The PDF file contains the front matter associated with SPIE Proceedings Volume 11895, including the Title Page, Copyright information, and Table of Contents.

Due to the highly general surface geometry of freeform optics, the measurement of freeform optical surfaces is still a challenging and rewarding issue. Here, we propose a simultaneous multi-surface measurement method based on deep learning for freeform refractive optics, in which the surfaces are reconstructed based on the transmitted wavefront measured with computer-aided deflectometry. By adopting the deep learning approaches in geometrical error calibration and wavefront reconstruction, both the efficiency and robustness is significantly improved, and the surface measurement accuracy in the order of nanometers can be achieved. The proposed method provides an effective, robust and accurate way for testing freeform refractive optics with multiple surfaces and a large slope range

A variable curvature mirror (VCM) fabricated by 3D printing technique which is thickness optimized in structure design to reduce spherical aberration and supposed to be used in zoom imaging system is investigated. First, measurement and parameters fix of the mirror blank printed by 3D printing of AlSi10Mg are done for its precision deviation introduce by the manufacturing method. Second, elementary optical polishing is done for the purpose of Nickel plated. Fine optical polishing is applied on the VCM after the Nickel plated. Third, an actuation test experiment is built and tested by piezoelectric actuators of PI with nanometer precision and Zygo interferometer. The original surface figure accuracy of 90% radius is 2.225 λ / 0.394 λ (λ = 632.8 nm). As a result, within the ultimate testing range of the interferometer, the VCM achieve about 8.68μm deformation with the corresponding position change of actuator is 18μm, which is about 50% of it. Finally, an experiment of zoom imaging effect is done. The experiment shows that it does have effect to the zoom imaging which can compensate the defocus within 230.7μm. From the performance of the VCM at this stage, it can be used in infrared imaging. For the following work, its structure will be further optimized and the precision problems will be solved through using more proper manufacture method to improve its radius change performance during actuation process. Therefore, it can be used in visible light imaging in the future.

Freeform lens design for LED beam shaping is a difficult inverse problem which generally doesn’t have a unique solution. Under point source approximation, we have proposed an iterative wavefront tailoring (IWT) method [Opt. Lett. 44, 2274-2277 (2019)] for manipulating the irradiance distribution on a planar or curved target. This method has the ability to generate a variety of freeform lens structures including plano-freeform, spherical freeform and double freeform lenses with high accuracy. However, such a point-source design method becomes less valid for a compact design where the LED size is no longer negligible. We integrate the IWT method with an adaptive over compensation to reduce the irradiance deformations caused by the extended LED source. The IWT designs are iteratively modified to approach the prescribed irradiance distributions with the help of an over compensation coefficients. The new composite method combines the advantages of both the IWT method and the over compensation method.

Designing a general method of freeform optics for illuminating hard-to-reach areas is a challenging but rewarding issue. Most of the current designs of freeform illumination optics are valid in the applications in which the region of interest is easily accessible. However, there are some applications in which the region of interest is inaccessible due to the obstacles that cannot be removed and high-quality illumination is still needed (this is usually the case in endoscopic lighting). In this paper, we present a general formulation of designing freeform lenses for illuminating hard-to-reach areas. In this method, the freeform lens consists of two elaborately designed surfaces, by which both the irradiance distribution and wave-front of the light beam are manipulated in a desired manner. The light beam after refraction by the freeform lens is further guided through a light-guiding system to produce a prescribed illumination on a target plane which is inaccessible. Here, the light-guiding system can be a light-guiding element [e.g., a gradient refractive index (GRIN) lens] or an optical system that consists of several optical components. The properties of the light-guiding system are taken into account in the tailoring of the freeform lens profiles to guarantee the prescribed illumination on the target plane. The result shows that the design of freeform optics for illuminating hard-to-reach areas in the presence of a light-guiding system can still be formulated into an Monge–Ampère equation (MA) with a nonlinear boundary condition. Two examples are given to demonstrate the elegance of this method in designing freeform optics for illuminating hard-to-reach areas.

Spectral reflectance plays an important role in the evaluation of the object surface, such as the color, the roughness. A new method is proposed to measure the spectral reflectance at a fixed incident angle. The chromatic confocal displacement sensor is modified with an annular stop to generate a hollow cone beam of incident light on the to-be measured sample surface. With self-reference strategy, the upper and lower envelops are derived from the axial scanning of the dispersion probe, whose minus is named as self-reference spectrum. Thus, the reflectance at every wavelength among the valid dispersion bandwidth can be achieved by comparing the self-reference spectra of the sample surface and a standard mirror with known spectral reflectance. With the proposed method and experimental setup, the spectral reflectance of several metal surfaces is obtained and compared with their theoretical spectral reflectance within ±0.04. It proves that the modified chromatic confocal can provide feasible results for the spectral reflectance measurement.

Miniaturization and compactness are the development direction of imaging spectrometer. More and more imaging spectrometers cannot be miniaturized because of traditional optical components. Thus, the optical design space that can highly benefit from the developments in transmission imaging spectrometer based on the metasurface. In this manuscript, we introduce the concept of transmission imaging spectrometer based on metasurface. The spectrometer has a high resolution from 700-800nm spectrum. The key element of the spectrometer is composed of dielectric metasurface, which is used to divide the incident light-spectrum. Meanwhile, the energy of the ultrasurface diffraction order is higher than that of the dispersion order of the traditional grating. The transmission metasystem design can be applied to many optical systems, interferometers, hyperspectral imagers, and computational optical systems, significantly reducing their sizes and increasing their mechanical robustness and potential for integration.

Many factors could lead to deviation of focal plane of a space-borne camera from its ideal position and thus on-orbit focusing are indispensable to capture satisfactory images of space targets. Among all typical focusing techniques, changing the position of focal plane directly through motor-driven worm and gear is the simplest one, but two drawbacks are obvious. First, mechanical movement is slow but the space targets usually move very fast. In this case, it is highly probable that focus adjusting is always lagging. Second, the targets especially the non-cooperative ones may appear anywhere and working distance of defocus compensation should be large enough which makes the focusing assembly much heavier. Factually, most large aperture space-borne cameras are all-reflective or all-reflective having lens correctors, therefore by changing the interval between the primary and secondary mirror or by changing intervals within lens correctors defocus could be compensated. Although the sensitiveness is improved, moving elements are still needed indicating underlying lagging. Therefore in this manuscript, a new focus adjusting method is proposed. By changing the secondary mirror into a variable curvature mirror (VCM), the defocus compensation could be realized by varying the curvature radius of VCM. One prototype space-borne optical camera whose focal length is 6000mm and aperture is 600mm is used to verify the method. Our research demonstrates that the VCM based focus adjusting is not only very sensitive but also suitable for very severe defocus. Specifically, only a slight saggitus variation of less than 4um could compensate amazing defocus of about 4mm while maintaining good linearity between the saggitus variation of VCM and defocus, which proves the potential of this focus adjusting method.

For the requirement of the great breadth and high spectral resolution of hyperspectral sensor, Offner spectral imaging system, which can be divided into two types: prisms and gratings, is designed, and methods to filter secondary spectrum are also discussed. Basic the design, an Offner spectral imaging system with gratings is developed and tested. The research shows that, compared to prisms, Offner spectral imaging system with gratings not only have high spectral resolution, large flat field, little spectral smile and keystone, but also can satisfy the requirement of hyperspectral sensor that the system can be mounted on small or mini satellites.

In response to the demands of wide field of view (FOV), high spatial resolution and high spectral resolution real time spectral imaging of dynamic scenes, a novel large aperture Wynne-Offner snapshot hyperspectral imaging system of concentric structure is designed. Astigmatism is the main residual aberration over the full FOV. Firstly, based on the first-order theory and aberration characteristics, the anastigmatic condition of the novel large aperture Wynne-Offner snapshot hyperspectral imaging system is analyzed. Then, to achieve a large FOV and to obtain minimum astigmatism, an aspheric surface was introduced to the proper surface. Finally, with a numerical aperture of 0.22 and the FOV of 14mm×3mm, a novel large aperture Wynne-Offner snapshot hyperspectral imaging system is optimized. The optimized system provides a data-cube of 112×24×293 samples over the 450-650nm working wave band. It achieves a spatial resolution of 9μm and a spectral resolution of 0.7nm. The astigmatism is less than 4μm and it verifies the correctness of the forward theory. The image quality evaluation shows that the root-mean-square radius of the spot diagram of the optimized system is less than 1μm and the MTF value is over 0.85@56 lp/mm. The smile and keystone are less than 1.4μm and 2.4μm, respectively. The excellent spectral imaging results demonstrate that the optimized system has a great potential application for real-time recognition of dynamic scenes. Moreover, the design method provides a profound theoretical reference for the design of snapshot hyperspectral imaging spectrometers

The goal of this project is to combine the power of modern optical design software and the ray tracing through metasurface to build new unprecedented models to support the development of technologies for the next generation of imaging modalities in consumer optics.

We present a generalized differentiable ray-tracing approach suitable for most optical surfaces, including freeform surfaces. The established freeform design method simultaneously calculates multi-surface coefficients with merely the system geometry known. In addition, we provide a ‘double-pass surface’ strategy with the desired overlap (not mutually centered) that enables a component reduction for very compact yet high-performing designs. Two different examples are used to demonstrate the effectiveness of the proposed method. This work provides a robust design scheme for reflective freeform imaging systems in general, and it unlocks a series of new ‘double-pass surface’ designs for very compact, high-performing freeform imaging systems.

Nowadays, large aperture space-borne optical camera is one important payload used to capture optical images of space targets based on satellite platform, but many factors could prevent space-borne camera from obtaining satisfactory images. Firstly, vibration during launch, moisture absorption, deflation and violent temperature variation and so on could make the focal plane of space-borne camera deviate from its ideal position. Secondly, space targets are usually distant, moving quite fast and especially noncooperative targets may even appear in unknown distances. In this case, frequent, rapid and precise on-orbit focusing mechanism are indispensable to traditional imaging system, but wave-front coded imaging provides another choice. In wave-front coded imaging system, by introducing a suitably designed phase mask, the optical transfer function will become insensitive to defocus and the clear images similar to diffraction limited ones could be obtained through digital restoration. Therefore in this manuscript, the experimental research is carried out to investigate the effectiveness of wave-front coding technique in realizing high-resolution imaging without introducing any focusing mechanisms. By only adding a cubic phase mask to the exit pupil with diameter of approximately 80mm and keeping other optical-mechanical structures of a prototype large aperture camera with focal length of 6000mm and aperture of 600mm unchanged, the extension of depth of focus could be obtained. In the collimator based testing, the depth of focus of that prototype space-borne camera could be extended 8.5x approximately, which provides another way to realize high-resolution imaging of space targets while designing space-borne optical camera in future.

Light field microscopy (LFM) can capture the 4D light field for high-speed volumetric imaging with single-shot image by introducing a microlens array in traditional microscopy and combing with Richardson-Lucy deconvolution algorithm, which leads to wide usage in neuroimaging and dynamics observing, etc. However, the spatial resolution of the reconstructed results shows non-uniformity along the axial optical axis due to its varying spatial-angular sampling ratio along axial axis, which limits its application in observing thick samples. In this paper, we propose a new method including light field microscope scanning strategy and a multi-image deconvolution algorithm to address this problem. First, by designing several groups of different distances between the native object plane and microlens array, we can ensure appropriate spatial-angular sampling ratio among a wide range of depth. Secondly, according to the characteristics of camera noise in the process of fluorescence microscopy imaging, we get the loss function by calculating the K-L divergence of the Poisson noise likelihood, then provide an iterative reconstruction deconvolution algorithm. Applying the multi-image deconvolution algorithm to the captured light field images, we can finally get an extended 3D volume with uniform spatial resolution. We validate our approach by using both simulation and real experiments, which contain resolution measurements of a USAF 1951 resolution target and fluorescent beads. Under the same configuration, the proposed method can reduce the variance of the resolution across 200 μm by 20%, compared with existing method, which demonstrates a more uniform resolution distribution.

Modern multi-camera computational imaging can enable new levels of performance beyond what is possible using conventional single-aperture imaging. We will report recent research that demonstrates how multi-camera computational imaging enables low-cost thermal-infrared imaging through 2pi steradians combined with three-dimensional imaging through obscurations. Modern consumer electronics commonly employ multiple cameras to provide multiple fields of view: we will describe how, for the first time, high-resolution imaging can be attained using an array of anamorphic cameras. Microscopy traditionally involves a trade of field of view, spatial resolution and depth of field: we show how multi-camera Fourier-ptychographic microscopy enables sub-micron gigapixel microscopy with a depth of field that is two orders-of-magnitude greater than using conventional microscopy.

Freeform surfaces are widely used in optical design, due to the high design degree of freedom. The aberration theory of freeform optics can better lead designers to obtain a good structure. However, the existing aberration theory of freeform optics is only suitable for the optical system with a relatively small field of view (FOV). In this case, each field area (footprint) shows approximately the same shape and size, and positions of footprints across a surface have a linear relationship with fields. A wide FOV freeform optical system is analyzed in this paper. Parameters of all fields based on real-ray trace and non-linear interpolation can be employed to calculate the aberration generated by freeform terms. Then, to correct aberrations, coefficients of freeform terms are calculated using the least-square fitting method. By bringing back the coefficients to the optical system, the result shows great performance when using non-linear interpolation.

In order to collect detail information of the object in dim, the telescope image system need to be high-resolution and can gather enough power. These requires telescope image system with a large-diameter. Considering the load ability of the aircraft, there is also a strong demand for miniaturization and lightweight of the telescope system. Diffractive optical elements (DOEs) have great advantages in meeting these requirements. We designed two sets of telescope image systems with the same technical specifications. The primary mirrors of the two systems use traditional refractive lenses and DOEs respectively. By comparing the traditional refractive lenses and DOEs under the same focus and diameter, we demonstrate that DOEs have obvious advantages when it be applied in airborne optical systems with high requirements on volume and weight.

Unlike the conventional design of aspheric shaping systems, in order to provide a laser source for applications such as multi-beam laser interference, which can maintain evenly distributed power over a large distance, the influence of shape parameter and aperture on long-distance propagation performance of Kepler refractive beam shaping system is studied. Current work describes the lens, designed automatically by using ZEMAX programming language (ZPL), and simulations of Kepler refractive shaping systems of flattened Lorenz (FL) beams with different shape parameters and apertures.

In response to the demands of light weight, small size, wide field of view (FOV) and real time airborne spectral imaging, a novel spectral imaging system with lightweight and compactness is designed based on fold cascade structure. A concentric cascade spectral imaging system is studied. It mainly consists of two optics, a front fold monocentric objective and an Offner spectral imaging array. The front fold monocentric objective achieves an intermediate curved image with wide FOV, then the Offner spectral imaging array divides the intermediate image into sub-images and obtains spectral sub images through dispersion and reimaging. Based on the first-order theory and aberration characteristics, the cascade spectral imaging system is optimized. The optimized cascade spectral imaging system is with a real time full FOV of 110°, focal length of 110mm, F number of 4.8 and a working wavelength band of 480nm to 760nm. After performance evaluation, both its smile and keystone are well balanced. The spectral resolution is about 0.6nm, the maximum RMS radius on image plane is less than 3μm, and the MTF value is over 0.5@85 lp/mm. The tube length of the optimized system is only 85mm. The obtained cascade spectral imaging system not only achieves a real time spectral imaging in a wide FOV, but also realizes the miniaturization and lightness. It has a great potential application for airborne remote sensing and will make profound theorical value in this field.

In this manuscript, we present an optical time of flight and a focusing system to measure and track a reflective target, respectively. The time-of-flight and tracking system is based on the reflectance of the targets. This system uses a commercially available variable focal length lens that changes focal planes when current is applied. The optical system is mounted on a motorized stage that moves the system closer to or away from the target to be located; This is to expand the dynamic focal range of the system. The system is controlled by a specially designed LabVIEW program that controls the entire system.

This paper reports a design of a high magnification mid-wave infrared (MWIR) continuous zoom lens system that is compatible with a high-resolution focal plane array (FPA). The zoom lens design has been developed via a series of optimization processes, from a global search to look for potential design candidates, to different local optimization strategies to balance out optical aberrations between different zoom configurations, then comes a few minor adjustments in order to mitigate the negative effects that the optical system might encounter during its operation. By using these processes, an F/5.5 continuous zoom lens system with a magnification ratio of 22x that works with an SXGA (1280 x 1024) cooled detector having a pixel pitch of 15 μm has been successfully designed. This zoom lens system only makes use of two movable lenses to maintain its performance throughout the entire zoom range. With a maximum focal length of 1200 mm, this optical system plays a major role in extremely long-range observation and surveillance applications.

We propose a generalized method for adapting and optimizing algorithms for efficient execution on modern graphics processing units (GPU). The method consists of several steps. First, build a control flow graph (CFG) of the algorithm. Next, transform the CFG into a tree of loops and merge non-parallelizable loops into parallelizable ones. Finally, map the resulting loops tree to the tree of GPU computational units, unrolling the algorithm’s loops as necessary for the match. The method provides a convenient and robust mental framework and strategy for GPU code optimization. We demonstrate the method by adapting a backtracking search algorithm to the GPU platform and building an optimized implementation of the ResNeXt-50 neural network.

The wide-angle lens is widely used with the advantage of a large field of view, but it is difficult to solve the problem of large distortion. Therefore, the research on how to design a wide-angle low-distortion lens with excellent imaging quality is very meaningful. In this paper, we propose a high-performance wide-angle small distortion optical system, which has a horizontal field angle of 110° and a vertical field angle of 77°, focal length of 2.03mm, f number of 1.65, and a total length of 16.5mm. By introducing a non-rotational symmetric freeform surface into the last side of the wide-angle optical system and combining with several even aspheric surfaces, the f-tan(theta) distortion in the X direction is controlled to -6%~+1%, and the f-tan(theta) distortion in the Y direction is controlled to less than 1%. At the same time, the MTF of the system is greater than 0.35 at 125lp/mm, so that the circular image plane can better adapt to the rectangular sensor. In addition, due to the introduction of the freeform surface in the system, the change of system structure with temperature becomes more complex. We carry out thermal analysis for this surface and calculate the change of structure with temperature. Finally, we completed the athermalized design of the lens, so that the wide-angle lens can work in the range of -40℃~+80℃. This optical system has great development potential in security monitoring, UAV detection and other fields that may encounter extreme environments.

Taking the spacing between elements as the initial quantity and the motion form of elements as the free quantity, the distribution of optical focal length and the motion form of elements are obtained by calculating the equations. The global method is used to solve the problem of high ratio multiconfiguration system, and the results have been used in engineering practice.

Dielectric elastomer (DE) is a remarkable ‘smart’ actuator to develop an adaptive liquid lens due to its lightweight, mechanical compliance, simple structure, low power consumption, and low cost. The traditional method to develop an adaptive liquid lens using a DE actuator often confines the liquid in the central region and the remaining part is coated with opaque compliant electrodes. However, this configuration reduces the available optical aperture and increases the overall dimension. A compact adaptive liquid lens actuated by DE with a transparent conductive droplet is proposed in this paper. The droplet not only acts as the material of the adaptive liquid lens because of its high transparency but also works as the compliant electrode of the DE due to its conductibility and flexibility. A mixture liquid of glycerol and sodium chloride droplet is dropped on the top and bottom surfaces of the DE. When the droplet is subjected to a voltage supply, the area of the DE where contacts the transparent conductive droplet expands, which induces an increase in the diameter and a decrease in the thickness of the droplet since the volume of the droplet is constant. Therefore, the focal length of the adaptive liquid lens increases. The effectiveness of the proposed approach has been validated by experiments. The results show that the adaptive liquid lens has a compact structure and transparency of 86.1% at visible wavelength. This method is beneficial for developing a compact adaptive liquid lens.

As the most widely used optimization method in optical system design, the damped least squares (DLS) method performs well in convergence speed. However, the fatal flaw of DLS method is that it is easy to get caught into local minima. Thus, some intelligent algorithms are adopted in optical system designing for global optimization. Genetic algorithm (GA) has the unique advantages of wide scope of application and powerful global search capability. In this paper, we proposed a new optimization method for optical system design, which is based on an improved genetic algorithm and combined with the damped least squares method. Besides, a machine vision lens is designed by the proposed method, which verified the effectiveness of the method.

When the spatial visible light camera images the detection target, non-imaged light in the space also reaches the imaging surface through the lens, forming an image on the detector. Some of the light is imaged on the image surface after multiple reflections inside the lens. These non-target images affect the image quality of the camera. In severe cases, the camera may not work properly. In order to reduce the influence of stray light on the imaging system and improve the imaging performance of the camera, firstly, the generation mechanism of stray light in the visible light system is analyzed, and the stray light suppression measures are proposed. Secondly, the system is then analyzed using ZEMAX software. The optical system design of the camera with the previous stray light problem was improved, and the stray light modeling analysis was performed on the improved result, and finally the space reconnaissance camera that satisfies the use requirements was obtained.

In this paper, the gradient force and scattering force of two kinds of different sinusoidal modulated Gaussian beams (SMGBs(n=2), SMGB (n=4)) and Gaussian beam (Gb) are analyzed, and their ability to capture particles are studied. It is found that sinusoidal modulated Gaussian beams have multiple stable capture positions at the focal plane than Gaussian beam. Under the same circumstance, Monte Carlo stochastic simulation method is used to simulate the tendency characteristics of particles under the effect of gradient force and scattering force, which verifies the theoretical analysis results. Therefore, the research results of this paper have certain guiding significance in the experiment and application of multi-position optical tweezers.

During the production of a new designed lens system, overweighted assembling and manufacturing errors can cause the degradation of the performance of the whole system. Therefore, optimizations to improve the assembling and manufacturing tolerances sensitivity are greatly required in lens design industry. Following the principle of Gaussian optics, there are some practical implications of the first order derivatives which are of great significance to analyse the sensitivity of a lens system with its structural parameters changing. It is demonstrated that manufacturing errors, such as tilting, decentering and so on, induce the real rays' height shifting on each surface of an imaging system, which subsequently induces the decline of image quality. Thus, we proposed a scheme to use the first order derivatives of the height of a real ray on the image surface in a lens system versus that on the pupil surface, which indicate the height variations of the real ray on the image surface of the lens system caused by the displacement of its corresponding height on the pupil surface, as a merit function to improve the tolerance sensitivity of the whole system. A test program using the ZPL language in Opticstudio has preliminarily confirmed the effectiveness of our proposed methods. And as it is aimed at controlling the real rays of a lens system to reduce its sensitivity according to assembling and manufacturing errors, our scheme is theoretically able to appropriate to all lens design systems.

In this manuscript, we develop a 3D-printing based microfluidic device for light scattering imaging of single cells. A rapid fabrication method to make microfluidic device that enables 3D-hydrodynamic focusing by utilizing 3D printing technique is proposed. The focusing effect of the microfluidic cytometer was measured and shows the ability to confine the cells to flow near the center stream along the channel. Also, the standard beads with 9.51 μm in diameter were used to test the reliability of the device. The collected light scattering images are in good agreement with simulation results. We suggest that the 3D-printing based light scattering microfluidic device is in principle applicable for fast, label-free detection of single cells.

Aiming at correcting the severe chromatic aberration of the long focal lens, the traditional optical design often requires employing complex structure, introducing special dispersive glasses or even utilizing the hybrid refractive-diffractive imaging method. However, complex structure will bring several drawbacks such as large volume and heavy weight. Special glasses and refractive-diffractive hybrid imaging will greatly increase the cost, which hardly meets the needs of miniaturization and low cost of optical imaging module. Although image restoration algorithm is commonly used to optimize the image quality to a certain extent, the optical design and image restoration process are independent of each other. Therefore, it is difficult to ensure the high resolution of the image while realizing the light weight, small volume and low cost of the optical system simultaneously. Utilizing the computational imaging theory, a simple long-focus optical system design method based on the optical/image co-design is proposed and deomonstrated in this paper. On the basis of the idea of global optimization, the reported approach considers the two independent links of optical design and image restoration as a combination. The imaging quality requirements in the optical system design are relaxed at the front end, and the image restoration algorithm is used to remove the residual aberrations in the back end. This method can not only obtain the same or even higher imaging performance, but also reduce the complexity of the optical system.

Recently, the time synchronization via optical fiber, (e.g., two-way fiber time transfer technique, and round-trip time transfer technique) is more and more attractive, due to its higher precision and longer distance. However, because this method is based on the assumption that the forward and backward propagation delays of one optical fiber are nearly the same, it may fail to achieve time synchronization due to link asymmetry. To resolve this problem, we propose a time filtering method to detect link asymmetry and mitigate time asynchronization caused by link asymmetry. Specifically, we create an array to record four time parameters, i.e., (1) round-trip time, (2) time offset between Server and Client, (3) the difference of round-trip time, and (4) the difference of time offset. The four time parameters are calculated for each synchronization period. The third and fourth parameters are used to detect link asymmetry, and the second parameter is used to compensate the symmetry of the transmission delay, and minimize the time asynchronization. We simulate our method on a two-way fiber time synchronization system with OptiSystem. Simulation results show that our method can quickly detect link asymmetry within 1 second, and achieves nanoseconds time synchronization in the presence of link asymmetry.

Spectral confocal displacement sensor is a high-precision, non-contact displacement sensor, which can be used to measure the surface morphology, thickness and distance. In this paper, the basic principle of spectral confocal displacement measurement is discussed, and a global lens group is designed by using CODEV optical design software. The design method of spectral confocal displacement sensor lens group and aberration analysis are given. The measurement range of the lens group is 2mm, the image space numerical aperture is 0.3, the axial response FWHM is better than 5um, and the resolution is higher. The linear regression analysis shows that the determination coefficient between wavelength and displacement is better than 0.9, and the linear relationship between displacement and wavelength is good.

Six-degree-of-freedom (6-DOF) grating encoders have a wide prospect of application. Aiming at the requirement of real-time detection of 6-DOF grating encoders, this study designs and builds a real-time calculation system platform based on field-programmable gate array (FPGA). We realized a real-time parallel calculation of 16-path displacement signal and 24-path angular displacement signal, respectively. Specifically, the optical interference signals, generated by the translation and rotation of the motion stages, are firstly shaped by the front-end analog circuit. We further sampled the front-end analog circuit into an FPGA through a analog-to-digital convertor (ADC) for the realization of the digital filtering, amplitude normalization, phase correction, and phase-information calculation. Thus, the calculated signals on the 6-DOF motions can be displayed in real time. The established system was evaluated with the experimental parameters in terms of the translation with a 50 μm/s moving speed and an 18 mm stroke and the rotation with a frequency of 0.5 Hz, a step length of 100 micro-rad, and within a reciprocating rotation of 24 s. Finally, a linear-displacement error of <1 nm and an angle displacement error of <0.9 micro-rad were achieved, respectively. Furthermore, the system delay of <15 ms is obtained, exhibiting a high performance for the real-time measurement and high integration in the practical application.

The weight distributions (WDs) of spherical and cylindrical power deviations with the multiple convolution processing schemes indicate that the areas of the far and near zones can be increased by changing the WD without changing the distribution of the mean sphere. When the number of the multiple convolution processing schemes changed from 0 to 15, the areas of the far and near areas increase by 35.7% and 76.5%, respectively, and the maximum peripheral astigmatism increased from 0.75 to 1.5 ADD. The increasing maximum peripheral astigmatism will lengthen the period for the wearer to wear the PALs, and increase discomfort.

We propose and numerically investigate a double-cladded athermal waveguide structure aiming at broadband low anomalous dispersion operation. Single-crystal aluminum nitride (AlN) is the core of the waveguide, cladding with silicon oxide (SiO2) and titanium dioxide (TiO2). TiO2 with a negative thermo-optic coefficient (TOC) is used to realize material thermal compensation for AlN. By optimizing the waveguide structure parameters, it shows a near-zero broadband effective TOC, ±4×10-6 /K over a 1770-nm bandwidth from 1830 to 3600 nm. Besides, it also has low anomalous dispersion, from -20 to 20 ps/nm/km in the same wavelength range. Different with the conventional strip waveguide, the waveguide is a double cladded structure, which is easy to fabricate in practice. Furthermore, this structure will not damage the single crystal state of aluminum nitride, maintaining its original excellent optical properties.

Computer-generated holograms (CGH) due to their wide capabilities to transform the wavefront of light beams are used to solve various problems including interferometric measurements spherical and aspherical wavefronts. The errors of the wavefront formed by CGH are primarily related with errors in the hologram structure. One of main reasons for the errors in the CGH fabrication by the laser writing technology is the positioning errors of the laser writing system. Earlier methods based on the analysis of the parameters of embedded microstructures were developed to define these errors. In these methods, separate microstructures are used to determine the error value for each coordinate of the beam scanning system. This paper presents the testing method based on writing and diffractometric analysis of embedded small 2D marks containing two pairs of linear gratings. In each pair, one linear grating is shifted relative to the other by given amount. The gratings in one pair are rotated 90 degrees relative to the gratings in the other pair. Each 2D-mark is formed in two stages. One grating in each pair is quickly formed before CGH writing and the second grating is formed directly in the process of the writing. Defining the deviation of the shifts from the given values for each grating pair allows one to estimate the positioning errors along both coordinates by one mark. When the 2D-mark is illuminated with a probe laser beam, the shift leads to a redistribution of the diffraction efficiency between the diffraction orders. The analysis of the obtained diffraction patterns from series of the 2D-marks makes it possible to control the errors of the CGH structure as function of time for whole writing process.

The core mismatch formed by the splicing of different fiber cores and tapered fiber is beneficial to the sensing. In this paper, a single-mode fiber (SMF)- tapered multi-mode fiber (tapered MMF)-single-mode fiber structure was fabricated and used as a sensor to detect uric acid. The gold nanoparticles (AuNPs)/zinc oxide (ZnO) nanoparticles were fixed on the tapered surface to enhance the localized surface plasmon resonance (LSPR) and its sensing performance. The experimental results show that the optical fiber sensor can detect different concentrations of uric acid solution successfully and has a linear response in a certain range for biomedical applications.

Diffractive Transmission Sphere (DTS) can be successfully used for interferometric testing. Unfortunately, phenomena of annular rings occur on interferogram in a case of small period of diffractive patter. This effect reduces quality of measurements and became critical for apertures close to f/1. This work is devoted to computer simulation of such effects and development of technique for their partial compensation. It was proposed to do this compensation by modifying duty cycle. Computer simulation on the base of the rigorous coupled wave analysis was performed. Experimental DTS with was fabricated and tested.

Recently, more and more attention is paid to the multichannel optical system. They are often used in microscopy. Examples include metallographic microscopy, confocal microscopy, laser scanning microscopy, optical coherence tomography, and others. Usually, one channel of such systems is lighting, and the other is observation. Such systems usually do not pay attention to the uniformity of the divided light flux. Here it is important to illuminate the object and obtain an image, and if the illumination is insufficient, the luminous flux given by the source is increased. However, if both channels of the system are used for imaging (possibly with different characteristics), the uniformity of this splitting of the optical emission is an important part. Otherwise, we risk not getting the image we need in one of the channels.

This paper presents a raytracing-based method of synthesis of realistic images in a complex space containing gradient lenses. The proposed solution is based on the Runge-Kutta method and allows raytracing in a space with a gradient medium. The authors have developed an effective solution, which allows dividing the complex lens boundary into voxels and providing a fast ray tracing procedure inside the voxel. In addition, the authors considered possible solutions for calculating luminance components within a gradient refractive index medium. The study showed that the most efficient way to calculate luminance is based on stochastic bidirectional raytracing with photon maps.

The paper describes a way of simple optical systems design. The presented computer tool synthesizes "photographic objective" type systems according to given aberration parameters. It is directly applicable to micro objectives, which are photographic systems in a backward ray trace. The paper compares lenses with f’=50 mm, NA=0,1, 2y=6 mm designed as cemented doublet plus single lens and as pair of cemented doublets. Despite the second lens is a more complex system, its image quality is no better than provided by simplified system.

The paper considers a method for calculating the distribution of light radiation on the receiver caused by its scattering on the surfaces of an optical device. The calculation is based on the method of bidirectional stochastic ray tracing with photon maps. The proposed method is highly efficient due to the simultaneous use of the forward and backward photon maps that accumulate the distributions of light radiation and the visibility of the scattering elements correspondingly. Effective methods have been developed for the forming, storage, and access to photon maps, which provide not only high computational efficiency but also the ability to visualize the sources of stray light in optical devices. The efficiency of this method was demonstrated by examples of calculating stray light for several optical devices.

Infrared Search and Track (IRST) System has become the main approach to cover a wide area with high resolution imagery of long-range targets. A fast-steering mirror (FSM) is generally integrated in the optical system to provide back scanned motion for maintaining the line-of-sight stability. However, the conventional optical designs can hold only the center of field relatively stable on the FPA during back-scanning; all other field points may wander during the exposure time due to imaging distortion characteristic of the optical system which reduces the quality of the observed images. This paper reports a lens design with implemented Non-Rotationally symmetric field mapping which can keep all field points stable on the FPA during back-scanning. This lens design covers a large Field of view (FOV) of 10° x 8° for single frame and a maximum scanning angle of 2.16°. With a F/2 SXGA (1280 x 1024) cooled detector, this optical system help scan a large number of objects in a long-range distance at a high scanning rate with diffraction limit performance.

Conformal correctors for high-power solid-state YAG: Nd3 + lasers are used for compensation of density variations inside active media. These correctors decrease laser beam aberrations and allows better focusing of laser light. Fabrication was done by direct laser writing on photoresist. Method of specular spectrometric reflectometry to control the shape of correctors at the stage of relief in a photoresist is considered. The combination of the methods used significantly increases the productivity of the production of correctors, combined with a reduction in the cost of the process.