We discuss over three decades of progress in nonmechanical beam steering, provide a comparison of approaches being developed, and comment on promising approaches not yet fully developed. Most of the work in nonmechanical beam steering has been for narrowband optical systems, but a brief discussion is provided of broadband. The majority of the nonmechanical approaches to beam steering create a tilted optical path delay (OPD) to change the wavefront, but some directly create a phase delay. OPD-based approaches may be true time delay, with no resets or modulo 2πn optical phased arrays that have resets. Most of the nonmechanical optical beam steering approaches tilt an existing wavefront and are called space fed approaches, because the beam is already formed when the wavefront is tilted. For the majority of radar nonmechanical beam steering, the tilted wavefront is formed by individual transmit/receive modules. Periodic structures (gratings) spread different wavelengths of light in angle, thus steering light, and are also used for nonmechanical steering. Our paper is derived from a conference paper presented at Photonics West in February 2019.

With the development of light-field acquisition technology from two-dimensional (2-D) to three-dimensional (3-D) sensors, point clouds are currently being used in the 3-D reconstruction of light-field imaging. The computational requirements of point cloud processing decrease the efficiency of 3-D object recognition in a light field reconstruction. An optimization strategy is proposed to improve the efficiency of object feature recognition in a 3-D light field reconstruction. The proposed method involves a normal estimation, uniform keypoint sampling, random Monte Carlo sampling, signature of histograms of orientations descriptor extraction, k-dimensional tree matching, and geometric consistency clustering estimation. During the experiments, all scenarios corresponding to each model are tested, 2711 times in three virtual and real international standard databases (i.e., Kinect, Mian, and Clutter). The experimental results indicate that the efficiency of the proposed method is improved by 9.26% on an average with the same accurate recognition rate of 84.67%.

The diffractive plenoptic camera (DPC) was developed as a system that would capture the spectral and spatial information of a scene in one snapshot. While the DPC couples a diffractive optic with plenoptic camera designs to provide snapshot spectral imaging capabilities, it produces rendered images with low pixel count and low spatial resolution. A modified setup of the DPC, the intermediate image (II)DPC, was built and tested for the first time and compared to both the DPC and a diffractive-optic camera as a system that could improve the cutoff spatial frequency of the rendered images. This paper reports on the spatial resolution achieved for different configurations of the IIDPC and looks at the factors limiting performance. The IIDPC improved on the cutoff spatial resolution over the DPC over a wavelength range of 750 to 790 nm for a design wavelength of 770 nm and improved resolution over a diffractive-optic camera at wavelengths below 750 nm or above 790 nm, with the best results achieved for IIDPC configurations with the largest magnification. Frequency analysis of each system determined that the optic limiting performance was the microlens array. Models showed that decreasing the microlens size improved resolution but reduced the spectral range for the DPC, while decreasing the f  /  # of the microlenses improved the resolution for the IIDPC. These results will help optimize the designs of future systems.

Digital image correlation (DIC) is a noncontact technique that is widely used for deformation measurement, but improving the calculation efficiency to achieve real-time DIC calculation has always been a big concern. A parallel temporal sequence DIC method is proposed, which chooses seed points to determine the integer-pixel displacement and applies the moving least-squares fitting technique to acquire the subpixel displacement. This method avoids traditional complex iterations and takes full advantage of the GPU parallel computing. Results of a simulation experiment and an actual experiment demonstrate the accuracy and efficiency of the proposed algorithm. The calculation speed in the simulation experiment of the proposed method achieved 463,320 POI/s, whereas the speed in the actual experiment was 432,866 POI/s, when the speed of the ICGN method was 2700 POI/s and 2074 POI/s under the same accuracy, respectively. Also, the subpixel displacement calculation made up less than 1% of the entire calculation. The computational efficiency could be further enhanced if a faster integer-pixel displacement calculation method is discovered or a parallel algorithm is used.

Channeled spectropolarimetry (CSP) is a spectral modulation technique that furnishes snapshot polarimetric measurements. Among the different spectropolarimetric methods, fiber-based techniques are fundamental requirements in specific biomedical procedures, such as endoscopy. However, the optical fiber exhibits high sensitivity to temperature changes, which subsequently incurs errors in the polarimetric reconstructions. We present a calibration technique for fiber-based CSP that leverages phase-shifting interferometry (PSI) to acquire and demodulate the fiber’s retardation phase accurately. This technique provides high robustness against temperature variations and improved polarimetric reconstruction performance. Experimental results demonstrated that the PSI calibrations offer higher stability and accuracy, at different optical fiber temperatures, as compared to reference-beam calibrations.

Multistaircase spiral phase plates (SPPs) are more commonly used to generate an optical vortex, as compared to ideal continuous surface SPPs. However, due to the complexities and difficulties involved in the manufacturing of the multistaircase SPPs, the number of the staircases M should not be high and should be sufficient to guarantee a similarity between the M staircase situation (considering an intrinsic topological charge l) and the ideal situation. Therefore, a Fraunhofer diffraction analysis model is proposed to quantitatively and quantificationally solve the diffraction field of the vortex generated by multistaircase SPPs. A finite hypergeometric series summation is applied to solve the diffraction fields of the vortices with different parameters, under the conditions of uniform and Gaussian incident beams. The simulation results show that the summation of the first certain terms of the Fourier expansions can appropriately approximate the diffraction field, and M is positively related with l to approach the ideal situations. Thus, the proposed model can provide a reference for designing and setting the parameters of multistaircase SPPs.

The solution of problems arising in fabrication of optical systems often requires the optimization of a process, design, test, or evaluation related to those systems. There are different optimization techniques that can be used to achieve this goal. In some problems, the parameters to be found have a linear dependence and may be subject to certain restrictions. We present the use of linear programming (LP) to solve optical devices’ fabrication problems. We first describe the LP concept, the standard form of an LP, and show how to give this form to an arbitrary problem. From there, fundamentals and steps of the simplex method and its use in finding an optimal solution are described. Next, we present its application to three different problems in the optical field, highlighting the advantages of modeling through LP: finding the shape of a surface, creating the optimal design of a polishing tool, and developing the analytical profile of a polishing tool. The objective is to exemplify the process of modeling an engineering problem in mathematical terms as an optimization problem of the LP type. We show the usefulness and easiness of implementing and potential for solving optimization problems through LP.

We present a technique for measuring the microlens radius of curvature (ROC). The technique is based on the principle of three-dimensional (3-D) surface topography using a white light interference microscope. By measuring 3-D point clouds of the surface combined with fitting the measured data to an ideal sphere, the radius of the surface is determined. We take advantage of the fast speed of the maximum intensity method and the anti-interference capability of the fitting method of fringe analysis techniques in white-light interferometry to measure the 3-D topography of the microlens array surface. To measure each microlens’s ROC, we use the fast geometric fit algorithm for sphere where the input data are the spherical surface point cloud. We have built a white light interference microscope and experimentally measured the geometric parameter and the surface curvature of some microlens of a commercial microlens array. Our measurement results of the ROC, the surface height, and the diameter of microlens showed a good agreement with the results obtained using the Alpha-Step D-500 stylus profiler and the values reported by the manufacturer, indicating the applicability of this technique.

The bidirectional reflectance distribution function (BRDF) data are essential for analyzing and modeling the material appearance of anisotropic surfaces. In order to acquire four-dimensional BRDF on the anisotropic material surfaces, a four-axis gonioreflectometer was designed and implemented. The instrument consists of a collimated, broadband light source, a four-axis rotation mechanism, a spectroradiometer, and a control system. The instrument is able to carry out spectral BRDF measurements over most of the incident and reflection hemispheres and the entire visible spectrum. One thousand twenty-four samples are obtained over the spectral range of 380 to 760 nm. The angular resolution of the BRDF measurement is <0.1  deg with good repeatability. A relative calibration method was adopted to obtain the absolute values of BRDFs. Various scanning schemes can be carried out by the instrument to scan the designated angular domains, enabling the instrument to capture material appearance with strong, distinctive anisotropic highlights and translucency. The obtained BRDF data of a textile sample demonstrate the instrument capability of capturing complex light scattering behaviors, including off-specular reflection peaks, off-plane reflection peaks, and backscattering. The designers of novel material appearance and computer graphics community will benefit from this work.

To improve the performance of wireless laser communication (WLC) systems, wavefront sensorless adaptive optics based on deformable mirror (DM) eigenmodes was used to correct the distorted far-field spot. A set of DM eigenmodes conforming to the derivative–orthogonal relationship is derived, and the system simulation model under different atmospheric turbulence intensities is established by combining Fresnel diffraction and multiphase screen transmission principle. The influence of mode bias on the correction effect is analyzed. The ability of the proposed method to correct the distorted far-field spot was studied by using Strehl ratio (SR) as the evaluation index. The influence of the proposed method on the coupling efficiency of single-mode fiber and bit error rate performance of the WLC system is discussed. Indoor and outdoor experimental systems were built. The indoor experiment results show that the proposed method can increase the SR of the system from 0.11, 0.32, and 0.56 to 0.57, 0.71, and 0.88, respectively. The outdoor experiment results show that the proposed method can effectively correct the wavefront distortion caused by dynamic atmospheric turbulence.

We demonstrate an all-optical quantization scheme by slicing the supercontinuum (SC) generated in the normal dispersion region of a highly nonlinear fiber. The −20  dB bandwidth of the SC is broadened from 12.9 to 49.7 nm when input average power varies from 0.062 to 0.692 mW, which is used for realizing subsequent quantization. In addition, in order to evaluate the system performance, we have calculated the values of differential nonlinear error, integral nonlinear error, and effective number of bit from the experimental results as 0.471 least significant bit (LSB), 0.519 LSB, and 4.39 bit, respectively.

The average bit error rate (BER) performance of direct single-input multiple-output (SIMO) free-space optical link over correlated non-Kolmogorov turbulence fading channels is studied. In particular, the new closed-form expressions of BER performance of maximal ratio combining (MRC) and equal gain combining (EGC) receive-diversity systems are derived by α-μ distribution approximation method. The influence of both spectral power law and the channel correlation on the BER performance of MRC and EGC diversity systems is systematically investigated and compared. Monte Carlo simulation results are also presented to illustrate the validity of the proposed approach. We will help to investigate the fading correlation in spatial diversity systems and provide useful information for the design of the diversity system.

Dynamic infrared scene projection is a technology for converting infrared (IR) digital image sequences into IR radiating image sequences. One of the most promising technologies is light down-conversion technology based on photoinduced opaque (PIO) effect. A parametric end-to-end steady-state model was proposed to describe the PIO mechanism. It consisted of three submodels such as the silicon parameter model, the photoinduced free carrier model, and the constitutive relation model. Furthermore, the parametric full-link from pump photons’ power density, photoinduced free carrier concentration, complex dielectric constant, and complex refractive index to the emissivity was constructed and mathematically analyzed by the above model. In order to verify the model, an intrinsic silicon wafer was pumped by a continuous-wave running Nd:YAG laser when the wafer was heated up to 321, 423, 459, and 498 K, respectively. Correspondingly, the emissivity integrated from 3 to 5  μm, with the increase of the pump power density measured by an IR camera. The measurement result agreed well with the theoretical result computed by the parametric end-to-end steady-state model. The maximum apparent temperature of the region illuminated by the laser with a pump power density of 407  W cm^−  2 is up to 453 K when the silicon wafer was kept at 498 K. At the same time, the background temperature was elevated to 330 K owing to the initial free-carrier absorption enhancement.

The detection and analysis of hazardous materials through opaque barriers is important for law enforcement agencies. Conventional Raman spectroscopy provides fingerprint signatures of materials but lacks the ability to detect materials through opaque containers. Spatially offset Raman spectroscopy (SORS) overcomes the limitation of conventional Raman spectroscopy and allows the detection of materials through most commercial bottles and packaging materials. Moreover, SORS has the potential to detect hazardous materials through colored glass bottles, high-density polyethylene (HDPE) bottles, Teflon layers, etc., which is required in the screening of commercial packaging at airports and other vital facilities. SORS was investigated in the visible range with a 532-nm excitation source for the detection of urea and sodium nitrate through commercial packaging, i.e., a white HDPE bottle with a thickness of 1 mm. The effects of the spatial offset and integration time on the Raman spectra of the contents and container were evaluated. The trend of the change in the relative contributions from the contents and container was studied by varying the offset and integration time. P-nitrobenzoic acid was detected through the colored bottles in the study of reduction of fluorescence in the SORS effect.