Within the realm of soft matter, particularly liquid crystals, the ability to leverage material properties to create switchable diffraction gratings holds significant importance in disciplines such as optics and information science. However, designing switchable patterns and compiling information based on output images remain challenging. Here, we introduce an approach to address these limitations by designing switchable gratings mediated by three-dimensional director solitons. We utilize photo-patterning, employing lithography systems with different ultraviolet light, to fabricate the desired patterns. This method allows solitons to nucleate and localize within the regions of the pattern where the anchoring energy is weaker. The periodic structures, alternating between solitons and uniform patterns, exhibit the ability to diffract light beams. By switching the voltage, we can control the generation and localization of solitons within periodic patterns and realize switching between the waveplate and grating. Our experimental findings, complemented by simulation outcomes, validate the feasibility of utilizing three-dimensional solitons in optical applications.

Wave mixing and the intricate optical interactions therein have traditionally been regarded as hallmarks of nonlinear optics. A quintessential example of wave mixing lies in the nonlocal triple correlation between the pump beam and the generated twin photons via spontaneous parametric down-conversion (SPDC). However, the SPDC process typically requires intense laser pumping and suffers from inherently low conversion efficiencies, necessitating single-photon detection. In this work, we establish that analogous triple correlations can be effectively produced using low-power continuous-wave illumination, achieved through a commercially available spatial light modulator (SLM) in a linear optical configuration. Specifically, we show how to spatially manipulate and customize this triple correlation and further investigate the applicability across diverse domains, including pattern recognition, intelligent nonlocal image processing, and sensitivity-enhanced optical metrology. Our findings establish, to our knowledge, a novel framework for classical, linear emulation of quantum and nonlinear optical information processing paradigms rooted in multi-wave mixing.

The near-eye display feature in emerging spatial computing systems produces a distinctive visual effect of mixing virtual and real worlds. However, its application for all-day wear is greatly limited by the bulky structure, energy expenditure, and continuous battery heating. Here, we propose a lightweight holographic near-eye display system that takes advantage of solar energy for self-charging. To guarantee the collection of solar energy and near-eye display without crosstalk, we implement holographic optical elements (HOEs) to diffract sunlight and signal light into a common waveguide. Then, small-area solar cells convert the collected solar energy and power the system. Compact power supply components replace heavy batteries, thus contributing to the lightweight design. The simple acquisition and management of solar energy provide the system with sustainable self-charging capability. We believe that the lightweight design and continuous energy input solution will significantly promote the popularity of near-eye display in our daily lives.

Holographic optical elements (HOEs) are integral to advancements in optical sensing, augmented reality, solar energy harvesting, biomedical diagnostics, and many other fields, offering precise and versatile light manipulation capabilities. This study, to the best of the authors’ knowledge, is the first to design and fabricate an HOE mutli-waveguide system using a thermally and environmentally stable photopolymerizable hybrid sol-gel (PHSG) for sensing applications. Using a 476.5 nm recording wavelength, 60% diffraction efficiency PHSG holographic waveguides of spatial frequency of 1720 lines/mm were successfully fabricated to function as in- and out-couplers at 632.8 nm and 700 nm wavelength, respectively. The waveguides were integrated into a polydimethylsiloxane (PDMS) microfluidic system, guiding excitation light of 632.8 nm wavelength into and extracting fluorescence light signal peaking at 700 nm from a location filled with methylene blue water solution. Further, to demonstrate the potential of the proposed optical system, four holographic waveguides were recorded by peristrophic and angular multiplexing in the same location of the material and the input beam was delivered into four spatially separated channels by total internal reflection in the sol-gel layer, thus, successfully highlighting the capabilities and advantages of HOE waveguides for parallel interrogation of multiple locations in a wearable sensor. This study demonstrates the efficiency and versatility of PHSG-based HOE waveguides, underscoring their potential to enhance photonic device design and performance across various optical applications.

Due to the high-dimensional characteristics of photon orbital angular momentum (OAM), a beam can carry multiple OAMs simultaneously thus forming an OAM comb, which has been proved to show significant potential in both classical and quantum photonics. Tailoring broadband OAM combs on demand in a fast and accurate manner is a crucial basis for their application in advanced scenarios. However, obtaining phase-only gratings for the generation of arbitrary desired OAM combs still poses challenges. In this paper, we propose a multi-scale fusion learning U-shaped neural network that encodes a phase-only hologram for tailoring broadband OAM combs on-demand. Proof-of-principle experiments demonstrate that our scheme achieves fast computational speed, high modulation precision, and high manipulation dimensionality, with a mode range of -75 to +75, an average root mean square error of 0.0037, and a fidelity of 85.01%, all achieved in about 30 ms. Furthermore, we utilize the tailored broadband OAM combs in conducting optical convolution calculation, enabling vector convolution for arbitrary discrete functions, showcasing the extended capability of our proposal. This work opens, to our knowledge, new insight for on-demand tailoring of broadband OAM combs, paving the way for further advancements in high-dimensional OAM-based applications.

Holographic near-eye augmented reality (AR) displays featuring tilted inbound/outbound angles on compact optical combiners hold significant potential yet often struggle to deliver satisfying image quality. This is primarily attributed to two reasons: the lack of a robust off-axis-supported phase hologram generation algorithm; and the suboptimal performance of ill-tuned hardware parts such as imperfect holographic optical elements (HOEs). To address these issues, we incorporate a gradient descent-based phase retrieval algorithm with spectrum remapping, allowing for precise hologram generation with wave propagation between nonparallel planes. Further, we apply a camera-calibrated propagation scheme to iteratively optimize holograms, mitigating imperfections arising from the defects in the HOE fabrication process and other hardware parts, thereby significantly lifting the holographic image quality. We build an off-axis holographic near-eye display prototype using off-the-shelf light engine parts and a customized full-color HOE, demonstrating state-of-the-art virtual reality and AR display results.

Multiplexing technology serves as an effective approach to increase both information storage and transmission capability. However, when exploring multiplexing methods across various dimensions, the polarization dimension encounters limitations stemming from the finite orthogonal combinations. Given that only two mutually orthogonal polarizations are identifiable on the basic Poincaré sphere, this poses a hindrance to polarization modulation. To overcome this challenge, we propose a construction method for the optical polarized orthogonal matrix (OPOM), which is not constrained by the number of orthogonal combinations. Furthermore, we experimentally validate its application in high-dimensional multiplexing of polarization holography. We explore polarization holography technology, capable of recording amplitude, phase, and polarization, for the purpose of recording and selective reconstruction of polarization multi-channels. Our research reveals that, despite identical polarization states, multiple images can be independently manipulated within distinct polarization channels through orthogonal polarization combinations, owing to the orthogonal selectivity among information. By selecting the desired combination of input polarization states, the reconstructed image can be switched with negligible crosstalk. This non-square matrix composed of polarization unit vectors provides prospects for multi-channel information retrieval and dynamic display, with potential applications in optical communication, optical storage, logic devices, anti-counterfeiting, and optical encryption.

Grating optics lie in the heart of X-ray spectroscopy instruments. The low efficiency and angular dispersion of conventional single-layer-coated gratings significantly limit the transmission and energy resolution of monochromators and spectrometers, particularly in the tender X-ray region (E=1-5 keV). Multilayer-coated blazed gratings (MLBGs) operating at high diffraction orders offer the advantage of achieving both high efficiency and high dispersion simultaneously. Tender X-ray monochromators and spectrometers using different high-order MLBGs have been designed, all demonstrating one to two orders of magnitude higher transmission compared to conventional systems. By employing a 2400 l/mm MLBG at the -4th or -8th diffraction order, the theoretical energy resolution of the instrument is improved by two to three times at 2.5 keV. Two MLBGs operating at the -2nd and -4th orders have been fabricated, showcasing remarkable efficiencies of 34%–12% at 2.5 keV, surpassing that of single-layer-coated gratings by an order of magnitude. Further optimization of manufacturing accuracy can yield even higher efficiencies. The measured angular dispersion agrees well with theoretical predictions, supporting the potential for high resolution. High-order MLBG optics pave the way for a new generation of tender X-ray monochromators/spectrometers that offer both high transmission and high resolution.

Numerical Fresnel diffraction is broadly used in optics and holography in particular. So far, it has been implemented using convolutional approaches, spatial convolutions, or the fast Fourier transform. We propose a new way, to our knowledge, of computing Fresnel diffraction using Gabor frames and chirplets. Contrary to previous techniques, the algorithm has linear-time complexity, does not exhibit aliasing, does not need zero padding, has no constraints on changing shift/resolution/pixel pitch between source and destination planes, and works at any propagation distance. We provide theoretical and numerical analyses, detail the algorithm, and report simulation results with an accelerated GPU implementation. This algorithm may serve as a basis for more flexible, faster, and memory-efficient computer-generated holography methods.

The metasurface possesses great potential in a 3D holographic display due to its powerful ability to manipulate optical fields, ultracompact structure, and extraordinary information capacity. However, the in-plane and interplane crosstalk caused by the coupling between the meta-atoms of the current 3D holographic metasurface limits the quality of the reconstructed image, which has become a significant obstacle to high-performance 3D display applications. Additionally, the interleaved or multilayer design strategy of metasurfaces increases the complexity of structural design and manufacturing, facing challenges in meeting the requirements for miniaturization and low cost-effectiveness. Here, we propose a strategy for a free-space 3D multiplane color holographic multiplex display based on a single-cell metasurface. By utilizing a modified holographic optimization strategy, multiple holographic information is encoded into three mutually independent bases of incident photons and integrated into a metasurface, thereby creating high-quality 3D vectorial metaholography with minimal crosstalk across the visible spectrum. The proposed metasurface has great potential for applications in augmented reality/virtual reality devices, polarization imaging, holographic data encryption, and information storage.

The fast algorithms in Fourier optics have invigorated multifunctional device design and advanced imaging technologies. However, the necessity for fast computations limits the widely used conventional Fourier methods, where the image plane has a fixed size at certain diffraction distances. These limitations pose challenges in intricate scaling transformations, 3D reconstructions, and full-color displays. Currently, the lack of effective solutions makes people often resort to pre-processing that compromises fidelity. In this paper, leveraging a higher-dimensional phase space method, a universal framework is proposed for customized diffraction calculation methods. Within this framework, a variable-scale diffraction computation model is established for adjusting the size of the image plane and can be operated by fast algorithms. The model’s robust variable-scale capabilities and its aberration automatic correction capability are validated for full-color holography, and high fidelity is achieved. The tomography experiments demonstrate that this model provides a superior solution for holographic 3D reconstruction. In addition, this model is applied to achieve full-color metasurface holography with near-zero crosstalk, showcasing its versatile applicability at nanoscale. Our model presents significant prospects for applications in the optics community, such as beam shaping, computer-generated holograms (CGHs), augmented reality (AR), metasurface optical elements (MOEs), and advanced holographic head-up display (HUD) systems.

Towards next-generation intelligent display devices, it is urgent to find a cheap and convenient dynamic optical control method. Conventional gratings are widely used as cheap diffractive elements due to their effective optical control capabilities. However, they are limited within multi-function or complex optical modulation due to the lack of accurate control of the amplitude/phase at pixel-level. Here, a metasurface-assisted grating-modulation system is originally proposed to achieve switchable multi-fold meta-holographic dynamics. By incorporating metasurfaces with traditional gratings and tuning their relative coupling positions, the modulation system gains the optical modulation capability to realize complex optical functionalities. Specifically, by varying the grating periods/positions relative to the metasurface, 2–8 holographic image channels are programmed to be dynamically exhibited and switched. The proposed metasurface-assisted grating-modulation approach enjoys cost-effective convenience, strong encoding freedom, and facile operation, which promises programmable optical displays, optical sensors, optical information encryption/storage, etc.

High-quality wide-angle holographic content is at the heart of the success of near-eye display technology. This work proposes the first digital holographic (DH) system enabling recording wide-angle scenes assembled from objects larger than the setup field of view (FOV), which can be directly replayed without 3D deformation in the near-eye display. The hologram formation in the DH system comprises free space propagation and Fourier transform (FT), which are connected by a rectangular aperture. First, the object wave propagates in free space to the rectangular aperture. Then, the band-limited wavefield is propagated through the single lens toward the camera plane. The rectangular aperture can take two sizes, depending on which DH operates in off-axis or phase-shifting recording mode. An integral part of the DH solution is a numerical reconstruction algorithm consisting of two elements: fringe processing for object wave recovery and wide-angle propagation to the object plane. The second element simulates propagation through both parts of the experimental system. The free space part is a space-limited angular spectrum compact space algorithm, while for propagation through the lens, the piecewise FT algorithm with Petzval curvature compensation is proposed. In the experimental part of the paper, we present the wide-angle DH system with FOV 25°×19°, which allows high-quality recording and reconstruction of large complex scenes.

Multimode fibers (MMFs) are a promising solution for high-throughput signal transmission in the time domain. However, crosstalk among different optical modes within the MMF scrambles input information and creates seemingly random speckle patterns at the output. To characterize this process, a transmission matrix (TM) can be used to relate input and output fields. Recent innovations use TMs to manipulate the output field by shaping the input wavefront for exciting advances in deep-brain imaging, neuron stimulation, quantum networks, and analog operators. However, these approaches consider input/output segments as independent, limiting their use for separate signal processing, such as logic operations. Our proposed method, which makes input/output segments as interdependent, adjusts the phase of corresponding output fields using phase bias maps superimposed on input segments. Coherent superposition enables signal logic operations through a 15-m-long MMF. In experiments, a single optical logic gate containing three basic logic functions and cascading multiple logic gates to handle binary operands is demonstrated. Bitwise operations are performed for multi-bit logic operations, and multiple optical logic gates are reconstructed simultaneously in a single logic gate with polarization multiplexing. The proposed method may open new avenues for long-range logic signal processing and transmission via MMFs.

Perfect optical vortex (POV) beams offer a phase-gradient route to convey small particles along a tunable circular path or belt. The prevailing generalized POV method can be used to reshape the conveyor belt, but it usually deteriorates the orbital energy flow of field, leading to unstable conveying speed or even creating unwanted optical traps that prevent transportation. Here, we demonstrate optical conveyor belts with customized profiles and a uniform orbital flow over the whole transporting region by integrating isometric uniform sampling and random phases into the generalized POV generation algorithm. Smooth delivery of metallic particles, inaccessible to conventional generalized POV methods, is achieved at an almost even speed. We also demonstrate a dual-belt conveyor for delivering large metal microparticles, which experience repulsive intensity-gradient forces and thus are unable to be manipulated by a single belt. Our results present a unique addition to the toolbox of optical manipulation and would facilitate the development of small-scale drug delivery microsystems.

The rapid advancement of computer-generated holography has bridged deep learning with traditional optical principles in recent years. However, a critical challenge in this evolution is the efficient and accurate conversion from the amplitude to phase domain for high-quality phase-only hologram (POH) generation. Existing computational models often struggle to address the inherent complexities of optical phenomena, compromising the conversion process. In this study, we present the cross-domain fusion network (CDFN), an architecture designed to tackle the complexities involved in POH generation. The CDFN employs a multi-stage (MS) mechanism to progressively learn the translation from amplitude to phase domain, complemented by the deep supervision (DS) strategy of middle features to enhance task-relevant feature learning from the initial stages. Additionally, we propose an infinite phase mapper (IPM), a phase-mapping function that circumvents the limitations of conventional activation functions and encapsulates the physical essence of holography. Through simulations, our proposed method successfully reconstructs high-quality 2K color images from the DIV2K dataset, achieving an average PSNR of 31.68 dB and SSIM of 0.944. Furthermore, we realize high-quality color image reconstruction in optical experiments. The experimental results highlight the computational intelligence and optical fidelity achieved by our proposed physics-aware cross-domain fusion.

Computer-generated holography (CGH) based on neural networks has been actively investigated in recent years, and convolutional neural networks (CNNs) are frequently adopted. A convolutional kernel captures local dependencies between neighboring pixels. However, in CGH, each pixel on the hologram influences all the image pixels on the observation plane, thus requiring a network capable of learning long-distance dependencies. To tackle this problem, we propose a CGH model called Holomer. Its single-layer perceptual field is 43 times larger than that of a widely used 3×3 convolutional kernel, thanks to the embedding-based feature dimensionality reduction and multi-head sliding-window self-attention mechanisms. In addition, we propose a metric to measure the networks’ learning ability of the inverse diffraction process. In the simulation, our method demonstrated noteworthy performance on the DIV2K dataset at a resolution of 1920×1024, achieving a PSNR and an SSIM of 35.59 dB and 0.93, respectively. The optical experiments reveal that our results have excellent image details and no observable background speckle noise. This work paves the path of high-quality hologram generation.

Metasurfaces have prompted the transformation from the investigation of scalar holography to vectorial holography and led various applications in vectorial optical field manipulation. However, the majority of previously demonstrated methods focused on the reconstruction of a vectorial holographic image located at a predefined individual image plane. The evolution of polarization transformation during propagation can provide more design freedoms for realizing three-dimensional holography with complicated polarization feature. Here, we demonstrated a Jones matrix framework to generate vectorial holographic images with continuously varied polarization distributions at multiple different image planes based on a height tunable metasurface. The proposed metasurface is composed of IP-L (a type of photoresist) nanofins with different lengths, widths, heights, as well as orientation angles fabricated by femtosecond laser direct writing. Such a fabrication method is in favor of 3D arbitrary structure processing, large area fabrication, as well as fabrication on curved substrates. Meanwhile, it is easy to fabricate structures that can be integrated with other devices, including optical fibers, photodetectors, and complementary metal–oxide semiconductors. Our demonstrated method provides a feasible way to generate high-dimensional vectorial fields with longitudinally varied features from the perspective of holography and can be used in the related areas including optical trapping, sensing, and imaging.

Most optical information processors deal with text or image data, and it is very difficult to deal experimentally with acoustic data. Therefore, optical advances that deal with acoustic data are highly desirable in this area. In particular, the development of a voice or acoustic-signal authentication technique using optical correlation can open a new line of research in the field of optical security and could also provide a tool for other applications where comparison of acoustic signals is required. Here, we report holographic acoustic-signal authentication by integrating the holographic microphone recording with optical correlation to meet some of the above requirements. The reported method avails the flexibility of 3D visualization of acoustic signals at sensitive locations and parallelism offered by an optical correlator/processor. We demonstrate text-dependent optical voice correlation that can determine the authenticity of acoustic signal by discarding or accepting it in accordance with the reference signal. The developed method has applications in security screening and industrial quality control.

Optical metasurfaces (OMs) offer unprecedented control over electromagnetic waves, enabling advanced optical multiplexing. The emergence of deep learning has opened new avenues for designing OMs. However, existing deep learning methods for OMs primarily focus on forward design, which limits their design capabilities, lacks global optimization, and relies on prior knowledge. Additionally, most OMs are static, with fixed functionalities once processed. To overcome these limitations, we propose an inverse design deep learning method for dynamic OMs. Our approach comprises a forward prediction network and an inverse retrieval network. The forward prediction network establishes a mapping between meta-unit structure parameters and reflectance spectra. The inverse retrieval network generates a library of meta-unit structure parameters based on target requirements, enabling end-to-end design of OMs. By incorporating the dynamic tunability of the phase change material Sb2Te3 with inverse design deep learning, we achieve the design and verification of dynamic multifunctional OMs. Our results demonstrate OMs with multiple information channels and encryption capabilities that can realize multiple physical field optical modulation functions. When Sb2Te3 is in the amorphous state, near-field nano-printing based on meta-unit amplitude modulation is achieved for X-polarized incident light, while holographic imaging based on meta-unit phase modulation is realized for circularly polarized light. In the crystalline state, the encrypted information remains secure even with the correct polarization input, achieving double encryption. This research points towards ultra-compact, high-capacity, and highly secure information storage approaches.

As an important three-dimensional (3D) display technology, computer-generated holograms (CGHs) have been facing challenges of computational efficiency and realism. The polygon-based method, as the mainstream CGH algorithm, has been widely studied and improved over the past 20 years. However, few comprehensive and high-speed methods have been proposed. In this study, we propose an analytical spectrum method based on the principle of spectral energy concentration, which can achieve a speedup of nearly 30 times and generate high-resolution (8K) holograms with low memory requirements. Based on the Phong illumination model and the sub-triangles method, we propose a shading rendering algorithm to achieve a very smooth and realistic reconstruction with only a small increase in computational effort. Benefiting from the idea of triangular subdivision and octree structures, the proposed original occlusion culling scheme can closely crop the overlapping areas with almost no additional overhead, thus rendering a 3D parallax sense. With this, we built a comprehensive high-speed rendering pipeline of polygon-based holograms capable of computing any complex 3D object. Numerical and optical reconstructions confirmed the generalizability of the pipeline.

Diffraction tomography is a promising, quantitative, and nondestructive three-dimensional (3D) imaging method that enables us to obtain the complex refractive index distribution of a sample. The acquisition of the scattered fields under the different illumination angles is a key issue, where the complex scattered fields need to be retrieved. Presently, in order to develop terahertz (THz) diffraction tomography, the advanced acquisition of the scattered fields is desired. In this paper, a THz in-line digital holographic diffraction tomography (THz-IDHDT) is proposed with an extremely compact optical configuration and implemented for the first time, to the best of our knowledge. A learning-based phase retrieval algorithm by combining the physical model and the convolution neural networks, named the physics-enhanced deep neural network (PhysenNet), is applied to reconstruct the THz in-line digital hologram, and obtain the complex amplitude distribution of the sample with high fidelity. The advantages of the PhysenNet are that there is no need for pretraining by using a large set of labeled data, and it can also work for thick samples. Experimentally with a continuous-wave THz laser, the PhysenNet is first demonstrated by using the thin samples and exhibits superiority in terms of imaging quality. More importantly, with regard to the thick samples, PhysenNet still works well, and can offer 2D complex scattered fields for diffraction tomography. Furthermore, the 3D refractive index maps of two types of foam sphere samples are successfully reconstructed by the proposed method. For a single foam sphere, the relative error of the average refractive index value is only 0.17%, compared to the commercial THz time-domain spectroscopy system. This demonstrates the feasibility and high accuracy of the THz-IDHDT, and the idea can be applied to other wavebands as well.

Combining the synthetic aperture radar (SAR) with the optical phase recovery, Fourier ptychography (FP) can be a promising technique for high-resolution optical remote imaging. However, there are still two issues that need to be addressed. First, the multi-angle coherent model of FP would be destroyed by the diffuse object; whether it can improve the resolution or just suppress the speckle is unclear. Second, the imaging distance is in meter scale and the diameter of field of view (FOV) is around centimeter scale, which greatly limits the application. In this paper, the reasons for the limitation of distance and FOV are analyzed, which mainly lie in the illumination scheme. We report a spherical wave illumination scheme and its algorithm to obtain larger FOV and longer distance. A noise suppression algorithm is reported to improve the reconstruction quality. The theoretical interpretation of our system under random phase is given. It is confirmed that FP can improve the resolution to the theoretical limit of the virtual synthetic aperture rather than simply suppressing the speckle. A 10 m standoff distance experiment with a six-fold synthetic aperture up to 31 mm over an object of size ∼1 m×0.7 m is demonstrated.

With the development of micro/nano fabrication technology, metasurface holography has emerged as a revolutionary technology for the manipulation of light with excellent performance. However, for applications of full-Stokes polarization encryption and time sequence holographic display, multiplexing strategies of metasurfaces with large bandwidths and simple operations still need to be developed. As one of the most popular schemes of multiplexing, polarization multiplexed metasurfaces have shown flexible recording abilities for both free-space beam and surface waves. Here, by using a dielectric metasurface equipped with double phase holograms, we have achieved flexible polarization multiplexed transformations from one full-Stokes space to another. The vectorial hologram is optimized by a hybrid genetic algorithm and digitalized with subwavelength modulated units. Based on a quantitative map and remarkable information capacity, time sequence holographic display and complex optical encryption are experimentally demonstrated by changing input/output polarization channels in real time. We believe our method will facilitate applications in smart compact devices of dynamic display, dynamic optical manipulation, optical encryption, anticounterfeiting, etc.

Reciprocity is ubiquitous in antennas for receiving and radiating electromagnetic (EM) waves, i.e., if an antenna has good receiving performance at a given direction, it also has good radiation performance in that direction. Inspired by this, we propose a method of designing a quasi-ominibearing retro-reflective metagrating (RRMG) protected by the reciprocity of antennas. Based on the second-order mode around 15.0 GHz of a short-circuited structured patch antenna (SPA), incident transverse magnetic waves can be received, channeled into the coaxial lines, reflected by the shortened end, and finally re-radiated into free space with a reversed wave vector. RRMGs are contrived consisting of this identical SPA, with a grating constant allowing ±2nd-, ±1st-, and zeroth-order diffractions. Oblique incidence, plus the tilted nulls of the re-radiation pattern, can eliminate -1st, zeroth, +1st, and +2nd orders, and only the -2nd order is left to achieve retro-reflections. Prototypes were fabricated and measured. Simulated and measured results show that the RRMGs maintain only -2nd-order diffraction for incident angles 32.2°≤θi90.0° in four quadrants, and that RRMGs can achieve quasi-omnibearing retro-reflections for θi=50.0°. The use of higher-order diffraction brings more degrees of freedom in manipulating EM waves, and this strategy can be readily extended to millimeter waves, THz wave, or even optical regimes.

Metasurface holography is becoming a universal platform that has made a considerable impact on nanophotonics and information optics, due to its advantage of large capacity and multiple functionalities. Here, we propose a correlated triple amplitude and phase holographic encryption based on an all-dielectric metasurface. We develop an optimized holographic algorithm to obtain quantitatively correlated triple holograms, which can encrypt information in multiple wavelength and polarization channels. We apply the “static” and “dynamic” pixels in our design, respectively. Two kinds of isotropic square nanofins are selected, one functioning as a transmitter and the other functioning as a blocker counterintuitively at both working wavelengths, while another anisotropic rectangle nanofin can transmit or block light in co-polarization selectively, mimicking “dynamic” amplitude switches. Meanwhile, such “dynamic” nanofins can simultaneously function as a phase modulator in cross-polarization only at the transmission wavelength. That is, through smart design, different dielectric meta-atoms functioning as spectral filters as well as phase contributors can compositely achieve triple hybrid amplitude and phase holograms. Such strategy promises to be applied in compact large-capacity information storage, colorful holographic displays, optical encryption, multifunctional imaging devices, and so on.

With the development of continuous-wave terahertz (THz) sources and array detectors, the pursuit of high-fidelity real-time imaging is receiving significant attention within the THz community. Here, we report a real-time full-field THz phase imaging approach based on lensless Fourier-transform THz digital holography. A triangular interferometric layout is proposed based on an oblique illumination of 2.52 THz radiation, which is different from other lensless holographic configurations at other frequencies. A spherical reference beam is generated by a reflective parabolic mirror with minor propagation loss. The complex-valued images are reconstructed using a single inverse Fourier transform of the hologram without complex calculation of the diffraction propagation. The experimental result for a Siemens star validates the lateral resolution of ∼346 μm in the diagonal direction. Sub-pixel image registration and image stitching algorithms are applied to enlarge the area of the reconstructed images. The dehydration process of an aquatic plant leaf (Hottonia inflata) is monitored for the first time, to the best of our knowledge, at the THz band. Rapid variations in water content and morphology are measured with a time interval of 0.6 s and a total time of 5 min from a series of reconstructed amplitude and phase images, respectively. The proposed method has the potential to become a powerful tool to investigate spontaneous phenomena at the THz band.

Massive usage scenarios prompt the prosperity of terahertz refractive index (THz RI) measurement methods. However, they are very difficult in measuring the full-field dynamical RI distributions of either solid samples without a priori thickness or liquid samples. In this study, we propose total internal reflection THz digital holography and apply it for measuring RI distributions for both solid and liquid samples dynamically. An RI measurement model is established based on an attenuated total reflection prism with a pitching angle. The pitching angle and the field of view can be numerically calculated from the spectrogram of the off-axis Fresnel hologram, which solves the adjustment of the visually opaque prism irradiated by the invisible THz beam. Full-field RI distributions of the droplets of solid-state soy wax and distilled water are obtained and compared with THz time-domain spectroscopy. The evaporation of an ethanol solution droplet is recorded, and the variation of the RI distribution at the sample–prism interface is quantitatively visualized with a temporal resolution of 10 Hz. The proposed method greatly expands the sample range for THz RI measurements and provides unprecedented insight into investigating spontaneous and dynamic THz phenomena.

We demonstrate, both analytically and experimentally, free-space pin-like optical vortex beams (POVBs). Such angular-momentum-carrying beams feature tunable peak intensity and undergo robust antidiffracting propagation, realized by judiciously modulating both the amplitude and the phase profile of a standard laser beam. Specifically, they are generated by superimposing a radially symmetric power-law phase on a helical phase structure, which allows the inclusion of an orbital angular momentum term to the POVBs. During propagation in free space, these POVBs initially exhibit autofocusing dynamics, and subsequently their amplitude patterns morph into a high-order Bessel-like profile characterized by a hollow core and an annular main lobe with a constant or tunable width during propagation. In contrast with numerous previous endeavors on Bessel beams, our work represents the first demonstration of long-distance free-space generation of optical vortex “pins” with their peak intensity evolution controlled by the impressed amplitude structure. Both the Poynting vectors and the optical radiation forces associated with these beams are also numerically analyzed, revealing novel properties that may be useful for a wide range of applications.

Imaging with an optical incoherent synthetic aperture (SA) means that the incoherent light from observed objects is processed over time from various points of view to obtain a resolution equivalent to single-shot imaging by the SA larger than the actual physical aperture. The operation of such systems has always been based on two-wave interference where the beams propagate through two separate channels. This limitation of two channels at a time is removed in the present study with the proposed SA where the two beams pass through the same single channel at any given time. The system is based on a newly developed self-interference technique named coded aperture correlation holography. At any given time, the recorded intensity is obtained from interference between two waves co-propagating through the same physical channel. One wave oriented in a particular polarization is modulated by a pseudorandom coded phase mask and the other one oriented orthogonally passes through an open subaperture. Both subapertures are multiplexed at the same physical window. The system is calibrated by a point spread hologram synthesized from the responses of a guide star. All the measurements are digitally processed to achieve a final image with a resolution higher than that obtained by the limited physical aperture. This unique configuration can offer alternatives for the current cumbersome systems composed of far apart optical channels in the large optical astronomical interferometers. Furthermore, the proposed concept paves the way to an SA system with a single less-expensive compact light collector in an incoherent optical regime that may be utilized for future ground-based or space telescopes.

Dual-wavelength in-line digital holography (DIDH) is one of the popular methods for quantitative phase imaging of objects with non-contact and high-accuracy features. Two technical challenges in the reconstruction of these objects include suppressing the amplified noise and the twin-image that respectively originate from the phase difference and the phase-conjugated wavefronts. In contrast to the conventional methods, the deep learning network has become a powerful tool for estimating phase information in DIDH with the assistance of noise suppressing or twin-image removing ability. However, most of the current deep learning-based methods rely on supervised learning and training instances, thereby resulting in weakness when it comes to applying this training to practical imaging settings. In this paper, a new DIDH network (DIDH-Net) is proposed, which encapsulates the prior image information and the physical imaging process in an untrained deep neural network. The DIDH-Net can effectively suppress the amplified noise and the twin-image of the DIDH simultaneously by automatically adjusting the weights of the network. The obtained results demonstrate that the proposed method with robust phase reconstruction is well suited to improve the imaging performance of DIDH.

Flat lenses thinner than a wavelength promise to replace conventional refractive lenses in miniaturized optical systems. However, Fresnel zone plate flat lens designs require dense annuli, which significantly challenges nanofabrication resolution. Herein, we propose a new implementation of detour phase graphene flat lens with flexible annular number and width. Several graphene metalenses demonstrated that with a flexible selection of the line density and width, the metalenses can achieve the same focal length without significant distortions. This will significantly weaken the requirement of the nanofabrication system which is important for the development of large-scale flat lenses in industry applications.

Transmission through seemingly opaque surfaces, so-called extraordinary transmission, provides an exciting platform for strong light–matter interaction, spectroscopy, optical trapping, and color filtering. Much of the effort has been devoted to understanding and exploiting TM extraordinary transmission, while TE anomalous extraordinary transmission has been largely omitted in the literature. This is regrettable from a practical point of view since the stronger dependence of the TE anomalous extraordinary transmission on the array’s substrate provides additional design parameters for exploitation. To provide high-performance and cost-effective applications based on TE anomalous extraordinary transmission, a complete physical insight about the underlying mechanisms of the phenomenon must be first laid down. To this end, resorting to a combined methodology including quasi-optical terahertz (THz) time-domain measurements, full-wave simulations, and method of moments analysis, subwavelength slit arrays under s-polarized illumination are studied here, filling the void in the current literature. We believe this work unequivocally reveals the leaky-wave role of the grounded-dielectric slab mode mediating in TE anomalous extraordinary transmission and provides the necessary framework to design practical high-performance THz components and systems.

We propose a method to generate specially shaped high-order singular beams of pre-designed intensity distributions. Such a method does not a priori assume a phase formula, but rather relies on the “cake-cutting and assembly” approach to achieve the azimuthal phase gradient for beam shaping, inspired by the orbital motion trajectory change of an artificial satellite. Based on our method, several typical vortex beams with desired intensity patterns are experimentally generated. As an example, we realize optical trapping and transportation of microorganisms with a triangle-shaped vortex beam, demonstrating the applicability of such unconventional vortex beams in optical trapping and manipulation.

An out-of-plane silicon grating coupler capable of mode-order conversion at the chip–fiber interface is designed and fabricated. Optimization of the structure is performed through finite-difference time-domain simulations, and the final device is characterized through far-field profile and transmission measurements. A coupling loss of 3.1 dB to a commercial two-mode fiber is measured for a single TE0→LP11 mode conversion grating, which includes a conversion penalty of 1.3 dB. Far-field patterns of the excited LP11 mode profile are also reported.

This paper presents a method to design a monolithic complete-light modulator (MCLM) that fully controls the amplitude, phase, and polarization of incident light. The MCLM is made of birefringent materials that provide different refractive indices to orthogonal eigen-polarizations, the ordinary o and extraordinary e states. We propose an optimization method to calculate the two relief depth distributions for the two eigen-polarizations. Also, a merging algorithm is proposed to combine the two relief depth distributions into one. The corresponding simulations were carried out in this work and the desired light distribution, including information on amplitude, phase, and four polarization states, was obtained when a laser beam passed through a 16-depth-level micro-structure whose feature size is 8 μm. The structure was fabricated by common photolithography. An experimental optical system was also set up to test the optical effects and performances of the MCLM. The experimental performance of the MCLM agrees with the simulation results, which verifies the validity of the algorithms we propose in this paper.

We demonstrate high-resolution and high-quality terahertz (THz) in-line digital holography based on the synthetic aperture method. The setup is built on a self-developed THz quantum cascade laser, and a lateral resolution better than 70 μm (～λ) is achieved at 4.3 THz. To correct intensity differences between sub-holograms before aperture stitching, a practical algorithm with global optimization is proposed. To address the twin-image problem for in-line holography, a sparsity-based phase retrieval algorithm is applied to perform the high-quality reconstruction. Furthermore, a new autofocusing criterion termed “reconstruction objective function” is introduced to obtain the best in-focus reconstruction distance, so the autofocusing procedure and the reconstruction are unified within the same framework. Both simulation and experiment prove its accuracy and robustness. Note that all the methods proposed here can be applied to other wavebands as well. We demonstrate the success of this THz synthetic aperture in-line holography on biological and semiconductor samples, showing its potential applications in bioimaging and materials analysis.