Spatial Light Modulator Device Research Articles

Novel PCA-Based Lower-Dimensional Remapping of the Solution Space for a Genetic Algorithm Optimization: Estimating the Director Distribution in LC-Based SLM Devices

This work introduces a novel computational approach based on Principal Component Analysis (PCA) for dimensionality reduction of the solution space in optimisation problems with known linear interdependencies among solution variables. By creating synthetic datasets with deliberately engineered properties and applying PCA, the solution space’s remapping significantly reduces its dimensionality, leading to faster computation and more robust convergence in optimisation processes. We demonstrate this method by integrating it with a Genetic Algorithm (GA) for solving the optimal director distribution in liquid crystal (LC) devices, specifically addressing 2D and complex 3D spatial light modulator (SLM) structures such as twisted nematic liquid crystals (TN-LC) and parallel-aligned liquid crystal on silicon (PA-LCoS), respectively. The phase profiles obtained from the director vector distributions for horizontal and vertical high-frequency binary phase gratings closely match the theoretical values derived from minimising the traditional elastic Frank–Oseen functional via Euler–Lagrange equations. Beyond this specific application, our method offers a general framework for reducing computational complexity in optimisation problems by directly reducing the dimensionality of the solution space. This approach is applicable across various optimisation scenarios with well-known linear interdependencies among solution variables, enabling significant reductions in computational costs and improvements in robustness and convergence.

Low-cost single-shot complex optical field imaging with a simplified aperture

We report a new computational imaging methodology for complex optical field based on a single-frame diffraction intensity pattern acquisition with a simplified aperture and an extremely low-cost industrial machine vision camera. The current design of the apertures for the recovery of complex optical field was suffering from specific coding associated with the use of spatial light modulator or digital micromirror device, where it is difficult to make the optical implementations compact and cost-effective. In this work, we demonstrate that a simplified aperture without any pattern-like coding is efficient to establish the physical constraint for computational reconstruction. The aperture attached to the object defines the imaging region of interest (ROI) with coherent trans-illumination, and only one snapshot of the diffraction intensity pattern is required for recovering the ROI's complex field. Proof-of-concept numerical simulations and optical experiments have been carried out to validate the feasibility, noise robustness, resolution, and potential biological imaging applications of the proposed computational method.

Structured light reconstruction by Computer-Generated hologram in defect state

The generation of structured light from Computer-Generated Hologram (CGH) using spatial light modulators (SLM) has a wide range of applications, but there is currently a lack of research on localized defects in SLM devices. Considering that the local damage of SLM can lead to hologram defect, its result can be equivalent to the process of normal hologram generated structured beam with its near field being blocked. In this paper, CGH loaded onto digital micromirror device (DMD) is used to generate structured beams, and two cases of local defect states at the center and edge of the DMD are discussed. The results show that the reconstructed light field obtained by central defect is quite similar to the original light field, while the reconstructed light field obtained by edge defect is a much similar to the lower case of the original light field. The article further demonstrates the reconstructed results in coherent superpositions of Hermite-Gaussian modes using DMD-generated structured beams based on the single mode regime. This study expands the application scenarios for the generation of structured light beams with SLM.

Beam‐Steering Metadevices for Intelligent Optical Wireless‐Broadcasting Communications

High‐performance beam‐steering devices play a crucial role for optical wireless communication (OWC), which can meet the demand for increasing number of wireless mobile devices and emerging high‐speed multimedia applications. Conventional beam‐steering optical components like spatial light modulator and digital micromirror device are limited to realize a small steering angle (typ. several degrees), thus dramatically limits the spatial scope of OWC. Herein, a beam‐steering metadevice utilizing an ultracompact metasurface assisted with a spatial light modulator is presented, which can significantly increase the beam‐steering angle without at the cost of complicated optical setup like conventionally used angle magnifier. Based on the actively tunable beam‐steering metadevice, an intelligent bidirectional optical broadcasting communication system is designed and experimentally demonstrated, which exhibits nine broadcasting areas covering a large field‐of‐view of 20° × 20°, with user‐defined dynamic beam‐steering ability in each area, and each user has a data rate of 10 Gbps for both upstream and downstream transmission. The proposed metadevices can meet the demand of intelligent optical wireless communication which requires both high‐performance and low‐cost for practical purpose, under currently available technical architectures.

Analysis of reconstruction quality for computer-generated holograms using a model free of circular-convolution error.

Continuous complex-amplitude computer-generated holograms (CGHs) are converted to discrete amplitude-only or phase-only ones in practical applications to cater for the characteristics of spatial light modulators (SLMs). To describe the influence of the discretization correctly, a refined model that eliminates the circular-convolution error is proposed to emulate the propagation of the wavefront during the formation and reconstruction of a CGH. The effects of several significant factors, including quantized amplitude and phase, zero-padding rate, random phase, resolution, reconstruction distance, wavelength, pixel pitch, phase modulation deviation and pixel-to-pixel interaction, are discussed. Based on evaluations, the optimal quantization for both available and future SLM devices is suggested.

Active focal-plane coronagraphy with liquid-crystal spatial-light modulators: broadband contrast performance in the visible.

The technological progress in spatial-light modulator (SLM) technology has made it possible to use those devices as programmable active focal-plane phase coronagraphic masks, opening the door to novel versatile and adaptive high-contrast imaging observation strategies. However, the scalar nature of the SLM-induced phase response is a potential hurdle when applying the approach to wideband light, as is typical in astronomical imaging. For the first time, to our knowledge, we present laboratory results with broadband light (up to ∼12% bandwidth) for two commercially available SLM devices used as active focal-plane phase masks in the visible regime (640 nm). It is shown that under ideal or realistic telescope aperture conditions, the contrast performance is negligibly affected in this bandwidth regime, reaching a sufficient level for ground-based high-contrast imaging, which is typically dominated by atmospheric residuals.

Spatial light modulator design and generation of structured electromagnetic waves using digital light processors

Spatial light modulators (SLMs) are versatile devices used for optical studies. These instruments have a wide area of application in photonics. Additionally, SLMs have potential utility in different applications, such as biomedical applications, laser based surgery for precise cutting and as optical tweezers to separate cells in a petri container. However, the high cost of SLM devices prevents their widespread use in many areas, including industrial areas and scientific research laboratories. This paper demonstrates how to design a digital light processor (DLP) based low-cost SLM and describes how to obtain structured electromagnetic waves with the designed SLM. Therefore, this research was undertaken to design and produce a low-cost SLM device for optical applications. For this purpose, two prerequisites had to be fulfilled, the first was to use suitable components of a projection device with DLP-based digital micro-mirror device (DMD), and the second was to eliminate unnecessary SLM components from the system. Finally, holographic images reflected on the SLM screen were created by using Mathematica software program to change the amplitude and phase of the electromagnetic waves in order to obtain the structured electromagnetic waves.

Electro-optical and dielectric characteristics of highly tilted ferroelectric liquid crystal material 4'-(3-pentanoyloxyprop-1-oxy)biphenyl-4-yl (S)-(+)-4-(1-methylheptyloxy) benzoate

The advancement on ferroelectric liquid crystals and their novel appliance is just changing from being largely focused on display devices and fast optical shutter elements to several other fields such as spatial light modulator, optical sensor, polarisation grating, photonic and optical devices. In the present work, we report the thermodynamical, textural, electrical and switching behaviour of a highly tilted FLC material. The studies have been performed on a 5 μm thick planar oriented sample. The above material possess cholesteric (N*), chiral smectic C* (SmC*) and hexatic (SmB*) phases in cooling cycle as confirmed by optical, thermodynamic and dielectric studies. The spontaneous polarisation is highly temperature dependent and increases while cooling in the SmC* phase. The maximum value of spontaneous polarisation is ∼117 nC cm−2 at 76 °C. The switching time is of the order of a few milli seconds (∼1.3 ms). The conductivity (ionic and dipolar both) of the material has also been determined in all the above exhibited phases.

Asymmetric Optical Wavelength Switch Based on LCoS-SLM for Edge Node of Optical Access Network

A novel design of optical wavelength switch, based on an asymmetric switching architecture for edge node implementation, is presented in this paper. Compared to previous research for optical core transport network applications, the proposed work has a unique aspect to build dynamic multicasting and spectral equalization, vital functionalities for optical wavelength switch in the edge of optical access networks. An optical wavelength switch was experimentally implemented and evaluated in a 4 × 16 switching architecture to demonstrate the concept. This dynamic multicasting and spectral equalization were achieved by utilizing liquid crystal on a silicon spatial light modulator (LCoS-SLM) device. An optimal design of computer-generated holograms (CGHs) through an improved GS algorithm was used to perform the beam steering and wavelength switching. A variety of wavelength switching scenarios has been experimentally evaluated. The measurement results showed an average insertion loss of around -12.5 dB, and the calculated crosstalks were all less than -28 dB. Its applications in digital data transmissions were evaluated to achieve a transmission speed larger than 2.5 Gbps. The eye diagram measurement results showed that most wavelength switching scenarios have nearly bit-error-free transmission. The scenario includes the multicasting with spectral equalization within the proposed asymmetrical switching architecture.

Optimal quantization for amplitude and phase in computer-generated holography.

Owing to the characteristics of existing spatial light modulators (SLMs), the computer-generated hologram (CGH) with continuous complex-amplitude is conventionally converted to a quantized amplitude-only or phase-only CGH in practical applications. The quantization of CGH significantly affects the holographic reconstruction quality. In this work, we evaluated the influence of the quantization for both amplitude and phase on the quality of holographic reconstructions by traversing method. Furthermore, we considered several critical CGH parameters, including resolution, zero-padding size, reconstruction distance, wavelength, random phase, pixel pitch, bit depth, phase modulation deviation, and filling factor. Based on evaluations, the optimal quantization for both available and future SLM devices is suggested.

Fast generation and detection of spatial modes of light using an acousto-optic modulator

Spatial modes of light provide a high-dimensional space that can be used to encode both classical and quantum information. Current approaches for dynamically generating and measuring these modes are slow, due to the need to reconfigure a high-resolution phase mask such as a spatial light modulator or digital micromirror device. The process of updating the spatial mode of light can be greatly accelerated by multiplexing a set of static phase masks with a fast, image-preserving optical switch, such as an acousto-optic modulator (AOM). We experimentally realize this approach, using a double-pass AOM to generate one of five orbital angular momentum states with a switching rate of up to 500 kHz. We then apply this system to perform fast quantum state tomography of spatial modes of light in a 2-dimensional Hilbert space by projecting the unknown state onto six spatial modes comprising three mutually unbiased bases. We are able to reconstruct arbitrary states in under 1 ms with an average fidelity of 96.9%.

Progress in Phase Calibration for Liquid Crystal Spatial Light Modulators

Phase-only Spatial Light Modulator (SLM) is one of the most widely used devices for phase modulation. It has been successfully applied in the field with requirements of precision phase modulation such as holographic display, optical tweezers, lithography, etc. However, due to the limitations in the manufacturing process, the grayscale-phase response could be different for every single SLM device, even varying on sections of an SLM panel. A diverse array of calibration methods have been proposed and could be sorted into two categories: the interferometric phase calibration methods and the diffractive phase calibration methods. The principles of phase-only SLM are introduced. The main phase calibration methods are discussed and reviewed. The advantages of these methods are analyzed and compared. The potential methods for different applications are suggested.

Applications of Spatial Light Modulators in Raman Spectroscopy.

Advances in consumer display screen technologies have historically been adapted by researchers across the fields of optics as they can be used as electronically controlled spatial light modulators (SLMs) for a variety of uses. The performance characteristics of such SLM devices based on liquid crystal (LC) and digital micromirror device (DMD) technologies, in particular, has developed to the point where they are compatible with increasingly sensitive instrumental applications, for example, Raman spectroscopy. Spatial light modulators provide additional flexibility, from modulation of the laser excitation (including multiple laser foci patterns), manipulation of microscopic samples (optical trapping), or selection of sampling volume (adaptive optics or spatially offset Raman spectroscopy), to modulation in the spectral domain for high-resolution spectral filtering or multiplexed/compressive fast detection. Here, we introduce the benefits of different SLM devices as a part of Raman instrumentation and provide a variety of recent example applications which have benefited from their incorporation into a Raman system.

Switchable Holographic Device Based on Reversible Electrodeposition

AbstractA new switchable holographic device concept using reversible electrodeposition (RED) technology is proposed. The proposed device has a structure in which the cavity structure is changed by the reversible deposition of Ag, and thus the characteristics of the reflected light are modulated. It has a high reflectance due to a mirror reflection structure and exhibits phase modulation by the reversible deposition of Ag. Because the proposed device is a current‐driven device, it is expected to overcome the limitation in the scaling down of the pitch in spatial light modulators, which is considered a limitation of liquid crystal device. A passive type switchable holographic device with a 1 µm pitch is implemented using the proposed device. The successful implementation of a switchable holographic image using the fabricated device is confirmed. The proposed device is expected to be applicable as an active metasurface and spatial light modulator device in the visible light region in the future because it has a large modulation in the visible light region.

Improvement in cyclic operation of unit pixel device using Sb-excess Ge2Sb2Te5 thin films for hologram image implementation

The effects of the atomic composition of Ge2Sb2Te5 (GST), especially the Sb-excess phase, on device reliability were investigated for applications of spatial light modulator (SLM) devices using phase-change materials. Sb-excess GST phases were prepared by cosputtering with two target systems. For Sb-excess GST thin films, amorphous phases were found to be more directly crystallized to more conductive hexagonal-close-packing phases at higher crystallization temperatures without the appearance of a less conductive face-centered-cubic phase with increasing amount of incorporated Sb. The marked changes in crystallization behavior and improved thermal stability were suggested as critical benefits for enhancing the device durability during cyclic operations, considering that the interdiffusion within the GST could be the main origin of the final device failure. The number of cyclic operations of the unit pixel device was markedly improved to more than 103 when the amount of excess Sb was modulated from 0 to 21 at. %.

27.1: Invited Paper: Study on the design and fabrication of intensity modulating liquid crystal spatial light modulator

Liquid crystal devices are one type of high quality optical information regulating devices, in addition to its wide application in displays field. Such as liquid crystal (LC) spatial light modulator (SLM), it can adjust both phase and amplitude of polarized light. Combined with other devices, LC device can also adjust the polarization state and transmission spectrum of light. In this study, a kind of intensity modulating LC‐SLM which can modulate wavelength light in 1064nm is designed and fabricated. Firstly, electro‐optic characteristic of ECB, VA and TN mode in the reflective LC‐SLM was analyzed; and TN mode was chosen as final design and prepared. Secondly, dependence of twist angle and phase modulation on contrast ratio and transmission level of final device were analyzed by Jones matrix. Thirdly, the influence of dielectric anisotropy on device contrast was analyzed by Jones matrix. Furthermore, with appropriate technical condition, such as rubbing direction, twist angle control, cell gap control, liquid crystal injecting and electric wire bonding, the final SLM device was successfully fabricated with targeted design. Finally, target devices were tested and realization standard of each design parameter was analyzed in this work.

Orthoscopic real-image display of digital holograms.

We present a practical solution for the long-standing problem of depth inversion in real-image holographic display of digital holograms. It relies on a field lens inserted in front of the spatial light modulator device addressed by a properly processed hologram. The processing algorithm accounts for pixel size and wavelength mismatch between capture and display devices in a way that prevents image deformation. Complete images of large dimensions are observable from one position with a naked eye. We demonstrate the method experimentally on a 10-cm-long 3D object using a single full-HD spatial light modulator, but it can supplement most holographic displays designed to form a real image, including circular wide angle configurations.

Structured illumination microscopy with interleaved reconstruction (SIMILR).

Structured illumination microscopy (SIM) is the commonly used super-resolution (SR) technique for imaging subcellular dynamics. However, due to its need for multiple illumination patterns, the frame rate is just a fraction of that of conventional microscopy and is thus too slow for fast dynamic studies. A new SR image reconstruction method that maximizes the use of each subframe of the acquisition series is proposed for improving the super-resolved frame rate by N times for N illumination directions. The method requires no changes in raw data and is appropriate for many versions of SIM setup, including those implementing fast illumination pattern generation mechanism based on spatial light modulator or digital micromirror device. The performance of the proposed method is demonstrated through imaging the highly dynamic endoplasmic reticulum where continuous rapid growths or shape changes of tiny structures are observed.

LCoS SLM Study and Its Application in Wavelength Selective Switch

The Liquid-Crystal on Silicon (LCoS) spatial light modulator (SLM) has been used in wavelength selective switch (WSS) systems since the 1990s. However, most of the LCoS devices used for WSS systems have a pixel size larger than 6 µm. Although there are some negative physical effects related to smaller pixel sizes, the benefits of more available ports, larger spatial bandwidth, improved resolution, and the compactness of the whole system make the latest generation LCoS microdisplays highly appealing as the core component in WSS systems. In this review work, three specifications of the WSS system including response time, crosstalk and insertion loss, and optimization directions are discussed. With respect to response time, the achievements of liquid crystal material are briefly surveyed. For the study of crosstalk and insertion loss, related physical effects and their relation to the crosstalk or insertion loss are discussed in detail, preliminary experimental study for these physical effects based on a small pixel LCoS SLM device (GAEA device, provided by Holoeye, 3.74 µm pixel pitch, 10 megapixel resolution, telecom) is first performed, which helps with predicting and optimizing the performance of a WSS system with a small pixel size SLM. In the last part, the trend of LCoS devices for future WSS modules is discussed based on the performance of the GAEA device. Tradeoffs between multiple factors are illustrated. In this work, we present the first study, to our knowledge, of the possible application of a small pixel sized SLM as a switching component in a WSS system.

Spatially resolved scatter measurement of diffractive micromirror arrays.

Spatial light modulators (SLMs) support flexible system concepts in modern optics and especially phase-only SLMs such as micromirror arrays (MMAs) appear attractive for many applications. In order to achieve a precise phase modulation, which is crucial for optical performance, careful characterization and calibration of SLM devices is required. We examine an intensity-based measurement concept, which promises distinct advantages by means of a spatially resolved scatter measurement that is combined with the MMA's diffractive principle. Measurements yield quantitative results, which are consistent with measurements of micromirror roughness components, by white-light interferometry. They reveal relative scatter as low as 10^-4, which corresponds to contrast ratios up to 10,000. The potential of the technique to resolve phase changes in the subnanometer range is experimentally demonstrated.