This PDF file contains the front matter associated with SPIE Proceedings Volume 11898 including the Title Page, Copyright information, and Table of Contents.

The widespread use of holographic VR/AR devices are limited by bulky refractive and diffractive optics. To address these problems, a NED system combining the 3D CGH based on Fraunhofer diffraction and a metalens with 5 mm diameter as an eyepiece is proposed in this paper. Because of the capability of wavefront shaping in a subwavelength scale, the metalens eyepiece surly facilitates lightening the CGH-NED systems. Experiments are carried out for this design, where Fraunhofer diffraction with digital lens phases of different focal lengths are applied, and the metalens transforms the holographic reconstructed 3D image into virtual image to realize NED. The metalens eyepiece composed of silicon nitride anisotropic nanofins is fabricated with the diffraction efficiency and field of view for 532 nm incidence of 15.7% and 31°, respectively. Our work combining of CGH and metalens may provide a promising solution in future for computer-generated holographic 3D portable display.

In this work, we proposed a parameter-free algorithm (PFA) for iterative wavefront shaping, in which the time-consuming parameter tuning process is not required. The simulation and experiment results show that PFA can achieve better performance than GA and BA, without a parameter tuning process. Furthermore, since the mutation rate in PFA is inherited from the dynamic mutation algorithm, which has demonstrated high adaptability against perturbations, the robustness of PFA is satisfactory. In the future, a field-programmable gate array (FPGA) based system can be implemented to accelerate iterative wavefront shaping and achieve real-time optical focusing in dynamic scattering media, such as biological tissue.

We present two applications of the hologram signal processing based on the mutual conversion between the hologram and light field. Both hologram and light field represent the light from three-dimensional objects but with different characteristics. This feature can be utilized to update the hologram for desired purpose without prior knowledge on the three-dimensional objects in the hologram. In this talk, we show how this mutual conversion can be used to update existing holograms to new ones for their speckle-free optical reconstructions. We also discuss hologram update which scales three-dimensional objects in the hologram with constant transverse and axial magnifications.

Fresnel incoherent correlation holography as a self-interference holographic technique is employed as three dimensional (3D) localization method of fluorescent microspheres, thus to obtain 3D microscopic imaging. In order to promote the localization accuracy and the reconstructed image quality, autofocus algorithm is introduced to help finding accurate reconstruction distance in the Fresnel Incoherent Correlation Holographic (FINCH) localization microscopic imaging. The performances of autofocus algorithm under different evaluation parameters of reconstruction images are investigated, and the suitable autofocus algorithm are used during hologram reconstruction. The localization algorithm is utilized based on the reconstructed image. The localization accuracy and imaging quality are compared with and without employing the autofocus algorithm. The enhanced localization accuracy is realized in the actual FINCH localization microscopic imaging system.

We present incoherent digital holographic microscopy systems for high-speed three-dimensional (3D) motion-picture sensing. Adopting single-shot phase-shifting interferometry to incoherent digital holography, high-speed motion-picture recording of spatially incoherent digital holograms can be enabled. Single-path self-interference incoherent digital holography systems are designed and constructed utilizing the polarization of light waves and birefringent optical elements. We describe the systems constructed until now and show experimental results including three-dimensional motion-picture recording of incoherent digital holograms for fluorescent nanoparticles in a flow, at the frame rate of more than 100 fps and with 1024 x 1024 pixels and the field of view of 148 um x 148 um. Furthermore, we have succeeded in extending the applicability of incoherent digital holography to 3D sensing of objects with compact optical systems. In the video presentation, single-shot quantitative phase imaging with a light-emitting diode will be introduced.

Diffraction limit is a limiting factor not only in imaging but also in generating an optical field or illumination. We focus on subdiffraction limit illumination created using a computer generated hologram and its applications. Structured illumination which consists of an array of subdiffraction limit spots or light sheets can be obtained by controlling the phase distribution in the optical field. Performance and properties of subdiffraction limit illumination are discussed. The method has a wide range of applications, and resolution improvement of laser scanning microscopy is presented as an example.

It is well known that the three-dimensional (3D) imaging has inherent advantages than the two-dimensional (2D) imaging. However, the existing 3D imaging methods are limited by expensive instruments or complex systems. And previous researches have shown that, owing to the fact that there exists a functional but determined relationship between the polarization information of light reflected from a target and the surface normal of it, the shape information of a 3D target can also be obtained by measuring and analyzing the polarization properties of the reflected lights. Indeed, the 3D reconstruction imaging method based on the light polarization has shown great potential in future 3D imaging applications due to its advantages of high reconstruction accuracy and simple detection equipment involved. Note that, in the process of reconstructing the 3D shape of an object based on the light polarization information, there always exists an inherent ambiguity problem, i.e., the ambiguity of the azimuth angle. To solve this problem, we propose a new method to determine each zenith angle by sorting them corresponding to all pixels in the same row of the image.

We proposed here a new method of encoding and extracting the 3D position of fluorescent micro particles. Cross-correlation matching method is employed to localize the axial position of fluorescent microsphere. And the localization accuracy of the proposal is compared with that of the traditional diffraction reconstruction algorithm. The effectiveness of the method is verified by both simulations and experiments, and the localization accuracy of the method are evaluated quantitatively. This method overcomes the limitation of the imaging depth in the traditional single molecule localization, reduces the influence of optical aberration on the localization accuracy, and it possess the potential of achieving the isotropic super resolution localization of the sample.

3D micro-particle field reconstruction with high accuracy and low latency is an ambitious and important task within various applications. Without using any focusing optics, the digital holography (DH) is used as a high throughput and compact imaging system to retrieve the particle 3D distribution information from two-dimensional(2D) gray-scale interference pattern. In this work, a one-stage digital in-line holography model is proposed with competitive performance in localisation accuracy and extraction rate with improved processing speed. This model facilitates the analysis of the dynamic displacements and motions for micro particles or cells and could be further extended to various types of computational imaging problems sharing the similar traits.

A method that realizes the three-dimensional holographic laser reconstruction and processing by using an optimized computer-generated hologram (CGH) was demonstrated. A pre-designed CGH that contains three-dimensional (3D) information displayed on a liquid-crystal-on-silicon spatial light modulator (LCOS-SLM) can obtain the desired 3D diffraction pattern in the optical system, called 3D holographic laser reconstruction, and when it is reduced by an objective lens and incident on a sample, it can realize the 3D holographic laser processing. Using an optimization method, called in-system optimization, to compensate for the imperfections that exist in the actual laser system, and obtain the high-quality CGH. Consequently, a high uniformity 3D holographic laser reconstruction was achieved, and the consistent scale of the corresponding processing holes proved the feasibility and significance of the CGH optimization.

Edge extraction is an important pre-processing operation in image processing and pattern recognition in machine vision. For example, coherent optical image processing for edge detection can be performed in a standard 4-f system with proper pupil designs. The possibility of pre-processing using digital holography for 3D image edge extraction is intriguing. In this talk, we will review some of the edge detection techniques used in single-pixel digital holography called optical scanning holography (OSH). OSH is a two-pupil system and different edge detection schemes through the different combinations of pupils are discussed.

Automatic optimization of diffractive structures is of great interest and has potential applications in see-through near-eye displays. Here, we propose an approach of on-demand design of diffractive elements using the physics-driven topological optimization. The topology is iteratively optimized according to the added constrains in dispersion and angle uniformity. The proposed model provides an effective way for the design of complex electromagnetic components that are essentially irregular and out of the box of human’s designing.

Currently most of the holographic waveguide near-eye display are based on flat waveguide structure. It is always required to add curved goggles for head mounted display (HMD) or helmet display. And consequently, the human eyes have to see through both the flat waveguide and the curved goggles when viewing see-through background. It suffers from bulky form-factor, low transmittance and limited application. Therefore, this paper proposes a near-eye display system based on curved holographic waveguide, which integrates both flat waveguide and curved goggles. This design includes cylindrical holographic waveguide and corresponding micro projection module. To ensure the rays transmitted regularly in the waveguide, we designed special holographic optical elements (HOEs) attached on the surface of cylindrical waveguide to achieve large exit pupil and field of view (FOV). Besides, the aspheric lenses in the micro projection module are employed to correct aberration caused by cylindrical waveguide. This novel design of the proposed HMD with cylindrical waveguide can achieve a binocular FOV of about 42° in diagonal, an eye relief of 15mm and exit pupil of 10mm×10mm. For the central FOV, the modulation transfer function is close to the diffraction limit, and the intensity is uniformly distributed at the exit pupil with high light efficiency. For the edge FOV, the image quality is still good and suitable for the human eye. This novel design integrates the waveguide with curved goggles into one curved waveguide based near-eye display, which can provide a new approach for portable near-eye display applied in the helmet or some other related usages.

Recently, the development of augmented reality (AR)/ virtual reality (VR) has brought new life to holographic display. Holographic Maxwellian display technology, also known as holographic retinal projection display (RPD), is considered as a promising AR near-eye display technology. It can provide consistently sharp two-dimensional images within a range of depth of field without being affected by human eye focusing. Several recent works of holographic Maxwellian near- eye display are introduced. Firstly, we have proposed a hybrid holographic Maxwellian near-eye display based on spherical wave and plane wave reconstruction to extend the depth of field. Secondly, we have proposed a lensless full- color holographic Maxwellian near-eye display with horizontal eyebox expansion using a single spatial light modulator (SLM). Thirdly, we have proposed a conjugate wavefront encoding method to efficiently expand the eyebox for the holographic Maxwellian near-eye display.

Coherent diffraction imaging (CDI) is a kind of computational technique seeking to reconstruct a complex wavefront from the measured intensity. To solve the phase retrieval problem, phase modulation is introduced to be a physical constraint. In this work, the alternative structured phase modulation (ASPM) and orbital angular momentum (OAM) are used to be the physical constraints. The ASPM can act as the phase grating. The modulated intensities are concentrated, which can be captured with a high signal-to-noise ratio (SNR). OAM is recently employed as a type of reliable modulation. The topological charge is robust during propagating in the atmosphere. The maximum value of the spectrum intensity is reduced by a factor of 170 under OAM modulation when topological charge is 50. The stagnation can be avoided using multiple ASPM and OAM modulations. The complex wavefront can be robustly reconstructed from redundant measurements without a priori knowledge.

The imaging quality of inline digital holography is challenged by the twin-image artefact because the phase retrieval problem is severely ill-conditioned. Sparsity-promoting regularizers such as the total variation (TV) seminorms have been explored to tackle the ill-posedness and proved effective in modeling real-world objects. However, previous works are mainly based on the TV seminorms for real-valued images, which limit their application in digital holography where we are often dealing with complex-valued signals. In this work, we introduce the complex constrained TV regularizers and propose an efficient proximal gradient algorithm for solving the phase retrieval problem. The proposed complex TV model and the corresponding algorithm are verified by numerical and experimental results. We believe that the proposed algorithmic framework can cast new light on solving a large class of optimization problems based on complex constrained TV regularization.

Interferenceless coded aperture correlation holography (I-COACH) is a recently developed technique for indirect 3D imaging without two-wave interference. The CPM calculated using G-S algorithm plays an important role in I-COACH system. However there are some problems with GS algorithm, such as poor convergence and cannot constrain the intensity, thus leading to noise accompany in the reconstructed images. We introduce a modified G-S algorithm to I-COACH in this work to optimize the CPM and enhance the reconstruction images quality. The results show that both the PSH and OH recorded with optimization CPM have lower noise and the reconstructions have better imaging quality.

Transport of intensity equation (TIE) is a non-interferometric and non-iterative quantitative phase imaging technique that utilizes multiple intensity recordings along the propagation direction. Apart from many advantages, it has some experimental and numerical challenges as well. The experimental challenge is the requirement of multiple intensity recordings which prohibit TIE for real-time imaging of dynamic samples. The numerical challenge is to work with boundary conditions in post-processing analysis. It is required because phase information is to be retrieved after solving second order partial differential equation relating the intensity derivative with phase. In recent years, we have worked on solving the experimental challenges such as alleviating the need of multiple intensity recordings along-with some applications of TIE.

Deep neural networks have been successfully applied to constrained object priors and parameter optimization. Here, we propose a novel learning-free deep neural network architecture to tackle uncertain system optimization. This blind system constraint deep neural network(BlindNet) need not to know all the parameters of the system and can simultaneously acquire the desired image and system parameters. In order to do so, we showed that the BlindNet can perform phase retrieval on the diffraction pattern with unknown diffraction distance.

Quantitative phase information which can reflect the internal structure and refractive index distribution of the object is able to be obtained by diffractive and interferometry techniques. However, the phase resolution achieved by the diffraction method is lower than that of interferometry method; while the setup for interferometry method is more complex. To obtain high-resolution phase images without reference beam path, we propose an end-to-end DL based super resolved quantitative phase imaging method (AF-SRQPI) based on generative adversarial network (GAN) to transform low-resolution amplitude images into super-resolved phase images. Meanwhile, considering the inevitable out-focusing during the long hours of observing, autofocusing function is also included by the network. In the training process, out-of-focus low-resolution amplitude images are used as the inputs and corresponding super-resolved phase images obtained by structured illumination digital holographic microscopy (SI-DHM) are used as the ground truth labels. The well-trained network can reconstruct the high-resolution phase image at high speed (20fps) from a single-shot out-of-focus amplitude image. Comparing with other DL-based reconstruction schemes, the proposed method can perform autofocusing and superresolution phase imaging simultaneously. The simulation results verify that the high-resolution quantitative phase images of different biological samples can be reconstructed by using AF-SRQPI .

Water scattering is a significant limiting factor for underwater imaging quality. It changes the transportation direction of the original light path, causes the attenuation of light intensity, and so on. In this work, we use a synthetic polarizing camera to capture the images with different polarization states and reduce the impact of water scattering in one step with the underwater light propagation model and the Stokes vector. In addition, an untrained deep network is designed to complete the image descattering processing. Compared with the methods based on deep learning or physical model prior, it is more efficient. This technology is suitable for use in portable underwater imaging optical systems for real-time imaging and detecting particulate matter such as microplastics and microbial particles. It also broadens the application of underwater polarization imaging.

From a practical point of view, single-shot phase microscopy systems have several hardware advantages in terms of deploying them for applications, e.g. at clinical sites. The problem of recovering full diffraction-limited phase information from single-shot image plane holograms is however not straightforward as the solution is not unique. Our work over the last several years shows that image sparsity ideas incorporated into hologram demodulation algorithms can effectively surpass several long-held limits on phase imaging performance in terms of resolution and accuracy. Our efforts in converting these algorithmic ideas into a microscope device and diagnostic application development will be covered briefly.

The planer grating with large area plays an important role in the optical encoder for large stroke measurement. Compared with the conventional fabrication techniques such as interference lithography and mechanically ruling for large-area manufacture, splicing small-area grating units into a large integral mosaic grating is promising to reduce the technical difficulty and time-consumption. We proposed a novel grating splicing method to construct large-area mosaic grating applicable for optical encoder. The splicing apparatus is capable of providing four degree-of-freedom including one outof-plane straight motion (ΔZ) and three rotation motions (Δθ_x, Δθ_y, Δθ_z) for mechanically adjusting the grating units. The diffracted beams from the spliced gratings are utilized to guide the adjustment, i.e., zero-order diffracted beams for ΔZ, Δθ_x, Δθ_y and first-order diffracted beams for Δθ_z, respectively. The diffracted-beams orientations of the first grating were adopted as the basic reference, and the posture of the other gratings are continuously adjusted by matching the position of the diffracted beams. Five grating units with 20×20 mm² area and 1 μm period were spliced together. Finally, a coordinate measuring machine was utilized to evaluate the flatness of the mosaic gratings, showing a good flatness as small as ~60 μm. It is demonstrated that our proposed splicing method is promising to achieve good flatness of mosaic grating potentially applied for large-stroke optical encoder.

A compact asymmetrical directional coupler composed of 70-nm-deep shallow etched dual grating structure waveguide and a 7.4-μm long coupling length, is proposed and fabricated to realize a broadband and high-extinction-ratio polarizing beam splitter. By carefully optimizing the structural parameters, the cross-coupling for TM light can be realized while little coupling happens for TE wave, which would have a broad application prospect for silicon-based photonics.

This paper presented a roadmap of optical computing, particularly, for optical implementation of convolution, in comparison with supercomputer. Optical computing power presented in this roadmap is predicted based on a simple mathematic equation of convolution where optics can do matrix convolution in full parallelism with single pass of light, which could be 500 times faster than supercomputer( Fugaku), while energy consumption of optical computing might be 1000 times lower than supercomputer (Fugaku), supposing 8K Spatial Light Modulator with extremely high updating rate <22000 frame per second might be obtained in the future. This roadmap indicates a bright future of optical computing for matrix convolution, which might take up 80% of total computing power required in deep-learning neural network.

Here, we proposed an arbitrary hybrid analog-digital coding method which can realize high-precision digital optical convolution calculation. In this framework, the initial high-bit matrix can be decomposed into a series of low-bit encoding matrices in temporal or spatial sequence. And the final convolution result is a hybrid analog-digital matrix and obtained after decoding similar to binary-decimal conversion. As an example, we implement the analog and digital convolution calculation of two 10×10 matrices in the optical convolution calculation system. Compared with analog optical computing, this coding method is further capable of improving the optical convolutional computing accuracy of large-scale matrices.

Bragg hollow-core PMMA tube waveguides with varying grating structures were theoretically and experimentally investigated for the terahertz (THz) chemical material sensor applications. Compared with single-layer tube, the multi-layer Bragg cases can produce a delayed response in the time domain with an improved extinction ratio. A double tube combination consisted of a thick double-groove chirped grating tube and a thin single-groove chirped grating one can realize an improved detection sensitivity. With different extinction ratio of the measured THz spectra, ethanol and vinegar can be distinguished with a sensitivity of about 18 dB/mL. The proposed multi-layer hollow-core grating waveguide can be further applied for the THz gas sensing applications.

In traditional lensless in-line holographic microscopy, phase recovery based on multi-defocus distance is a common pixel-super-resolution technique. This method usually requires accurate displacement as a predictive condition, and the introduction of a precision mechanical displacement platform can bring about accurate displacement, but makes a simple lensless system complicated and expensive. In this paper, the samples are illuminated by a nearly coherent illumination system, and holograms at different heights are captured by the sensor driven by a low-cost servo motor without feedback system. Inaccurate displacement interval results in poor phase recovery. We propose a multi-height phase recovery algorithm based on z-axis correction to recover the phase information of the sample, which can improve the result by 1.58 times compared with that before correction. The reconstruction USAF target demonstrates a half-pitch lateral resolution of 775 nm across a large field-ofview of ∼29.84 mm² , surpassing 2.15 times that of the theoretical Nyquist–Shannon sampling resolution limit imposed by the pixel size of the imaging sensor （1.67 μm）.

We propose a hybrid algorithm based on genetic algorithm (GA) and ant colony optimization (ACO) for optical focusing inside/through scattering media. The hybrid algorithm has the basic structure of a GA, where the offspring generation procedures (i.e., parent selection and crossover) are replaced by the path generation procedures in ACO. The GA-ACO is advantageous by the rapid discovery of good solutions from ACO and enhanced solution diversity from GA. Therefore, the algorithm has a strong ability to search for a global optimal solution quickly, and experimentally we can achieve optimization results approaching the theoretical optimum.

Digital Holography microscopy is a widely applied technique in biological imaging for retrieving quantitative phase information relating to a samples three-dimensional morphology and has received considerable interest in the investigation of real-time cellular dynamics. However, the traditional off-axis architecture has drawbacks in terms of a requirement for frequent calibration when the sample is changed as a consequence of the optical path length variation. This inconvenience can be overcome using a common-path design microscopy. Here we report on a portable module utilizing an off-axis architecture and an inexpensive laser diode source. The portability of the system enables it to be added to easily to the output port of an existing life-science microscope. An important feature of the module is that it is based on the self-reference principle, whereby the reference wavefield is generated from the image wavefield that is exiting the microscope image port using a suitable beam splitter and filter. This facilitates the source laser to be completely decoupled from the module. We investigate the application of the module to image samples of cells prepared using a common pathology slide preparation method known as ThinPrep, which is often used to prepare ovarian cancer, urine/bladder, and oral cytology samples for diagnostic inspection and to provide quantitative morphological information. In particular, we are interested in imaging samples that are fixed and air dried such that no mounting medium or coverslip is present, with the motivation of recording phase images immediately prior to cell staining and mounting.

A hybrid optimization model of physical optics and geometric optics is implemented for optimizing the imaging brightness uniformity by changing the profile depth distribution of a grating-based exit pupil expander (EPE). A specially modified reactive ion-beam etching system capable of modulating the etching depth distribution in two orthogonal dimensions is used to fabricate crossed-grating-based EPEs with variable profile depth. Two EPEs with uniform profile depth and optimized variable profile depth are fabricated and measured. The results show that compared with using the EPE with uniform profile depth, using the EPE with optimized variable profile depth, the imaging brightness uniformity can be improved by 37.8%.

We present a spectrum filtering approach for reconstruction of off-axis digital holograms. The high frequency aliasing terms in Fourier spectrum domain of hologram are generated by non-fitting interpolation. After interpolation processing, the zero-order terms in the aliasing spectrum region are obviously suppressed. Accordingly, for the spectrum filtering of high-frequency signal terms, the available range of frequency band will increase significantly, which can result in the improvement of resolution of the reconstructed images. In order to avoid the effect of non-uniform distribution on the aliasing spectrum terms, all the same-order signal terms in the aliasing spectrum (positive or negative first-order spectrum) are intercepted, respectively, and then added together to reconstruct the complex amplitude distribution of the sample. We perform the reconstruction imaging with a conventional method and the presented method from the same hologram in simulation. The imaging results show that such interpolation method can obviously improve the resolution of the reconstructed amplitude and phase images. This method for off-axis digital holographic reconstruction only relies on a single frame acquisition to achieve high resolution reconstruction imaging without additional requirements to the optical setup, which will have a promising application in real-time imaging for living biological cells or moving objects.

Benefitting from properties including high sensitivity, high resolution, immunity to electromagnetic interference and remote sensing ability, optical-grating-based displacement measuring technologies have been widely used in many fields such as semiconductor manufacturing, precision machining, microscopic techniques and photolithography recently. In this work, high-resolution displacement measuring is demonstrated with an ultracompact structure consist of only a few optical components by using self-interference effect of a single nanograting. The resolution is demonstrated to be as low as 0.1-nm level. This method shows great potential in developing miniaturized high-resolution displacement devices and systems, which are highly demanded for future integrated high-precision machinery manufacturing systems.

In this paper, automatic filtering for amplitude and phase reconstruction in off-axis digital holography is developed. A user-friendly interface for automatic filtering is given via program design with MATLAB. The hologram to be processed is input at the front end, and automatic spectrum filtering in Fourier spectrum domain of digital holograms is realized by using clustering algorithm at the back end. The amplitude and phase images are reconstructed from the intercepted spatial-frequency spectrum by using the reconstruction algorithm. This automatic filtering program has high robustness, which can achieve reconstruction imaging for off-axis holograms correctly and effectively in the case of different off-axis angles or different image sizes. For the user interface, upon inputting an off-axis digital hologram and confirming the operation, the reconstructed amplitude and phase images can be quickly output. This user interface has the advantages of simple operation, adjustable parameters and clear feedback. Since K-means clustering is used, this filtering algorithm increases the efficiency in processing experimental data and the reliability of reconstruction imaging. The digital hologram computer-generated is used to simulate filtering processing. The results show that the quality of reconstructed images by using the presented automatic filtering is not inferior to that by conventional manual filtering.

In this paper, we present a method to eliminate the zero-order term in Fourier spectrum of off-axis digital holograms based on the linear change of the hologram. In a typical digital holographic setup, the three off-axis holograms are recorded by the object waves and the reference waves with the different intensity ratios. The three holograms were Fourier transformed, and then the spectra were linearly fitted to obtain two fitting coefficients. Then, the second and third holograms are multiplied by the corresponding coefficients, and the first hologram is subtracted from the hologram that is multiplied by the coefficient to obtain the hologram with the zero-order term eliminated. In the procedure of spectrum filtering, more high-frequency information can be intercepted in this spatial-frequency spectrum after removing the zero-order. The experiment results show that this method can obviously eliminate the zero-order term.

In this paper, we propose a method to realize complex amplitude modulation with a 4-level phase plate and an amplitude-modulated SLM. We implement this complex amplitude modulator system in classical 4f system and use this system to realize highly precise convolution to verify its feasibility. The optical convolution accuracy is higher than the phase-only modulator or the amplitude-only modulator method. We then incorporate this system with a one-layer CNN as its convolutional layer to accomplish a handwriting recognition inference, the image classification accuracy is also comparable to all-electrical result with the same framework.

Holographic stereogram opens up a new way for holographic 3D display of objects, and has high research value and significance in commercial, military and other aspects. In order to write real and virtual three-dimensional (3D) scenes in holographic stereogram at the same time, so as to achieve the display effect of augmented reality, a light field fusion method is proposed. The basic principle of light field fusion is introduced. The light field sampling is introduced and completed, and depth image based rendering (DIBR) algorithm is applied for regularization and densification of sampled images. The projection relationship of the light rays are analyzed, and the pixel level light field fusion is accomplished. Effective perspectives segmentation and mosaicking (EPISM) holographic stereogram printing method is used to write and reproduce the fused light field which further verifies the effectiveness of the proposed method.

Thanks to the precise control of the amplitude, phase and polarization at the subwavelength scale, metasurfaces have attracted tremendous attention on achieving multifunctional applications, such as metalens[1], meta-holograms [2], vortex generators [3] and so on. In order to multiplex multiple information in a single metasurface, various channels of metaholograms have been explored, including color channel in near or far field, amplitude channel, polarization channel, and position channel [4-8]. However, the polarization channel in far field has not been deeply investigated. Due to the ignored phase of reconstructed holograms in far field, the polarization at the overlapping area of different meta-holograms is generally distributed randomly. Actually, the phase difference plays an important role in determining the vectorial distribution. Up to now, only a few work has explore the importance of controlling the phase difference in far field [9-11]. Here, we study the relationship between the phase distributions in both near and far field and proposed a flexible strategy to multiplexing holographic images with a dielectric metasurface that can encode vectorial holographic images in far field via the controllability of phase difference of two arbitrary holographic images designed for the right circular polarized (RCP) light and left circular polarized (LCP) light on the imaging plane.

We propose an attention-based deep convolutional neural network for computer generated hologram (CGH) compression, where a channel attention mechanism is applied to both computer generated hologram compression and reconstruction. By applying deep convolutional neural networks in the compression process, we can extract more compact and representative information than bicubic interpolation. Additionally, a channel attention mechanism is applied to selectively emphasize informative features and suppress less useful ones for both CGH compression and reconstruction. By employing attention mechanisms to enhance the feature representation ability of deep convolutional neural networks, we can further improve the performance of the reconstructed computer generated hologram. Experimental results show our method can better recover the compressed computer generated hologram than only employing convolutional neural networks in the reconstruction process.

A method for compressing computer-generated holograms (CGHs) using genetic algorithm optimized quantum-inspired neural network is proposed. Genetic algorithm is a global optimization algorithm, which can provide better initial weights for the quantum-inspired neural network. The global optimization ability of genetic algorithm is combined with the local optimization ability of the quantum-inspired neural network enables the network to achieve better convergence effects. Under different compression ratios, CGHs are compressed by the genetic algorithm optimized quantum-inspired neural network and the quantum-inspired neural network respectively, and Fresnel transform technology is used to reconstruct the decompressed CGHs. The experimental results show that the genetic algorithm optimized quantuminspired neural network can obtain better quality reconstructed images than the quantum-inspired neural network while using fewer learning iterations.

Imaging spectrometer is an important optical instrument for monitoring the content of carbon dioxide (CO2) in the atmosphere. Using an immersion grating as the dispersive element in the spectrometer can significantly reduce the size of the grating while maintaining the same spectral resolution. The immersion grating with dielectric film is one of the key elements in greenhouse gases imaging spectrometer. In this paper, the quartz immersed grating was designed for weak CO₂ band. The rectangular groove structure with high refractive index dielectric film was designed in consideration of possible fabrication errors. In the 1.595 ~ 1.625 μm band, the duty cycle of the rectangular groove is 0.3 to 0.35, the thickness of TiO₂ is 110 to 125 nm, and the grating groove depth is 560 to 640 nm, the diffraction efficiency can reach more than 80%. When the duty cycle is 0.4~0.45, the TiO₂ thickness is 95~105 nm, and the grating groove depth is 570~700 nm, the diffraction efficiency can reach more than 80%. For the trapezoidal groove, when the duty cycle is 0.3~0.35, the bottom angle of the trapezoid is 82°~86°, the thickness of TiO₂ is 120~125 nm, and the grating groove depth is 565~620 nm, the diffraction efficiency can reach more than 80%. When the thickness of TiO₂ is 115~120 nm, the overall degree of polarization is less than 0.1.The immersed grating with the period of 697nm in a quartz substrate of 245 mm × 138mm will be fabricated by holographic lithography - ion beam etching in late 2021. The TiO₂ film will be deposited by atomic layer deposition.

Computational imaging opens up new ideas for complex system imaging solutions from the level of information generation and transmission. Based on the modeling of super-resolution technology, computational power is introduced into the traditional imaging in order to break through the limitations of this kind of photoelectric information processing. And the available configurations from single sensor to composite sensor are explored, and the global optimization and the system complex structure that control methods are fully used to solve the adaptive design problems of the composite linear compensation multi configuration systems. And the criteria group have shown the significant improvement of system resolution, which can be used as an important basis for engineering application.

The harmonic sawtooth microstructure allows the diffractive lens to operate with polychromatic radiation, in particular, with the radiation of RGB LEDs, but only with restrictions due to axial color and specific field curvature. Its reason is the jump in the working diffraction order with an increase of the wave angle of incidence. The permissible wave angles of incidence at the microstructure were estimated using the example of a harmonic diffractive lens made of crown-like plastic E48R.

As an increased demand in high resolution display, the pixel size in the image sensor is reduced to increase the resolution. Although there have been recent studies on metasurface color routers to overcome the limitation of the conventional image sensor, there are still limitations in that the designed devices do not show the advantages of router or are difficult to fabricate. In this study, the fabricable metasurface that distribute three visible wavelengths to each targeted color sensor is proposed numerically. For the distribution like the Bayer pattern, a dual focal phase profile is utilized for green color. The designed metasurface size is 2 μm by 2 μm, and the routing efficiencies are 12 %, 25 %, and 30 % for 473 nm, 532 nm, and 660 nm, respectively, where the performance in red light exceed the fundamental limit of efficiency of the conventional Bayer color filter array.

Our current work discusses an alternative cost-effective method for producing elliptical zero-order Bessel beams with a simple optical system based on a commercially available transmission grating. A zero-order Bessel beam is made to pass through a diffraction grating with a groove density of 600 lines per mm. An elliptical Bessel beam intensity profile is obtained with the 1st-order (m = 1) diffracted beam when the grating is rotated about an axis parallel to the grating vector. For a grating tilted by 20 deg from the vertical, non-diffraction of the elliptical Bessel beam is observed over a propagation range from 10 to 95 cm with an average core diameter of 404 um. The elliptical Bessel beam at m = 1 has an eccentricity of 0.6 for a grating tilt of 20 deg.