Application Of Spatial Light Modulator Research Articles

High-Precision Calibration of Phase-Only Spatial Light Modulators

In the fields of optics and photonics, phase-only spatial light modulators (SLMs) play an increasingly important role in wave-front engineering. However, the SLMs are subject to wavefront distortion arising from the imperfection in the birefringence effect and physical structure of modulators. This paper presents a simple self-interference phase calibration method applicable to liquid-crystal SLM. We build an interferometric imaging system based on the Pancharatnam phase-shifting to measure the phase distribution of a light beam coming from SLMs. Two types of phase modulation errors of SLMs can be characterized in the measurement process: the erroneous gamma curve and shape aberration. The former belongs to dynamic phase distortion and is measured through a four-step Pancharatnam phase-shifting interference, which allows a one-shot recording of interference pattern via a polarization camera; the latter represents static phase distortion and is extracted from the interference between light waves coming from different regions of the SLM panel by using Zernike polynomial fitting. Our method has the advantages of high-precision pixel-wise phase correction and robustness against environmental disturbance and thus can facilitate the applications of SLM in optical field manipulation.

LCOS Spatial Light Modulator for Digital Holography

Liquid crystal on silicon (LCOS) spatial light modulator (SLM) is the most widely used optical engine for digital holography. This paper aims to provide an overview of the applications of phase-only LCOS in two-dimensional (2D) holography. It begins with a brief introduction to the holography theory along with its development trajectory, followed by the fundamental operating principle of phase-only LCOS SLMs. Hardware performance of LCOS SLMs (in terms of frame rate, phase linearity and flicker) and related experimental results are presented. Finally, potential improvements and applications are discussed for futuristic holographic displays. Full Text: PDF ReferencesM. Wolfke, Physikalische Zeitschrift 21, 495 (1920). DirectLink D. Gabor, "A New Microscopic Principle", Nature 161, 777 (1948). CrossRef H. Haken, "Laser Theory", Light and Matter 5, 14 (1970). CrossRef S. Benton, "Selected Papers on Three-dimensional displays", SPIE Press (2001). DirectLink X. 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Fast-Response Liquid Crystal for Spatial Light Modulator and LiDAR Applications

We report a new nematic mixture for liquid-crystal-on-silicon spatial light modulator (SLM) and light detection and ranging (LiDAR) applications. The mixture exhibits a relatively high birefringence (Δn), moderate dielectric anisotropy (Δɛ), low viscosity, and reasonably good photostability. To achieve 2π phase change at 5 V, the response time (on + off) is 2.5 ms at 40 °C with λ = 633 nm, and 5.9 ms with λ = 905 nm. After exposure by a blue laser (λ = 465 nm) with a total dosage up to 20 MJ/cm2, this mixture shows no sign of photodegradation. Widespread applications of this material for high brightness SLMs, LiDAR, near-eye displays, and head-up displays are foreseeable.

26.1: Invited Paper: Command splay‐bend switching in an optically‐compensated bend cell with polymerized liquid crystal photoalignment layers

We demonstrate a fast‐switching optically‐compensated bend (OCB) configuration with polymerized liquid crystal photoalignment (PAL). The experimental results show the dependency of the electro‐optical properties of OCB cells on the morphology‐mediated surface anchoring of polymerized liquid crystal PAL. Furthermore, the polymerized liquid crystal PAL exhibits superior stability against UV exposure and thermal stress tests, which make PAL applicable in display and spatial light modulator applications.

Single ultra-high-definition spatial light modulator enabling highly efficient generation of fully structured vector beams.

Ultra-high-definition (UHD) spatial light modulators (SLMs) enhance the degree of freedom in the versatile engineering of optical field. Among efforts to explore the capability of SLMs, enhancing the efficiency of light utilization is an everlasting quest to find SLM-based applications. We propose a new method to efficiently generate arbitrary vector beams with a phase-only UHD-SLM. By enabling the UHD-SLM with a rectangle window to work in an in-line and split-screen manner with the help of a polarizing beam splitter, the total conversion efficiency as high as 49% of light beams is realized. Several complex beams, including cylindrical vector beams and higher-order Poincaré sphere beams, are experimentally demonstrated. Our method can facilitate application of SLM in optical field manipulation.

Special Issue on Liquid Crystal on Silicon Devices: Modeling and Advanced Spatial Light Modulation Applications

Since the first liquid crystal displays (LCDs) at the beginning of the seventies—based on the twisted-nematic cell configuration [...]

Wavefront correction for spatial nonuniformity of the liquid crystal on silicon based spatial light modulator

Liquid crystal on silicon (LCoS) based spatial light modulator (SLM) is widely used in many research areas, such as holography display, optical measurement, and optical tweezers, due to its programmable capability of phase modulation. However, a certain aberration term to the incident wavefront is introduced due to the spatial nonuniformity of the LCoS backplane, and the correction of this phase aberration is important to improve the accuracy of phase modulation by the SLM, which will then influence the SLM applications, e.g., the image quality in holography display, or the beam shaping for optical tweezers and free-space communications. Fortunately, the LCoS based SLM has the programmable capability of phase modulation; therefore, the spatial nonuniformity can be compensated by a wavefront correction. Conventionally, this aberration is corrected by adjusting the Zernike coefficients of the generated wavefront manually. However, this procedure is time-consuming and subjective, since there are dozens of coefficients to be adjusted, and the adjustment is evaluated manually by monitoring the interferogram. In this paper, we propose to use several phase retrieval techniques to measure the corresponding wavefront directly and employ the obtained wavefront to correct the aberration introduced by the spatial nonuniformity. A Twyman-Green interferometry is used, and an interferogram acquisition technique based on the self wavefront modulation of SLM is proposed. Besides, a method for determining the corresponding active area of the LCoS backplane and parameters of 2-D projective transformation is proposed to transform the active area to the fitted resolution of the SLM. RMS value of the aberration to approximately λ/32 can be obtained by the proposed method. Consequently, more accurate phase modulation by SLM for applications such as holography display and beam shaping is achievable. Effectiveness of the proposed method is validated by experiment, and the correction results by different phase retrieval techniques are evaluated and compared.

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.

The application of SLM in shearography detecting system

The paper presents a new shearography system which applies a spatial light modulator (SLM). The system can control the shearing amount and direction as well as introduce the phase shift accurately and automatically, making shearographic testing easier and more practical. Shearography has the known advantages for nondestructive test and strain measurements of being fast, full-field, and having high sensitivity. Traditionally, the shearing amount is controlled by adjusting a reflector mechanically. Mechanical adjustment of the reflector is slow, inconvenient and not well suited for in-field NDT practice. For application of phase shift techniques, a piezoelectric transducer (PZT), which is usually used for application of phase shift techniques, introduces random error due to its tendency to be nonlinear. This paper introduces a new shearographic detection system with a spatial light modulator. The spatial light modulator controls the liquid crystal by using a birefringence effect and twisted nematic effect. The spatial light modulator can change the phase of the light and shearing amount accurately and automatically, thus eliminating the nonlinear random error in the phase shift method. Furthermore, this system also improves testing efficiency. In this paper, the fundamental of SLM shearography is presented. The capability of this optical configuration is demonstrated theoretically as well as through experiments.

Simplified physical modeling of parallel-aligned liquid crystal devices at highly non-linear tilt angle profiles

In recent works, we demonstrated the accuracy and physical relevance of a highly simplified reverse-engineering analytical model for a parallel-aligned liquid crystal on silicon devices (PA-LCoS). Both experimental measurements and computational simulations applying the rigorous split-field finite difference time domain (SF-FDTD) technique led to this conclusion in the low applied voltages range. In this paper, we develop a complete rigorous validation covering the full range of possible applied voltages, including highly non-linear liquid crystal (LC) tilt angle profiles. We demonstrate the applicability of the model for spectral and angular retardation calculations, of interest in spatial light modulation applications. We also show that our analytical model enables the calculation of the retardance for novel PA-LC devices as a function of the LC compound and cell gap, becoming an appealing alternative to the usual numerical approaches for PA-LC devices design.

Mathematical model of digital optoelectronic spectrum analyzer

Background. Digital optoelectronic spectrum analyzer (DOSA) used for spatial-frequency analysis of two-dimensional signals occupies a significant place among optical information processing systems. Diaphragms and the photographic plates with transmission corresponding to investigating signals were used as an input transparency until recently. Such static transparents severely limit the possibility of input signals into spectrum analyzer, which vary in time and space. The appearance of the liquid-crystal spatial light modulators (SLM) allows to change transmission of input transparency in time and space with computer. At the same time there are no researches related to usage of such modulators in DOSA. Objective. There is a justification for features of application of the matrix spatial light modulator in the optical spectrum analyzer. Methods. The method for determining the light amplitude in the spectral field of DOSA analysis was developed by analyzing of physical-mathematical model of SLM. Results. It was found that the distribution of the amplitude of the light field in the spectral analysis plane is equal to the sum of the maximums. There are some features of the sum: positions of the maximums are determined by period of SLM matrix structure, and width of the maximums – by the modulator size; the diffraction efficiency of each maximum is determined by ratio of the transparent area of the pixel to pixel’s total area. Conclusions. Number of monographs and articles is devoted to the physical principles of coherent (laser) spectrum analyzers operation. At the same time there is practically no scientific and technical literature devoted to the research of the DOSA with spatial light modulators. Analysis of SLM mathematical model shows that the minimum distortion in the measurement of the signal spectrum will be in the case when amplitude distribution in the plane of analysis is forming with zero-order maximum only. The formula, which allows us to calculate the limit period of the SLM matrix structure was obtained, which provides the minimum error of the signal spectrum measurement.

Low voltage blue phase liquid crystal for spatial light modulators.

We demonstrated a low-voltage polymer-stabilized blue phase liquid crystal (BPLC) for phase-only modulation with a liquid-crystal-on-silicon (LCoS). A new device configuration was developed, which allows the incident laser beam to traverse the BPLC layer four times before exiting the LCoS. As a result, the 2π phase change voltage is reduced to below 24V in the visible region. The response time remains relatively fast (∼3 ms). The proposed device configuration enables widespread applications of BPLC spatial light modulators.

Application of spatial light modulators for generation of laser beams with a spiral phase distribution

Application of spatial light modulators for generation of laser beams with a spiral phase distribution

Predictive capability of average Stokes polarimetry for simulation of phase multilevel elements onto LCoS devices.

Parallel-aligned (PA) liquid-crystal on silicon (LCoS) microdisplays are especially appealing in a wide range of spatial light modulation applications since they enable phase-only operation. Recently we proposed a novel polarimetric method, based on Stokes polarimetry, enabling the characterization of their linear retardance and the magnitude of their associated phase fluctuations or flicker, exhibited by many LCoS devices. In this work we apply the calibrated values obtained with this technique to show their capability to predict the performance of spatially varying phase multilevel elements displayed onto the PA-LCoS device. Specifically we address a series of multilevel phase blazed gratings. We analyze both their average diffraction efficiency ("static" analysis) and its associated time fluctuation ("dynamic" analysis). Two different electrical configuration files with different degrees of flicker are applied in order to evaluate the actual influence of flicker on the expected performance of the diffractive optical elements addressed. We obtain a good agreement between simulation and experiment, thus demonstrating the predictive capability of the calibration provided by the average Stokes polarimetric technique. Additionally, it is obtained that for electrical configurations with less than 30° amplitude for the flicker retardance, they may not influence the performance of the blazed gratings. In general, we demonstrate that the influence of flicker greatly diminishes when the number of quantization levels in the optical element increases.

P‐124: Submillisecond‐Response Polymer Network Liquid Crystal for Next‐Generation Spatial Light Modulators

AbstractWe report a scattering‐free polymer network liquid crystal (PNLC) for spatial light modulator (SLM) applications. In reflective mode, the PNLC exhibits V2π~23V at λ=514 nm and 250 μs response time at room temperature. This enables PNLC to be integrated in a high resolution liquid‐crystal‐on‐silicon device for next‐generation SLM applications.

纯相位液晶空间光调制器相位校正方法

Based on the Tyman-Green interference system,the phase modulation character of the phaseonly liquid crystal spatial light modulator at 808nm was studied.In order to increase the simulation fidelity of the atmospheric turbulence,the approximation method and the inverse interpolation method were used to compensate the phase nonlinearity of the spatial light modulator,and the calibration effect were compared with each other. Results show that,although the approximation method is straightforward,the inverse interpolation method can get a higher linearity of 0.991 6and a lower calibration error of 0.06rad.Moreover,after analyzing the calibration process and the error source,the inverse interpolation method is found to be more flexible to get a further improvement in the linear calibration,which is more significant to the pratical application of the liquid crystal spatial light modulator.

LCoS spatial light modulators as active phase elements of full-field measurement systems and sensors

Spatial light modulators (SLM) are devices used to modulate amplitude, phase or polarization of a light wave in space and time. Current SLMs are based either on MEMS (micro-electro-mechanical system) or LCD (liquid crystal display) technology. Here we report on the parameters, trends in development and applications of phase SLMs based on liquid crystal on silicon (LCoS) technology. LCoS technology was developed for front and rear projection systems competing with AMLCD (active matrix LCD) and DMD (Digital Mirror Device) SLM. The reflective arrangement due to silicon backplane allows to put a high number of pixels in a small panel, keeping the fill-factor ratio high even for micron-sized pixels. For coherent photonics applications the most important type of LCoS SLM is a phase modulator . In the paper at first we describe the typical parameters of this device and the methods for its calibration. Later we pres ent a review of applications of phase LCoS SLMs in imaging, metrology and beam manipulation, developed by th e authors as well as known from the literature. These include active and adaptive interferometers, a smart holographic camera and holographic display, microscopy modified in illuminating and imaging paths and active sensors.

Application of a liquid crystal spatial light modulator to laser marking

Laser marking is demonstrated using a nanosecond (ns) pulse duration laser in combination with a liquid crystal spatial light modulator to generate two-dimensional patterns directly onto thin films and bulk metal surfaces. Previous demonstrations of laser marking with such devices have been limited to low average power lasers. Application in the ns regime enables more complex, larger scale marks to be generated with more widely available and industrially proven laser systems. The dynamic nature of the device is utilized to improve mark quality by reducing the impact of the inherently speckled intensity distribution across the generated image and reduce thermal effects in the marked surface.

Operation speed limited by the electric properties of the photorefractive spatial light modulator

With excellent photo-electric and electro-optical effects, the photorefractive spatial light modulators can work as optically addressed modulators in optical information processing systems and parallel optical computing systems. The photo-induced current pulses of the photorefractive spatial light modulator observed in the experiments are analyzed to conclude the characteristics, and to find the relationship between the properties of the current pulse and the structural parameters. Furthermore, the origin of the photo-induced current pulse is analyzed, and the methods to improve the operation speed of the spatial light modulators are proposed. The research results will be significant for extending the applications of the photorefractive spatial light modulators, and pushing ahead the research of all-optical modulation materials and devices for optical supercomputing.

Phase calibration of spatial light modulators by means of Fresnel images

Reliable application of spatial light modulators (SLMs) as programmable diffractive optical elements requires a thorough calibration. In this paper, we propose a method for calibrating SLMs based on the evaluation of Fresnel images. Fresnel images generated by a binary phase diffraction grating consist of binary irradiance distributions whose visibility depends on the phase modulation. Displaying on our device a diffraction grating with a binary phase step along one direction and a linearly increasing phase along the orthogonal direction, we perform a complete phase calibration. In this way, the phase modulation for every pixel and for every value of the entrance signal can be determined experimentally. Additionally, data acquisition can be significantly simplified with this scheme.