Ferroelectric Liquid-crystal Spatial Light Modulator Research Articles

Synchronization and clock recovery in a ferroelectric liquid crystal spatial light modulator based free-space optical communication link.

Synchronization of the transmitter and receiver is crucial in a free-space optical communication system for the proper transfer and retrieval of user information. In this work, we propose a method for the synchronization and recovery of the clock signal at the receiver from the optical signal modulated by a ferroelectric liquid crystal spatial light modulator (FLCSLM) in the transmitter. We have demonstrated our scheme by building an experimental arrangement that comprises an FLCSLM based computer generated holography assembly for modulating the laser beam in the transmitter and a photodiode cum micro-controller circuit in the receiver to generate the synchronized clock. We present the experimental results to demonstrate the accuracy of the recovered clock and the successful retrieval of the transmitted user information. The scheme can work for amplitude modulated, phase modulated, or complex amplitude modulated information transfer based on the FLCSLM.

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. Liang et al, "3D holographic display with optically addressed spatial light modulator", 3DTV-CON 2009 - 3rd 3DTV-Conference (2009). CrossRef J. Chen, W. Cranton, M. Fihn, "Handbook of Visual Display Technology", Springer (2012). CrossRef D. Rogers, "The chemistry of photography: From classical to digital technologies", Royal Society of Chemistry (2007). CrossRef S. Reichelt et al, "Depth cues in human visual perception and their realization in 3D displays", Proc. SPIE 7690, 76900B (2010). CrossRef A.W. Lohmann, D. Paris, "Binary Fraunhofer Holograms, Generated by Computer", Appl. Opt. 6, 1739 (1967). CrossRef J.W. Goodman, R.W. Lawrence, "Digital Image Formation from Electronically Detected Hologtrams", Appl. Phys. Lett 17, 77 (1967). CrossRef D.C. O'Brien, R.J. Mears, and W.A. Crossland, "Dynamic holographic interconnects that use ferroelectric liquid-crystal spatial light modulators", Appl. Opt. 33, 2795, (1994). CrossRef R.W. Gerchberg, and W.O. Saxton, "A practical algorithm for the determination of phase from image and diffraction plane pictures", Optik 35, 237 (1972). DirectLink M. Ernstoff, A. Leupp, M. Little, and H. Peterson, "Liquid crystal pictorial display", Proceedings of the 1973 International Electron Devices Meeting, IEEE, 548 (1973). CrossRef W.A. Crossland, P.J. Ayliffe, and P.W. Ross, "A dyed-phase-change liquid crystal display over a MOSFET switching array", Proc SID 23, 15 (1982). DirectLink M. Tang, and J. Wu, "Optical Correlation recoginition based on LCOS", Internation Symposium on Photoelectronic Detection and Imaging 2013, Optical Storage and Display Tech., 8913 (2013). CrossRef A. Hermerschmidt, et al. Holographic optical tweezers with real-time hologram calculation using a phase-only modulating LCOS-based SLM at 1064 nm, Complex Light and Optical Forces II, International Society for Optics and Photonics, 30282 (2008). CrossRef M. Wang, et al. "LCoS SLM Study and Its Application in Wavelength Selective Switch", Photonics 4, 22 (2017). CrossRef Z. Zhang, Z. You, and D. Chu, "Fundamentals of phase-only liquid crystal on silicon (LCOS) devices", Light Sci. & Appls. 3, e213 (2014). CrossRef D. Yang, and S. Wu, Fundamentals of liquid crystal devices, 2nd edition (Wiley 2015). CrossRef B. Prince, Semiconductor memories: A handbook of design, manufacture, and application, 2nd ed. (John Wiley & Sons 1996). DirectLink J.C. Jones, Liquid crystal displays, Handbook of optoelectronics: Enabling Technologies, 2nd ed. (CRC Press 2018). DirectLink A. Ayriyan, et al. "Simulation of the Static Electric Field Effect on the Director Orientation of Nematic Liquid Crystal in the Transition State", Phys. Wave Phenom. 27, 67 (2019). CrossRef S.M. Kelly, and M. O'Neil, Liquid crystal for electro-optic applications, Handbook of advanced electronics and photonic materials and devices 7, 15 (2000). DirectLink Y. Ji, et al., "Suspected Intraoperative Anaphylaxis to Gelatin Absorbable Hemostatic Sponge", J. SID 22, 4652 (2015). CrossRef X. Chang, Solution-processed ZnO nanoparticles for optically addressed spatial light modulator and other applications, Ph.D. thesis, (University of Cambridge, Cambridge 2019) CrossRef E. Moon, et al. "Holographic head-mounted display with RGB light emitting diode light source", Opt. Express 22, 6526 (2014). CrossRef G. Aad, et al. "Study of jet shapes in inclusive jet production in pp collisions at √s=7 TeV using the ATLAS detector", Phys Rev. D 83, 052003 (2011). CrossRef M. Pivnenko, K. Li, and D. Chu, "Sub-millisecond switching of multi-level liquid crystal on silicon spatial light modulators for increased information bandwidth", Opt. Express 29, 24614 (2021). CrossRef H. Yang, and D.P. Chu, "Phase flicker optimisation in digital liquid crystal on silicon devices", Opt. Express 27, 24556 (2019). CrossRef P. Bach-Y-Rita, et al. "Seeing with the Brain", Int. J. Hum. -Comput. Interact 15, 285 (2003). CrossRef Y. Tong, M. Pivnenko, and D. Chu, "Improvements of phase linearity and phase flicker of phase-only LCoS devices for holographic applications", Appl. Opt. 58, G248 (2019). CrossRef Y. Tong, M. Pivnenko, and D. Chu, "Implementation of 10-Bit Phase Modulation for Phase-Only LCOS Devices Using Deep Learning", Adv. Dev. & Instr. 1, 10 (2020). CrossRef H. Yang, and D. Chu, "Phase flicker optimisation in digital liquid crystal on silicon devices", Opt. Express 27, 24556 (2019). CrossRef J. García-Márquez, et al. "Mueller-Stokes characterization and optimization of a liquid crystal on silicon display showing depolarization", Opt.Express 16, 8431 (2008). CrossRef

A laser scanning microscope executing intraframe polarization switching of the illumination beam.

The polarization of the illumination beam in a beam scanning microscope such as the confocal microscope plays an important role in extracting the orientational information of the molecules in the specimen. In this paper, we present the development of a beam scanning microscope comprising a custom designed optical arrangement to obtain images of the same target with different polarizations of the illumination beam. The optical arrangement, based on a ferroelectric liquid crystal spatial light modulator (FELCSLM), can generate homogeneous as well as non-homogeneous user defined polarization profiles over the cross-sectional area of the illumination beam. Here, we employ a computer generated holography technique and exploit the programmability of the FELCSLM display to considerably reduce the time gap between two successive illuminations of each location of the specimen with two different polarizations. We demonstrate the working of the beam scanning microscope where the polarization profile of the illumination beam is switched at the end of every line scanned, in contrast to a conventional beam scanning microscope where the polarization can be switched at the end of every frame scanned. Preliminary experimental results obtained using a polarization sensitive target confirm the feasibility of the proposed scheme.

Addressable spatial light modulators for eye-tracking autostereoscopic three-dimensional display using a scanning laser.

A scanning laser-based back light three-dimensional (3D) display capable of rendering full-resolution, low crosstalk, and vivid 3D depth perception has been developed by incorporating time-sequential multiplexing and eye-tracking technologies. This system includes three main subsystems: a scanning laser module, a relay transfer unit created by combining multiple transmissive-type electrically addressed ferroelectric liquid crystal spatial light modulators (FLC-SLMs), and a dual-directional transmission screen (DDTS) unit that can produce different angular magnification factors in both the tangential and sagittal planes. The light beam is directed by the DDTS after transmission through FLC-SLMs, and left and right eye viewing zones are produced sequentially in accordance with the locations of clear apertures in the FLC-SLM that are controlled based on data from the eye-tracking system. Owing to the persistence of human vision, 3D images are formed as a result of the high-speed scanning backlight and fast response characteristics of the FLC-SLM. A prototype of the proposed 3D display was designed and built, and experiments were carried out. The experimental results verify the feasibility of the proposed scheme, and full-resolution images with natural 3D perception are demonstrated by the prototype.

A ferroelectric liquid crystal spatial light modulator encoded with orthogonal arrays and its optimized design for laser speckle reduction

In laser projectors, speckle reduction can be achieved by projecting a changing binary phase diffuser onto the screen. Here, we sequentially encoded a commercialized ferroelectric liquid crystal spatial light modulator (FLC-SLM) with the rows of a two-level orthogonal array of order sixty-four, thus obtaining a changing binary phase diffuser. With the help of this binary phase diffuser, the subjective speckle contrast ratio on the screen is reduced from Cb=0.71 to Ca=0.1. Based on the experimental results, a simplified transparent FLC-SLM design is first proposed. This newly designed FLC-SLM has two phase modulation depths and can be driven with the passive matrix addressing scheme. Therefore, the control electronics of the proposed FLC-SLM can be significantly simplified compared to the currently used one.

Double pass, common path method for arbitrary polarization control using a ferroelectric liquid crystal spatial light modulator

We present a method for arbitrary control of the polarization of a light beam. Our method uses two holograms on a binary ferroelectric liquid crystal spatial light modulator (FLCSLM), and so has the potential to allow polarization state switching at kilohertz rates. Unlike previous methods that achieve polarization control using FLCSLMs, our method is common path and requires only the simplest optical components. For this reason, the method is very easy to setup, align, and maintain. In addition, it has the ability to modulate unpolarized input light. We demonstrate the formation of radially, azimuthally, and circularly polarized beams by imaging their focal spots formed at low numerical aperture.

Wavelength-compensated time-sequential multiplexed color joint transform correlator

We report a wavelength-compensated three-channel (RGB) joint transform correlator (JTC) for color pattern recognition using a ferroelectric liquid-crystal spatial light modulator (SLM) operating in binary pure phase modulation. We apply a previously reported time-multiplexing technique useful in creating wavelength-compensated diffraction patterns, based on the synchronization of properly scaled diffraction masks with the input wavelength selection obtained by applying a rotating RGB color-filter wheel to an Ar-Kr laser. The application of this technique to a JTC architecture permits real-time color object detection. In order to achieve a high light efficiency for the correlation process, we combine the design of zero-order joint power spectra in all color channels with the selection of a certain polarization configuration of the SLM, producing a broadband phase-only modulation. Excellent experimental results demonstrating color-object detection are provided.

All optical phase-only filtering correlation with binarized inputs by a ferroelectric liquid-crystal spatial light modulator

All optical phase-only filtering correlator is constructed with an optically addressed ferroelectric liquid-crystal spatial light modulator (FSLM) for a binarized input object and a twisted-nematic liquid-crystal spatial-light modulator for a computer-generated phase-only filter. In order to improve the discrimination capability of a phase-only filtering correlator, a binarized amplitude with maximum contrast in a FSLM is used for an object input. The contrast of binarized intensities can be maximized by adjusting the rotation angles of a FSLM and polarizers. The threshold level of binarized input objects can be controlled by changing the power of a laser incident on a FLSM. Experimental results with a high discrimination capability are presented to support the numerical correlation performance.

Spiking voltages for faster switching of nematic liquid-crystal light modulators

Electrical address circuits developed for driving fast-switching ferroelectric liquid-crystal spatial light modulators (SLM) can be programmed to increase the speed of much slower responding nematic liquid-crystal SLMs. Using an addressing circuit that can switch as fast as 0.164 ms, voltages are programmed for values of phase that exceed the desired phase, and when the phase reaches the desired value, the voltage is switched to the required steady-state voltage. For a SLM that has a phase range of 3.5pi and that is programmed over a 2pi range, switching speed is reduced from 400 ms to between 71 and 77 ms. The speedup algorithm is applied to each pixel of the SLM together with a digital correction for a spatially nonuniform phase.

Free space adaptive optical interconnect at 1.25 Gb/s, with beam steering using a ferroelectric liquid-crystal SLM

A free space adaptive optical interconnect is reported, in which an optically modulated channel from a vertical-cavity surface-emitting laser at 1.25 Gb/s is steered using reconfigurable binary phase gratings displayed on a ferroelectric liquid crystal on silicon (LCOS) spatial light modulator (SLM), to correct for misalignment. The optical system, and addressing scheme to maintain a transparent optical path, is described. The measured optical losses total 13.6 dB, sufficient to give a bit error rate (BER) of 10/sup -12/ with current optical transmitter and receiver technology. This is, to our knowledge, the first demonstration of a high-speed data transmission through an adaptive optical interconnect using an off-the-shelf commercial ferroelectric display panel.

Binary phase only filters for rotation and scale invariant pattern recognition with the joint transform correlator

The joint transform correlator (JTC) is one of the two main optical image processing architecture which provides a highly effective way of comparing images in a wide range of applications. Traditionally, an optical correlator is used to compare an unknown input scene with a pre-captured reference image library, to detect if the reference occurs within the input. Strength of the correlation signal decreases rapidly as the input object rotates or varies in scale relative to the reference object. The aim of this paper is to overcome the intolerance of the JTC to rotation and scale changes in the target image. Many JTC systems are constructed with the use of ferroelectric liquid crystal (FLC) spatial light modulators (SLMs) as they provide fast two-dimensional binary modulation of coherent light. Due to the binary nature of the FLC SLMs used in the JTC systems, any image addressed to the device need to have some form of thresholding. Carefully thresholding the grey scale input plane and the joint power spectrum (JPS) has significant effect on the quality of correlation peaks and zero order (DC) noise. A new thresholding technique to binarise the JPS has been developed and implemented optically. This algorithm selectively enhances the desirable fringes in the JPS which provide correlation peaks of higher intensity. Zero order noise is further reduced when compared to existing thresholding techniques. Keeping in mind the architecture of the JTC and limitations of FLC SLMs, a new technique to design rotation and scale invariant binary phase only filters for the JTC architecture is presented. Filers design with this technique have limited dynamic range, higher discriminability among target and non-target objects, and convenience for implementation on FLC SLMs. Simulation and experiments shows excellent results of various rotation and scale invariant filters designed with this technique. A rotation invariant filter is needed for various machine vision applications of the JTC. By fixing the distance between camera and input object, the scale sensitivity of the correlator can be avoided. In contrast to the industrial machine vision applications, scale factor is very important factor for the applications of the JTC systems in defence and security. A security system using a scale invariant JTC will be able to detect a target object well in advance and will provide more time to take a decision.

Fast Face-Recognition Optical Parallel Correlator Using High Accuracy Correlation Filter

We designed and fabricated a fully automatic fast face recognition optical parallel correlator [E. Watanabe and K. Kodate: Appl. Opt. 44 (2005) 5666] based on the VanderLugt principle. The implementation of an as-yet unattained ultra high-speed system was aided by reconfiguring the system to make it suitable for easier parallel processing, as well as by composing a higher accuracy correlation filter and high-speed ferroelectric liquid crystal-spatial light modulator (FLC-SLM). In running trial experiments using this system (dubbed FARCO), we succeeded in acquiring remarkably low error rates of 1.3% for false match rate (FMR) and 2.6% for false non-match rate (FNMR). Given the results of our experiments, the aim of this paper is to examine methods of designing correlation filters and arranging database image arrays for even faster parallel correlation, underlining the issues of calculation technique, quantization bit rate, pixel size and shift from optical axis. The correlation filter has proved its excellent performance and higher precision than classical correlation and joint transform correlator (JTC). Moreover, arrangement of multi-object reference images leads to 10-channel correlation signals, as sharply marked as those of a single channel. This experiment result demonstrates great potential for achieving the process speed of 10000 face/s.

Design and analysis of an adaptive board-to-board dynamic holographic interconnect.

We describe the design and analysis of an adaptive free-space optical interconnect between two circuit boards in a standard electronic backplane. An array of vertical-cavity surface-emitting lasers is used as the transmitter, and this communicates with a detector array on the receiver circuit board. Routing is achieved with a holographic crossbar that has a ferroelectric liquid-crystal spatial light modulator to display binary phase computer-generated holograms. A detailed analysis of a 48-channel interconnect designed to operate at 1 (Gbytes/s)/channel indicates that such a switch will operate successfully given typical components and card misalignments.

Beam steering experiment with two cascaded ferroelectric liquid-crystal spatial light modulators.

The design, construction, and evaluation of a laser beam steerer that uses two binary ferroelectric liquid-crystal (FLC) spatial light modulators (SLMs) operated in conjunction are presented. The system is characterized by having few components and is in principle lossless. Experimentally, a throughput of approximately 20% was achieved. The simple system design was achieved because of the high tilt angle FLC material used in the SLMs, which were specifically designed and manufactured for this study. By coherently imaging the first SLM onto the second SLM, pixel by pixel, we obtained an effective four-level phase structure with a phase step of 90 degrees. An appropriate alignment procedure is presented. The beam steering performance of the system is reported and analyzed.

Study on a lateral-electrical-field pixel architecture for FLC spatial light modulator with continuously tunable grayscales

A novel type of ferroelectric liquid crystal (FLC) pixel structure, in which a lateral electrical field is applied between slit-type electrodes, is proposed for ferroelectric spatial light modulator (SLM) in this brief. The novel FLC pixel architecture driven by a DRAM circuit is investigated with varied external fields, and its electrooptical property is shown as U-type curves, which implies the optical output is tunable by the applied lateral field. A numerical analysis, based on the continuum theory, corresponds well with the experiments and shows that unlike the in-plane switching process in nematic liquid crystals, the FLC molecules are rotated along their cone surface by external fields with a result of a continuously varied optical output, which promises this new pixel architecture for a ferroelectrical display with continuously tunable grayscales.

Active aberration correction for the writing of three-dimensional optical memory devices.

We describe an active optical system that both measures and corrects the aberrations introduced when writing three-dimensional bit-oriented optical memory by a two-photon absorption process. The system uses a ferroelectric liquid-crystal spatial light modulator (FLCSLM) configured as an arbitrary wave-front generator that is reconfigurable at speeds as great as 2.5 kHz. A method of aberration measurement by the FLCSLM wave-front generator is described. The same device is also used to correct the induced aberrations by preshaping the wave fronts with the conjugate phase aberration as well as to scan the focal spot in three dimensions. Experimental results show the correction of both on- and off-axis aberrations, allowing the writing of data at depths as great as 1 mm inside a LiNbO3 crystal.

Computer-generated complex filter for an all-optical and a digital-optical hybrid correlator

We present results of a correlation filter utilizing a computer-generated hologram using an analog ferroelectric liquid-crystal spatial light modulator (SLM). The SLM amplitude-modulates light and can induce a 0-p phase shift, which is equivalent to modulating along the real axis. Two pixels are combined into a macropixel using a phase-detour technique enabling full complex modulation. The method is used as the filter for a conventional optical correlator and in a digital-optical hybrid correlator. © 2002 Society of Photo-Optical Instrumentation Engineers.

Adaptive aberration correction in a two-photon microscope

We demonstrate aberration correction in two-photon microscopy. Specimen-induced aberrations were measured with a modal wavefront sensor, implemented using a ferro-electric liquid crystal spatial light modulator (FLCSLM). Wavefront correction was performed using the same FLCSLM. Axial scanned (xz) images of fluorescently labelled polystyrene beads using an oil immersion lens show restored sectioning ability at a depth of 28 &mgr;m in an aqueous specimen.

Closed-loop aberration correction by use of a modal Zernike wave-front sensor

We describe the practical implementation of a closed-loop adaptive-optics system incorporating a novel modal wave-front sensor. The sensor consists of a static binary-phase computer-generated holographic element, which generates a pattern of spots in a detector plane. Intensity differences between symmetric pairs of these spots give a direct measure of the Zernike mode amplitudes that are present in the input wave front. We use a ferroelectric liquid-crystal spatial light modulator in conjunction with a 4-f system and a spatial filter as a wave-front correction element. We present results showing a rapid increase in Strehl ratio and focal spot quality as the system corrects for deliberately introduced aberrations.

Programmable array microscopy with a ferroelectric liquid-crystal spatial light modulator

We present a programmable array microscope that uses a ferroelectric liquid-crystal spatial light modulator (SLM) for dynamic generation of scanning apertures. A single SLM serves as both the source and the detector aperture array in a double-pass confocal system. Successive aperture frames scan the array across the viewing area for complete imaging of a sample while preserving depth discrimination. Integration of the microscope output across all aperture frames produces a confocal image.