Liquid Crystal On Silicon Research Articles

Pursuing High Quality Phase-Only Liquid Crystal on Silicon (LCoS) Devices

Fine pixel size and high-resolution liquid crystal on silicon (LCoS) backplanes have been developed by various companies and research groups since 1973. The development of LCoS is not only beneficial for full high definition displays but also to spatial light modulation. The high-quality and well-calibrated panels can project computer generated hologram (CGH) designs faithfully for phase-only holography, which can be widely utilized in 2D/3D holographic video projectors and components for optical telecommunications. As a result, we start by summarizing the current status of high-resolution panels, followed by addressing issues related to the driving frequency (i.e., liquid crystal response time and hardware interface). LCoS panel qualities were evaluated based on the following four characteristics: phase linearity control, phase precision, phase stability, and phase accuracy.

Microparticle Manipulation and Imaging through a Self-Calibrated Liquid Crystal on Silicon Display

We present in this paper a revision of three different methods we conceived in the framework of liquid crystal on silicon (LCoS) display optimization and application. We preliminarily demonstrate an LCoS self-calibration technique, from which we can perform a complete LCoS characterization. In particular, two important characteristics of LCoS displays are retrieved by using self-addressed digital holograms. On the one hand, we determine its phase-voltage curve by using the interference pattern generated by a digital two-sectorial split-lens configuration. On the other hand, the LCoS surface profile is also determined by using a self-addressed dynamic micro-lens array pattern. Second, the implementation of microparticle manipulation through optical traps created by an LCoS display is demonstrated. Finally, an LCoS display based inline (IL) holographic imaging system is described. By using the LCoS display to implement a double-sideband filter configuration, this inline architecture demonstrates the advantage of obtaining dynamic holographic imaging of microparticles independently of their spatial positions by avoiding the non-desired conjugate images.

High-Efficiency Beam Steering LCOS for Wavelength Selective Switch

A liquid crystal on silicon (LCOS) device exhibiting high diffraction efficiency at a large deflection angle is demonstrated. An LC mixture with a large birefringence ( $\Delta \text{n}\,\,=0.25$ at $\lambda =1550$ nm) and a large dielectric constant ( $\Delta \varepsilon = 10.4$ ) is developed to obtain the high-phase retardation, more than $4\pi $ , at 1550 nm within a relatively low operation voltage of 5.5 V on LCOS. When compared with the conventional modulation method of $2\pi $ phase retardation, both grating period and phase retardation are doubled in $4\pi $ modulo modulation. Using the high-phase retardation modulation method, the LCOS may achieve high diffraction efficiency more than 56.6% at 4.5° deflection angle of C-band wavelength with an optimized phase retardation profile. The high diffraction efficiency phase modulator shows the great potential application of beam steering for the wavelength selective switch and the holographic display.

High-frame-rate liquid crystal phase modulator for augmented reality displays

ABSTRACTWe optimise a new liquid crystal mixture with wide nematic range, high birefringence (Δn), high resistivity, moderate dielectric anisotropy (∆ε) and relatively low rotational viscosity for augmented reality display applications. High Δn and large Δε allow a thin cell gap (d ≈ 1.5 μm) to be employed in a reflective liquid-crystal-on-silicon (LCoS) device to achieve 2π phase change at 5 V and 2.87 ms average phase-to-phase response time at 40°C without complicated overdrive circuitry. Such a fast response time enables an LCoS panel to achieve 240 Hz frame rate for field sequential colour operation to avoid image flickering.

Optical Arbitrary Waveform Processing of Over 100 Spatial Channels for Optical Performance Monitoring

We developed an optical processing platform that handles over 100 space-division-multiplexed signals in the C-band. The device consists of free-space optics based on liquid crystal on silicon (LCOS) with a waveguide frontend. Thanks to the holographic wavefront modulation by the LCOS spatial light modulator, the device arbitrarily manipulates the optical amplitude and phase in the space and spectral domains simultaneously. This ability enables us to create various optical processing functions such as tunable wavelength filtering, variable optical attenuation, and flexible delay line interferometry with arbitrary spatial and wavelength channel dependence. These functions are highly suitable for large-scale optical performance monitoring (OPM). As an application, we demonstrate OPM for 100 spatial channels over the C-band. The constructed OPM can monitor not only the power spectrum but also the optical signal-to-noise ratio (OSNR) by setting different LCOS phase patterns. We achieved channel power monitoring and OSNR monitoring with 1.8- and 1.9-dB accuracy over 100 spatial channels.

Experimental Demonstration of an LCoS-Based Access Node for Bidirectional Optical Wireless Communications

An liquid crystal on silicon (LCoS)-based access node using optical fibers as the transmitter and receiver to deliver high-speed data transmission is proposed and experimentally demonstrated. This access node can be applied to a variety of networks ranging from passive optical networks to indoor home area networks through optical wireless communications without optical/electrical/optical (O/E/O) conversions. The link of system, which operates over ~2.5 m with a possible wide field-of-view of nearly 97°, has been achieved through the implementation of a LCoS-based spatial light modulator in conjunction with a static grating element. A bidirectional optical wireless communication system was established to demonstrate the concept and evaluate the performance of the proposed access node, which uses typical WDM wavelengths (the channel spacing is 100 GHz) and is modulated at a data speed of more than 2.5 Gb/s. The results show that in downlink transmission, the multiple wavelengths delivered from optical fibers can be dynamically transmitted directly to the terminal users through the proposed access node architecture without performing any O/E/O conversion. Similarly in uplink transmission, all the wavelengths received at the proposed node architecture can be arbitrarily switched to a desired output fiber port of the access node to connect with the external fiber networks in the same manner. The bit error ratios of all the transmitted wavelengths in both uplink and downlink transmission scenarios are less than 10 -9 .

Wavelength and bandwidth tunable passively mode-locked fiber laser based on semiconductor saturable absorber mirror and liquid crystal on silicon device

Using a liquid crystal on silicon (LCoS) device as tunable filter, we experimentally demonstrate a wavelength and bandwidth tunable passively mode-locked fiber laser. The key feature of this laser is that any wavelength with any bandwidth can be tuned independently over the whole C-band, which is flexibly driven by only a single LCoS chip. The outputs exhibit excellent tuning capacity and high consistency in the C-band, using a 0.1 nm wavelength-tuning step. The filter bandwidth can be set to any width within the wavelength range, while the pulse width varies from 9 to 50 ps.

Precise calibration of spatial phase response nonuniformity arising in liquid crystal on silicon.

In order to calibrate the spatial phase response nonuniformity of liquid crystal on silicon (LCoS), we propose to use a Twyman-Green interferometer to characterize the wavefront distortion, due to the inherent curvature of the device. During the characterization, both the residual carrier frequency introduced by the Fourier transform evaluation method and the lens aberration are error sources. For the tilted phase error introduced by residual carrier frequency, the least mean square fitting method is used to obtain the tilted phase error. Meanwhile, we use Zernike polynomials fitting based on plane mirror calibration to mitigate the lens aberration. For a typical LCoS with 1×12,288 pixels after calibration, the peak-to-valley value of the inherent wavefront distortion is approximately 0.25λ at 1550nm, leading to a half-suppression of wavefront distortion. All efforts can suppress the root mean squares value of the inherent wavefront distortion to approximately λ/34.

1 × 25 LCOS-based wavelength selective switch with flexible passbands and channel selection

Abstract Wavelength-selective-switching based reconfigurable optical add-drop multiplexers are the essential components of current and next generation dynamic optical networks. A proof-of-concept 1 × 25 wavelength selective switch is demonstrated experimentally based on liquid crystal on silicon (LCOS) technology and 2-foptical system. Each of the input C-band wavelength channel can be independently selected and switched into arbitrary output ports. The channel passband and channel spacing can be adjusted flexibly by applying holograms onto an LCOS chip. The insertion loss for polarized beam ranges from 5.4 to 7.5 dB for 1–20 output ports and increases up to 9.6 dB at side ports for 100 GHz spaced ITU-T channels over the C-band. The general channel crosstalk is below −20 dB. The minimum resolution of center frequency for each channel is 5 GHz (0.04 nm). The performance can be further improved by using an LCOS chip with smaller pixel pitch, higher-quality optical components and accurate alignment of the fiber-lenslet array.

Supracricoid partial laryngectomy for radiorecurrent laryngeal cancer: a systematic review of the literature and meta-analysis.

The objective of the current systematic review with meta-analysis was to report the pooled survival outcomes of supracricoid partial laryngectomy in the setting of radiorecurrent laryngeal cancer to investigate if and when an organ-sparing surgical treatment is adequate. The search included all original papers from 1990 to December 2017. The search terms included the following: cricohyoepiglottopexy; cricohyoidopexy; cricohyopexy; horizontal laryngectomy; and partial, subtotal, supracricoid, and supraglottic laryngectomy. Inclusion criteria were as follows: (1) data clearly distinguish results of partial laryngeal procedures; (2) clear description of tumor stage and selection criteria; (3) clear description or derivability of local control and survival rates. Eleven out of 270 papers were analyzed, and a total of 251 cases were included. Two-year LC, 3-year DFS, and 5-year OS were 92, 80, and 79%, respectively. Heterogenicity evaluated with the I2 parameter was 14, 0, 0%, respectively. The larynx preservation rate was 85.2%, the decannulation rate was 92.1%, and swallowing recovery was 96.5% (PEG dependence and the aspiration pneumonia rate were 3.5 and 6.4%, respectively). SCPL is oncologically sound, guaranteeing a high percentage of success. The homogeneity of data should encourage the use of SCPL as salvage treatment for recurrent LSCC.

21.4: Invited Paper: Near‐to‐Eye Display Application Based on Digital Electro‐optics Platform (X‐on‐Silicon)

Digital Electro‐optics Platform is the main concept of Jasper Display Corp. (JDC) to develop various applications. These applications are based on our X‐on‐Silicon technologies, for example, X‐on‐Silicon technologies could be used on Liquid Crystal on Silicon (LCoS), Micro Light‐Emitting Diode on Silicon (pLEDoS), Organic Light‐Emitting Diode on Silicon (OLEDoS), and Cell on Silicon (CELLoS), etc. In this paper, we provide novel concepts and real cases for near‐to‐eye applications based on phase‐only LCoS‐SLM and μLEDoS, such as holographic near‐to‐eye displays and focal surface displays.

P‐9.10: Design and Fabrication of Micro‐lens Array Based on Micro‐LED Projector

LEDoS(Light Emitting Diode on Silicon) is developing rapidly as a new type of projection technology compared with DLP(Digital Light Processing) and LCoS(Liquid Crystal on Silicon). In addition, Micro‐LED is playing an important role in display and lighting areas because of its high display quality. Therefore, researching and designing a Micro‐LED based LEdoS has obvious advantages in brightness and color saturation, when used in projectors, it can not only completely eliminate the backlight, but also improve the LEE(Light extraction efficiency) by minimizing the optical components. This experiment aims to develop a Micro‐lens array that matches the LEDoS chip and combines the Micro‐lens array with the LEDoS chip to optimize the design by using Tracepro, including the material and shape of Micro‐lens. The Micro‐lens is used to optimize the LED pixels light output angle to reduce color mixing problems between adjacent LED pixels. At the same time the Micro‐lens can also improve the efficiency of LED light coupling, thereby further improving the LED light output efficiency.

LCoS display phase self-calibration method based on diffractive lens schemes

An experimental method to calibrate Liquid Crystal on Silicon (LCoS) displays by self-generating lens configurations on the studied device is proposed in this paper. On the one hand, a split-lens is displayed in the LCoS to self-generate an interference pattern from which the phase-voltage curve of the modulator is calculated. On the other hand, a microlens array is displayed on the LCoS, within a same experimental set-up, to implement a Shack-Hartmann (S-H) wavefront sensor, from which the display surface profile is retrieved. Specifically, by means of a feasible set-up, the proposed method allows measuring the deviation from flatness of the LCoS displays as well as to determine the phase-voltage response of phase-only SLMs. Experimental results demonstrate a linear tendency phase-voltage curve that ranges from 0 rad up to ∼6.28 rad, for the used light wavelength. Moreover, by extracting the LCoS phase distribution measured with the S-H configuration, the LCoS surface inhomogeneity is corrected by 95%.

Scene-adaptive coded aperture imaging

Coded aperture imaging systems have recently shown great success in recovering scene depth and extending the depth-of-field. Tremendous efforts have been focused on designing good coded patterns. The ideal pattern, however, would have to serve two conflicting purposes: 1) it should be broadband to ensure robust deconvolution and 2) it should have sufficient zero-crossings for a high depth discrepancy. This paper presents a simple but effective scene-adaptive coded aperture solution to bridge this gap. We observe that natural scenes often exhibit a dominant edge direction that can be caused by structure, texture, shading, etc. We therefore apply depth-discriminative codes along the dominant direction and broadband codes along its orthogonal direction. To physically implement this scheme, we adopt a two-shot scheme. Firstly, we capture a scene image with a pinhole aperture and analyze image content to determine the dominant direction. Secondly, we apply the proposed coding scheme using the programmable Liquid Crystal on Silicon (LCoS). Experiments on a broad range of synthetic and real scenes show that our technique is able to combine advantages of the state-of-the-art patterns for recovering better quality depth map and all-focus images.

Fast-response liquid crystal phase modulators for augmented reality displays

We report three new liquid crystal mixtures optimized for the phase modulator of an augmented reality display. The mixtures exhibit a relatively high birefringence (Δn) yet low viscosity, modest dielectric anisotropy (Δe), and acceptable resistivity and UV stability. High Δn enables a thin cell gap (d≈1.7 μm) for achieving 2π phase change with a reflective Liquid-Crystal-on-Silicon (LCoS) device and ~2 ms average phase-to-phase response time at 40°C. The modest Δe helps lower the operation voltage to 5V. To improve the response time of a full-color LCoS, we propose a new driving method by shifting the operation voltage away from the threshold. We also applied such a high Δn LC mixture to LCoS based amplitude modulators and achieved submillisecond response time. Widespread applications of these materials for the emerging augmented reality displays are foreseeable.

Extracting sub-exposure images from a single capture through Fourier-based optical modulation

Through pixel-wise optical coding of images during exposure time, it is possible to extract sub-exposure images from a single capture. Such a capability can be used for different purposes, including high-speed imaging, high-dynamic-range imaging and compressed sensing. In this paper, we demonstrate a sub-exposure image extraction method, where the exposure coding pattern is inspired from frequency division multiplexing idea of communication systems. The coding masks modulate sub-exposure images in such a way that they are placed in non-overlapping regions in Fourier domain. The sub-exposure image extraction process involves digital filtering of the captured signal with proper band-pass filters. The prototype imaging system incorporates a Liquid Crystal over Silicon (LCoS) based spatial light modulator synchronized with a camera for pixel-wise exposure coding.

Improved generation method utilizing a modified Fourier spectrum for Airy beams with the phase-only filter technique.

We present an improved method to generate Airy beams utilizing a liquid crystal on silicon (LCoS) device. In this method, the phase and amplitude information of a modified Fourier spectrum of an Airy beam together with a Fresnel holographic lens is encoded onto the LCoS using the phase-only filter technique; thus, a desired Airy beam is formed in the focal plane of the Fresnel holographic lens. In this paper, the principle of the proposed method is described in detail, and both the excellent numerical simulations and experimental results for verifying this method are demonstrated. It is shown that the new generation method is accurate and simple; in particular, the setup is more compact compared to the conventional Fourier transform method, which comprises only the input polarized laser and a LCoS device. This effective method will further promote investigations into the properties and applications of Airy beams.

Reflective blue phase liquid crystal displays with double-side concave-curved electrodes

ABSTRACTReflective blue phase liquid crystal display (BPLCD) is a promising candidate for field sequential colour displays with reflective liquid-crystal-on-silicon (LCoS). However, the issue of high operation voltage still hinders its widespread applications. We propose a reflective BPLCD with double-side concave-curved electrode and research its operation voltage and electro-optic characteristics in simulation, which is compared to the transmissive mode. The effect of double-side electrodes on horizontal electric field and operation voltage is analysed. The improvement of concave-curved electrodes on reflectance is discussed. A reflective BPLCD has two times the optical path difference compared to the transmissive mode. By using double-side concave-curved electrodes, the reflectance increased by 23% and the operation voltage reduced by 32% compared to the traditional in-plane switching mode. This work enables BPLC to be integrated with reflective LCoS.

Analysis and suppression of high-order diffractions in liquid-crystal-based spatial light modulator for photonic switch application

Spatial light modulators based on liquid crystal on silicon (LCOS) are widely used for large-scale photonic switches in optical telecom network. For this application, high-order diffractions in LCOS is a critical issue because it causes signal crosstalk. In this paper, we analyze the impact of phase inaccuracy due to the fringing electric field in LCOS on the signal crosstalk in optical switches. We also propose a crosstalk reduction method that is analogous to frequency modulation in signal processing. The method is simple and optimized by only using a few parameters of the applied phase pattern without the need to modify the optics or electronics in use. With the proposed method, the worst crosstalk of a photonic switch was decreased from −16.2 to −31.6 dB.

Focal surface displays

Conventional binocular head-mounted displays (HMDs) vary the stimulus to vergence with the information in the picture, while the stimulus to accommodation remains fixed at the apparent distance of the display, as created by the viewing optics. Sustained vergence-accommodation conflict (VAC) has been associated with visual discomfort, motivating numerous proposals for delivering near-correct accommodation cues. We introduce focal surface displays to meet this challenge, augmenting conventional HMDs with a phase-only spatial light modulator (SLM) placed between the display screen and viewing optics. This SLM acts as a dynamic freeform lens, shaping synthesized focal surfaces to conform to the virtual scene geometry. We introduce a framework to decompose target focal stacks and depth maps into one or more pairs of piecewise smooth focal surfaces and underlying display images. We build on recent developments in "optimized blending" to implement a multifocal display that allows the accurate depiction of occluding, semi-transparent, and reflective objects. Practical benefits over prior accommodation-supporting HMDs are demonstrated using a binocular focal surface display employing a liquid crystal on silicon (LCOS) phase SLM and an organic light-emitting diode (OLED) display.