This PDF file contains the front matter associated with SPIE Proceedings Volume 12768, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Accelerating computer-generated holograms (CGHs) is crucial for practical three-dimensional (3D) displays with electro-holography. The authors developed a fast CGH calculation algorithm that focuses on projecting only 3D wireframes because the formulas or algorithms for generating CGH become simpler and, in many cases, the expressivity of the wireframe is sufficient to provide users with all necessary information, such as which direction to move in a car navigation system. In this presentation, we provide an overview of how to accelerate the CGH calculation of wireframe art and discuss our future research directions with respect to the remaining issues.

It is realized that real time 2K (1,920 x 1,080 pixel) full color image hologram display with a transmission liquid crystal panel which is taken from low-cost video projector. The liquid crystal panel is 70 mm (2.76") diagonal size with RGB color filter and polarizers. Therefore, full color hologram can be reconstructed with a white light LED and a lens. Although the pixel pitch of the panel is 31 μm that does not provide binocular observation, it is suitable for near-eye or eye-tracking type display. With real time hologram generation program running on a note PC, holographic video display can be realized easily.

Volume holographic storage technology expands two-dimensional storage to multi-dimensional high-density storage, which can realize the advantages of large data storage capacity and fast data transmission speed. For holographic storage, material selection is very important. Photoinduced polymers are considered as one of the most promising holographic storage materials due to their high resolution, real-time recording and rapid preparation. Among them, phenquinone doped polymethyl methacrylate (PQ/PMMA) photoinduced polymer has negligible shrinkage rate, sensitivity to light polarization, anisotropy and other properties, and can be preserved for a long time, which is a good choice for holographic storage materials. However, due to the low solubility of PQ in methyl methacrylate (MMA), the diffraction efficiency and sensitivity of the material are still limited, which cannot meet the requirements of high speed writing of holographic stored data. In this paper, vinylpyrrolidone (NVP) monomer was introduced into PQ/PMMA photoinduced polymer system. Because PQ has better solubility in NVP, doping NVP monomer into the original system can increase the concentration of PQ from 1.0wt% to 1.2wt %. Compared with the basic PQ/PMMA materials with 1.0wt% PQ, the photosensitivity of the NVP-PQ/PMMA material are increased by 2 times (from 0.35 cm/J to 0.70 cm/J), and the diffraction efficiency are increased by 20%(from 57% to 77%). Finally, by using NVP-PQ/PMMA materials in collinear holography systems, holographic data storage can be achieved faster and with lower bit error rate than basic materials. In conclusion, the introduction of vinylpyrrolidone (NVP) monomer into PQ/PMMA photoinduced polymer system effectively improves the holographic properties of the material and has the potential to be an excellent holographic storage material.

Distinguishing an authentic hologram from a replicated one presents a notable obstacle, chiefly attributable to the factor of reflectivity. A hologram's reflection pattern can undergo a significant transformation due to even a minor variation in lighting conditions. As a result, the creation of a standardized duplicate hologram detection device has proven to be difficult to achieve. The present study proposes a new methodology for distinguishing between genuine and replicated holograms. This is achieved through the utilization of a portable and economical housing module that employs snapshot hyperspectral imaging (HSI) algorithm. The proposed module comprises a Raspberry Pi 4 processor, a Raspberry Pi camera, a display, and a light-emitting diode lighting system equipped with a dimmer. By employing a visible HSI algorithm, the RGB image captured by the Raspberry Pi camera can be converted into a hyperspectral image. Following this, a particular area of focus is designated within the spectral image, and assessments are conducted to determine the average gray value (MGV) and reflectivity. The experimental results indicate that shorter wavelengths are most suitable for differentiating holograms when utilizing MGV as the classification parameter. On the other hand, the utilization of reflectivity for discrimination is more efficient with longer wavelengths. The distinctive attributes of this design encompass its affordability, simplicity, absence of moving parts and the absence of a requirement for an additional decoding key. Subsequent research endeavors may delve into additional improvements and modifications aimed at maximizing the efficiency of the housing module and broadening its scope of potential implementations.

The introduction of nanoparticles into photopolymers has been proven as an effective approach to enhance the holographic performance of photopolymers. Among these nanoparticles, nano-diamonds (NDs) with high hardness, stability, and refractive index represent an ideal doping component. In this study, we investigate the impact of doping different concentrations of ND nanoparticles on the holographic performance of Irgacure 784/PMMA photopolymers. The doping of ND nanoparticles leads to significant enhancements in diffraction efficiency for the photopolymer samples. Notably, photopolymers doped with 0.5×10^-3 wt% ND nanoparticles achieve a maximum diffraction efficiency of approximately 87%, nearly doubled when compared to undoped photopolymers. Subsequently, holographic imaging of real objects is conducted on ND-doped photopolymers. Experimental results show that our investigated polymers have high peak diffraction efficiency and is capable of reconstructing high-quality and stable holographic reconstructed images. This investigation shows enhancement of holographic performance by doping ND nanoparticles into the photopolymer, providing a new pathway for the further advancement of holographic technology and significant guidance for designing high-performance holographic recording materials.

A high-resolution computer-generated hologram can be displayed on a low resolution spatial light modulator with a high-resolution mask attached. Three different masks are discussed here. The regular grid down-sampling (RG) mask, the regular grid jittered down-sampling (RGJD) mask, and the asymmetrical regular grid jittered down-sampling (A-RGJD) mask. We found the RGJD method can retain the high-resolution information but also produce significant noise. By contrast, the RG method can produce clear image with reduced bandwidth. The two methods can be combined as the A-RGJD method, in which the horizontal bandwidth of the object remains large, and the noise is well controlled.

This article describes experiments to create a sensitive element of a holographic wavefront sensor. The changes made made it possible to record wavefront aberrations in the Zernike polynomials on holograms and reliably reproduce them with a reference beam.

The principle of computer-generated holograms (CGHs) for holographic displays is to use the computer to simulate the propagation of light and obtain the wavefront information of an object on the hologram plane. In recent years, algorithms for CGHs based on physical diffraction models have been gradually developed and improved. Hologram calculation methods based on points, lines, polygons and layers have been proposed, named the point-source method, the wireframe method, the polygon method and the layer method, respectively. All the four methods simulate and accumulate the physical diffraction process of the elements, i.e. points, lines, polygons and layers. Their numbers of elements differ greatly, and the reconstructed images have their own features. The type and number of elements affect the calculation speed and reconstruction quality of the hologram. This paper introduces the principles and research status of these four methods and analyze their characteristics. The total calculation time and the average elementary calculation time of the four methods are compared through numerical experiments using the same model. The calculation speed and reconstructed image quality of different methods are evaluated by the equivalent-sample-point method. This paper hopes to provide a guidance and a reference for future research on hologram calculation.

Microelectromechanical systems (MEMS) are electronic devices with movable micromechanical structures, which possess morphology and deformation in scales difficult to observe by traditional microscopic methods. In this paper, the surface morphology and deformation value of MEMS with complex structure was recovered by digital holographic technology, and the high precision detection of MEMS was realized. The local magnification was carried out through the microscope objective lens, and the magnification was calibrated by the resolution test chart. Due to the introduction of spherical wave by the magnification of the objective lens, this paper carried out the elimination of the quadratic term error. The shape of the comb tooth was reconstructed by setting a mask in the phase disturbance area. The deformation of the surface before and after voltage applied was measured, and the actual displacement deformation value was solved.

Optimized method of complex-amplitude holographic display and computer-generated holograms (CGHs) based on complex-valued convolutional neural network are presented. The wavefront frequency decomposition is carried out on the object light wave to generate two frequency images. The low frequency image is determined by amplitude CGH loaded with an amplitude spatial light modulator (SLM). The high frequency image is decided by phase CGH loaded with a phase SLM. The mentioned two sub-holograms are reconstructed and integrated at the identical location, and the amplitude and phase information are enhanced. Complex-valued convolutional neural network (CCNN) is used for real-time CGH generation. Complex-valued convolutional and ReLU layers are combined in CCNN, which is designed based on the feature of complex amplitude. Instead of processing amplitude and phase respectively, CCNN processes the complex amplitude directly. CCNN-CGH architecture can generate 1920×1072 and 3840×2160 resolution CGH with an average PSNR of more than 30dB in real-time. The speckle noise in display images is reduced, which gives the credit to the reconstruction of complex-amplitude modulation. The experimental results show that the method simultaneously enables high image quality and efficient calculation to be provided, which is more suitable for the real time 3D display. The quality of reconstructed images can be noticeably improved.

As an important three-dimensional (3D) display technology, holographic 3D display has great application prospects in virtual and augmented reality applications. However, it has been challenging to generate 3D hologram rapidly with high‑reconstruction quality. Here, we proposed a high-speed 3D hologram generation method via convolutional neural network (CNN). The CNN network is trained by unsupervised training, and the trained CNN can generate 3D hologram with 1024×1024 resolution at 100 planes within 60 ms. The feasibility and effectiveness of the proposed method have been demonstrated by simulation. This method will further expand the application of holographic 3D display in remote education, medical treatment, entertainment, and other fields.

Holography always records the 3D object information via interference and then reconstructs the 3D object via diffraction. A holographic optical element (HOE) can be fabricated by analog holographic exposure or digital holographic printing. Since HOE can be recorded on a thin plate or film of holographic material, it is always utilized as a combiner for augmented reality near-eye displays to achieve a compact form factor. The traditional method of HOE fabrication is to divide a coherent light beam into both a signal beam and a reference beam, and then make both beams meet at the holographic material for interference. The optical path of the traditional fabrication system employs more optical devices with complex optical designs. Therefore, a HOE fabrication system based on common optical path interference is proposed in this paper. This paper presents the eyeglass-style HOE fabrication method based on common optical path interference. The HOE fabrication system with a common optical path is designed with fewer optical devices and less vibration effect. As the reference beam, the incident beam illuminates the hologram film. Part of the incident beam passes through the film and is reflected by the curved mirror to illuminate the hologram film from the other side, which works as the signal beam. The crucial device of the proposed system is the curved mirror. We analyzed the effects on HOE fabrication using an off-axis parabolic mirror and a spherical mirror. The experiment finally fabricated the HOEs and verified them for the AR near-eye display.

Phase space can be used for generalization of optical signals in high-dimension representation. In this study, from the perspective of phase space defined by space and spatial frequency, the near-eye display (NED) systems are unified as how to generate the optimal space-bandwidth product (SBP) distributions required by the human eye on the exit pupil plane. The microdisplay and NED optical system are equivalent to the input SBP and the SBP modulator, respectively. The input SBP is modulated by the NED optical system, and finally reaches the exit pupil plane to generate the desired SBP distribution. The proposed method can fully describe the performance of different NEDs, such as the field of view (FOV), exit pupil diameter (EPD), uniformity, display depth and ray aberration, etc. This unified phase-space analysis framework provides a brand-new approach for the classification of current near-eye display systems and the design of future near-eye display systems, especially the high-quality 3D display.

Generation of dual-combs in frequency shifted feedback laser seeded only with optical amplifier spontaneous emission and containing single frequency shifting loop with single acousto-optic tunable filter as the frequency shifter is demonstrated. It is also shown that it is possible to obtain a pair of dual-combs simultaneously and to implement further down-conversion achieving the frequency spacing between the spectral components of the resulting optical comb equal to the frequency difference of these dual-combs and amounting to several tens of kHz. The OFC with 40 kHz frequency spacing containing more than 5000 spectral lines was observed. It is demonstrated that the generated dual-combs may be applied for optical materials refraction coefficient measurements.

This article describes an experimental study of the optical vortex generation with the use of light that was reflected from the combination of two cube-corner reflectors (retroreflectors) and its analysis in far field. The main goal of our research was to confirm the theoretical data from the article. Shearing interferometer was used for optical vortex detection and analysis. Our previous studies were focused on cases with linear polarization forming a polarization vortex. This time we were using light circular polarization to produce an optical vortex with m=2.

Digital holographic microscopy (DHM) is a typical quantitative phase imaging technique, in which the entire complex wavefront information is interferometrically encoded as a fringe pattern (so-called hologram) and then quantitatively demodulated by fringe analysis methods. Yet the off-axis digital holographic phase demodulation typically requires sufficiently high carrier spatial frequency for separating ±1-order and 0-order spectrum in the Fourier domain, limiting the space-bandwidth product (SBP) of the system. The in-line holographic configuration can realize full detector-bandwidth phase reconstruction at the cost of time resolution. In this work, we proposed a high-accuracy artifacts-free single-frame low-carrier frequency fringe demodulation scheme for the slightly off-axis digital holography, optimizing the system’s SBP effectively. This scheme acts as a method of deep-learning assisted physical model, incorporating a convolution neural network into a complete physical model by the idea of residual compensation, which enhances the imaging precision of the physical method while promises the interpretability of deep learning. The effectiveness of the proposed method is quantitatively analyzed through numerical simulation and experimentally verified by live-cells experiment. The phase recovered accuracy can be improved by one order of magnitude (the MAE up to 0.0065) compared with the traditional physical method. The live-cells experiment demonstrates the practicality of the method in biological research. Furthermore, it’s worth noting that the proposed method achieves a higher reconstruction accuracy utilizing only a small fraction of the datasets of the classical end-to-end deep learning model (without a physical model). The proposed deep learning-assisted physical model idea in this article is expected to bring more solutions for diverse computational imaging techniques.

Deep learning is an emerging technique for computer hologram generation, and the training dataset is critical for the quality of the learning-based hologram. In this study, we propose a phase hologram generation method based on a deep neural network (DNN) trained with Fourier basis functions. As the training dataset is generated by recombining the Fourier basis functions, its statistical frequency characteristics can be directly manipulated to improve the performance of DNN. With this physics informed training strategy, the external generalization of the model, as well as the image quality of the holographic reconstructions, can be improved. Experiments demonstrate that the proposed method is effective for achieving high-quality optical reconstructions.

In this paper, We propose a highly parallel optical matrix convolution architecture based on optical Fourier transform (OFT). The matrix multiply-accumulate (MAC) operations consists of matrix multiplication and addition. In the matrix multiplication section, the light intensity signals of matrix A and matrix B carried by two SLMs are used. Matrix C is obtained by matrix multiplication by projecting the uniform light intensity of matrix A onto matrix B through a Dammann grating (DG). The matrix C is received by a CMOS camera after a lens, and the spot array of matrix C is summed up, The convolution results of matrix A and B are obtained. This matrix convolution architecture provides an interesting method for large-scale matrix convolution. The optical matrix convolutional architecture has advantages such as high parallelism, high accuracy, and low power consumption. In the future, the optical computing will be perfectly applied in areas such as deep learning algorithms.

After decades of development, artificial neural network has become one of the most important research directions of artificial intelligence, and has a wide range of applications and important value in computer vision, natural language processing and other fields. Today, most of the applied artificial neural networks are based on von Neumann electronic hardware. As the semiconductor process approaches the physical limit, the performance growth encounters bottlenecks, and the power consumption problem is difficult to solve, limiting the application and further development of deep learning. Optical neural network provides a way to break through the bottleneck due to its high speed, high parallelism and low power consumption. At present, most optical neural networks are difficult to expand the depth of the network and have limited performance. In this paper, a multilayer optoelectronic hybrid convolutional neural network with an optical 4f-system recurrent structure is proposed. The electronic convolutional layer is replaced by an optical convolutional layer based on the 4f system, and the depth of the neural network is extended by the recurrent structure of the 4f system to improve its performance. Experiments show that the recognition accuracy of CIFAR-10 dataset of the proposed hybrid neural network is close to that of a corresponding electronic neural network. This work provides a possible way to build a deeper optoelectronic hybrid convolutional neural network when dealing with complicated problems.

This paper reviews recent advancements in digital holographic microscopy, whereby a simple and inexpensive module can be added to an existing life science microscope to imbue it with quantitative phase capabilities while leveraging on the utility of pre-existing functionalities such as fluorescence imaging. Common-path interferometry is one such approach, whereby both the reference and object wavefield propagate through the same optical elements. Other approaches employ beamsplitters to separate the paths. A key feature of many of these both cases is the principle of self-referencing, whereby a clean reference plane wave can be produced from a copy of the object wavefield. As well as review the basic principles of digital holographic microscopy in general, we review the various variants of modular digital holographic microscopy that have been proposed over the past decade and offer insights into their performance and limitations.

Coherent diffraction imaging (CDI) is an alternative way to achieve high performance, obviating the necessity for high-quality imaging lenses. A high degree of coherence of the source is essential for CDI. Coherent modulation imaging (CMI) improved CDI's algorithmic convergence and applicability to general samples. Here, we proposed a single-shot broadband phase retrieval method to increase the tolerance to low temporal coherence by employing the deconvolution approach with the CMI. The feasibility of broadband coherent modulation imaging (bCMI) was verified with optical experiments. This work could pave the way for implementing CMI on laboratory x-ray sources or electron microscopes.

We propose and experimentally demonstrate a technique for the single-shot imaging through a scattering medium based on speckle correlation assisted digital in-line holography. The proposed method enables the reconstruction of the complex amplitude information of the object located at any arbitrary planes behind the scattering medium by retrieving the digital in-line hologram. The technique exploits the potential of speckle correlation approaches and machine learning schemes for the efficient reconstruction of complex amplitude information from the digital in-line hologram scrambled in the speckle pattern. The complex amplitude imaging capability of the proposed technique is theoretically introduced and experimentally validated by imaging various standard and unknown objects.

In this work we review the implementation of phase-only diffraction gratings on phase-only liquid-crystal spatial light modulators for full amplitude, phase, and polarization control. First, we review designs of continuous phase profiles that generate arbitrary number of diffraction orders with customized relative intensity and phase. Then we extend the technique to consider their application to generate polarization diffraction gratings, by combining arbitrary phase gratings affecting orthogonal polarizations. We show how these gratings can be experimentally produced with liquid-crystal spatial light modulators.

Polarization grating (PG) divides the incident wave into the left- and right-handed circularly polarized waves, the intensities of two waves depending on the state of polarization of incident wave. Large deflection angle of the commercial PG is usually made by the grating cascade due to the limit of grating period. While using the tensor polarization holography theory, arbitrary deflection angles of PGs have been designed, where the polarization-sensitive material phenanthraquinone-doped polymethyl methacrylate (PQ/PMMA) is utilized as the recording medium in our experiments. We have made PG with the deflection angle of 40°.

Fresnel zone aperture lensless imaging encodes incident light into a hologram-like pattern. However, the uncertain target distance leads to a blurry image with artifacts, which brings challenge to the estimation of object distances. We proposed an autofocusing method for FZA lensless imaging which is a superior solution for distance estimation. The image sharpness metrics are incorporated into the back-propagation process to obtain the focusing distance and reconstruct high-contrast and noise-free images. The Tamura gradient, nuclear norm of gradient and the gradient of the image are combined together to obtain a new evaluation metric. The acquisition accuracy is higher and the time is faster by using this new metric to obtain the focus distance. The proposed method paves the way to the micro sensors.

Various methods for implementing triplicator diffraction gratings in a pixelated liquid-crystal display (LC-SLM) are discussed. The optimum design features a continuous phase profile. We analyze the limits imposed by the quantization inherent to the LC-SLM when a low number of pixels per period is required, that affect the performance of the displayed triplicator gratings. The binary-phase grating with proper phase shift proves to be a simple alternative with good diffraction efficiency. Also, a random approach provides a triplicator with less efficiency but free of higher harmonics.

The propagation of optical beams through turbulence presents a significant challenge in various applications. This article explores recent advancements in the generation of stable optical beam (STOB) in turbulence, employing the innovative mechanism of transverse wave vector elimination. STOB, generated by the spatial light modulator, offers compelling advantages over conventional Gaussian beams for the privilege of peak intensity, robust propagation, extended depth of focus (DOF) beam profile, and dynamic wavefront modulation over a long distance under strong turbulent media. These findings hold immense potential across a wide range of applications and have the capability to promote the development of novel technologies aimed at mitigating turbulence-induced effects in free-space optical communication system.

A low-loss and wideband silicon polarizing beam splitter is demonstrated with the assistance of a nano-bridge waveguide. Transverse magnetic light can be coupled to the cross port through the nano-bridge waveguide, while the transverse electric light comes out mainly from the through port. The designed device has a coupling length of 19.6 μm, which can realize an extinction ratio of 32.43 dB for TM mode or 34.23 dB for TE mode at a 1565-nm wavelength. Compared with the conventional three-waveguide coupler structure, the proposed device is based on a resonant tunneling principle, which can help to effectively improve the fabrication tolerance. The device is fabricated with a commercial CMOS processing facility, which can achieve an extinction ratio of 23.07 dB for TM or 23.46 dB for TE mode with a low excess loss, and the extinction ratio of more than 10 dB can be realized in the wavelength range from 1525 to 1610 nm for both modes. The device performance can be further improved, which would facilitate its practical applications in commercial integrated optical circuits.

Holographic optical element (HOE) are widely used due to their lightweight, miniaturization, and multifunctional characteristics. However, making HOE that can be applied in the infrared band is a challenging task, especially when HOE has multiple function. This paper proposes a design and fabrication method for a near-infrared multifunctional HOE that can be recorded using visible light. The three recording beams of this multifunctional HOE include a plane beam and two spherical beams. Therefore, on the basis of achieving beam redirection, it can also achieve beam splitting and the convergence of each split beam. To solve the problem of wavelength mismatch while achieving multiple functions of HOE. The decrease in diffraction efficiency caused by wavelength shift is compensated by the angle shift of recording light. The wavefront aberration caused by wavelength mismatch is compensated by introducing a cylindrical lens in the recording optical path. The multifunctional HOE has the potential to be used in infrared optical systems to achieve system miniaturization, and this paper provides an application example for laser Doppler velocimeter (LDV). The designed HOE successfully achieved two sets of stripes with opposite slopes in the measurement volume of LDV at different working wavelengths, proving the feasibility of the design and fabrication methods. Furthermore, the method proposed in this paper can provide reference for the design and fabrication of other HOEs working in the near-infrared band.

Fourier ptychographic microscopy is a new computational imaging method developed in recent years, which can obtain the complex amplitude information of the sample simultaneously maintaining the large field-of-view and improving the imaging resolution. Meanwhile, the diffraction tomography technique can realize the three-dimensional (3D) refractive index imaging of the object. So, the combination of Fourier ptychographic microscopy imaging and the diffraction tomography algorithm can obtain high-resolution 3D complex refractive index distribution of thick samples. In visible light, recent studies have shown that diffraction tomography reconstruction algorithms based on the multi-scattering forward propagation model can overcome the limitations of the Born/Rytov approximation and reduce the impact of multi-scattering effects on the reconstructed refractive indices of 3D objects. In this paper, we propose a method to accurately describe the image acquisition process of the FPM system using a multiple scattering forward propagation model, and then combine iterative optimization methods to obtain high-quality diffraction tomography reconstruction results. The multiple-sphere sample is employed to do the simulation, and the results show that the method can effectively solve the multiple scattering problem inside complex structure samples and obtain better reconstructed results than traditional diffraction tomography reconstruction algorithms for samples that do not meet the Born/Rytov approximation requirements. The method provides a new perspective on image recovery methods for Fourier ptychographic microscopy imaging systems.

The frontier research of optics is about to enter the field of picometer optics from the current field of micro-nano optics, and picometer measurement is the key to picometer optics research. If we use a laser interferometer with nanoscale resolution to measure a grating with good periodic uniformity and thousands of periods, then for one single period, the resolution can be obtained at picometer scale. Based on this theory, the interference field period is measured by the SRG (scanning reference grating) method, and the periodic average value of picometer accuracy can be measured when the movement of the grating is monitored with a laser interferometer. When we know the grating period of picometer accuracy, we can modulate the holographic interference field by slightly changing the angle of the two beams of light, and make two exposures to make a grating with a slightly different picometer accuracy period, which we call a picometer comb. When the picometer comb is irradiated by the laser beam, interference fringes are generated along the propagation direction, and its period T is inversely proportional to the period difference Δd of the two-exposed picometer comb. This has far-reaching implications for the future of picometer measurement.

This paper proposed a transmission two-dimensional (2D) slanted grating based on a double-layer cylindrical structure. We used rigorous coupled-wave analysis (RCWA) and simulated annealing algorithm (SA) to optimize the grating parameters. Results show that the diffraction efficiency of the (-1,0) and (0,-1) order exceed 35% under normal incidence in the range of 429–468 nm wavelength for TE and TM polarization. Meanwhile, the total diffraction efficiency can reach up to 78%. We also discuss the tolerances for the grating parameters to ensure high quality manufacturing processes. The relatively large tolerances ensure fabrication of the two-dimensional slanted grating and provides the possibility for practical applications. The proposed 2D slanted grating can be applied to 2D exit pupil expansion, which is of great importance in AR/VR applications.

The diffraction grating is an important optical component in the field of optics, used in various optical instruments. Therefore, researching and analyzing the characteristics of gratings holds great significance. RCWA (Rigorous Coupled-Wave Analysis) is an electromagnetic field solving algorithm applied to periodic structures and is an important tool for grating analysis. This paper proposes a diffraction grating phase calculation method based on RCWA. Using a one-dimensional rectangular aluminum metal grating as an example, it calculates the phase of the incident light after encountering the grating and compares the phase calculation results with those obtained from the KAPPA software. Based on the phase calculation, we propose a method for characterizing grating morphology and detecting defects using the principle of phase change after light passes through the grating, offering new possibilities for grating fabrication quality control.

In the displacement measurement of the wafer stage of the lithography machine, the two-dimensional grating measurement system has attracted much attention because of its short optical path and less impact from the environmental disturbances. Meanwhile, the high-efficiency polarization-independent two-dimensional grating can not only reduce the Abbe error but also improve the signal accuracy. In this paper, we propose a reflective two-dimensional metal-dielectric grating with excellent polarization-independent and high diffraction efficiency. Calculated by rigorous coupled wave analysis (RCWA) , when the incident azimuth angle is 45°, the (-1, -1) order diffraction efficiencies of transverse electric polarization (TE) and transverse magnetic polarization (TM) are 95.6% and 94.9% at 632 nm incident wavelength under Littrow mounting, respectively. The diffraction efficiency equilibrium is 98.9%. The high efficiency of TE and TM polarization makes them have great application potential in 2D grating measurement system (GMS). Furthermore, the structure based on the frustum of a cone performs well in manufacturing tolerance, which provides possibility for practical applications.

In this paper, a grating defect detection system based on the principle of darkfield imaging is proposed for the surface defect detection of existing large-size gratings, and the corresponding mechanical device is built. The device mainly includes two categories: hardware system and software system, of which the hardware system has lighting module, image acquisition and displacement module, and the software system has target edge reconstruction module and target edge detection module. Through the device, the surface defects of two-dimensional diffraction gratings of different sizes and different process conditions (substrate, mask grating, etching grating and coating grating) are automatically detected, and the statistical data of different types of defects are given. Through the analysis and study of the cause, transmittance and how to avoid different kinds of grating defects, whether it will affect the optical performance of grating use.The experimental results show that the proposed system meets the needs of large-size grating surface defect detection and evaluation in terms of accuracy and accuracy of defect detection, and the mechanical structure of the device is simple and compact, which has the potential of industrial large-scale detection. The device is of great significance for evaluating large-size high-precision grating manufacturing technology.

Hyperspectral imaging (HI) technology allows us to obtain the spatial and spectral information of target objects, thus having important and various application prospects among remote sensing detection, military reconnaissance, and other fields. Recently, snapshot HI systems have been favored widely due to their advantages including the miniaturization and the lightweight, to maintain the mainstream of HI technology research. D. S. Jeon et. al. used a single diffractive optical element (DOE) instead of multiple complex elements to modulate the diffractive wavefront which greatly reduce the system volume and be significant application potential in portable equipment and small payloads1. However, the minimum line width of surface micro structure on the DOE is restricted by the current processing capability, which has a negative impact on the wavefront modulation. Consequently, the high-performance DOE design method considering for machinability is an urgent problem to be solved. We proposed a high-performance processable DOE design method which utilizes the physical model to constrain the minimum line width in the DOE surface. By using the end-to-end deep learning method, achieving processable design of DOE has almost no impact on its performance and imaging quality of hyperspectral imaging systems. Proposed model overcomes the processing problem of DOE from a design perspective without sacrificing their functionality. Comparing to the results without the constraint of the physical model, the proposed physical model has significant effects in constraining surfaces.

Atmospheric turbulence has severe influence on laser beam propagations. The well accepted method of compensating for the aberrations in the turbulence is generating a beacon on the target or at the point-ahead location. In most scenarios, the wavelength of the beacon is similar to or shorter than the launched beam. However, when the strength of the turbulence gets stronger, intensity scintillations and wavefront branch points also arise, making it difficult to accurately measure the wavefront. As scintillations and branch points weakens with wavelength increases, it is reasonable to consider using beacons with longer wavelengths to improve wavefront detection accuracy. To further investigate the feasibility of beacons with longer wavelengths, we established a simulation model of wavefront detection and correction in horizontal path under strong turbulence. A split-step multi-phase screen method is employed to simulate the propagations of laser beams. Then a series of simulations with different refractive index structure parameter Cn² and beacon wavelengths are studied. We show that under weak turbulence, the optimal wavelength of beacon is similar to the launched beam, as is widely investigated and concluded. However, beacons with longer wavelength are preferred under strong turbulence, especially with a general wavefront reconstruction algorithm without considering branch points. This research would be helpful to for designing adaptive optics systems to improve beam qualities in strong turbulence with adaptive optics systems.

We present a method of fractional Fourier transform digital holographic recording by setting an extended Lohmann I-type optical setup in the object arm of a typical off-axis digital holographic recording system. In the experiment, the resolution and the field of view for the reconstructed images of a fractional Fourier transform holograms and an image plane hologram are investigated. When the lens focal length meets a certain condition, the reconstruction imaging resolution of fractional Fourier transform holograms is higher than that of conventional image-plane holograms. The reconstruction results demonstrate that the reconstructed images of the fractional Fourier transform holograms have the higher imaging resolution when the fractional order p is closer to 1.

Due to its ease of processing and modulation, pixelated spatial light modulators (SLMs) are extensively used in the applications where wavefront modulation is needed, including holographic displays, optical manipulation, diffractive optics, and beam physics. Many prevailing diffraction calculation methods are predicated on the premise of band-limited input fields, which have been proven to be inefficient and inaccurate when computing the diffraction field of a pixelated SLM in some cases where the influences from high diffraction orders are not neglectable. Here we present a diffraction computation framework for efficient computing of the wave propagation from a pixelated SLM. Numerical and optical experiments are presented to verify the analysis.

In point-scanning microscopy, such as confocal laser scanning microscopy (CLSM), the imaging resolution is limited by the size of the focal spot. Breaking through the diffraction limit by inserting a modulation phase mask in the objective pupil plane is a compact, high efficiency and adaptable scheme. Here, we propose a feedback phase design method based on genetic algorithm to control the 3D shape of the focal spot. The lateral and axial size can be jointly designed for various usages. Simulation and experimental results present the feasibility of this method. The axial size can be decreased by 50% while the lateral size is decreased by 15% simultaneously. This method of 3D super-diffraction limit focusing may potentially be used in CLSM for 3D super resolution imaging.

A deep neural network with differential architecture is proposed to reconstruct turbulence phases from single-shot intensity images of extended targets, and a phase spatial modulator (SLM) is used for wavefront correction. The neural network takes the inputs of an aberrated intensity image and a background image and separates the turbulence phase from the target structure by comparing the high-dimensional features of the two inputs. The SLM is used to simulate atmospheric turbulence in the optical path and for correction of the external turbulent field. This method is verified in the optical path with the flame field.

Digital Holographic Interferometry (DHI) provides a non-contact measurement at the wavelength level of light. Due to the application of the interferometric principle, non-Gaussian speckle noise introduced during the measurement process is unavoidable and is difficult to eliminate. Thus, denoising is critical and affects measurement accuracy. A method for speckle denoising via self-supervised deep learning, based on a Cycle-Generative Adversarial Network (CycleGAN), is proposed in this paper. The method employs unpaired datasets and integrates a 4-f optical speckle noise simulation module to reduce training costs while improving training accuracy. The proposed method was tested on both simulated and experimental data, with results showing a 4.6% performance improvement in PSNR over competitor algorithms. The proposed method has great potential and advantages in DHI studies with huge datasets.

Optical neural networks (ONNs) have the potential for accelerating the inference of AI models, since ONNs have the advantage of high compute speed, and high parallelism. Integrated diffractive optical network for implementing parallel Fourier transforms has been proved efficient and is promising for large scale ONNs. We propose a novel on-chip Fourier transform implementation based on etched concave mirrors, enabling the construction of a photonic integrated 4F system to perform the convolution computation in the Convolutional Neural Networks (CNNs). One of the input vectors is encoded in a modulator array at the object plane, and the Fourier transform of the other vector is encoded in another modulator array at the spectrum plane. We simulated the computing process by the diffractive propagation of the optical field from the object plane to the image plane according to the Kirchhoff's diffraction formula. Finally, we used our simulation system to replace the traditional convolution layers in the electronic system to implement CNNs on three different datasets, Iris- Flower, MNIST and Fashion-MNIST, and obtained 96.67%, 95.6% and 89.4% classification accuracies, respectively, demonstrating comparable performance with the electronic counterpart.

This study proposes a method for reconstructing the wavefront phase of coherent radiation using a physical model of light propagation, instead of Fourier transforms. The method uses a back-propagating beam with a conjugated optical phase to efficiently account for real properties of optical elements. Experimental demonstration is provided of beam formation in a real optical system with a pre-defined transverse intensity distribution with the help of a phase spatial light modulator (SLM), whose state is calculated by using the proposed method on Zemax software for light propagation modelling.

The paper presents the results of developing a technology for direct laser writing of grayscale photomasks on thin (30-50 nm) chromium films. The contrast of grayscale microimages reaches 10, which is comparable to the characteristics of LDW-glass. The technique is based on dependence of chromium oxide layer thickness formed at laser heating on exposure dose. The oxide layer is then used as a analog mask for underlaying Cr film. The written grayscale masks are used to fabricate multilevel diffractive optical elements by the method of grayscale lithography. The photoresist layer was exposed by contact printing through the grayscale mask. Diffractive optical elements with a sawtooth profile depth in the range of 1-4 μm are made. The angle of the backward slope of the diffractive zones was 60 degrees. The article discusses examples of the use of chromium grayscale masks for fabrication of various 3D structures.

Compared with monochromatic holographic displays, color holographic displays have rich depth and color information, which can give observers a more pleasant visual effect. Inspiring by the adaptive weighted GS method, we introduced an optimized iterative method based on exponential weighted constraint to calculate phase-only holograms of color images. After channel separation of the target image to obtain each component image, the input complex amplitude is formed with quadratic phase and iterated. During the iteration, subtract the amplitude of the reconstructed image from the amplitude of the target image to construct an exponential constraint. This exponential constraint is applied to the signal area of the image plane. After calculating the three-channel phase hologram, a color holographic reconstruction can be obtained using the time multiplexing method. Simulated and optical experiments verify the effectiveness of this method.

Diffractive neural networks (D²NNs) have been transformative in many fields, motivating the development of various optical computing components. However, these optical computing components, achieving in diffractive optical elements (DOEs) fabricated using commercial 3D printers, are bulky, and the size of individual neurons is only comparable to the wavelength scale. They simultaneously suffer from challenges posed by high-order diffraction and low spatial utilization. Here, we present a design of D²NNs based on all-dielectric metasurfaces, which reduces the size of individual neurons of optical D²NNs to scales significantly smaller than the wavelength. In order to demonstrate that our metasurface-based D²NNs are smart and sensitive enough comparable to state-of-the-art DOE-based D²NNs, we numerically simulated the design of two D²NNs including an optical 1-bit half-adder and a full-adder. Our experiment on aforementioned half-adder proofs the advantages of our architecture. Metasurface-based optical computational elements can offer higher spatial neuron density, while completely eliminate high-order diffraction to demonstrate the feasibility. Our metasurface-based D²NNs can facilitate miniaturization and integration on all-optical information processing especially optical computing components, and will find applications in numerous space-constrained fields such as 6G communication, optical smart sensors, and robotics.

The spatial photonic Ising machine (SPIM) is a simple and elegant architecture capable of expanding the spin scale with ease, and thus this optical architecture is attractive for its potential in solving large-scale combinatorial optimization problems. Here, we propose a scheme for aberration compensation to improve the computing accuracy of the SPIM based on a spatial light modulator (SLM), resulting in good scalability. First, the gamma curve of the SLM is corrected with the help of double-hole interference fringes. Then, an enhanced phase shift interferometry is used to measure the aberration of the entire optical system, and this aberration is compensated by loading the compensation phase on the SLM. Moreover, an iterative algorithm using self-adaptive cluster flipping is proposed for accelerating the convergence of SPIM. During the converging process, the number of flipped spins within the cluster is updated dynamically according to the convergence speed and accuracy, which makes it possible to achieve a good balance between high speed and high accuracy. Further, a proof-of-principle experimental set-up of the optimized SPIM is implemented, and the ground-state search of an antiferromagnetic Ising model is demonstrated. As an example, this optimized Ising machine is used for solving the number partitioning problem. It is shown that the partition of 40,000 random numbers is well demonstrated, and the final partitioning accuracy is as high as 99.88%.

The lensless in-line holographic microscope offers a compact, low-cost, and wide-field solution for microscopic imaging. Instead of using lenses, lensless microscopy relies on diffraction patterns to reconstruct images of the sample. Therefore, coherent light sources such as lasers are typically used to illuminate the sample for reconstruction images. However, lasers will introduce speckle and multiple reflection interference noise, while also being high in cost. As a result, LED illumination sources have been employed in lensless microscopy systems. However, the temporal coherence of LEDs affects the imaging resolution, which results in poor quality of the reconstructed images. In this paper, we propose an iterative twin image removal method based on a single diffraction pattern based on a lensless on-chip microscopy with a partially coherent illumination source. This method combines the wavelength demultiplexing method with positive absorption constraint and phase flipping. It can not only reduce the temporal coherence limitation of broadband light sources but also improve the convergence speed during iteration and provide better support estimation for complexshaped samples, thus improving the quality of reconstructed images. We provide numerical simulations and optical experiments to illustrate the effectiveness of our method. This work helps extend the application of lensless in-line holographic microscopy based on partially coherent light sources in biomedical detection, offering a more convenient and cost-effective option for microscopic imaging.

In this work we investigate the integration of optical and electronic hardware to create ML and DL accelerators with reduced computational complexity and energy consumption. We compare the performance of optical or hybrid optical-electronic neural networks and verify that by using these computation architectures it is possible to perform classification tasks with performances comparable with standard electronic neural networks but saving computational resources up to a factor of 10.

Hard apertures in imaging systems create artifacts at discontinuous points in an image. When we zoom in on such an image, Gibbs ringing can be a factor in the confusion of small features with artifacts, or in errors in measurements made of the features. In previous works, we have systemically analysed certain algorithms for suppressing artifacts, and developed metrics and procedures to make a quantifiable comparison between algorithms in that field. A common assumption in the literature is that zero-padding in the Fourier domain (sinc interpolation) is used for the zoom algorithm. Other algorithms make use of linear interpolation for a similar reason. In this paper, we analyse several interpolation formulae and compare them with sinc interpolation in a quantitative fashion. We further consider the interaction of the interpolation formulae with filtered Fourier reconstruction. Our results are foundational to establishing a quantitative evidence base for preferring certain ringing suppression algorithms over others, and provide grounds for revisiting assumptions that have long stood in commercial imaging pipelines.

Generating structured light beams has become a research hotspot to target many emerging practical applications like optical sensing, super-resolution imaging, and optical communication. Ingenious tailoring of spatial structures of light helps to manifest several intriguing beams like Bessel beams, Airy beams, vortex beams, etc. Among them, optical vortices (OVs) hold distinctive promise to meet the anticipated demands for optical communication, optical trapping, microscopy, quantum information processing, and many more. Due to their spatial dimensions, traditional methods of generating OVs are not viable to fit with the cutting-edge on-chip optical systems. In contrast, subwavelength structured devices enormously aggravate the capability to realize chip-integrated devices via abrupt phase discontinuity. Besides the many exotic features of optical metasurfaces, their fixed functionality limits the realization of breakthroughs in many real-life applications. Here, we present an exquisite design that enables multifunctional metastructures to develop multichannel focused optical vortices of like or distinct topological charges on the same focal plane regardless of the input polarization state. Our design is based on a symmetric array of nanocylinders where the index waveguide theory concept is utilized effectively to accumulate the desired phase in the direction of propagation. Moreover, zinc sulfide, as a prime material used in device prototyping, enables a highly transmissive structure. Our work regarding the multidimensional generation of optical vortices has far-reaching effects on multifunctional optical devices.

Multi-operational metasurfaces have received a lot of interest because of their significant design improvements for ultra-compact and highly integrated meta-optics. The emergence of near and far-field holography offers an effective solution to enhance the capacity of information encoding in a single metasurface. However, the existing strategies of layer stacking and interleaving, where distinct functionalities are embedded with the help of the combination of multiple meta-atoms, have challenges in terms of design complexity and efficiency. This manuscript proposes a new simplest approach for a tri-channel highly efficient meta-holography based on the photonics spin Hall Effect (PSHE) and Mauls’ Principle of amplitude manipulation. A multi-functional metasurface constituent of a single nano-rectangular pillar over a glass substrate is designed as evidence of conception to highlight the feasibility of parallel manipulation upon near and far-field activities. To achieve control over the entire phase range (0-2π), geometric phase modulation is utilized. Zinc sulphide (ZnS) is used as a constituent material for highly efficient broadband response over the whole visible spectrum due to its characteristics of an extraordinary refractive index and low absorption coefficient. For authentication of the proposed methodology, the designed metasurface is simulated in FDTD, effectively validating the execution of a multi-functional design scheme. For the proof of the broadband operation, optical response over three visible wavelengths (i.e., blue, green, and red) is measured, and it reconstructs all three holograms with high efficiency. Thus, the proposed optical response multiplication approach is a viable contender for various high-end applications in photonics, data storage, and communication.

Conventional optical elements are typically designed for a specific wavelength and have limited functionality, hindering their practical applications and integration with on-chip devices. Recently developed artificially engineered structures overcome this constraint but at the cost of added design complexity. Here, we present broadband single-layered metadevices capable of integrating multiple functionalities that generate nondiffracting perfect vortex beams for visible wavelengths (475 to 650 nm). To realize highly efficient all-dielectric meta-devices, zinc sulfide material is exploited due to its large transparent window with a sufficiently high refractive index in the visible regime. The nondiffracting response provides a significantly long propagation distance without abrupt divergence. Moreover, shorter optical wavelengths provide more data bandwidth when mixed with a high topological charge (n = 8) of the perfect vortex beam, which paved the path towards the realization of numerous applications such as optical tweezing, quantum information processing, and optical communication.

In recent years, metasurfaces, a flat version of three-dimensional metamaterials, have become a versatile nanophotonics platform for unprecedented light manipulation. Amongst the numerous realizations of exotic optical phenomena through metasurfaces such as meta-lensing, meta-holography, and structured beams, Bessel beam generation caught significant attention due to its non-diffracting and self-healing nature. Bessel beams can be produced using various conventional methods, including spatial light modulators, composite holograms, and diffractive optical elements. These methods, however, are unfit to integrate with cutting-edge on-chip devices due to low throughput, polarization dependence, excessive bulkiness, and limited numerical aperture. In the method of generating Bessel beams through flat optics, the selection of suitable material is a crucial factor. Thus, due to constraints of inherent material properties, broadband operation with high efficiency remains challenging. Here, we demonstrated highly efficient broadband Bessel beams generating meta-devices in the visible domain using single-layer all-dielectric transmissive metasurfaces. The constituent nanoresonators of zinc sulfide (ZnS) are optimized for high-resolution phase modulation. ZnS offers the best-suited optical properties that ensure high transmission efficiency throughout the visible spectrum. To verify the proposed design technique, we realized single-element-driven meta-devices to generate Bessel beams with higher numerical apertures and different topological charges, illustrating their exceptional non-diffraction properties. For real-life applications like optical communication, the proposed design strategy could speed up consumer-level device implementation.

Metasurfaces, the planner counterpart of three-dimensional metamaterials, promise a superior degree of freedom and design flexibility due to their unprecedented capability to manipulate the wavefront of incident light. These nanostructures can precisely tailor the intrinsic properties of the light to implement multifunctional and miniaturized nanophotonic devices. Due to the ever-increasing demand for compactness, it is essential to independently control the amplitude, phase, and polarization of light and integrate multiple functionalities in a single-layered device. This paper introduces multifunctional all-dielectric metasurfaces that integrate numerous optical phenomena in a single meta-device for the ultraviolet spectrum. A nanoantenna made of bandgap-engineered material silicon nitride (Si₃N₄) is used as a fundamental building block of proposed metasurfaces. The proposed design methodology is verified by realizing multiple metasurfaces to generate focused optical vortices of different topological charges. The multifunctional capability of the proposed metasurfaces is achieved by exploiting the spin-decoupling technique that provides a unique optical response under different handedness of the incidence light. To further validate the functionality of the proposed metasurfaces, a unique design technique is also presented that resolves the value of the topological charge embedded in any optical vortex beam by reading the number of spirals and their spinning directions. The proposed approach can lead to a new paradigm in realizing multifunctional nanophotonic devices for optical wave manipulations, such as high-density information encryption, optical anti-counterfeiting, optical storage, and multiplexing of optical vortices.

Fast steering mirrors (FSMs) play a critical role in optical systems that require high stability and fast response speed, particularly in high-speed rotating systems responsible for image stabilization, such as back-scanning step-and-stare imaging systems. However, high-speed mirror control is limited by factors such as mechanical size, fatigue strength of the flexure as well as the fact that motor parameters such as force and force constant are also limited and varied by temperature. This paper proposes a control architecture with a moving trajectory and an optimized algorithm for high-speed movement in the condition of small displacement angles. The control algorithm employs a model-based adaptive control method to adapt the FSM's behavior and optimize the trajectory based on the desired performance criteria. The simulation results demonstrate the effectiveness of the proposed approach in improving the FSM's positioning accuracy and robustness. The proposed approach achieves a remarkably small position deviation during the exposure time, while maintaining a small displacement angle, ensuring the stability and long-term operability of the mechanical system.