Space Light Modulator Research Articles

P‐52: Scalable Multi‐layered Real‐time Holography Processor Architecture with High Bandwidth Memory (HBM)

In this paper, we present a fast and efficiently scalable 3D holographic video processor using a layer‐based method using a modified inverse Fresnel transform. In our previous paper, we designed a single‐layer holographic core using a fixed‐point model and tested its operation on an FPGA. This paper implements an 8‐layer, 15FPS real‐time hologram processor by receiving RGB and depth input. For fast CGH processing, we utilized HBM memory, which is faster than DDR4, to store FFT results. After applying 2× linear interpolation, the implemented real‐time holography processor converts into real‐time holograms using a 4K color space light modulator

Spatiotemporal diffractive deep neural networks.

A spatiotemporal diffractive deep neural network (STD2NN) is proposed for spatiotemporal signal processing. The STD2NN is formed by gratings, which convert the signal from the frequency domain to the spatial domain, and multiple layers consisting of spatial lenses and space light modulators (SLMs), which conduct spatiotemporal phase modulation. An all-optical backpropagation (BP) algorithm for SLM phase tuning is proposed, with the gradient of the loss function computed by the inner product of the forward propagating optical field and the backward propagating conjugated error field. As a proof of concept, a spatiotemporal word "OPTICA" is generated by the STD2NN. Afterwards, a spatiotemporal optical vortex (STOV) beam multiplexer based on the STD2NN is demonstrated, which converts the spatially separated Gaussian beams into the STOV wave-packets with different topological charges. Both cases illustrate the capability of the proposed STD2NN to generate and process the spatiotemporal signals.

Optical deformations of azobenzene polymers: orientation approach vs. other concepts.

It has been 30 years since the discovery of surface restructuring in thin azopolymer films by two independent research groups. A wide variety of topographical structures have been created by the application of two-/four-beam interference patterns, space light modulators and even helical beams. There are a number of comprehensive reviews which describe in detail the advances in superficial photopatterning of azopolymer films and macroscopic deformations of azonetworks. The theoretical approaches are only briefly touched on in these reviews and often are accompanied by the remark that the phenomenon is far from being understood. In this review, we would like to present the polymer theoretist's point of view on this intriguing problem. We begin by describing a multitude of theoretical approaches and commenting on the pluses and drawbacks of each. Importantly, we show that in most cases the presence of an azopolymer matrix is either ignored or limited to a specific class of azopolymers (liquid-crystalline or elastomeric). We then move to early orientation approaches based on the hypothesis that reorientation of azo-chromophores by modulated polarized light is the sole cause of superficial patterning. At the end of the review a modern orientation approach, as proposed by our own group, is presented. This approach has high predictive power because it can explain a large pool of experimental data for different classes of azopolymers including glassy and liquid-crystalline materials. This is made possible by taking into account both the light-induced orientation process and the change of anisotropic interactions between the chromophores upon their isomerization. Last but not least, this is the only approach that provides an estimate of the light-induced stress large enough to cause plastic deformations of glassy azopolymers. Recent finite element modeling results show remarkable similarity to real patterns and even time-dependent data are well explained. With this, we claim that the puzzle is finally understood and the orientation approach is ready for its implementation for major azopolymer classes.

Development of a quasi-ring airy vortex beam using an all-dielectric geometric phase metasurface

The quasi-ring Airy vortex beam (QRAVB) is a special type of vortex beam was recently proposed, which performs efficiently in turbulent environments. However, bulky optical elements, such as the spatial light modulator, used for generating the QRAVB hinder its application in modern integrated optical communication devices. Here, we present a type of compact optical element developed for generating the QRAVB by using an all-dielectric geometric phase metasurface. We simulate the performance of the designed metasurface and discuss several properties, such as autofocusing and self-healing of the metasurface-generated beams, are similar to Airy beams. This type of metasurface has potential applications in integrated free-space optical communication and on-chip optical information processing in the future.

The electro-optic spatial light modulator of lithium niobate metasurface based on plasmonic quasi-bound states in the continuum.

Metasurface has attracted massive interest owing to its ability to control light arbitrarily in a wide range of applications, such as high-speed imaging, optical interconnection, and spectroscopy. Here we propose a free space light modulator combined with a gold grating metasurface based on lithium niobate (LiNbO3). The quasi-bound states in the continuum (quasi-BIC) are achieved in the metasurface. In addition, the plasmonic quasi-BIC and the guided-mode resonance (GMR) can be modulated by controlling the polarization of the incident light without any geometric adjustment. Thus, the working wavelength range from 1480 nm to 1620 nm was achieved, and the maximum resonance depth reached about 51% at the resonant wavelength. In addition, the insertion loss of the device was -2.8 dB at a wavelength of 1510 nm. Furthermore, the dynamic modulation speed reached up to 190 MHz and the highest signal-to-noise ratio (SNR) could reach about 49 dB at a frequency of 65 MHz. The data showed potential for the material for applications such as near-infrared imaging, beam steering, and free-space optical communication links.

Performance analysis of modulating retro-reflector link based on orbital angular momentum coding in underwater channels

The modulating retro-reflector (MRR) communication is developed to solve the problem of insufficient terminal power in underwater optical communication (UOC) where size, weight and power are severely restricted. Here, we propose a new MRR link scheme using the optical orbital angular momentum (OAM) for such scenarios to realize high-order coding. Furthermore, we simulate the OAM MRR link in the oceanic turbulence channel and use the convolutional neural network (CNN) to classify OAM patterns. The simulation results show that the OAM MRR link can realize error-free image transmission under weak turbulence strength of Cn2=10−15K2m−2/3 within 15 m distance using 8/16-ary OAM superposed modes, and with the increasing of the distance and the turbulence strength, the performance is decreasing, where the 16-ary format has a higher coding efficiency but lower performance than the 8-ary format. An experiment of the OAM MRR link using CNN to classify 16-ary OAM superposed modes is also demonstrated, where two space light modulators (SLMs) are used to simulate the short-distance oceanic turbulence channel and modulate the OAM beam, respectively. Our experiment result shows the recognition rate of 16-ary OAM set with different types of channel conditions. Our work may provide a novel way for high-order coding MRR links in underwater channels and hopefully increase the data rate of the MRR link in the future.

Direct generation of ultrafast vortex beam from a Tm:CaYAlO4 oscillator featuring pattern matching of a folded-cavity resonator.

Optical vortices, beams with spiral wavefronts and screw phase dislocations have been explored in applications in optical manipulation, quantum optics, and the next generation of optical communications. In traditional methods, optical vortices are generated using space light modulators or spiral phase plates, which would sharply decrease the integration of optical systems. Different from previous transverse mode conversion outside the cavity, here we experimentally demonstrate a direct generation of ultrafast vortex beam from a Tm:CaYAlO4 oscillator by pattern matching of a six-mirror-folded-cavity resonator. By accurately adjusted the angle of the end mirror and the distance L between the M4 and the SESAMs to control the beam diameter of laser incidence on the gain medium in the sagittal and tangential planes, a stable 2 µm ultrafast vortex laser emission of annular Laguerre-Gaussian (LG) mode was obtained with a maximum output power of 327 mW and pulse duration of 2.1 ps. A simple YAG crystal plate was used as handedness selector and a homemade Mach-Zehnder (MZ) interferometer has verified the vortical property of the LG01 mode. By furtherly controlling the cavity mode pattern matching, other stable transverse-mode operations for TEM00, high-order Hermite-Gaussian (HG) transverse mode and doughnut-shaped beams were successfully realized. This work provides a flexible and reliable way to generate mid-infrared ultrafast vortex beams and is of special significance for applications in the areas of molecular spectroscopy and organic material processing amongst others.

Electrically Tunable Multifunctional Polarization-Dependent Metasurfaces Integrated with Liquid Crystals in the Visible Region.

Metasurfaces open up new avenues for designing planar optics, enabling compact dynamic metadevices. Numerous dynamic strategies have been proposed, among which liquid crystal (LC) based metasurfaces are expected due to the maturity of LC materials. However, existing schemes rarely exploit the polarization manipulation capabilities of metasurfaces and the limited performance hinders the development of practical addressable devices. Here, we demonstrate an electrically tunable multifunctional polarization-dependent metasurface integrated with LCs in the visible range. By a combination of the helicity-dependent metasurface and the birefringent LCs, continuous intensity tuning and switching of two helicity channels are realized. Electrically tunable mono- and multicolor switchable metaholograms and dynamic varifocal metalenses are demonstrated with a simple and performance-enhancing integration scheme. Further, electrically addressable dynamic metasurfaces are achieved. The proposed modulation and integration schemes pave the way for addressable dynamic metasurface devices in various applications, such as space light modulators, light detection and ranging systems, and holographic displays.

Tunable converge optical elliptical vortex based on elliptical helical lens

We present a new scheme to produce a tunable converge elliptical optical vortex (EOV) with a phase-only element: elliptical helical lens (EHL), which is studied theoretically and experimentally. As a result, the properties of converge EOVs can be controlled by adjusting the parameters of EHL. The topological charges of the EOVs can be directly read from the received intensity pattern. Because EHL is a hologram programmed in space light modulator (SLM), converge EOVs can be controlled just by reprogramming the SLM instead of replacing actual instruments. This work has potential applications in particle manipulation, as well as generation of OAM-entangled photons.

空间光调制器扫描接收的距离选通成像激光雷达

空间光调制器扫描接收的距离选通成像激光雷达

Adaptive Demodulator Using Machine Learning for Orbital Angular Momentum Shift Keying

An $m$ -ary adaptive demodulator based on machine learning for light beams carrying orbital angular momentums (OAMs) over free-space turbulence channels is proposed and demonstrated. Benefiting from natural advantages in the image recognition, convolutional neural network (CNN) is selected to construct the adaptive demodulator. Without extra space light modulators and digital signal processing at the reception, the adaptive demodulator transforms the sequence of intensity patterns of received Laguerre–Gaussian beams carrying different OAM modes into initial signals efficiently. As comparison, K-nearest neighbor (KNN), naive Bayes classifier (NBC), and back-propagation artificial neural network (BP-ANN) are also studied. Furthermore, the demodulating accuracy of 4-, 8-, and 16-ary OAM is investigated with the comprehensive consideration of the atmospheric turbulence, OAM mode spacing, and transmission distance. The simulation results show that the demodulating error rate (DER) of CNN outperforms KNN, NBC, and BP-ANN, especially under stronger turbulence and longer distance. The DER of CNN is ~0.86% for the 1000-m 8-OAM system under strong turbulence, ~30 % less than those of KNN, NBC, and BP-ANN.

Microwave waveform generation with reconfigurable envelope and high fidelity based on spectrum compensated frequency-to-time mapping

Abstract A photonic approach for generating radio frequency (RF) chirped and non-chirped waveforms with reconfigurable envelope and high fidelity is proposed and experimentally demonstrated based on frequency-to-time mapping (FTM). A space light modulator based pulse shaper is used for spectral shaping. To make full use of the available bandwidth of the pulse shaper, the output of an amplified mode-locked laser is used as a broadband optical source. A feedback scheme is proposed to compensate the absence of the amplified spontaneous emission spectrum in frequency-to-time mapping. Based on the spectrum compensated FTM, chirped and non-chirped waveforms with different envelopes and high fidelity are experimentally generated.

M N Wavelength Selective Switches Using Beam Splitting By Space Light Modulators

We propose a multiple-input-multiple-output (M x N) optical switch with the same optical system as that used for a single-input-multiple-output (1 x N) switch based on a liquid crystal on silicon (LCOS). The proposed M x N switch can route multiple signals simultaneously from different plural inputs to plural outputs, which is called multipole multithrow (MPMT). In addition, our switch configuration can multiply an MPMT switch due to its multicast capacity by beam splitting with holographic phase modulation on the LCOS. We demonstrate a two-degree ROADM using our proposed 4 x 4 wavelength selective switch. The experimental results show that a two-degree ROADM node can be realized by using this switch. The increase in the insertion loss caused by the MPMT switching function is 3 dB due to beam splitting and 3-4.1 dB due to imperfections in the holographic phase modulations. The maximum port crosstalk (XT) is -20.0 dB.

A planar chiral meta-surface for optical vortex generation and focusing.

Data capacity is rapidly reaching its limit in modern optical communications. Optical vortex has been explored to enhance the data capacity for its extra degree of freedom of angular momentum. In traditional means, optical vortices are generated using space light modulators or spiral phase plates, which would sharply decrease the integration of optical communication systems. Here we experimentally demonstrate a planar chiral antenna array to produce optical vortex from a circularly polarized light. Furthermore, the antenna array has the ability to focus the incident light into point, which greatly increases the power intensity of the generated optical vortex. This chiral antenna array may have potential application in highly integrated optical communication systems.

测量空间相机像移量的联合变换相关器的改进

As traditional joint transform correlators based on space light modulators can not adapt to the radioactive environment in space, a new correlator implemented by an electronic processor was introduced and testified. First, the traditional optical device was replaced by a digital processor to allow the new correlator to adapt to the radioactive environment. Then, a self-correlation calculation was added to the joint transform processing to eliminate the influence of zero-level diffraction, and the over-sampled discrete Fourier transform method was introduced to increase the measurement precision. Finally, the static measurement with a linear platform was performed to testify the improved joint transform correlator. Experimental results indicate that the measuring precision of the system on subpixel displacement is within 0.22 pixel(Root Mean Square, RMS). The improved joint transform correlator is good at both space environment adaptability and realization, its measurement precision can satisfy the system requirements of satellite cameras for the image motion compensation, and has a good application prospect.

Optical tweezers technique and its applications

Since their advent in the 1980s, optical tweezers have attracted more and more attention due to their unique non-contact and non-invasion characteristics and their wide applications in physics, biology, chemistry, medical science and nanoscience. In this paper, we introduce the basic principle, the history and typical applications of optical tweezers and review our recent experimental works on the development and application of optical tweezers technique. We will discuss in detail several technological issues, including high precision displacement and force measurement in single-trap and dual-trap optical tweezers, multi-trap optical tweezers with each trap independently and freely controlled by means of space light modulator, and incorporation of cylindrical vector optical beams to build diversified optical tweezers beyond the conventional Gaussian-beam optical tweezers. We will address the application of these optical tweezers techniques to study biophysical problems such as mechanical deformation of cell membrane and binding energy between plant microtubule and microtubule associated proteins. Finally we present application of the optical tweezers technique for trapping, transporting, and patterning of metallic nanoparticles, which can be harnessed to manipulate surface plasmon resonance properties of these nanoparticles.

Comparative analysis for measurement precision of phase retrieval wavefront sensor

In order to analyze the performance of phase retrieval wavefront sensor (PRWS), an experimental based on the PRWS method has been built. In this paper, we utilize liquid crystal space light modulator (LC-SLM) to produce single aberration and random aberration, and validate the ability of PRWS measurement for any aberrations. Mathematic model of phase retrieval measurement is constructed based on the diffraction theory, and solved using gradient based optimization algorithm. Experimental results demonstrate that good agreement is obtained among the errors distribution, PV value and RMS value of ZYGO interferometer. The measurement precision of wavefront is 3/1000 wavelength RMS. Therefore, the feasibility and accuracy of the proposed method can be confirmed.

A hogel-based holographic recording system and its hologram reconstruction improvement

This paper presents a holographic pixel (hogel)-based recording system and its hologram reconstruction improvement for three-dimensional (3D) displays. In this system, both a ground glass and a beam expander are utilized to expand an object beam in order to reduce the discontinuities in the reconstructed images. Moreover, a digital mirror device (DMD) instead of a liquid crystal display (LCD) is used as a space light modulator (SLM) to display the encoding images with information about hogels. The pixel period and resolution of the DMD panel are 12μm and 1024ÿ768 grids, respectively. With computer controlled movement of a holographic plate, a synthetic hologram constituted of thousands of hogels with a sub-millimeter resolution (0.8mm) is recorded hogel by hogel on the holographic plate of 200mmÿ140mm in size. Experimental holographic reconstructions of synthetic holograms prove the feasibility of the proposed method by using a self-generated plane model with a resolution of 225ÿ150 pixels.

Research on dynamical-gradual greyscale digital mask lithography

Dynamical-gradual greyscale digital lithography is proposed in this article. This technique is based on a space light modulator (SLM). The digital mask group was designed according to zones. Exposure energy was accumulated by controlling time and grey value. Each mask in the designed mask group was displayed on a PC sequentially, so the exposure of each zone could be finely controlled. This lithographic skill was illustrated by fabricating a microlens array. During fabrication, the zones were divided equally from the microlens’ diameter, and each unit was formed by pixels of the space light modulator. In this way, a microlens’ profile and optical property could be improved. In the experiment, we fabricated patterns of microlenses of 64 µm in diameter and 7 µm in height.

A HDRI Camera Based on SLM

A high dynamic range image camera (HDRI) is a kind of camera which captures the HDRI image. HDRI means the image with high dynamic range, it can record the gray information of the object with much wider dynamic range. HDR image has great applications in many fields. The existing HDRI camera needs either the special image sensor or can capture the still object only. In this paper, a new kind of camera is proposed. In this camera, a space light modulator (SLM) is used to acquire images with different exposure, then a HDRI is made with these images. This camera can acquire dynamic image and it is cheap and easy to extend.