This PDF file contains the front matter associated with SPIE Proceedings Volume 12318, including the Title Page, Copyright information, and Conference Committee lists

In this presentation, we briefly review the development of optical metalenses from the single metalens to the metalens array and to the metalens systems, especially focusing on the progress of silicon nitride metalenses. We then show the optical properties of silicon nitride films with different refractive index in our lab. With such silicon nitride films, we introduce our researches on the broadband achromatic metalens array, and the microscope meta-objectives with cascade metalenses, showing the visible imaging applications on noncoherent 3D integral imaging and high-resolution biological imaging.

Optical metasurfaces are optical elements with artificial subwavelength nanostructures, and it can achieve functions that cannot be realized by traditional optical elements. Combining holography and metasurface boosts performance of light controlling and expanding the application scenario. Here, we will report our works on the methods of holographic multiplexing and realized plenty of channels for information reconstruction, including code division multiplexing method (CDM) for metasurface holography for optical information projection, and a multiplexing optimization method for independent light field manipulation in diffraction orders of metasurface holography. All these methods have bright potential to be applied in fields of optics.

Animation for a multicolor metasurface hologram was achieved based on a cinematographic approach. Time-lapse images were reconstructed using sequentially arranged metasurface hologram frames. We adopted three kinds of meta-atoms: Au nanoaperture, c-Si nanopillar, and SiN nanopillar. An Au rectangular nanoaperture was adopted as a meta-atom pixel based on Pancharatnam–Berry phase. It achieved a high-contrast monochromatic animation at the wavelength of 633 nm. Dielectric nanopillar meta-atoms utilize propagation phase delay, which offers high transmittance in the visible region. Overlapping of multiple-wavelength images at 445 nm, 532 nm, and 633 nm was achieved by maintaining the ratio between the wavelengths and the pixel periods constant. The multicolor movie consisting of 20 frames was successfully reproduced using a c-Si meta-atom. In addition, by using SiN nanopillars, holography with high color reproducibility was achieved.

Multi-functional metasurfaces have gained broad attention recently, as they bring great possibilities for high-dense multi-functional meta-devices, such as projecting holograms and displaying continuous gray-scale images simultaneously. However, currently reported metasurfaces to perform these operations separately. Furthermore, their complex multilayer and super-cell design strategies complicate both design and fabrication processes. This applies a limit on miniaturized, low-cost, integrated multi-functional meta-optics. Here we report a novel single-unit cell-based design strategy to demonstrate a tri-functional metasurface. By merging the spin-decoupling strategy with Mull’s law amplitude manipulation, a three-in-one metasurface is designed to project two independent holographic images in the far field and one continuous gray-scale image in the near-field of the metasurface. Specifically, far-field holographic images are projected on orthogonal helicities of white CP light, whereas a near-field image is decoded by creating an orthogonally linearly polarized light path. Furthermore, we optimized a novel gallium phosphide (GaP) material to verify the proposed design strategy for a tri-channel metasurface. The proposed metasurface has high transmission efficiency in the visible regime and verified our design strategy without adding extra complexities to conventional nano-pillar geometry. Therefore, our metasurface opens new avenues in multi-functional meta-device designing and has promising applications in anti-counterfeiting, optical storage, image displays, etc.

Metasurfaces provide a miniaturized and superficial solution for implementing various nanophotonic devices by exploiting their unprecedented ability to spatially tailor the phase, amplitude, and polarization of the incident light. These meta-devices intriguing significant attention from the research community and have become a prominent hotspot for the realization of state-of-the-art on-chip devices. Various types of information can be encoded independently into a single metasurface, strengthening the cutting-edge technology of nanophotonic for practical applications such as holograms, lenses, beam steering, high-density optical storage, and displays. The integration of metasurfaces and holographic technology makes it the most desirous, but many of the presented techniques lack multifunctional capabilities. Here, we proposed a straightforward strategy for spin manipulation and wavelength multiplexing via geometric phase to overcome the limitations of multifunctionality through anisotropic nanoantennas in the ultraviolet regime. The proposed design methodology provides a superior degree of freedom to increase the multifunctional capabilities of metasurfaces for independent wavefront manipulation. By simultaneously controlling the polarization of the incident and transmitted wave vector, a trifunctional all-dielectric metasurface is implemented. For the proof of concept, we designed a structure that displays two holograms at focal planes. The proposed metasurface features the nanostructured pixels of the silicon nitride material, a lossless, high-refractive index dielectric material that ensures high transmission efficiency in the ultraviolet regime. It is expected that the proposed design strategy can be applied to broaden the horizon for implementing multifunctional nanophotonic devices and multiple optical phenomena

Here in this paper, we proposed a metasurface, which consists of silicon nitride as dielectric material possessing a high transparent window in the ultraviolet regime. We designed a single-layer dual-band metasurface instead of stacking and interleaved technique to overcome noise and low resolution, which gives broadband response for UV wavelengths. The proposed spin multiplexed metasurface is capable of generating two independent holographic images for right circularly polarized (RCP) and left circularly polarized (LCP) light. We achieved maximum cross-polarization efficiency on the designed wavelength i.e. 350nm and negligible zero-order efficiency. The unit cell and the proposed metasurface are simulated using Finite Difference Time Domain-based FDTD Solution from Lumerical Inc. for the specific wavelength while it gives broadband response for the wavelength band almost covering 290nm to 390nm.

The rapidly growing demand for miniaturized multifunctional devices and systems constantly brings new structural challenges to the research community. The planar metamaterials (metasurfaces) provide a revolutionary way for wavefront manipulation of electromagnetic waves and promise the achievement of superior degrees of freedom. Compared to conventional refractive optical elements, a distinct advantage of metasurfaces can be accomplished by embedding multi-functionality through encoding various sets of information into a single metasurface. Herein, we proposed a unique angle multiplexing strategy that provides wavefront modulation independently in a flat metasurface by controlling the incidence angle of the input light. The fundamental unit cell of the meta-platform of the proposed structure includes a rectangular tetrad with distinct structural geometry. Due to the proposed geometry's geometrical characteristics, the angle multiplexed phenomena are induced in the structure by the mutual coupling of tetrads made of hydrogenated amorphous silicon (a-Si:H). For the proposed metasurface, we exploited the meta-platform comprised of two Meta-atoms, one for positive incidence angle and another for negative incidence angle of light. To increase the applicability of the metasurface, we proposed a single multifunctional meta-device that will project the image of one information for one angle while another information for the opposite angle of the input light. The angle multiplexing phenomena designed for a wavelength can open promising avenues for real-time applications in switchable multifunctional devices, holography, information encryption, and security purposes.

Optical scanning cryptography (OSC) is an optical image encryption method encrypting information incoherently based on two-pupil heterodyne scanning optical system. But numerical reconstruction of a 3-D volumetric image from an optical scanned hologram is a difficult task. The main problems are the intensive computational load, and the heavy blurring of each reconstructed section with the defocused noise from other sections.In this talk, we propose a deep-learning based reconstruction algorithm in optical scanning holography, which can generate reconstruction images in high quality. DNNs are created based on the U-net structure to learn the mapping between holograms and reconstruction images. Simulation and experimental results showed that the deep-learning based method is able to reconstruct the optical scanning hologram in real time for the removal of defocus noise.

We numerically investigate the performance of optical implementations of deep neural network for complex field data processing in the form of multi-layer nanoscale diffractive neural networks, trained to perform image classification tasks. We discuss the parameter optimization and the limitations that fabrication errors put on the performance of such direct phase retrieval systems. The diffractive neural networks studied here may have transformative impact on adaptive optics, data processing and sensing and may be crucial in the development of robust and generalized quantitative phase imaging methods.

Deep learning networks are widely used for optical problems solving in recent years. With the explosive developments of deep learning, learning-based computer-generated holography (CGH) has become an effective way to achieve real-time high-quality holographic display. Various learning-based methods have been proposed to accelerate the computation and improve the reconstruction quality. Deep neural networks (DNNs) have a great influence on the research of holography for their high quality and high computing speed. We focus on the rapid progress on DNN-based CGH in recent years and give our introduction to the principles of CGH as well as the structure of the deep neural networks frequently used in CGH, including U-Net, ResNet and GAN, etc. We introduce the developments of the learning-based CGH and express the expectation of the prospect.

Spectral processing is of great importance in optical research and applications. However, there are currently no multifunctional spectral processing devices with advanced processing capabilities. In this work, we implement on-demand spectral processing using a compact optical diffraction neural network (D2 NN), which includes only an SLM and a plane mirror. Spectral processing functions can be easily switched by changing the phase diagram on the SLM, which is obtained by computer pre-training of the D² NN for a specific task. Tunable single and dual-band spectral filtering and wavelength demultiplexing are achieved.

Digital holographic microscopy (DHM) is a non-contact and high accuracy measurement technique widely used in biomedicine, microstructure,and other fields.The quality of the reconstructed image and the effectiveness of holographic microscopy were easily affected by speckle noise. Inspired by the idea of Noise2Noise, we propose a self-supervised noise2noise hologram speckle noise removal method. From the holograms that need denoising to generate the input and labels with the same noise distribution to form a training pair for training. Solve the problem that clean holograms are difficult to obtain.The training sets of this self-supervised method are generated from the holograms to be processed. As such, it avoids the need of collectting a large number of training sets. The proposed method is therefore less vulnerable to the background noises and more convenient and reliable for practical hologram speckle denoising applications.

The rapid development of artificial intelligence has stimulated the interest of the novel designs of photonic neural networks (PNNs) because of the high speed, low energy consumption and parallelism nature of the light. Based on optical holographic technology, a kind of three-dimensional PNNs, diffractive neural networks (DNNs), have demonstrated their superb performance in parallel two-dimensional data processing. DNNs are composed of multi-layer cascaded holographic plates. Relying on the diffraction of the incident light, each pixel in every layer can be connected with multiple pixels in the next layer to mimic the architecture of the biological nervous system. Important applications, such as image recognition, optical logic operation, and image reconstruction, have been realized on DNNs with high operation efficiency. However, in most of the reported works, the layers of DNNs are spatially separated with a large size of centimeter-scale, which greatly limits the on-chip integration of DNNs. In this work, we reported a green-light bilayer integrated DNNs. The two layers of the DNNs were integrated on the double sides of a quartz wafer respectively by lithography followed by dry etching. Based on the theory of diffraction, the DNNs were trained with a size of millimeter-scale. When the DNNs work, the incident optical signal first passes through the 1st layer of the DNNs, then diffracts inside the quartz wafer, and finally emitted out from the 2nd layer of the DNNs on the backside. Handwritten digital recognition of 0~1 (89 % accuracy) or 0~9 (65% accuracy) was successfully realized. The high stability of quartz provides the basis for the long-term reliable operation of DNNs. The manufacturing of the DNNs is compatible with the mature semiconductor manufacturing technology, which provides a feasible route for the macro fabrication of DNNs.

Quantitative phase imaging (QPI) is a vital label-free measurement modality in biomedicine, providing both morphology and quantitative biophysical information. Nevertheless, applying QPI in vivo or in hard-to-reach areas remains challenging. The multicore fiber bundle (MCF) is an emerging ultra-thin probe with a diameter of less than half a millimeter. QPI through MCFs is still difficult to achieve due to the different phase delays in 10,000 fiber cores. We propose a novel speckle reconstruction method using deep learning to achieve real-time phase reconstruction through a bare MCF. High fidelity phase image reconstruction of complex image datasets like ImageNet is achieved. The network further demonstrates good generalization behavior. Phase images belonging to a different data type, such as cancer tissue and test charts, can still be reconstructed through the MCF using the network. Such a powerful technique could open new perspectives for fiber endoscopic imaging.

In recent years, the concept of a fully optical neural network (ONN) has attracted attention for its potential to reach significantly higher speed and lower energy consumption compared to semiconductor electronics-based artificial neural network (ANN). Although the technology promises significant improvements through the utilization of light instead of digital signals, an ONN also requires physical fabrication on a planar substrate that introduces new limitations and constraints to the network when compared to the conventional NN. Limitations on node connectivity, choices of possible nonlinear neuron activation functions, as well as constraints on parameters in the case of a passive-circuit ONN are among the few peculiar challenges that are faced by the ONNs. In this study, we aim to understand the effect of ONNs’ limitations and constraints on their fitting ability when compared to the unconstrained NN. We use digital NNs that simulate the properties of ONNs to investigate the potential and limitations of the ONNs and might be useful as a practical way to pre-calibrate the ONNs’ parameters before their physical production. The ONNs performance and potential are evaluated and compared with the conventional NN by comparing their fitting ability on different datasets. Furthermore, the use-case for ONNs’ application is built and demonstrated on the material and financial datasets.

In this paper, we introduced our research and development progress on phase-only spatial light modulator (SLM), and our key liquid crystal on silicon (LCOS) technologies to realize it. Based on these technologies, which have achieved high image quality with world-class contrast, we detailed how phase-only SLMs can benefit a wide range of application scenarios such as holographic displays, image projection devices, and other infrared applications.

This review starts from various demands on periodic microstructures array in nanoscience and nanoengineering, such as photon crystal, diffraction gratings, and framework for self-assembly, to various nanofabrication technologies including mask based and maskless lithography, direct writing using EB, FIB or ultra-fast laser, and ultra-precision single diamond cutting. In the second part, the most proper technology for patterning microstructures abovementioned, laser interference lithography (LIL), is introduced. Fundamentals of the LIL is briefly presented and followed by an intensive survey of recent advances in LIL field. Laser sources, interferometer layouts, strategies for forming complex structures, integration of LIL with other fabrication technologies, and promising application areas for LIL are reviewed step by step.

Higher requirements have been put forward for the performance of two-dimensional (2D) gratings, such as polarization independence, high efficiency, wide broadband and so forth. In this letter, we employ the characteristic of diffraction in the grating and propose a 2×2 2D silver cylindrical array grating under normal incidence with excellent polarization independent high diffraction efficiency (DE) over communication band for beam splitting. The simulation and optimization of the DE are based on rigorous coupled wave analysis (RCWA) and simulated annealing (SA) algorithm, respectively. Under the optimal structural parameters, the highest DE of (±1, 0) orders and (0, ±1) orders can achieve over 24% at 1550nm in both Transverse Electric (TE) and Transverse Magnetic (TM) polarizations. Within moderate manufacture tolerance, the final discrete rotationally symmetric 2D periodic surface pattern has been fabricated by the holographic exposure technology, wet chemical development process and Electron Beam Evaporation. The measurement results of fabricated grating fully verify the correctness and accuracy of the calculation. Therefore, this 2D grating has considerable application potentials in optical communication, displacement measurement and semiconductor manufacturing.

Augmented reality(AR) glasses are smart wearing devices which is promising to be the next generation computing platform. The most important components in AR glasses is the near eye display module, which can be built dependent on different optics structures, for example, free-form optics, bird-bath and light or wave-guide. The diffractive wave-guide makes it possible to be a colorful near-eye display with high transparency and ultra-small form factor. Compared with other structures, the two-dimensional diffraction grating wave-guide is able to provide larger field of view with certain area, because it can expand and out-couple the light in the same region. To ensure the uniformity of lightness, it requires high flexibility of control on diffraction energy distribution. In this work a new 2D structure is proved as effective and efficient to concentrate light on the desired diffraction orders under different condition. The new structure was optimized by using Rigorous Coupled Wave Analysis (RCWA) method. The wave-guide model based on this structure had been simulated by VirtualLab software as a benchmark. The simulation results demonstrate that the uniformity of eye box and field of view is good enough for human perception.

In the displacement measurement of the wafer stage in lithography machines, signal quality is affected by the relative angular position between the encoder head and the grating. When the measurement orientation is tangential to the center of the chuck, the influence of the homogeneous expansion of the chuck on the measurement can be reduced. In this research, we propose a reflective two-dimensional metal dielectric grating based on frustum array. With an incident azimuth angle of 45°, the (-1, -1) order diffraction efficiencies of transverse electric polarization (TE) and transverse magnetic polarization (TM) are 81.4% and 84.8% at 1550 nm incident wavelength under Littrow mounting, respectively. the diffraction efficiency balance is 95.99%. The high efficiency of TE and TM polarization makes them have great application potential in grating displacement measurement. Furthermore, the structure based on the frustum of a cone performs well in manufacturing tolerance, which provides possibility for practical applications.

Space-time (ST) wave packets are pulsed beams endowed with tight spatio-temporal spectral correlations, whereby each spatial frequency is associated with a single wavelength resulting in propagation invariance at an arbitrary group velocity. Previously, our group introduced an experimental methodology to synthesize 2D ST wave packets, i.e. light sheets, based on 2D pulse shaper. Here, we demonstrate a new experimental method to synthesize ST wave packets localized in all dimensions, including 3D space and 1D time. We show that 3D ST wave packets propagate longer distances without spreading compared with traditional Bessel beams, and propagate at subluminal and superluminal

Due to the threshold nature of the thermochemical oxidation process, it is possible to use a non-Gaussian intensity distribution within the writing spot, for increasing of spatial resolution of direct laser writing technology. The non-Gaussian distribution was obtained by distorting the Gaussian beam with an annular diaphragm. The width of the central peak (FWHM) is 40% smaller than the width of the Gaussian spot. It has been shown that by distorting the Gaussian spot, a smaller single line width can be obtained. The effect of side lobes during multipass writing on the width of the resulting single line was studied.

The coded aperture lensless imaging is a flexible system that replaces bulky lenses with a coded mask. The convolutional model expresses its forward imaging process compactly but fails when the measurements are distorted due to hardware restrictions. To overcome this problem, we generalize the convolutional model by introducing restricted factors to the imaging forward model explicitly. In detail, hardware restrictions are categorized into the linear part and the noise-like part. A compressed sensing algorithm based on the gradient sparsity of natural images is employed to solve the ill-posed inverse problem. Both numerical and experimental tests verify that the proposed model alleviates the artifact effect caused by down-sampling while performing reconstruction with higher resolution. This method is also valid for multi-wavelength and 3D imaging, lowering the using threshold of lensless cameras.

Quantitative phase imaging with high resolution remains a long-term pursuit of many biomedical applications. However, the performance of coherent imaging systems is challenged by the intensity-only measurement mechanism and the sampling limit of the pixels. In this work, we introduce an imaging system that achieves pixel super-resolution quantitative phase imaging based on modulation diversity. A programmable phase-only spatial light modulator is used to generate various phase modulation patterns to the wavefront, providing data diversity for phase recovery at subpixel resolution. The system requires no mechanical displacements, enabling high-speed image acquisition, providing a competitive approach to high-throughput quantitative phase imaging applications.

Measuring the refractive index (RI) and topography of samples can be realized by decoupling the obtained quantitative phase image. However, flattening the sample, changing the surrounding medium, or illuminating sample that immerse in the highly dispersive medium with different wavelength lights encounter some problems in practice. With the help of Cauchy’s dispersion formula, RI and topography can be independently calculated from a three-wavelength-based quantitative phase imaging. Neither special highly dispersive medium nor additional assistant technology is required. After characterization of the method, the capabilities for RI measurement and substance identification are demonstrated.

Optical microscopic techniques are most commonly used methods in biology and medical research. This talk will introduce multi-depth imaging systems, which are based on multiplexed volume holographic (MVH) gratings acting as spatial-spectral filters used in conventional optical imaging systems. This allows the acquisition of spatial images with spectral selectivity but without scanning in both transverse and longitudinal directions. In addition, fluorescence microscopy with optical sectioning ability is extensively used in biological research and biomedicine for obtaining three-dimensional structural information of volumetric samples. With hybrid illumination, optical sectioning can be achieved in wide-field fashion. This talk will cover optical imaging incorporating state-of-the-art diffractive optical elements for biomedical applications.

Structured light three-dimensional (3D) imaging has been widely used for 3D surface measurement applications. However, it is limited for objects with high reflectivity in complex scenes. There are flying points or missing point clouds for the 3D imaging due to the overexposure by strong reflection or multiple reflections. In this work, we propose a method using two cameras to share the same projector. Gray codes with multi-step phase shift images compose the projected patterns. We adopt the partition fusion method for the captur images from different perspectives to reduce the influence of strong reflection and multiple reflections. The 3D measurement with the fusional captured images is realized.

Lensless imaging is a promising technique with a large field of view and high throughput imaging capacity. Limited by its imaging modulations, it suffers from twin image problems due to missing phases. Hence, it requires phase retrieval to recover the phase information as well as suppress the artifact. As the original algorithm, the Gerchberg-Saxton algorithm (GS) retrieves the phase data from at least two intensity measurements. It has low convergence and is sensitive to the initial guess. In this work, we apply denoising in the object field with a guided filter into the iterative framework of the GS algorithm named Guided filtering GS (GFGS). The approach in this paper requires only a single hologram measurement. To suppress artifact noise, guided filtering is performed on the real and imaginary parts of the complex-valued distribution with an appropriate smoothing parameter at the object field.

In view of the fact that the current research of detection technology for large-size grating surface defect was very little, this paper builds a set of grating defect detection device based on the principle of darkfield imaging. The scheme includes three subsystems: displacement system, monochrome light illumination system and image acquisition system. When the displacement system drives the motion stage to move, the monochromatic light illumination system and the image acquisition system jointly complete the acquisition of the grating surface images. In this study, the surface of the diffraction grating with 170×170mm2 was detected for defects, and the statistical data of different defects is given. Experimental results show that, the device meets the needs of defect detection and evaluation on large-size grating surfaces and the mechanical structure is simple and compact, which has the great potential for large-scale detection.

We propose and experimentally demonstrate a highly stable on-axis near common-path snapshot Fizeau-polarization phase-shifting interferometer by combining the polarization phase-shifting scheme with Fizeau on-axis interferometry. The compact on-axis design of the Fizeau interferometry is achieved by utilizing the characteristic feature of a wire grid polarizer, which generates the orthogonal polarization components required for the proposed polarization phase-shifting scheme. The quantitative phase measurement capability is experimentally validated by estimating the phase profile of various phase-sensitive standard and unknown phase samples.

This paper introduces a new device for one-dimensional grating period measurement with high accuracy. The scheme includes two subsystems: a grating interferometer and a laser interferometer. As the grating moves, the grating interferometer obtains periodic signal related to the grating period, while the laser interferometer measures the displacement simultaneously. The grating period is then obtained through data processing and least-square-fitting. Most of the grating period measurement devices have scattered structures, poor stability, which could be affected by the environment easily. In order to overcome this shortcoming, we adopt the structure of glued prisms, which is compact, and will significantly improve the stability of the system. Thus, the scheme has advantages in measurement accuracy as well as resolution. The system benefits from simple structure and cheap components, which can be widely used in grating period measurement technology.

Stochastic gradient descent (SGD) algorithm with weighted constraint strategy is proposed to solve the vortex stagnation problem in CGH optimization and improve the image quality for computational holographic near-eye display. The weighted constraint strategy includes weighted phase constraint and weighted amplitude constraint. The weighted phase constraint is used to smooth the phase profile of reconstructed field, which helps to solve the vortex stagnation problem caused by optical vortices and eliminate the speckles in reconstructed field. The weighted amplitude constraint is used to broaden the optimization space by introducing the amplitude freedom of non-signal region in the reconstructed field, which helps to further improve the image quality in the signal region. The weighted constraint SGD algorithm can ensure the stable convergence of CGH optimization and avoid the vortex stagnation, which helps to eliminate the speckles and improve the image quality for holographic near-eye display.

Holographic near-eye display (H-NED) is one of the most promising technologies in three-dimensional (3D) augmented reality and virtual reality displays due to its ability to provide all depth cues. The numerical calculation of diffraction fields is the basis and key step in the design flow of H-NEDs, and the sampling is the core. In this study, from the perspective of phase space optics, a systematical analysis on the sampling of the wavefield and intensity in H-NEDs is presented. The space-bandwidth product evolution of the wavefield and intensity are given via Wigner distribution function. The sampling criteria, minimum number of samples and conservation law of nonuniform sampling points of the intensity are provided. Such a comprehensive sampling analysis provides guidelines for the correct numerical calculation of diffraction fields in H-NEDs.

In holographic near-eye displays, the generation of computational holograms requires using various free-space propagation numerical methods. Traditional free-space propagation is mainly focused on the propagation calculation between parallel planes, which is widely utilized in on-axis holographic displays. But for practical usage of the wearable holographic near-eye displays, the propagation between non-parallel planes is crucial for the hologram generation of off axis projection to the holographic-optical-element (HOE) based combiner. However, at current few methods are reported for generating holograms with non-parallel-plane propagation. This paper proposes a novel method with Wirtinger derivatives to solve the problem of phase hologram retrieval between non-parallel planes. Using the Wirtinger derivatives can transfer the hologram phase retrieval to a quadratic problem. With different loss functions and stochastic optimization methods, this quadratic problem can be minimized by first-order optimization, resulting in a phase-only hologram of the tilted plane. The proposed method using the Wirtinger derivatives to calculate the tilted plane phase hologram can improve image quality significantly. The proposed method can achieve better PSNR and lower computational cost in the simulation than the traditional GS algorithm. The diffraction calculation of the tilted plane can further extend the propagation from two-dimensional(2D) to three-dimensional(3D), which will provide a new way for the hologram generation of 3D scenes.

The Gerchberg–Saxton (GS) algorithm is a widely employed algorithm for phase-only hologram (POH) generation. However, the POHs which can strictly satisfy the amplitude constraints on the object and the holographic plane may not exist or be obtained, resulting in speckle noise and reduction of the reconstruction quality. Relaxing the amplitude constraint during the iterations is an effective method to solve the above problem. In this work, a GS-double amplitude freedom (GS-DAF) algorithm is proposed. The amplitude constraint relaxation is realized by both the combined amplitude constraint and the support constraint. The spherical initial phase and oversampling method are applied to further improve the optical reconstruction quality of the GS-DAF algorithm. An enhanced reconstruction quality with less speckle noise has been achieved.

Holographic display technology has emerged as one of the most attractive 3D display technologies. However, the speckle noise in the holographic reconstructed image seriously affects the viewing experience. Here, three methods for suppressing the speckle noise have been proposed.

In this paper, RGB holographic waveguide devices are separately fabricated with the multiwavelength laser exposure method using the prepared wide-band sensitive acrylate photopolymer. Thus, for verifying the function of the prepared device, the full-color holographic waveguide near-eye display module with diagonal 30° field of view using the LCoS projector engine was developed. The results demonstrate the potential of holographic waveguide fabricated with the wide-band sensitive acrylate photopolymer in augmented reality near-eye display.

Holography is considered to be the ultimate solution for 3D display, because which can provide realistic 3D perception and solve the dizziness and fatigue symptoms. The full-color holographic 3D display system usually requires 3 SLMs, which will result in a large, expensive and complex display system. To solve such problems, numerous research works for full-color display using single SLM are proposed. In this work, a series of such methods are surveyed, such as the time division multiplexing, spatial division multiplexing, frequency division multiplexing method, etc. The principles of such methods are explained and the characteristic will also be discussed.

In this paper, we focus on improving the performance of the SLM based on Liquid Crystal on Silicon, like frame rate, color control, phase linearity, surface flatness and surface process. The colorfulness is realized by lighting different laser light source with color sequential driving method. With this method, the color could be recovered simply using compact three color light sources, like in the present AR glasses. The lights are collimated and illuminate the SLM panel in pre-set time sequence, synchronized with the display content. Light efficiency has always been a great concern. It is important to increase the light efficiency while not decrease the diffraction efficiency at the same time.

Our several recent works on holographic retinal projection display (RPD) are introduced here. First, a lensless dynamic full-color holographic RPD with horizontal eyebox expansion using a single spatial light modulator (SLM) was demonstrated.Secondly, we propose to efficiently extend the eyebox of holographic Maxwellian near-eye display by encoding the conjugate wavefront as the multiplication of plane wave phase with the target image. Thirdly, a holographic super multi-view (SMV) RPD is proposed to provide depth cues for a monocular vision.Fourthly, a multi-channel holographic RPD was proposed, which can provide multi-channel image sources simultaneously, thus greatly increasing the information content.The proposed method provides a good prospect that the future AR glasses can play dozens of video channels in parallel, and the user can switch among channels freely and efficiently just through a simple eye rotation.

When watching stereoscopic three-dimensional (S3D) display, most people will feel visual discomfort due to the color asymmetry of left and right eyes. However, a stereo pair consisting of one gray image and one color image can be perceived by a human observer as a 3D color scene, and there is no depth perception degradation and only limited color degradation. This novel presentation approach of stereoscopic display can reduce the redundancy of color information, optimize the video compressions and greatly save the transmission bandwidth. And it may also alleviate the visual comfort problem of asymmetric color stereoscopic content by reducing the visual system load. In this paper, visual comfort was evaluated for stereoscopic videos with different gray-color allocation schemes. Three allocation schemes are used to investigate the changes of visual comfort of stereoscopic video. The subjective evaluation results show that different binocular color allocation schemes have an impact on the visual comfort assessment (VCA) scores. Among them, the binocular color coding of the left half of all frames in stereoscopic video are color and the right half of all frames are gray, which may reduce the amount of color information processing by the visual brain and therefor has a more comfortable visual experience. We suggested that the color allocation scheme also can reduce the flicker of video, and the visual comfort of stereoscopic contents with only half color information is We demonstrated that this color allocation scheme also can reduce the flicker of video, and the visual comfort of stereoscopic contents with only half color information is within the acceptable range.

This communication presents the realization of complex-valued Fourier transform (FT) holograms displayed onto phase-only liquid-crystal spatial light modulators (LC-SLM). Different encoding techniques are described, and the advantages are discussed in relation to the SLM modulation characteristics and other related effects like flicker or fringing. Finally, an experimental technique for evaluating the quality of the reconstruction will be introduced, which uses the SLM itself to build a polarization phase-shift self-interferometer useful to measure the complex distribution generated in the far field domain

It is realized that real time generation of 4K (3,840 x 2,160 pixel) full color rainbow hologram on a personal computer without special hardware such as GPU or FPGA. Although the rainbow hologram sacrifices vertical parallax, it can be generated faster than image hologram and can be reconstructed full color image with single SLM. Holograms are generated over 10 frames per second with sub-million point cloud, converted from polygonal computer graphics data.

In this paper, we propose a volume-reduced floating display based on a holographic optical element (HOE). The critical problem of a conventional floating display is a huge size, and this drawback limits its practical application. To overcome this drawback, the proposed floating display used the HOE for a reduction of the volume instead of a half mirror. Generally, the HOE can control the diffraction angle of the propagating wavefield. Also, the suitable HOE can be designed depending on the structure or a requirement of the floating display. So, the volume of the proposed floating display can be reduced through the HOE when the HOE is designed to reduce the diffraction angle. In the proposed floating display, the HOE is inclined at a certain angle in front of the retroreflective film. And, the projector and diffuser are set up the bottom of the inclined HOE. Wavefields propagated from the projector are formed as an image on the diffuser and, diffracted by the HOE into the retroreflective film. These diffracted wavefields are reflected by the retroreflective film back toward the direction of the propagating wavefields. As a result, the floated image is formed in the real space. For the optical experiment, we designed a HOE and set up the proposed floating display. Experimental result shows that the image is formed in real space like the conventional floating display. Also, we confirm that the volume of the floating display is reduced by as much as 35.6 % compared with the conventional floating display.

We report a novel wide-field lens-free 3D microscopy, which is based on Fourier ptychography diffraction tomography (FPDT) technique. This method uses only one illumination angle to obtain a large enough number of diffractograms by scanning a wide range of wavelengths, applying an iterative method to fill the 3D spectrum, and finally recovering the refractive index (RI) distribution of the sample. And the effectiveness of the method in the 3D RI distribution reconstruction of a tilted phase target is experimentally verified.

Fourier ptychographic microscopy (FPM) is an effective computational imaging method that incorporates many advantages such as large field of view, high resolution, label-free, and quantitative phase-contrast imaging. Typically, an LED array is used as the illumination source. Due to the small size and narrow spectral width of the LED unit, FPM is usually treated as a coherent imaging system. However, practically, each LED unit is a spatially-extended light source with a certain emitting area, rather than an ideal point source. The ideal point source approximation will decrease the quality of the reconstructed image, to a certain extent. In this paper, the spatial coherence characteristics of FPM system based on LED illumination is analyzed, and it is found that the optical field on the object plane is partially coherent. Thus, the artifacts exist when the coherent transfer function is used as the frequency domain constraint. To address this problem, a Butterworth-weighted transfer function is proposed as the frequency domain constraint in the iterative reconstruction process. The simulation and experimental results demonstrate that this new constraint approach can not only reduce the ringing effect in low-resolution images, but also improve the reconstruction quality due to its following better the actual physical mechanism inherent in FPM. In addition, it may reduce the requirement of the spatial coherence of the illumination source, which has great significance for promoting the application of FPM.

We propose a single-frame lensfree phase retrieval(SFLFPR) method based on coherence-limited light-emitting diode (LED) illumination. Combining multi-wavelength scanning iteration for broad-spectrum illumination with phase support constraint, SFLFPR corrects resolution loss caused by the temporal coherence of LED, obtaining quantitative phase imaging results. Using only one hologram, our method can retrieve the high signal-to noise(SNR) phase of the sample and achieve a half-width resolution of 977 nm across a large field-of-view (FOV) of 19.53 mm² , surpassing 1.41 times the resolution achieved by the conventional single-frame method. We confirmed the effectiveness of this method in quantitative phase imaging (QPI) by measuring various label-free samples including polystyrene microspheres, phase resolution target (PRT) and HeLa cell slices. Considering its fast real-time single-frame imaging capability, our method has a wide range of biological and medical applications.

A prototype of two-coordinate spatial light modulator (SLM) based on acousto-optic diffraction in KY(WO4)2 monoclinic crystal is proposed. The SLM design is based on a special configuration of isotropic Bragg diffraction in monoclinic crystals, which used autocollimation of the acoustic beams and operation with unpolarized light. This enables a unique design of a two-coordinate Bragg cell, which can be used as a monolithic X-Y deflector or as an SLM. Experimental results and limitations of the prototype performance are discussed in the report. Overall efficiency over 50% at 4 W of driving RF power has been demonstrated for the laser wavelength of 532 nm. Optical modulation rise/fall time is ~220 ns/mm for each coordinate.

Off-axis optical scanning holography (OSH) has been recently proposed to perform scanning holography without the use of heterodyning. In the present work, we combine the principle of off-axis scanning holography operating in the coherent mode with the idea of a layer-based method to achieve a new computational imaging technique for optical tomography. The point cloud data of a complex three-dimensional (3D) scene is layered along the depth direction as the 3D object is divided into a series of planar layers parallel to the hologram along the optical axis direction. The data of each layer generates a single-layer hologram under coherent off-axis scanning holography. Finally, the hologram of a complex three-dimensional object is obtained by superimposing all the single-layer holograms. We use a single-sideband filter to extract the hologram spectrum to obtain a positive first-order reconstruction and demonstrate numerical reconstruction with different diffraction distances. Also, optically reconstructed images are displayed by a spatial light modulator. The results indicate that the proposed method can realize the holographic recording and reconstruction of a complex three-dimensional object without the zeroth-order beam and the twin image, providing a new computational method for the generation of holograms of large-scale and long-depth 3D objects.

The orbital angular momentum (OAM) owning to the special superiority with the inherent orthogonality, has been identified as an information carrier. In this paper, we proposed a simple and direct method for measurement the OAM of the vortex beam by using vortex grating encrypted OAM holography. When the detected beam illuminates the designed OAM holography, the topological charge (TC)value will be directly read from the reconstruct results which appear as a series of solid Gaussian or ring spots at the output surface of the system. Thus, according to the reconstruct results, we can not only easily detect the modulus but also the sign of the incident beam. Furthermore, it can simultaneously identify OAM modes of multiple incident vortex beams. It's demonstrated that the proposed method is an efficient and flexible method.

Pulsed digital holography, which combines femtosecond pulsed laser and digital holography, is a novel technology for detecting ultrafast transient processes in real-time. Pulsed digital holography can obtain a series of amplitude and phase information of the ultrafast process in one shot at the femtosecond or picosecond order, and comprehensively characterize the whole picture of the ultrafast process. However, the system of pulsed digital holography currently has the defects of complexing, poor stability, small number of pulse frames, and low utilization of space bandwidth, which seriously limits practical applications. In this work, a real-time detection system is designed for ultrafast transient processes, which has the property of high stability, femtosecond or picosecond time order resolution, and adjustable pulse frames. The pulsed lasers are used instead of traditional continuous lasers. The proposed system design provides a competitive approach to ultrafast transient imaging.

The tensor polarization holography theory has predicated some phenomena and been verified by the experiments. In the theory, the parameters α and β represent the scalar and tensor coefficients of the photoinduced change in dielectric tensor respectively. The ratio of α to β, called the exposure response coefficient, is a key to manipulate the polarization state of reconstructed waves and deepen the understanding of tensor polarization holography theory. In this work, for the polarization-sensitive material, phenanthrenequinone-doped poly methyl methacrylate (PQ/PMMA), we analyze the effect of interference angle and the polarization states of signal wave on the initial exposure response coefficient when the reference wave is s-polarized in linear polarization holography.

A single-shot dual-wavelength lensless digital holography based on a dichroic mirror is presented to achieve quantitative phase imaging. The lensless digital holography is designed by a wavefront division transmission configuration with only a plane mirror and a beam splitter. By merely adding a dichroic mirror between plane mirror and beam splitter in lensless transmission digital holography, the propagation direction of two reference waves for different wavelengths can be adjusted separately by dichroic mirror and plane mirror. Therefore, a multiplexed hologram with different fringe directions for two wavelengths can be simultaneously obtained. Our technique is capable of real-time wavelength-multiplexing with minimum optical element and system modification.

Polarization holography based on tensor theory can accurately describe the reconstruction characteristics at arbitrary interference angles, so some optical elements such as wave plates can be produced by polarization holography. The wave plates are important optical elements that can control the phase and polarization state of wave. Conventional wave plates convert the polarization state of the incident wave through crystal birefringence and then require the accurate thickness. Based on the polarization holography described by tensor theory, we produce the half-wave plate whose azimuthal angle of fast axis may be arbitrary by using the polarization sensitive material, phenanthrenequinone-doped poly methyl methacrylate (PQ/PMMA).

In the analytical method of polygon-based computer-generated holography, the spectrum of the surface function of an arbitrary polygon (triangle) is expressed in terms of the spectrum of a unit right triangle, which is known analytically. We perform texture mapping by dividing the triangle into many unit right sub-triangles which contain the texture information. The method has been verified by computer simulations and optical experiments.

This paper proposes an approach for acoustic field imaging using simultaneous multi-view digital holography based on three-color digital off-axis holography. Considering spatio-chromatic multiplexing and the recording with a monochrome sensor, the numerical processing of time-sequences of holograms yields both the amplitude and phase of the acoustic field along three different directions of observation. Experimental results with an emitter at 40kHz establish the proof-of concept of the proposed multi-view imaging for acoustic fields. Tomography imaging of the acoustic field is provided with multiple recordings when rotation the transducer.

A new scheme for optimizing a computer-generated hologram (CGH) in holographic laser processing system is proposed. The CGH that generates two- and three-dimensionally arranged focusing spots is optimized during laser processing. The scheme called as an in-system optimization has the potential to compensate for static imperfections and dynamic changes of the laser processing system by the rewritable capability of a liquid crystal on silicon spatial light modulator (LCOS-SLM).

Holographic displays have gained attention as ideal displays because of their advantageous properties for perfectly controlling light wavefronts. However, their realization is hindered by the considerable amount of computation required for large holograms. We developed special-purpose computers for holography using field-programmable gate arrays. In this paper, we discuss strategies for next generation special-purpose computers, in which we will implement an oriented-separable convolution, which can compute holograms at high speed. This algorithm has almost the same circuit configuration as that of the previous special-purpose computers and can speed up computation by two to three orders of magnitude. In addition, we describe herein a post-processing technique using deep learning in which low-precision holograms calculated using a special-purpose computer are converted to high-precision holograms via a simple deep neural network.

Optimal sampling method is effective in generating phase-only hologram. In this approach, the intensity of a source image is multiplied with an optimal sampling lattice, and converted into a hologram. Subsequently, the phase component of the hologram is retained as a phase-only hologram. The optimal sampling lattice is optimized through direct binary search so that the reconstructed image is closest to a given training image. A hologram generated with this method is known as an optimal sampled phase-only hologram (OSPOH). The reconstructed image of an OSPOH is generally good, but its quality cannot be further improved by extending the optimization process. In this paper, an enhancement on the reconstructed image of OSPOH through time-division filtering is presented. Experiment results revealed that the proposed method can lead to significant enhancement on the reconstructed image.

Digital holography is a powerful technology for a wide range of applications. It combines digital hologram with spatial light modulators (SLMs) and can deliver superior performance which has not been demonstrated before by other technologies. This work proposes a novel method of calculating and optimizing the computer-generated holograms (CGHs) so that a single CGH could be used for white light illumination. The results of this research show that colour dispersion can be reduced by using an iterative algorithm with the aid of a defined perceived image quality, while the shape and sharpness of the target replay fields are maintained.

Look-up table (LUT) is a widely used method for computing computer-generated holograms (CGHs) but usually demands a large memory space. For this reason, we propose a new LUT method to produce binary CGHs. We quantized the lookup table, which allowed us to use smaller data types for storage and computation. Simulation results show that this method reduces the memory space, and its speed is at least 3 times faster than the original LUT method without reducing the quality of the reconstructed image.

Speckle de-noising can improve digital holographic interferometric phase measurements but may affect experimental accuracy. A deep learning-based speckle de-noising algorithm is developed referring to the U-Net and the DenseNet architectures using a conditional generative adversarial network established by the generator and the discriminator network. The loss functions that guide generator training consist of a mixture of a static spatial distance norm metric designed by considering the peak signal-to-noise ratio parameter, and a dynamic metric generated from the discriminator that grows with the generator in training. Datasets obtained from speckle simulations 4-f system are shown to provide improved noise feature extraction. Therefore, the proposed method offers better performance than other de-noising algorithms For processing experimental strain data from digital holography.

Reconstructing super-resolution images typically requires three or four phase-shift holograms for spectrum decomposing and combination. In the process of recording holograms, the phase shift accuracy of the instrument and environmental vibration will affect the spectrum decomposing results, resulting in reconstruction artifacts. In the simulation, with respect to two kinds of phase shift biases, the digital holographic reconstruction results with three-step and four-step phase-shift methods are compared. All the phase shift methods are much dependent on the accuracy of phase shift values. The four-step phase shift method needs to record more holograms, so its ability to cope with bias is poor, and its spectrum decomposing results is inferior to that with the three-step phase shift method. In a structured-illumination off-axis digital holographic system, the super-resolution imaging for amplitude and phase reconstructions is performed in experiment by using three-step phase shift processing. The results demonstrate that the resolution of the reconstructed images is improved.

Optical imaging through complex, inhomogeneous media is a long-standing challenge due to the presence of scattered light, which causes a degradation of resolution. Thanks to the discovery of the optical memory effect (OME), a variety of novel and breakthrough approaches have been proposed to find the hidden information behind the scattering media. However, those ME-based methods usually suffer from a limited field-of-view (FOV). An object of size beyond the ME region cannot be reconstructed completely and will produce artifacts. Here, we propose a non-invasive method that exploits a moving object behind the scattering media to extend the FOV

Digital holography microscopy (DHM), as a non-phototoxic non-destructive imaging technique, encodes a complex optical field into intensity modulations by the interference of scattered sample wave and reference wave and performs quantitative analysis of wave-matter interactions by decoding phase delay from a hologram. In this work, we propose a complete high-precision high-robust DHM-based quantitative phase microanalysis scheme (DHM-QPMS) for living cells. The whole scheme provides algorithmic support for 3D morphological information on cell area, circumference, irregularity, and volume. We quantitatively validated this scheme for the human cervical cancer (HeLa) cells under a ×20/0.45NA objective lens. Though the used sample is adherent and bizarre, the system can still achieve accurate target identification and cellular 3D feature extraction. Moreover, we believe that DHM-QPMS will be an important research tool for biological researchers.

Selecting a suitable autofocus critical function to accurately obtain the defocused distance in a digital holographic microscope (DHM) is the key to digital reconstruction. Several typical autofocus methods have been proposed to calculate the defocused distance by ascertaining the global extreme value of the critical functions to determine the best focused plane. In this work, a novel digital holographic autofocus algorithm based on the weighting factor of the discrete cosine transform (DCT) is proposed. We compare the proposed method with several typical methods involving SPEC, DIF, GRA and LAP under different noise conditions to evaluate the capability of our method.The experimental results of HeLa cells and phase resolution target verify that our method had a good performance in terms of applicability and noise-resistance.

In this paper, the method using lensless microscopic imaging techniques, to reconstruct the three-dimensional morphology of tumor cells is given. We demonstrate lensless microscopic platform which only use a CMOS image sensor and a controllable color LED array. Based on the principle of lensless computational imaging, we use the phase recovery algorithm under multi-wavelength and the diffraction tomography algorithm under multi-angle illumination, to reconstruct the three-dimensional morphology of tumor cells. Experiments have verified that this method can achieve large field of view imaging without labeling and reconstruct the three-dimensional morphology of tumor cells, which provides reliable morphological parameters for clinical research and is of great significance to the development of portable medical care.

Head-up displays(HUDs) are used to integrate assistance information with realistic road information to improve driving safety. The current HUDs generally present the virtual image at a near fixed distance. When the drivers’ vision focus on a far distance to observe the road conditions, they need to zoom back to see the virtual image, which may causes accidents. In this paper, we designed a color holographic HUD, it can flexibly produce color image at any depth to adapt to the conditions need. Another issue of current HUD is the small eyebox caused by the limited spatial bandwidth product (SBP) of spatial light modulator (SLM). To expand the eyebox, a folding optical path module consisting of trans-reflective mirrors and reflective mirrors is designed. The folding optical path module has two functions. Firstly, it duplicates wavefront Liquid crystal on silicon(LCOS) into two sub-wavefront path to expand the eyebox by two times. Secondly, it makes it possible to observe a clear virtual image of the same depth by controlling the optical path. The feasibility of this system was demonstrated through experiments.

In the THz band, the spoof surface plasmon polariton (SSP) can limit the light to the designed specific spatial frequency by constructing a sub-wavelength structure on the metal surface. This ability makes it possible to break through the diffraction limit of THz imaging. In this paper, a one-dimensional metal groove structure is used to generate the SSP, and the frequency shift characteristics of the object's spatial spectrum under the excitation of a 2.52 THz beam are analyzed. On this basis, a grating-coupling-based SSP excitation structure is designed, which consists of a combined array of subwavelength metal grooves and subwavelength slits with different periods. This structure is used to generate strong intensity and make full use of the incident beam. It is promising for generating illumination beams for terahertz far-field super-resolution imaging of subwavelength-spacing samples.

ulti-channel acousto-optic modulator is an acousto-optical device with multiple transducers modulated in parallel, which main applications are in microfabrication and direct writing lithography. Crosstalk has been a key problem in multi-channel acousto-optical devices due to the proximity of the channels and the diffraction of the acoustic waves. Acoustic crosstalk is caused by a certain dispersion angle of the sound beam in the process of spatial propagation, resulting in the sound field of the acousto-optical action medium in a certain propagation distance overlap. Ultrasonic transducer is an important element of the sound energy emission, which generates sound waves through the inverse piezoelectric effect. The shape of the electrodes on the transducer controls the area where the piezoelectric crystal vibrates, further affecting the distribution of the sound field. Therefore, the shape of the electrodes can be changed to improve the collimation of the acoustic beam and thus effectively reduce the acoustic crosstalk problem between channels. Rectangular electrodes are used by most conventional multi-channel acousto-optic modulator. The rectangular electrodes have more acoustic field side lobes, which can cause acoustic crosstalk between sensors and thus affect the quality of the diffracted beam. In this paper, crossed trapezoid array electrodes shape is proposed, for improving the crosstalk problem of multi-channel acousto-optical devices. From the spectral analysis, the crossed trapezoid array electrodes can effectively suppress the side lobes of the acoustic field and improve the collimation of the beam, thus reducing the acoustic beam crosstalk between channels. Simulation and experiments show that multi-channel acousto- optic modulator with crossed trapezoid array electrodes can effectively solve the acoustic beam crosstalk problem between channels and enhance the performance of multi-channel acousto-optic devices.

Holographic display can reconstruct the optical wave field of three-dimensional (3D) scenes. Computer- generated hologram (CGH) can simulate the optical transmission process from the 3D object to the hologram plane and avoid complicated experiments. Wavefront recording plane (WRP) is a fast algorithm for CGH, which is placed between the 3D object and the CGH. However, the computational amount is increased when the depth range of the 3D object is expanded. In this paper, we propose a fast calculation algorithm for real-time interactive CGH using a novel Fresnel zone plate (FZP) extension method and ray tracing. In the first step, ray tracing is used to get the amplitude value and the depth value of each object point. The maximum resolution of each FZP is determined according to the distance from the object point to the WRP. In the second step, a preset square portion of each FZP is used to calculate the complex amplitude of the WRP. Then diffraction calculation is performed from the WRP to the hologram plane for calculating CGH, and the computational domain of each FZP is gradually extended as the number of frames increases. The above calculation is repeated when interacting. The computational complexity is effectively reduced because the resolution of each FZP is increased until the maximum resolution is reached, instead of directly calculating each FZP with the maximum resolution. Experiments demonstrate the proposed method can generate CGH in real-time. The resolution of the hologram is 1024x024 and the CGH generation rate is 45.81 frames per second when interacting.

An objective function that closely represents the maximum optical pathlength difference on the entire grating surface for designing a flat-field holographic concave grating is proposed. Compared to design methods that minimize certain aberration coefficients of the optical pathlength function, the present objective function has a clearer physical meaning of optical pathlength difference and guarantees a smaller spot size. Compared to design methods that minimize the spot size based on ray tracing, the present method requires less computing time, but is equally effective in minimizing spot size, and it even provides a better image quality in the sagittal direction.

Pixelated micro-polarizer array is an attractive polarization imaging device because of its real-time fully detecting capability to Stokes parameters and high integration level. However, this micro-device is commonly fabricated by electron beam lithography, thus is often high-cost. Since periodic unit of this device is a 2×2 array of four types of one-dimensional (1D) gratings with different orientations (0°, 45°, 90°, 135°), a low-cost grating fabrication technique, interference lithography (IL), is possible to be used to fabricate this device. In this research, a four-steps exposure patterning method of micro-polarizer array based on single Lloyd’s mirror interferometer IL is developed. This interferometer is composed by two perpendicular parts: a mirror and a photoresist holder, and a 1D grating parallel with mirror can be fabricated in the exposure region on photoresist through lithography. A Cr-based mask, whose transparent pattern is a square array of square windows with 15×15 μm2 window size and 17 μm window spacing, is introduced and clamped onto the photoresist to cut exposure region. In four exposure steps, each 15×15 μm2 quadrant area of a polarizer array with 2 μm quadrant spacing will be exposed on photoresist, respectively. Between two exposure steps, mask and photoresist substrate need to be simultaneously horizontal rotated, to adjust the orientation of grating fabricated in next exposed quadrant on photoresist. Based on this method, we fabricated the single-state patterned micro-polarizer array, which effectively controls the cost and fabrication cycle. The experimental results show that the photoresist grating within a single window has stable structure, uniform period and good directivity.

As applied to a maskless laser lithography writing system Heidelberg DWL 66+ and the photoresist-chromium technology, we have found the tolerances on fabricating the binary-phase Dammann gratings having 7x7 useful diffraction orders and a structure separable in X and Y components and illuminated by a beam with a wavelength of 633 nm. It has been found that the obtained tolerances guarantee the production of Dammann gratings with a total diffraction efficiency close to the theoretical one and a root-mean-square error of departure of the intensity of useful diffraction orders of less than 10%.

We present detection of strain solitary waves in polystyrene waveguides using pump-probe digital holography. Analysis of spectral components of the detected longitudinal strain waves was performed at several locations of the waves inside the waveguide in the course of their propagation. The data obtained allowed us to evaluate attenuation of relatively short- and long-wavelength components and to demonstrate much faster decay of high-frequency wavelets in comparison with the long solitary wave. Along with the spectral analysis monitoring of variations of solitary wave shape in the course of its propagation was performed. The dependence of spectral composition of the strain wave on the energy of the initial shock wave showed an increase in the relative contribution of long-wave components with the strain wave energy.

We report investigation of HeLa cells’ response to photodynamic treatment in vitro using three realizations of quantitative phase microscopy. Reconstruction of phase images was performed by means of off-axis digital holographic microscopy with coherent HeNe laser source, and two approaches utilizing partially coherent illumination: transport of intensity equation (TIE) and spatial light interference microscopy (SLIM). All of these methods can be successfully used for analysis of optical and morphological characteristics of living cells and cells exposed to photodynamic treatment, however each technique has its own advantages and disadvantages in implementation and data processing.