Liquid Crystal On Silicon Research Articles

Reciprocating Reflective Double Gratings Based LCOS Spectral Filter With Sharp Response

Optical filter based on liquid crystal on silicon (LCOS) is widely used in wavelength selective switch (WSS) to allocate the optical spectrum flexibly. Constrained by the achievable spectral resolution of single grating used in the WSS, the roll-off bandwidth of optical filter is challenging to improve for the purpose of precise and efficient spectrum allocation. In this article, we demonstrate a novel double gratings configuration to realize higher spectral resolution by repeatedly enlarging and accumulating the dispersion, under the condition of the maintenance of the final light spot size. After examining the filtering performance with respect to the diffraction number, we are able to achieve a spectral resolution of 1.63 GHz, indicating of almost tenfold enhancement in comparison with traditional single grating configuration. In particular, an LCOS-based optical filter with a spectral roll-off bandwidth of 1.26 GHz and addressable resolution of 187 MHz is demonstrated. Meanwhile, the insertion loss and the range of operation wavelength are investigated to determine the optimal number of diffractions for various applications. The proposed LCOS-based filter enables spectral manipulation of GHz roll-off bandwidth, fulfilling the performance requirements of future flexible optical networking.

Programmable High-Resolution Spectral Processor in C-band Enabled by Low-Cost Compact Light Paths

The flexible photonics spectral processor (PSP) is an indispensable element for elastic optical transmission networks that adopt wavelength division multiplexing (WDM) technology. The resolution and system cost are two vital metrics when developing a PSP. In this paper, a high-resolution 1 × 6 programmable PSP is investigated and experimentally demonstrated by using low-cost compact spatial light paths, which is enabled by a 2 K (1080p) liquid crystal on silicon (LCoS) and two cascaded transmission gratings with a 1000 line/mm resolution. For each wavelength channel, the filtering bandwidth and power attenuation can be manipulated independently. The total insertion loss (IL) for six ports is in the range of 5.9~9.4 dB over the full C-band. The achieved 3-dB bandwidths are able to adjust from 6.2 GHz to 5 THz. Furthermore, multiple system experiments utilizing the proposed PSP, such as flexible spectral shaping and optical frequency comb generation, are carried out to validate the feasibility for the WDM systems.

Zoomable head-up display with the integration of holographic and geometrical imaging.

Head-up displays (HUDs) have already penetrated into vehicle applications and demand keeps growing. Existing head-up displays have their image fixed at a certain distance in front of the windshield. New development could have two images displayed at two different yet fixed distances simultaneously or switchable upon request. The physical distance of HUD image is associated with the accommodation delay as a safety issue in driving, and could also be a critical parameter for augmented reality (AR) function. In this paper, a novel architecture for HUD has been proposed to make the image distance continuously tunable by exploiting the merit of both holographic and geometrical imaging. Holographic imaging is capable of changing image position by varying the modulation on a spatial light modulator (SLM) without any mechanical movement. Geometrical imaging can easily magnify longitudinal image position with short depth of focus by using large aperture components. A prototype based on liquid crystal on silicon (LCoS) SLM has demonstrated the capability of changing image position from 3 m to 30 m verified with parallax method.

Optical design and tolerance of a high efficiency laser polarization grating-polarization conversion system based and diffraction limited heads up display projector

In this paper, a compact and diffraction limited heads up display (HUD) image source is presented. The great benefit of this design is its diffraction limited optic, compacted structure, economic considerations, simplicity in manufacturing and high efficiency image quality. The innovation of this design is the use of a polarization grating-polarization conversion system (PG-PCS). This module transforms the unpolarized Gaussian beam to a linearly polarized beam and it simultaneously homogenizes the spatial intensity profile. With this module, it is possible to increase the efficiency of illumination and to utilize the ordinary micro LCD instead of using a digital micro mirror device (DMD) and liquid crystal on silicon (LCOS) micro displays. The diameter of the image plane is 76.2 mm (in accordance with conventional types). Our design yielded uniform illuminated image and its high efficiency facilitates display readability in see-through HUDs operating in high ambient light as well as low ambient light.

Unitary matrix approach for a precise voltage dependent characterization of reflective liquid crystal devices by average Stokes polarimetry

Precise characterization of parallel-aligned liquid crystal on silicon microdisplays has an important impact in many advanced photonics applications. We show liquid crystal on silicon (LCoS) modeled as a non-absorbent reciprocal device. Combined with time-average Stokes polarimetry, LCoS enables us to demonstrate robust measurements across the whole applied voltage range for the retardance and its flicker, and also as a novelty for the director orientation. We obtain that the director orientation changes across the voltage range, especially at larger applied voltages. This is a small effect, but it may provide a deeper insight into the internal dynamics in the liquid crystal layer, and in sensitive phase-only applications will produce a coupling between amplitude and phase.

2D optical wireless broadcasting system enabled by a liquid crystal on silicon and rotated-splitting-SLM algorithm.

In this paper, a 2D optical wireless broadcasting system with low path loss is proposed and experimentally demonstrated based on a commercial liquid crystal on silicon (LCoS) device and rotated-splitting-SLM algorithm. The low path loss is realized by our designed pair of fiber collimators with large beam waist, which can significantly reduce the coupling loss. By using the proposed system and algorithm, a 60-Gb/s PAM-4 signal is successfully broadcasted over 2-km standard single mode fiber and 14 m free space link with 16 dB path loss for up to four mobile users. The experimental results reveal that the LCoS based on the proposed rotated-splitting-SLM method can be used for multi-user broadcasting in the high-speed in-building dynamic networks.

Recent Progress of Wavelength Selective Switch

Wavelength Division Multiplexing (WDM) networks with reconfigurable optical add/drop multiplexers (ROADMs) realize automatic scheduling and restoration at the wavelength level and are therefore part of the solution to meet increasing bandwidth and routing flexibility requirements for transport networks. The wavelength selective switch (WSS) is the key component in all commercial ROADM systems. Liquid crystal on silicon (LCoS) technology dominates current WSS installations as LCoS-based WSS can support Flexgrid technology enabled networks, and high port counts with excellent performance. WSS designs are becoming increasingly specialized for a wide variety of applications. For single WSS used in broadcast and select (B&S) architecture, superior port isolation is key for the desired signal to be filtered from the whole spectrum. While for twin WSS deployed in route and select (R&S) nodes, many features are desired for various network applications. These include multiple common ports, premium ports with superior port isolation, and high port counts. Future WSS may be asked to address a number of different end user applications, and as such there is a demand for combinations of custom spectrum range, compact form factors, increased WSS port count, low cost, thermal and mechanical ruggedization. The first commercially available quad WSS is part of this increasing trend of utilization of WSS throughout network architectures.

Journal of the Society for Information Display

Jiun-Haw Lee Editor in Chief Congratulations! JSID's 2019 journal impact factor, a metric that reflects the average number of times the articles in a journal were cited in a particular period, made a “quantum jump” to 1.645. That's a record high—and what's more, it means JSID's impact factor has increased for five successive years. The jump was driven in part by the Distinguished Papers from Display Week 2017 and 2018, which garnered substantial attention and citations. As a reminder, the Distinguished Papers of Display Week 2020 (which have been published in issues 4, 5, and 6) will remain open access through the end of 2020. Please take this chance to browse through Display Week 2020's best papers for free! The July 2020 and August 2020 issues of JSID each contain three invited papers. Together, they span a wide spectrum of topics, including OLED, augmented reality (AR), liquid crystal on silicon (LCOS), oxide thin-film transistor (TFT), automotive interior lighting and display, and quantum dots (QDs). Papers in the July issue characterized soluble hole-injection materials and used LCOS as the spatial light modulator for AR applications while presenting a new algorithm for enhancing the image quality of dual-plane holographic projection. A review of oxide TFT fabricated with vacuum deposition summarized 370 related works in this field. Further, a new automotive interior lighting that considers safety issues, user experience, and ambient conditions was proposed. This is a highly practical and exciting paper that sheds light on possible interiors for future car models. Next, fabricating and characterizing a fine metal mask is disclosed for high-resolution OLED production, achieving more than 800 pixels per inch (ppi). Additionally, the issue details the latest progress on cadmium-free QD. Invitation to Submit Review Papers The Journal is soliciting review papers on any display-related topic. If you have a great idea for a review paper, please contact the editor at editor@sid.org. Page charges for invited review papers will be waived. Analog LCOS SLM devices for AR display applications | Kuan-Hsu Fan-Chiang et al.| doi: 10.1002/jsid.881 Analog LCOS with precise linearity control is demonstrated using an improved fabrication process and driving technique. The authors also explore how they achieved a fast response time of 2.5 milliseconds full-on-full-off, which can be used as a spatial light modulator for multiplane holograms in AR applications. They propose the multiconstraints angular spectrum algorithm (MASA) to improve image quality for the conventional angular spectrum algorithm (ASA) for dual-plane content, even when there is a long distance between two planes (20 centimeters [cm] and 60 cm to the observer, respectively). High-performance vacuum-processed metal oxide thin-film transistors: A review of recent developments | Hee Jun Kim et al.| doi: 10.1002/jsid.886 In this review, the authors summarized recent developments of n- and p-type oxide TFT fabricated by a vacuum process from different viewpoints of materials, processes, and device structures. N-type oxide TFTs, such as indium gallium zinc oxide, have been applied for the mass production of active-matrix displays, including LCD and OLED with a field-effect mobility of ∼10 cm2/Vs. On the other hand, the p-type oxide TFTs based on cuprous oxide, tin monoxide, and nickel oxide are still in the early stages. Tables of benchmark device performances were summarized alongside channel and insulator materials, fabrication techniques, and device architectures, which provide a fair comparison. Note that this paper cited 370 references, which is quite a complete summary for the oxide TFT field. Information About the Journal JSID is published monthly by Wiley. Subscription fees apply, but SID members and student members have free online access via sid.org/Publications.aspx. Many universities also have an institutional subscription. JSID is indexed in the Web of Science. Submit your original manuscript online via mc.manuscriptcentral.com/sid. Author guidelines can be found on the Journal's homepage: tinyurl.com/jsidhome. Editorial board: tinyurl.com/jsideb. Please direct any questions about JSID to its editor in chief at editor@sid.org. EarlyView: accepted papers about to be published can be accessed online via tinyurl.com/jsidev.

Measuring the spatial deformation of a liquid-crystal on silicon display with a self-interference effect.

We present a simple technique to characterize the spatial non-uniformity of a liquid-crystal on silicon (LCOS) spatial light modulator (SLM). It is based on illuminating the display with a wavelength out of the operation range, so there is a significant reflection at the output surface. As a consequence, a Gires-Tournois interferometer is directly created, without any alignment requirement and insensitive to vibrations. The beam reflected at the output surface is the reference beam, while the beam reflected at the silicon backplane is modulated with the addressed gray level in order to quantitatively derive its deformation. We provide an experimental demonstration using a LCOS-SLM designed to operate in the near-infrared range but illuminated with visible light.

Quantitative characterization of holographic displays based on liquid-crystal-on-silicon spatial light modulator

This report discusses the effect of speckle size on the quality of holographic images based on a liquid-crystal-on-silicon (LCoS) spatial light modulator (SLM). Further, it proposes methods of quantifying the average speckle size and holographic image resolution. These methods enable both characteristics to be compared using the same unit (the number of pixels in the holographic image), providing an intuitive and effective comparative analysis method. In particular, by varying the LCoS resolution ratio, the change in the resolvable minimum pixels of the holographic image is interpreted in conjunction with the average speckle size; moreover, an analysis of the correlation between the latter two is presented. This approach, based on LCoS resolution division, could provide useful insights into single-SLM-based, full-color holographic displays using space division. Furthermore, it could be extended to other components, including more advanced LCoS SLMs, and used to identify the relative effects on image quality with speckles.

A compact synthetic aperture digital holographic microscope with mechanical movement-free beam scanning and optimized active aberration compensation for isotropic resolution enhancement

This study proposes and demonstrates a compact synthetic aperture digital holographic microscope (SA-DHM) with mechanical movement-free beam scanning and optimized active aberration compensation. The SA-DHM system is equipped with a phase-only liquid crystal on silicon (LCoS) device as an active optical element to achieve a compact mechanical movement-free beam steering architecture with aberration correction. A rigorous optimization is conducted to modulate the LCoS device using the designed computer-generated holograms (CGH) to generate a high-quality point spread functions (PSF) for a wide range of scanning angles. An accurate aberration correction is studied with and without oil immersed conditions on microscope objective lens. The performance of the proposed method is analyzed with Siemens star target and the results show its potential capability to achieve isotropic resolution enhancement.

24 [1×12] Wavelength Selective Switches Integrated on a Single 4k LCoS Device

This article demonstrates the design, assembly, optimisation, and characterisation of 24 [1 × 12] wavelength selective switches (WSSs) based on a single set of optics and a 4k liquid crystal on silicon (LCoS) device. The average insertion loss was measured to be 8.4 dB with an average crosstalk level of 26.9 dB. To our knowledge, this module with 312 fibre ports is the highest-capacity WSS demonstrated so far. The module can be flexibly reconfigured into different switches and port counts for advanced reconfigurable optical add/drop multiplexer (ROADM) applications.

Super-resolution with a complex-amplitude pupil mask encoded in the first diffraction order of a phase grating

Diffraction imposes a barrier to resolve objects smaller than half the wavelength used to illuminate them. In optical microscopy, this barrier was surpassed 25 years ago. One form of achieving super-resolution is the use of complex-amplitude pupil masks. Spatial light modulators can be used to produce these masks, if we compensate the aberrations introduced by them. In this paper we propose a method to encode a complex-amplitude pupil mask in a phase-only spatial light modulator of the Liquid Crystal on Silicon (LCoS) variety. We describe the form in which the pupil mask is encoded in a phase grating generated with an LCoS spatial light modulator, and how the aberrations introduced by this device can also be compensated with this grating. We present numerical and experimental results that validate the method.

A Hybrid Algorithm for Multi-Beam Steering of LCOS-Based Wavelength Selective Switch

Iterative Fourier transform algorithm (IFTA) has been widely applied to achieve holograms in diffractive optical elements, however it is insufficient for designing holograms uploaded on liquid crystal on silicon (LCOS) to steer multi-beams in a wavelength selective switch (WSS). In this paper, a three-step hybrid algorithm including IFTA, Symmetrical IFTA with both phase and amplitude freedoms (SIFTA-2) and Genetic algorithm (GA) is developed to optimize the multi-casting hologram and experimentally demonstrated the multi-casting function of WSS. The reconstructed output field not only has max 128 fan-out patterns with flexible power ratio, but also can be adjusted to balance multi-indicators like reconstructed root mean square error (RMSE), diffraction efficiency and crosstalk power by setting flexible weightings of fitness functions in GA.

Transient Crosstalk in Holographic Optical Switching Based on Wavefront Encoding

This work demonstrates that wavefront encoding technique can be used reduce the peak transient crosstalk by >10 dB in holographic optical switches based on the liquid crystal on silicon (LCOS) technology, when compared with switches based on the conventional Fourier transform optical setup. At the same time, this technique also reduces the switching time, without any modifications needed to either the LCOS device or its driving circuits.

Design of Optical Tunnel Switching Networks for Big Data Applications

In this paper, we proposed large-scale optical tunnel switching networks based on the Torus topology network with WSS (Wavelength Selective Switch) for future big data applications. All nodes of the large-scale optical tunnel switching networks use WSS switch modules, and the communications between nodes use multiple λs (wavelengths), where a tunnel is established with a wavelength which can be reused. The widely used MEMS (Micro-Electro-Mechanical Systems) and LCoS (Liquid Crystal on Silicon) technologies are all millisecond-level switching speeds, so the frame size of the optical frame switch is very large, and this will reduce switching performance. Therefore, they are only suitable for optical tunnel switching networks design, but are not suitable for optical frame switch design. This multi-plane Torus topology network architecture not only increases network throughput, but also has fault tolerance to increase network reliability. When the traffic is changed, the number of tunnels between nodes can be scheduled in time to balance the load traffic and avoid traffic loss. Therefore, it can not only schedule the number of tunnels in time to balance the load traffic, in order to avoid traffic loss, but also because the channel is fixedly established, this does not generate any buffer delay, and this because of the transmission using optical transmission unlimited speed, so it is a good choice for future big data applications that require high speed, high bandwidth and low latency.

A Novel ReRAM-Based Architecture of Field Sequential Color Driver for High-Resolution LCoS Displays

Liquid crystal on-silicon (LCoS) display is one of the most representative micro-display technologies, and is widely adopted in virtual reality (VR) and augmented reality (AR) devices thanks to a relatively simple structure using a semiconductor manufacturing process to realize high-resolution displays. However, the structural complexity to handle color frames by field sequential color (FSC) scheme hinders more widespread adoptions of the LCoS displays. In this article, to resolve the problem, we propose a novel FSC driver architecture using resistive random access memory (ReRAM) that diminishes the driver’s structural complexity with matrix-vector multiplications. The proposed architecture leverages fast matrix-vector multiplications with a memristor crossbar array to expedite the FSC operation that extracts the individual red, green, and blue color sub-frames from an entire image. We present the hardware performance of our architecture that is implemented using the crossbar array and peripheral circuits. Compared to the conventional static random access memory (SRAM)-based architecture, we confirm that the proposed design is much superior in terms of chip size, leakage power, and frame rate in various image resolutions. Specifically, the chip size and leakage power are reduced by up to 96% and 99%, respectively, and the frame rate is improved by up to 36%. We also analyze image quality loss caused by ReRAM read and write noise.

Realizing a Low-Power Head-Mounted Phase-Only Holographic Display by Light-Weight Compression.

Head-mounted holographic displays (HMHD) are projected to be the first commercial realization of holographic video display systems. HMHDs use liquid crystal on silicon (LCoS) spatial light modulators (SLM), which are best suited to display phase-only holograms (POH). The performance/watt requirement of a monochrome, 60 fps Full HD, 2-eye, POH HMHD system is about 10 TFLOPS/W, which is orders of magnitude higher than that is achievable by commercially available mobile processors. To mitigate this compute power constraint, display-ready POHs shall be generated on a nearby server and sent to the HMHD in compressed form over a wireless link. This paper discusses design of a feasible HMHD-based augmented reality system, focusing on compression requirements and per-pixel rate-distortion trade-off for transmission of display-ready POH from the server to HMHD. Since the decoder in the HMHD needs to operate on low power, only coding methods that have low-power decoder implementation are considered. Effects of 2D phase unwrapping and flat quantization on compression performance are also reported. We next propose a versatile PCM-POH codec with progressive quantization that can adapt to SLM-dynamic-range and available bitrate, and features per-pixel rate-distortion control to achieve acceptable POH quality at target rates of 60-200 Mbit/s that can be reliably achieved by current wireless technologies. Our results demonstrate feasibility of realizing a low-power, quality-ensured, multi-user, interactive HMHD augmented reality system with commercially available components using the proposed adaptive compression of display-ready POH with light-weight decoding.

Implementation of 10-Bit Phase Modulation for Phase-Only LCOS Devices Using Deep Learning

A deep learning model was built to optimize the phase flicker performance for given pulse width modulation (PWM) driving patterns of a liquid crystal on silicon (LCOS) device. 10-bit phase modulation was physically realized with a phase flicker of 0.055% over 1024 addressed phase levels in respect to the total modulation range of 2 π and a separation probability of 62.63% for the phase to stay within its level without overlapping with the adjacent ones. The spatial information bandwidth of the full high-definition (HD) LCOS device at 100 Hz was improved by 25%, from ~1.6 Gb/sec to ~2 Gb/sec.

Nonlinear effect on sinc-shaped optical filter demultiplexing all-optical OFDM system

We propose a novel all-optical orthogonal frequency division multiplexing (OFDM) systems without the requirement for discrete fast Fourier transform (FFT). The liquid crystal on silicon (LCOS) programmable wavelength selective switch (WSS) is employed in this all-optical OFDM for filtering, which can generate multiple orthogonal sub-carriers on the modulated optical source of super-continuum spectrum. Based on the proposed all-optical OFDM, the error-free transmission with high spectral efficiency can be achieved in the case of no dispersion and nonlinear effect. Furthermore, we systematically analyze the impact of nonlinear effect on the all-optical OFDM transmission systems, known as the main limiting factor in dense multi-carriers systems. And system simulation indicates that in the absence of local oscillating laser and extra dispersion and nonlinear compensation algorithms, our proposed all-optical OFDM can achieve 5 km single mode optical fiber transmission with less than 5*10−3 bit error rate (BER) and 1*10−2 BER when employing no more than 16 and 64 sub-carriers, respectively. From the perspective of spectral efficiency and system complexity, our proposed all-optical OFDM system shows a huge superiority over single sideband modulation in short distance transmission.