with reduce its width, the nonlinear effects have a small role on the pulse power, but they effect on the modulation stability of the laser and lead to generate sideband, the behavior of the pulse converted to chaotic when increasing the frequency.

Bonding layers, serving as the strain transmission mediums, may bring undesirable effects to the sensing properties of fiber Bragg grating (FBG) strain sensors during their fatigue process. To analyze the strain sensitivity and the reflected spectrum of FBG strain sensors in different fatigue stages of bonding layers, their strain sensitivities were derived according to strain transfer models. Resorting to T-matrix formalism, the affected reflected spectra were stimulated. Theoretical analysis results show that there is a gradual decline in the strain sensitivity during the stage of fatigue crack initiation, and that significant distortions emerge in the reflected spectrum during the stage of fatigue crack propagation. In addition, a cyclic loading fatigue test was conducted and the phenomenon observed in the test showed a good agreement with the theoretical prediction.

Solar cells are widely used in various applications. However, they are only used to harvest solar power. We propose and demonstrate a technique to use a solar cell as a simultaneous receiver of solar power and visible light communication (VLC) signals. First, we investigate the optic-to-electric conversion efficiency and the frequency response of a solar cell. Then, we demonstrate that a solar cell receiver can receive both solar power and VLC signals simultaneously. We also investigate the effect of solar power interference on the VLC performance. The results show that the VLC operation is successful even when the solar power is the maximum.

High-speed modulation characteristics are investigated for microdisk lasers theoretically and experimentally. In rate equation analysis, the microdisk resonator is radially divided into two regions under uniform carrier density approximation in each region. The injection current profile, carrier spatial hole burning, and diffusion are accounted for in the evaluation of small-signal modulation curves and the simulation of large-signal responses. The numerical results indicate that a wide mode field pattern in radial direction has merit for high-speed modulation, which is expected for coupled modes in the microdisk lasers connected with an output waveguide. For a 15-μm-radius microdisk laser connected with a 2-μm-wide output waveguide, the measured small-signal response curves with a low-frequency roll-off are well in agreement with the simulated result at a 2-μm radial width for the mode intensity distribution. The resonant frequencies of 7.2, 5.9, and 3.9 GHz are obtained at the temperatures of 287, 298, and 312 K from the small-signal response curves, and clear eye diagrams at 12.5  Gb/s with an extinction ratio of 6.1 dB are observed for the microdisk laser at the biasing current of 38 mA and 287 K.

By adopting the orthogonal frequency division multiplexing technology, spectrum-sliced elastic optical path networks can offer flexible bandwidth to each connection request and utilize the spectrum resources efficiently. The routing and spectrum assignment (RSA) problems in SLICE networks are solved by using heuristic algorithms in most prior studies and addressed by intelligent algorithms in few investigations. The performance of RSA algorithms can be further improved if we could combine such two types of algorithms. Therefore, we propose three hybrid RSA algorithms: DACE-GMSF, DACE-GLPF, and DACE-GEMkPSF, which are the combination of the heuristic algorithm and coevolution based on distance-adaptive policy. In the proposed algorithms, we first groom the connection requests, then sort the connection requests by using the heuristic algorithm (most subcarriers first, longest path first, and extended most k paths’ slots first), and finally search the approximately optimal solution with the coevolutionary policy. We present a model of the RSA problem by using integral linear programming, and key elements in the proposed algorithms are addressed in detail. Simulations under three topologies show that the proposed hybrid RSA algorithms can save spectrum resources efficiently.

2.5 and 10  Gb/s InP/InGaAs avalanche photodiodes (APDs) have been widely used in optical communication systems. However, the study on InP/InGaAs APDs above 10  Gb/s is insufficient. Recently, high-speed and high-sensitivity APDs for 100  Gb/s or even 400  Gb/s optical communication systems have drawn a lot of attention. On basis of the physical model for frequency response of APD including the dead space effect, a waveguide separate absorption, grading, charge, and multiplication (WG-SAGCM) InP/InGaAs APD has been designed for 25  Gb/s operation. Also, the frequency response of WG InAlAs/InGaAs APD was also simulated, which is perfectly in accordance with the experimental data. The comparison between InP/InGaAs APD and InAlAs/InGaAs APD with the same thickness of multiplication layer shows that the speeds of carriers in the nonionization layers are also important for the gain-bandwidth characteristics of SAGCM WG-APD. The higher drift velocity of carriers returned from multiplication layer and the lower drift velocity of carriers injected into multiplication layer result in a higher gain-bandwidth product and a higher dc gain. This work is helpful for the design of high-speed APDs.

The blind equalization of minimum-shift keying (MSK) in coherent optical communication is investigated. After the classical constant modulus algorithm (CMA) equalization step, the output of the equalizer does not necessarily coincide with a delayed and rotated version of the input MSK signal. In our MSK coherent optical system, a blind equalization criterion is proposed to eliminate the latter indeterminacy. Simulation results show that the 10-Gb/s MSK system successfully recovers MSK signal from various transmission impairments.

A polarization independent Fabry–Perot liquid crystal tunable filter coupled to an optical fiber is demonstrated using polarization diversity. Using a Wollaston prism, the beam splits into two orthogonal beams, while the polarization of one of the beams is rotated by 90 deg using a variable half wave plate. The two beams are then combined into an optical fiber. Tuning of unpolarized light over the range 720 to 800 nm is demonstrated.

A new detector technology was developed, particularly suitable for low-cost radioactivity monitoring in radwaste storage sites. It consists of a scintillating optical fiber coupled at each end to a silicon photomultiplier (SiPM). The single-photon sensitivity of the SiPM, along with the left-right coincidence constraint, allows the achievement of a reasonable sensitivity to gamma radiation even though a thin 1-mm-diameter plastic scintillating fiber is used. Simulation results are in perfect agreement with the measured behavior, and several implementations are under way. The possibility of choosing the fiber length and shape makes them very flexible both conceptually and mechanically. Any improvement in the SiPM development technology reflects immediately into an improvement in the detector performance.

The laser-induced bulk damage and stress behaviors of fused silica are studied by using a neodymium-doped yttrium aluminum garnet laser operated at 1064 nm with pulse width of 11.7 ns. Three zones of bulk damage are defined: columned cavity zone, compacted zone, and crack zone. The damage morphology and stress distribution are characterized by a three-dimensional digital microscope and a polarizer stress analyzer. The results show that the stress in the columned cavity zone and compacted zone is approximately zero. From the laser beam center to fringe, both tensile and compressive stresses in the crack zone increase abruptly and linearly and then decrease exponentially. Thermal annealing is used to prove the phase retardation caused by the residual stress. The formation mechanism of bulk damage is also discussed.

In a Laue lens made of single crystals oriented to diffract parallel x-rays at the lens focus, the energy and angular resolution are limited by the crystal size and by the crystal mosaicity. The use of extended crystals bent according to the lens curvature provides better focusing, with the resolution given essentially by the crystal mosaicity. With this approach, a crystal mosaicity as low as 15–25 arcsec, well below the mosaicity value of copper crystals, was found suitable for the new design of the Laue lens. The reflectivity and transmission profiles and the integrated intensity have been measured in flat and bent GaAs and Si crystals prepared by the method of surface damaging by using sandpaper of different grain size. The surface grinding induces a local lattice strain which produces a self-standing bent crystal. Bent crystals with radius of curvature lower than a critical value given by the extinction length behave as ideal mosaic crystals, maximizing the diffraction efficiency at high x-ray energies. It is found that the surface grinding does not affect the crystal diffraction efficiency, the damage thickness being limited to a few tens microns near the crystal surface.

An adaptive liquid iris for an optical switch based on electrowetting is demonstrated. The device consists of a clear conductive liquid and an opaque insulate oil. In the voltage-off state, the dome of the clear liquid touches the top substrate, and an iris-like opening is formed in its central area, and the aperture of the opening is at its largest. When a voltage is applied to the device, the shape of the conductive liquid is deformed due to the electrowetting effect. As a result, the diameter of the opening is reduced. Our results show that the aperture of the device can be tuned from ∼6.4  mm to 0 as the applied voltage is changed from 0 to ∼60  V . The device can obtain a high optical attenuation (∼872∶1 ). The response time was measured to be ∼117  ms (shrinking time is ∼25  ms , and relaxing time is ∼92  ms ) with turnaround speed of 55  mm/s . Our device has potential applications in light shutters, variable optical attenuators, adaptive irises, and displays.