Hybrid optical amplifiers (HOAs) are crucially important for broadband band amplification, and are widely deployed in high-capacity dense wavelength division multiplexed systems. We summarize the present state-of-the-art in this rapidly growing field. In addition, theoretical background and various inline configurations of optical amplifiers have been presented. Various issues such as gain flatness, gain bandwidth, transient effect, and crosstalk were presented in HOAs. Results show that the HOAs provide better gain flatness without using any expensive gain flattening techniques, and an acceptable range of gain, noise figure, bit error rate, and transience.

This review describes the recent advances in plasmonic nanostructures for various sensing applications. In particular, significant advances in surface-enhanced Raman, surface plasmon resonance, and metal-enhanced fluorescence-sensing methodologies associated with the introduction of plasmonic nanostructures, made over the past decade, are highlighted. Plasmonic properties of the various nanostructures employed for each sensing technique are also tabulated to provide a systematic overview of the state-of-the-art in each sensing field. This review is not intended to be a comprehensive compilation of the literature but rather a critical review of the recent significant advances in plasmonic nanostructures for each sensing regime.

We describe the experimental implementation of a virtual optical beam propagator system. This virtual propagator system allows the experimental study of beam propagation without physically moving any element. The approach uses a Fresnel diffraction algorithm (usually called the angular spectrum method) and its implementation on a spatial light modulator. We discuss the limits of the technique and provide a detailed description of the experimental procedures. Experimental results are included where we design a hologram capable of producing two patterns at two different distances, and we can change the effective plane of observation by changing the encoded propagation instead of by moving any element on the experimental system.

Aiming at detecting the random and complicated characteristic of wood surface, we proposed a comprehensive detection algorithm based on computer vision and compressed sensing. First, integral projection method was used to trace and locate the position of a wood plate; then surface images were obtained by blocks. Second, multiscaled features were extracted from image to express the surface characteristic. Third, particle swarm optimization algorithm was used for multiscaled features selection. Finally, the defects and textures were detected by compressed sensing classifier. Five types of wood samples, including radial texture, tangential texture, wormhole, live knot, and dead knot, were used for tests, and the average classification accuracy was 94.7%.

This paper proposes a color characterization model for predicting colorimetric information of all types of displays with high accuracy. Light leakage from black pixels causes errors in colorimetric information. By considering it, the proposed color characterization model accurately estimates colorimetric information of the red, green, and blue subpixels independently. In order to verify the universality of the proposed model, we apply it to all types of displays, including the organic light-emitting diode display. In addition, we show that the proposed model is more accurate than two of the most commonly used models, namely, the piecewise linear assuming chromaticity constancy model and the piecewise linear assuming variation in chromaticity model.

Despite an increased need for three-dimensional (3-D) functionality in curved displays, comparisons pertinent to human factors between curved and flat panel 3-D displays have rarely been tested. This study compared stereoscopic 3-D viewing experiences induced by a curved display with those of a flat panel display by evaluating subjective and objective measures. Twenty-four participants took part in the experiments and viewed 3-D content with two different displays (flat and curved 3-D display) within a counterbalanced and within-subject design. For the 30-min viewing condition, a paired t-test showed significantly reduced P300 amplitudes, which were caused by engagement rather than cognitive fatigue, in the curved 3-D viewing condition compared to the flat 3-D viewing condition at P₃ and P₄. No significant differences in P300 amplitudes were observed for 60-min viewing. Subjective ratings of realness and engagement were also significantly higher in the curved 3-D viewing condition than in the flat 3-D viewing condition for 30-min viewing. Our findings support that curved 3-D displays can be effective for enhancing engagement among viewers based on specific viewing times and environments.

We propose a pose transfer method for fine-grained classifications of birds that have wide variations in appearance due to different poses and subcategories. Specifically, bird pose is transferred by using Radon-transform-based contour descriptor, k-means clustering, and K nearest neighbors (KNN) classifier. During training, we clustered annotated image samples into certain poses based on their normalized part locations and used the cluster centers as their consistent part constellations for a particular pose. At the testing stage, Radon-transform-based contour descriptor is used to find the pose a sample belongs to with a KNN classifier by using cosine similarity, and normalized part constellations are transferred to the unannotated image according to the pose type. Bag-of-visual words with OpponentSIFT and color names extracted from each part and from the global image are concatenated as feature vector, which is input to support vector machine for classification. Experimental results demonstrate significant performance gains from our method on the Caltech-UCSD Birds-2011 dataset for the fine-grained bird classification task.

Film-type patterned retarder (FPR) three-dimensional (3D) displays differ from two-dimensional (2D) displays with respect to two distinct features: (1) vertical subsampling caused by a film circularly polarized on a display and (2) luminance loss caused by 3D glasses. To reveal the negative effects of these differences, we analyze the spectrum of an image on an FPR 3D display and investigate the contrast sensitivity of human vision for that image. Based on the analysis results, a preprocessing method is proposed for the aliasing problem caused by the vertical subsampling. In addition, because contrast sensitivity decreases with decreasing luminance, we propose sharpness compensation based on Barten’s contrast sensitivity function model. The proposed method performs more effectively than other methods in terms of 3D image representation.

Fast image restoration method is proposed for vibration image deblurring based on coded exposure and vibration detection. The criterion of the code sequence selection is discussed in detail, and several factors are considered to search for the optimal coded exposure sequence. The blurred vibration image is obtained by the coded exposure technique. Meanwhile, the vibration track information of the camera is detected by a fiber-optic gyroscope. The point spread function (PSF) is estimated using a statistical method with the selected code sequence and vibration track information. Finally, the blurred image is quickly restored with the estimated PSF through a direct inverse filtering method. Simulation experiments are conducted to test the performance of the approach with different vibration forms. A real imaging system is constructed to verify the effectiveness of the proposed algorithm. Experimental results show that the presented algorithm could yield better subjective experiences and superior objective evaluation values.

This paper presents a low-complexity interpolation method that minimizes image quality losses at edges, which are easily perceivable by the human eye. Deinterlacing, which converts an interlaced video into a progressive video, is a problem in image interpolation that doubles the number of vertical lines. Applying averaging, or any linear algorithm, achieves time-efficient deinterlacing but produces artifacts. However, applying other complex methods tends to reduce unwanted artifacts but at the cost of high computation time. The proposed deinterlacing scheme is based on an algorithm called “edge slope tracing” which simply predicts the slope on the basis of information on adjacent slopes. Predicted slopes are used to perform deinterlacing in slope-based line averaging. The simulation results show that this scheme provides better results and reduces complexity compared to conventional state-of-the-art algorithms.

This paper develops a log-likelihood ratio test statistic for resolved target detection in dual-band imagery because the previous work indicates that most of the processing gains come from processing just two bands. Simple, closed-form equations for the closed-form probabilities of false alarm and detection are given. A computer simulation validates the theory. A constant false alarm rate version of the theory is applied to real available multiband data with quasi-resolved target sets and fixed clutter noise. The results show very reasonable performance in target detectability using three sets of correlated dual-band images. Finally, this paper shows that the resolved target detection problem depends on the weighted difference between the dual-band target contrasts. The theoretical development reaffirms that the signal-to-noise ratio or contrast-to-noise ratio is approximately the weighted difference squared, divided by the normalized total image noise variance.

We present three-dimensional (3-D) target tracking based on fused radar and infrared (IR) sensor data with the inclusion of target orientation in the measurement vector. We provide the noise statistic of IR-sensor measurements, including target orientation measured from the IR image. The track-to-track fusion with extended Kalman filter is used to combine radar with IR sensor data. In conventional tracking approaches, there is a fundamental limitation in that it is difficult to accurately estimate the current acceleration of the target, even with nearly perfect measurements of range and angle relative to the target. The correlation between target orientation and velocity can be used to overcome this limitation. We evaluate tracking performance to show how much improvement is obtainable through the inclusion of the target orientation in the measurement data for a realistic 3-D scenario.

The infrared imaging technique is characterized as high-precision and noncontact and provides the temperature information of the object, leading to its broad application in civil and military fields. Currently, the research on infrared thermography is mainly focused on two-dimensional images, lacking the information in depth orientation. To extend the range of application and provide spatial information, a three-dimensional (3-D) infrared imaging system based on binocular stereo vision is presented. The system is composed of two visible-light cameras, an infrared camera, and a digital projector. The proposed system fuses the metric information and the infrared information to acquire the 3-D surface temperature distribution by combining the 3-D reconstruction technique with infrared thermography. The registration of the metric information and the infrared image is accomplished according to the properties of three-view geometry. Experiments have been undertaken with a storage box, a rudder model, and a person’s stretching arm, respectively, and the results demonstrated the good performance of the proposed method.

We propose an image adaptive backlight dimming method that quantitatively measures the perceived image quality degradation in terms of brightness and contrast. Unlike conventional methods, the proposed adaptive dimming considers the spatial distribution characteristics of the clipped pixels via a new measure, clusterization, to effectively estimate the perceived contrast loss and prevent the clipping artifact (light saturation). The proposed adaptive dimming achieves an average 17.71% power reduction while keeping the image quality difference to a tolerably low amount, as shown by the subjective mean opinion score test results. Comparing the optimal backlight levels estimated by the proposed method with results from other methods, the proposed backlight dimming is closer to the ground truth backlight levels that are favored by human subjects.

To register partially overlapping three-dimensional point sets from different viewpoints, it is necessary to remove spurious corresponding point pairs that are not located in overlapping regions. Most variants of the iterative closest point (ICP) algorithm require users to manually select the rejection parameters for discarding spurious point pairs between the registering views. This requirement often results in unreliable and inaccurate registration. To overcome this problem, we present an improved ICP algorithm that can automatically determine the rejection percentage to reliably and accurately align partially overlapping laser-radar (ladar) range images. The similarity of k neighboring features of each nonplanar point is employed to determine reasonable point pairs in nonplanar regions, and the distance measurement method is used to find reasonable point pairs in planar regions. The rejection percentage can be obtained from these two sets of reasonable pairs. The performance of our algorithm is compared with that of five other algorithms using various models with low and high curvatures. The experimental results show that our algorithm is more accurate and robust than the other algorithms.

A circular wire grid polarizer (WGP) as a device to produce high quality radially polarized light at near UV wavelength range (in particular at the wavelength of λ=405  nm) is presented starting from design modeling followed by fabrication and performance analysis. The wire grid consists of concentric subwavelength metallic cylinders covering a high quality glass substrate and fabricated using an electron beam pattern generator and etching techniques. The theoretical modeling using the rigorous finite-element method and measurements of the transmitted light through the mask have been evaluated. An analysis on adjustments of the geometry of the WGP to produce the optimum focused spot of the longitudinal component of the electric field, its implementation, and qualitative testing are also presented.

Soil emissivity signatures were constructed using the digital imaging and remote sensing image generation (DIRSIG) model and Blender three-dimensional (3-D) graphic design software. Using these tools, the geometry, radiometry, and chemistry of quartz were exploited to model the presence of particle size effects in the thermal spectra of disturbed soil. Using the physics engines within the Blender 3-D graphic design software, a physical representation of a granular soil scene was created. Chemical and optical properties of pure quartz were assigned to particles in the scene based on particle size. The spectral signature of disturbed soil was modeled by the physical mixture of small fine particles (50  μm diameter) and larger grains (500  μm diameter). The study demonstrated that by combining realistic target geometry and spectral measurements of pure quartz, emissivity of complex soil mixtures could be modeled without functional data fitting or rigorous analysis of material dynamics.

A preliminary investigation into the use of slitless spectroscopy for characterization of geosynchronous satellites is described. A 100  line/mm diffraction grating is used as the dispersing device, and the spectral data obtained are compared to a model with good results. A method used to collect and calibrate slitless spectral observations accounting for pixel to wavelength conversion, pixel response as a function of wavelength, and solar features is presented. Observations of several geosynchronous satellites throughout a night reveal reflectance with noticeable and different profiles indicating that slitless spectroscopy offers the potential for another modality for identifying and discriminating satellites.

The advent of fully coherent free-electron laser and diffraction-limited synchrotron radiation storage ring sources of x-rays is catalyzing the development of new ultrahigh accuracy metrology methods. To fully exploit these sources, metrology needs to be capable of determining the figure of an optical element with subnanometer height accuracy. The major limiting factors of the current absolute accuracy of ex situ metrology are drift errors due to temporal instabilities of the lab’s environmental conditions and systematic errors inherent to the metrology instruments. Here, we discuss in detail work at the Advanced Light Source X-Ray Optics Laboratory on building of advanced environmental control that is a key component in the development of ultrahigh accuracy ex situ metrology for x-ray optics. By a few examples, we show how the improvement of the environmental conditions in the lab allows us to significantly gain efficiency in performing ex situ metrology with high-quality x-ray mirrors. The developed concepts and approaches, included in the design of the new X-Ray Optics Laboratory, are described in detail. These data are essential for construction and successful operation of a modern metrology facility for x-ray optics, as well as high-precision measurements in many fields of experimental physics.

Ion beam machining technology has been extensively adopted to obtain an ultraprecision surface in ultraviolet lithography optics. However, there exist complex mechanisms leading the surface to evolve complicated topographies and increasing roughness. We build a kinetic model integrating with the typical sputter theory and a bond-counting Monte Carlo algorithm based on the compound materials to investigate the surface roughness evolution during ion beam sputtering. The influences of primary sputter, reflection, secondary sputter, geometrical shadowing, redeposition, and thermal diffusion were all taken into consideration to compose a dynamic evolution process. In calculation, using this model the surface first possesses a period of smoothing and then goes into a roughening stage, where the roughness follows the regular power law. Quantitative analyses of surface roughness derived from calculations are also examined and compared with experiments.

A method for measurement of misalignment in an optical system using wavefront sensing in a two-lens telescopic system is reported. Using Shack-Hartmann wavefront sensor data and ABCD matrix, mapping between Zernike coefficients with known misalignment of optical system is carried out. Results are validated experimentally using a two-lens telescopic system, and then compared with simulated values of a Ritchey-Chretien telescopic system for measuring misalignment. Also, it was demonstrated that ABCD matrix can only work for on-axis misalignment estimation and cannot work for off-axis.

Beam pointing angle (BPA) is one of the key parameters that affects the operation performance of the laser Doppler velocimetry (LDV) system. By considering velocity sensitivity and echo power, for the first time, the optimized BPA of vehicle LDV is analyzed. Assuming mounting error is within ±1.0  deg, the reflectivity and roughness are variable for different scenarios, the optimized BPA is obtained in the range from 29 to 43 deg. Therefore, velocity sensitivity is in the range of 1.25 to 1.76  MHz/(m/s), and the percentage of normalized echo power at optimized BPA with respect to that at 0 deg is greater than 53.49%. Laboratory experiments with a rotating table are done with different BPAs of 10, 35, and 66 deg, and the results coincide with the theoretical analysis. Further, vehicle experiment with optimized BPA of 35 deg is conducted by comparison with microwave radar (accuracy of ±0.5% full scale output). The root-mean-square error of LDV’s results is smaller than the Microstar II’s, 0.0202 and 0.1495  m/s, corresponding to LDV and Microstar II, respectively, and the mean velocity discrepancy is 0.032  m/s. It is also proven that with the optimized BPA both high velocity sensitivity and acceptable echo power can simultaneously be guaranteed.

Multicamera systems have many advantages and are widely used. However, many situations require camera parameters that are more accurate than those that are currently available. A new algorithm is proposed to improve the accuracy and consistency of these systems by adjusting the camera parameters. The algorithm assumes that the distribution of the measured point positions follows the Gaussian mixture model. Based on this model, point positions in space are estimated, and new camera parameters are computed from the estimation. A metric is defined to describe the difference between the newly computed and precalibrated camera parameters, following which the parameters are adjusted by minimizing this difference. Finally, the validity of the algorithm is confirmed by conducting experiments. Two indicators that describe the accuracy and consistency are defined and applied to analyze the experimental data.

Stitching is used to reduce dry-core (incomplete infusion of T-joint core) and reinforce T-joint structure. However, it may cause new types of flaws, especially submillimeter flaws. Microscopic inspection, ultrasonic c-scan, pulsed thermography, vibrothermography, and laser spot thermography are used to investigate the internal flaws in a stitched T-joint carbon fiber-reinforced polymer (CFRP) matrix composites. Then, a new microlaser line thermography is proposed. Microcomputed tomography (microCT) is used to validate the infrared results. A comparison between microlaser line thermography and microCT is performed. It was concluded that microlaser line thermography can detect the internal submillimeter defects. However, the depth and size of the defects can affect the detection results. The microporosities with a diameter of less than 54  μm are not detected in the microlaser line thermography results. Microlaser line thermography can detect the microporosity (a diameter of 0.162 mm) from a depth of 90  μm. However, it cannot detect the internal microporosity (a diameter of 0.216 mm) from a depth of 0.18 mm. The potential causes are given. Finally, a comparative study is conducted.

A simple strategy based on wavefront propagation in the Fresnel regime to reduce a ringing effect by using an ideal filter in off-axis digital holography (DH) is presented. In addition, we demonstrate a better focusing capacity by using this ideal filter than Butterworth and Gaussian methods. It also provides a way to increase the visibility of the refocused plane by reducing the influence of the out-of-focus planes. We also use the unique feature of the refocusing capability of DH in the reconstructed and enhanced image, which is obtained from the averaging operation between the image at the focused image plane (z=z_hd0) and the first Talbot distance order (z=z_hd1). This distance is determined by the periodic ringing. Reductions of 50% of these anomalies are computed in simulation and 30% is obtained experimentally (nearly 2 nm). Also a numerical simulation shows that the focusing resolution is directly related to the filter size and shows a 0.8 mm focus zone with an ideal filter. Numerical simulations and experimental results are carried out to validate the proposal.

A static scene statistical nonuniformity correction (S³NUC) method was developed based on the higher-order moments of a linear statistical model of a photodetection process. S³NUC relieves the requirement for calibrated targets or a moving scene for NUC by utilizing two data sets of different intensities but requires low scene intensity levels. The first-, second-, and third-order moments of the two data sets are used to estimate the gain and bias values for the detectors in a focal-plane array (FPA). These gain and bias values may then be used to correct the nonuniformities between detectors or to initialize other continuous calibration methods. S³NUC was successfully applied to simulated data as well as measured data at visible wavelengths.

Optical coherence tomography (OCT) is a very high-resolution imaging technique whose resolution depends on source bandwidth. Improving resolution is an important topic of research in OCT. Thus, to improve resolution, the bandwidth of the source must be increased. Practical sources have finite bandwidth. Therefore, it is suggested to use more sources. Previous work expected that resolution will be inevitably improved without mentioning to what extent it will be improved and without any referencing to the effect of spectral separation between the sources. We study the resolution of a Fourier-domain OCT (FD-OCT) system based on two sources. First, we show to what extent resolution is improved and we show that this improvement not only depends on the spectral widths of the sources but also on spectral separation of the sources. Second, we show that in most cases resolution will become poorer and discuss mathematically the origin of resolution worsening and reveal the problems encountered in such a system. Third, we propose two techniques to overcome these problems. One of them is by shifting spectral interferograms and the other is by multiplying the spatial interferogram. Then, we clarify their advantages, disadvantages, major drawbacks, and limitations.

Self-imaging beams consisting of three-dimensional intensity voids are generated via photorefractive volume holography. Reconstruction of a volume hologram recorded at 594 nm is performed with a Bessel readout beam. The holographic output is similar in appearance to a Bessel beam, with the central spot oscillating between maximum and zero intensity over a propagation distance of 10 to 55 cm. The oscillation period for the on-axis intensity is 30 cm. The reconstruction is capable of self-healing, with a fully recovered central core after the beam propagates 40 cm. Dual-wavelength reconstruction at 632.8 nm produces an output beam with similar self-imaging and self-healing properties. A theoretical framework based on the interference of a plane wave and a Bessel beam simultaneously reconstructed from a volume hologram is able to describe our experimental results.

Improvements described consist of modifications of a composite fringe pattern in both frequency and direction of carrier fringes. Through these modified changes, the range of the measurable frequency under the scope of this study is increased nearly fourfold above its normal range. Theoretical and experimental results are presented.

A new ion beam figuring (IBF) technique, obliquely incident IBF (OI-IBF), is proposed. In OI-IBF, the ion beam bombards the optical surface obliquely with an invariable incident angle instead of perpendicularly as in the normal IBF. Due to the higher removal rate in oblique incidence, the process time in OI-IBF can be significantly shortened. The removal rates at different incident angles were first tested, and then a test mirror was processed by OI-IBF. Comparison shows that in the OI-IBF technique with a 30 deg incident angle, the process time was reduced by 56.8%, while keeping the same figure correcting ability. The experimental results indicate that the OI-IBF technique is feasible and effective to improve the surface correction process efficiency.

Reddish-orange emitting phosphors, Sr₃Gd(PO₄)₃:  Sm³⁺, were successfully synthesized by a conventional solid-state reaction. The crystal structure of the phosphors was characterized by x-ray diffraction. The excitation spectra and emission spectra were utilized to characterize the luminescence properties of the as-prepared phosphors. The results show that the phosphor consisted of some sharp emission peaks of Sm³⁺ ions centered at 564, 600, 647, and 707 nm, respectively. The critical distance of Sr₃Gd_0.93(PO₄)₃: 0.07Sm³⁺ was calculated to be 19.18  Å and the lifetime value of the sample was 1.63 ms. The band gap of Sr₃Gd(PO₄)₃ was estimated to be about 2.74 eV from the diffuse reflection spectrum. The optimum doping concentration is 7 mol. % and the quenching occurs via dipole–dipole interaction according to Dexter’s theory. The Commission Internationale de L’Eclairage value of Sr₃Gd(PO₄)₃:  Sm³⁺ phosphors presented that it has high color purity. These results indicated that the Sr₃Gd(PO₄)₃:  Sm³⁺ may be a promising reddish-orange emitting phosphor for cost-effective near ultraviolet white light-emitting diodes.

We have described a method to detect characteristics of an oscillation system based on the moiré technique. We can determine amplitude, resonance frequency, and damping coefficient of an oscillating system both in vertical and horizontal directions. For this approach, the displacement of the oscillatory mass must be accurately determined. The displacement is recorded by the moiré detecting procedure. A spring-suspended mass, whose position is monitored by moiré technique, is used to test this idea. Our detecting system consists of a pair of similar gratings which are installed near each other without physical contact. The planes of the gratings are parallel and the lines of gratings have a small angle with respect to each other. Also, a laser diode, a silicon photo-diode, and a narrow slit have been used and fixed to the frame to illuminate fringes’ displacement due to the suspended mass movement. The displacement of the mass relative to the fixed grating changes the light intensity on the detector. The intensity of the light is recorded as voltage by the light detector. The output voltage can be used to measure the oscillator movement. This method can detect displacements of the order of microns. Also, the experimental result and theoretical simulation are compared.

As a key component of the subcarrier-based optical phase-locked loop, an optical voltage controlled oscillator (OVCO) suffers a penalty due to various factors, such as the nonoptimal peak drive voltage, the bias voltage deviation, and the inevitable imperfections of the modulator and the driver. We have performed a systematic study to investigate the influence of these factors on the performance of the OVCO. Our theoretical analysis and experimental demonstration show that by setting the peak drive voltage to around 1.172V_π, employing a proper automatic bias control technology for the Mach–Zehnder modulator, and applying a driver with adequate output saturation voltage, the optimal performance of the OVCO with high power efficiency and stable output can be achieved. Our results may provide useful guides for the design of an OVCO or the production of a commercially integrated OVCO component.

In the last decade, new architecture designs such as nBn devices or unipolar barrier photodiodes have been proposed to achieve high-operating temperature (HOT) detectors. This idea has been also implemented in HgCdTe ternary material systems. However, the implementation of this detector structure in an HgCdTe material system is not straightforward due to the existence of a valence band discontinuity (barrier) at the absorber-barrier interface. We report on midwavelength infrared HgCdTe barrier detectors with a zero valence band offset, grown by metal organic chemical vapor deposition on GaAs substrates. The experiments indicate the influence of the barrier on the electrical and optical performances of the p+B_pnN+ device. The devices exhibit very low-dark current densities in the range of (2−3)×10−³  A/cm² at 230 K and a high-current responsivity of about 2  A/W in the wide range of reverse bias voltage. The estimated thermal activation energy of about 0.33 eV is close to the full Hg_0.64Cd_0.36Te bandgap, which indicates diffusion limited dark currents.

This paper proposes a bionic accommodating intraocular lens (IOL) for ophthalmic surgery. The designed lens has a solid–liquid mixed integrated structure, which mainly consists of a support ring, elastic membrane, rigid lens, and optical liquid. The lens focus can be adjusted through the deformation of the lens front surface when compressed. The integrated structure of the IOL is presented, as well as a detailed description of the lens materials and fabrication process. Images under different radial pressures are captured, and the lens deformation process, accommodating range, density, and optical property are analyzed. The designed lens achieves a 14.6 D accommodating range under a radial pressure of 51.4 mN and a 0.24 mm alteration of the lens outer radius. The deformation property of the lens matches well with the characteristic of the eye and shows the potential to help patients fully recover their vision accommodation ability after the cataract surgery.

A feedforward control based on data fusion is proposed to enhance closed-loop performance. The target trajectory as the observed value of a Kalman filter is recovered by synthesizing line-of-sight error and angular position from the encoder. A Kalman filter based on a Singer acceleration model is employed to estimate the target velocity. In this control scheme, the control stability is influenced by the bandwidth of the Kalman filter and time misalignment. The transfer function of the Kalman filter in the frequency domain is built for analyzing the closed loop stability, which shows that the Kalman filter is the major factor that affects the control stability. The feedforward control proposed here is verified through simulations and experiments.

Large-scale triangulation scanning measurement systems are widely used to measure the three-dimensional profile of large-scale components and parts. The accuracy and speed of the laser stripe center extraction are essential for guaranteeing the accuracy and efficiency of the measuring system. However, in the process of large-scale measurement, multiple factors can cause deviation of the laser stripe center, including the spatial light intensity distribution, material reflectivity characteristics, and spatial transmission characteristics. A center extraction method is proposed for improving the accuracy of the laser stripe center extraction based on image evaluation of Gaussian fitting structural similarity and analysis of the multiple source factors. First, according to the features of the gray distribution of the laser stripe, evaluation of the Gaussian fitting structural similarity is estimated to provide a threshold value for center compensation. Then using the relationships between the gray distribution of the laser stripe and the multiple source factors, a compensation method of center extraction is presented. Finally, measurement experiments for a large-scale aviation composite component are carried out. The experimental results for this specific implementation verify the feasibility of the proposed center extraction method and the improved accuracy for large-scale triangulation scanning measurements.

Fabrication and testing results of sine-top, high-efficiency, broadband gold-coated gratings (BGCG) for high-power laser pulse compression applications are reported. These gratings differ from conventional metal-on-photoresist pulse compression gratings in that the gratings patterns are generated by directly etching the quartz substrate. The groove depth and duty cycle of the photoresist mask was controlled by changing photoresist thickness and adjusting exposure and development times, respectively. The duty cycle of the photoresist mask was further corrected by oxygen plasma etching. Using this method, high efficiency, sine-top, BGCG with line densities of 1740  lines/mm was achieved. The average diffraction efficiency at the-1st order was 89.2% and the peak value was 90% for TM polarized light as the wavelength increases from 750 to 850 nm.

We analyze the effect of diffuse reflection on indoor localization systems based on visible light communication. The target position is estimated using a received signal strength indication technique. Two lighting systems are considered: distinct and uniform lighting systems. Each utilizes commercially available light-emitting diodes and photodiodes with an illumination level conforming to standards. We introduce a comparative study between the two lighting systems through different transmitter (Tx) and receiver (Rx) essential parameters. The results show that the uniform lighting system achieves less localization error (≤20.43  cm) than a distinct lighting system (≤45.9  cm). The uniform lighting system is well adapted to low-Rx field of view (FOV) and narrow radiation angle (error=1  mm when semiradiation angle=5  deg). In the case of a distinct lighting system, low-Rx FOV is also required, while the Tx semiradiation angle needs to be determined carefully (error≤3.08  cm when semiradiation angle=20  deg). Finally, the uniform lighting system shows flexibility in the process of Tx and Rx designs. A uniform lighting system can utilize Rxs with narrow FOVs (≥8.6  deg), while a distinct lighting system is limited to Rx with a wide FOV (≥53.96  deg).

Because of the laser beam waist and diffraction effect of the lens, the focal spot light field in femtosecond laser microprocessing has an ellipsoidal spatial distribution. This leads to the gap between two processing layers increasing along the axial direction, and the distribution density of processing points decreasing along the horizontal direction. This directly reduces the resolution of the microprocessing, and badly affects the machining accuracy and surface quality. We established a mathematical model for three-dimensional (3-D) laser beam shaping based on the Fresnel diffraction theory and designed a kind of four-ring complex amplitude transmittance phase plate by using a global optimization algorithm and genetic algorithm to simultaneously realize transverse and axial 3-D shaping. We numerically showed that the transverse and axial gains of the focal facula after 3-D shaping are 0.77 and 0.68, respectively, where the corresponding peak energy ratio is 0.36, the transverse and axial sidelobe energies are 0.28 and 0.62, respectively, and the defocusing amount is −0.08. We also constructed a confocal/two-photon microscope system to experimentally achieve a better shaping effect in the case of femtosecond laser fabrication at a point on the thin film of a photochromic material.

The design of high-quality imaging lenses continues to strive for the best color trueness over wider and wider wavelength ranges such as for multiwavelength fluorescence microscopy or hyperspectral imaging. Glasses suitable for sharp images at more than two wavelengths must differ in their dispersion from the classical crown and flint glass types, which gather along a straight line in a plot of the relative partial dispersion against the Abbe number. Glasses suitable for multicolor correction can be recognized by a considerable deviation of their relative partial dispersion from this normal line. Originally, the normal lines for different relative partial dispersions were defined by using the SCHOTT glass types K7 and F2. Today’s data sheets of all glass manufacturers contain numerical values for deviations of relative partial dispersions from the normal lines. A comparison of almost identical glasses shows differences between these deviations being too large, obviously coming from different versions of K7 and F2 dispersion curves used. For preselection in designs and for direct comparison of glass types, it is necessary to agree on common dispersion curves each for K7 and for F2 in order to obtain really comparable values for deviations of the relative partial dispersion from the normal line.

Reaction-sintered silicon carbide (RS-SiC) is a promising optical material for the space telescope systems. Anodically oxidation-assisted polishing is a method to machine RS-SiC. The electrolyte used in this study is a mixture of hydrogen peroxide (H₂O₂) and hydrochloric acid (HCl), and the oxidation potential has two modes: constant potential and high-frequency-square-wave potential. Oxide morphologies are compared by scanning electron microscope/energy dispersive x-ray spectroscopy and scanning white-light interferometer. The results indicate that anodic oxidation under constant potential can not only obtain a relatively smooth surface but also be propitious to obtain high material removal rate. The oxidation depth in anodic oxidation under constant potential is calculated by comparing surface morphologies before and after hydrofluoric acid etching. The theoretical oxidation rate is 5.3  nm/s based on the linear Deal–Grove model. Polishing of the oxidized RS-SiC is conducted to validate the machinability of the oxide layer. The obtained surface roughness root-mean-square is around 4.5 nm. Thus, anodically oxidation-assisted polishing can be considered as an efficient method, which can fill the performance gap between the rough figuring and fine finishing of RS-SiC. It can improve the machining quality of RS-SiC parts and promote the application of RS-SiC products.

This paper investigates the timing synchronization problem of a space optical orthogonal frequency division multiplexing (OOFDM) communication system. First, based on the good autocorrelation property of generalized chirp-like sequence, a training sequence is constructed to fit the non-negative light intensity signal requirement of the OOFDM system, of which the front and rear portions are cyclical and the whole is mirror-symmetric. No longer a periodic-repetition structure, the mirror-symmetric structure can effectively avoid the side lobe of objective function and reduce the complexity of correlation calculation, and thereby can improve the synchronization performance. Then, the constructed training sequence is superimposed on a complete data symbol for transmission to efficiently utilize transmitting power and spectrum resources of the communication system. At the receiver, the position of timing synchronization is estimated using maximum-likelihood algorithm and the correlation between the local sequence and the received signal. Simulation results show that, compared with several existing methods, the proposed timing synchronization method achieves better synchronization performances under both strong and weak atmospheric turbulence channels.

We propose an optimized quasiperiodic microcavity with the aim of achieving the highest quality factor. The proposed structure consists of two quasicrystal rings with different geometries. By performing several optimizations on the structure, the highest quality factor of 8.16×10⁷ for a femtosecond laser with a wavelength of 1040 nm can be achieved. The quasiperiodic microcavity is used for a quantum dot laser application that obtained the highest output power of 3800  W/m². The most important characteristics of this structure are the improvement of the quality factor and a simultaneously stable cavity wavelength.

We research the refractive index (RI) sensing characteristic based on the bandpass spectrum caused by the self-imaging effect in the single-mode-multimode-single-mode (SMS) fiber structure theoretically and experimentally. A new selectable parameter, i.e., no-core fiber (NCF) length, is investigated for improving the sensitivity of the sensor. The results show that the sensor’s sensitivity will be enhanced by shortening the NCF length when the self-imaging number remains constant. Experimentally, a maximum sensitivity of 1923  nm/RIU (RI unit) has been achieved when the RI ranges from 1.334 to 1.434. This work demonstrates a method to improve the sensitivity of SMS-fiber-structure-based RI sensors featuring a low cost, compact size, low insert loss, and high sensitivity optical fiber RI sensor.

A smoothly tunable 1.432  μmNd:YAlO₃ laser was assembled for potential remote sensing of atmospheric CO₂ at high altitudes. Continuous laser tuning from 6982.8 to 6984.6  cm−¹ was demonstrated, and CO₂ absorption lines relatively free of atmospheric water absorption interference at 6983 and 6984  cm−¹ were experimentally observed, confirming feasibility of atmospheric CO₂ sensing.

Polymer optical fibers (POF) offer only transmission so far with one wavelength at 650 nm. In order to increase the overall transfer rate, the key element for wavelength division multiplexing (WDM) over POF will be presented. This element is a demultiplexer (DEMUX), which was designed in polymethylmethacrylate with an optical grating on an aspherical mirror to be produced by injection molding in a further development steps. The master was produced by diamond turning as a master for injection molding replication. The results of the different simulations followed by the development steps and the measurements of the prototype are presented. This prototype is used as a DEMUX in a WDM system with four wavelengths. In the WDM system, bit-error ratio (BER) measurements with an 8.26  Gb/s cumulated data rate in an offline processed discrete multitone modulation technique have been achieved over 100 m SI-POF at a BER of 10−³.

We proposed and analyzed a scheme of generating an optical multicarrier using a linear optical modulator–based hybrid interferometer modulator and a dual parallel Mach–Zehnder modulator. Fifteen-tone comb lines within 0.5-dB spectral power variation are obtained; the side-mode suppression ratio is about 35 dB; and the system is tolerant to radio-frequency phase differences. Some analysis on the noise characteristics and the impact of parameter drifting is also made. These features indicate that the proposed multicarrier generator is a good multiwavelength source for quantum key distribution wavelength division-multiplexing passive optical networks.

The mode characteristics of few-mode step-index optical fibers composed of a center core and a few assistant cores are investigated. Each fourfold mode in the optical fiber can be split into two twofold modes, avoiding strong mode coupling during the transmission process. In addition, two-mode operation in the fiber with a wide wavelength range of 1.42 to 1.9  μm is demonstrated numerically. We also investigated the coupling characteristics of the two-core configuration that can effectively separate the LP₀₁ and LP₁₁ modes.

Weighted interframe averaging (WIFA)-based channel estimation (CE) is presented for orthogonal frequency division multiplexing passive optical network (OFDM-PON), in which the CE results of the adjacent frames are directly averaged to increase the estimation accuracy. The effectiveness of WIFA combined with conventional least square, intrasymbol frequency-domain averaging, and minimum mean square error, respectively, is demonstrated through 26.7-km standard single-mode fiber transmission. The experimental results show that the WIFA method with low complexity can significantly enhance transmission performance of OFDM-PON.

A differential phase-shift keying modulation for free-space optical (FSO) communication is considered in atmospheric turbulence modeled by the exponentiated Weibull distribution. The selection combining (SelC) spatial diversity is used to mitigate the effects of atmospheric turbulence. We analyze the average bit error rate (BER) of the system using SelC spatial diversity by Gauss–Laguerre approximation. The effect of aperture averaging and spatial diversity on the outage probability is also studied. The numerical results show that it requires a smaller level of signal-to-noise ratio to reach the same BER when large aperture and SelC spatial diversity are deployed in the FSO system. Moreover, it is proved that aperture averaging and SelC spatial diversity are effective for improving the performance of the system’s outage probability.

An all-optical scheme aimed at minimizing distortions induced by semiconductor optical amplifiers (SOAs) over modulated optical carriers is presented. The scheme employs an additional SOA properly biased to act as a saturated absorber, and thus counteract the distortions induced by the first amplifying device. The scheme here is demonstrated in silico, for 40 and 100  Gb/s (10 and 25 Gbaud, 16 QAM), with reasonable total gain (<20  dB) for symbol error rate below the forward error correction limit.

A scheme for all-optical repetition rate multiplication of pseudorandom bit sequences (PRBS) is demonstrated with a precision delay feedback loop cascaded with a terahertz optical asymmetric demultiplexer (TOAD)-based power equalizer. Its feasibility has been verified by experiments, which show a multiplication for PRBS at cycle 2^{^7}−1 from 2.5 to 10  Gb/s . This scheme can be employed for the rate multiplication of a much longer cycle PRBS at a much higher bit rate over 40  Gb/s if the time-delay, the loss, and the dispersion of an optical delay line are all precisely managed.

The problem of optics orthogonal frequency division multiplexing (optical-OFDM) communication lies in the peak to average power ratio (PAPR), which seriously affects the quality of communication systems. A composite technique, which combines the Hartley transform and KC companding technique to reduce the PAPR of an optical-OFDM system, is proposed. The proposed technique can obtain the same quality of OFDM signals and offer an improved bit error rate performance by using Hartley transform instead of the traditional Fourier transform, while the computational complexity is almost halved. Theoretical analysis and simulation results show that the proposed technique has a superior performance for reducing the PAPR when compared to the traditional technique.

A nonlinear hybrid plasmonic waveguide (HPW) with a metal cap on a nonlinear material-on-insulator rib is proposed. By using a finite-difference time-domain method, its light confinement and effective nonlinearity coefficient of the Kerr effect for all-optical switches are analyzed in detail. Numerical simulations illustrate that the nonlinear HPW structure has nanoscale confinement and high effective nonlinearity coefficient at the wavelength of 1550 nm. Consequently, the HPW can be used in all-optical signal processing of integrated photonics.

The magnetic field is a physical medium used to realize the levitation and motion control of magnetic bearings. It is necessary to conduct the air-gap flux density measurement so as to validate theoretical analyses and provide instructions for practical design. A thin-slice fiber Bragg grating-giant magnetostrictive material (FBG-GMM) sensor, in which the FBG was stuck perpendicular to the principal magnetostriction orientation of a thin GMM slice, was proposed to measure magnetic-flux density in the small air gap. The configuration of FBG-GMM sensor was the same with that of a sensor of 1.5  mm×14  mm×7  mm TbDyFe slice stuck with a 1300 nm-wavelength FBG on the side of the slice. The FBG-GMM magnetic field sensor was tested on an U-shape electromagnet test setup under static conditions. The sensor had a linear region of 0.121 to 0.261 T with the sensitivity of 1089.056  pm/T. The FBG-GMM magnetic field sensor was introduced to measure the air-gap flux density of radial magnetic bearings. Measurement of static flux density was conducted with 2 FBG-GMM sensors compensated with a temperature FBG; and the measured data showed that the FBG-GMM sensor had feasible linear region and sensitivity to measure the air-gap flux density of magnetic bearings.

A type of single crystal sapphire optical fiber (SCSF) design is proposed to reduce the number of guided modes via a highly dispersive cladding with a periodic array of high- and low-index regions in the azimuthal direction. The structure retains a “core” region of pure single crystal (SC) sapphire in the center of the fiber and a “cladding” region of alternating layers of air and SC sapphire in the azimuthal direction that is uniform in the radial direction. The modal characteristics and confinement losses of the fundamental mode were analyzed via the finite element method by varying the effective core diameter and the dimensions of the “windmill”-shaped cladding. The simulation results showed that the number of guided modes was significantly reduced in the windmill fiber design, as the radial dimension of the air and SC sapphire cladding regions increase with corresponding decrease in the azimuthal dimension. It is anticipated that the windmill SCSF will readily improve the performance of current fiber optic sensors in the harsh environment and potentially enable those that were limited by the extremely large modal volume of unclad SCSF.

Plasmonics have enabled the realization of new optical components in nanostructures such as polarizers. We construct nanostructures by polycarbonate grating comprising silver nanospikes prepared by an oblique angle deposition technique. Surface, wavelength, and polarization properties of these devices have been investigated by atomic force microscopy, fiber-coupled spectrometer, and rotating analyzer, respectively. Our results show that we can reach 31% polarization ratio with the aid of two pieces of metalized gratings placed back to back by index-matching gel. Also, we can reach the broadband optical polarizer in the visible region according to the concentration and direction of nanospike in each of metalized nanogratings, which can open up directions toward cheap and one-dimensional optical polarizers.

We present microwave self-collimated properties in two-dimensional ferromagnetic photonic crystals (FPCs) made of an array of ferrite rods. Through utilizing the time reversal symmetry-breaking nature of the FPCs, a technique, i.e., unidirectional self-collimation transmission, can be exhibited near the magnetic surface plasmon resonance and the spin wave resonance by designing the appropriate structure. An incident self-collimated beam can be absorbed completely at a particular bending channel, while an obvious transmission is observed at the symmetrically opposite direction. The working frequency of the unidirectionality can be controlled as well by tuning the external static magnetic field.

We propose and analyze a gyroscope using active three-dimensional vertically coupled resonators (3D-VCRs), which allows for loss compensation, unidirectional propagation, and a larger sensing area while maintaining the same bulk volume. For the ideal uniform case, the minimum detectable rotation rate ΔΩ_min of the active 3D-VCR gyroscope can be decreased by above three orders of magnitude after optimization compared with the passive case. The minimal measurable rotation rates of the 3D-VCR gyroscope, the loss-compensated coupled resonator optical waveguide (LC-CROW) gyroscope, and the equivalent resonant waveguide optical gyroscope (RWOG) decrease with a higher number N of the resonators. Finally, it is shown that the uniform active 3D-VCR gyroscope has a better resolution ΔΩ_min than the equivalent LC-CROW and RWOG.

We report on the impurity-free vacancy-disordering effect in InAs/GaAs quantum-dot (QD) laser structure based on seven dielectric capping layers. Compared to the typical SiO₂ and Si₃N₄ films, HfO₂ and SrTiO₃ dielectric layers showed superior enhancement and suppression of intermixing up to 725°C, respectively. A QD peak ground-state differential blue shift of >175  nm (>148  meV) is obtained for HfO₂ capped sample. Likewise, investigation of TiO₂, Al₂O₃, and ZnO capping films showed unusual characteristics, such as intermixing-control caps at low annealing temperature (650°C) and interdiffusion-promoting caps at high temperatures (≥675°C). We qualitatively compared the degree of intermixing induced by these films by extracting the rate of intermixing and the temperature for ground-state and excited-state convergences. Based on our systematic characterization, we established reference intermixing processes based on seven different dielectric encapsulation materials. The tailored wavelength emission of ∼1060─1200  nm at room temperature and improved optical quality exhibited from intermixed QDs would serve as key materials for eventual realization of low-cost, compact, and agile lasers. Applications include solid-state laser pumping, optical communications, gas sensing, biomedical imaging, green–yellow–orange coherent light generation, as well as addressing photonic integration via area-selective, and postgrowth bandgap engineering.