Liquid Crystal On Silicon Spatial Light Modulator Research Articles

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.

High Performance Liquid Crystal on Silicon Spatial Light Modulator (LCOS-SLM) and Flicker Noise Reduction of Multiple Spots

High Performance Liquid Crystal on Silicon Spatial Light Modulator (LCOS-SLM) and Flicker Noise Reduction of Multiple Spots

High Performance Liquid Crystal on Silicon Spatial Light Modulator (LCOS-SLM) and Flicker Noise Reduction of Multiple Spots

High Performance Liquid Crystal on Silicon Spatial Light Modulator (LCOS-SLM) and Flicker Noise Reduction of Multiple Spots

Optimization of random phase diversity for adaptive optics using an LCoS spatial light modulator.

Phase retrieval is an attractive approach for sensor-less adaptive optics (AO) because of its relatively simple implementation. Recently, random phase diversity has shown fast convergence for phase retrieval algorithms. In this study, design optimization using random phase diversity is discussed with respect to a sensor-less AO system using a liquid-crystal-on-silicon (LCoS) spatial light modulator. The extrinsic phase disturbances studied are due to Kolmogorov turbulence. Simulation analysis shows that the size of super-pixel segments of the random phase patterns on the LCoS and the cropped image area of the phasorgrams are determined by Fried's parameter for high-Strehl-ratio and low-iteration-number reconstruction. AO experiments with an LCoS spatial light modulator confirm the simulation results.

49‐1: Invited Paper: Analog LCOS SLM Devices for Display Applications

Liquid‐crystal‐on‐silicon (LCOS) device is a potential candidate for spatial light modulators (SLMs) due to its high resolution and the wide range of tunable phase retardation. Besides the telecom applications, SLM is also very promising for display applications, especially for the augmented reality (AR) displays. In this paper, we will discuss the advantages of analog LCOS SLM compared with the digital one. A 0.6” short‐loop sample test result with precise cell gap controlled is introduced. Some CGH images are demonstrated using different algorithms. Finally, the liquid crystal response time performances are also discussed.

Simultaneous aberration and aperture control using a single spatial light modulator.

A method to simultaneously control aberrations and the aperture of an optical system using a single phase-only spatial light modulator was investigated. The experiment was performed using a liquid-crystal-on-silicon spatial light modulator (LCoS-SLM) within an adaptive optics system used for visual testing, although the method has broader applications in adaptive optics field. The performance of the technique was characterized through the estimation of the system's modulation transfer functions (MTFs) by using a random chart method. MTFs obtained from the phase modulation-based approach were compared with those from using a real aperture (diaphragm). The areas under the MTFs for the two conditions were similar up to 98%, confirming that the low-pass filter effect associated to the size of the entrance pupil was similar for the phase-modulated pupil and the physical pupil. As an example of application, both aberrations and pupil were controlled by a single phase-only modulator to study the through-focus visual performance in real subjects. Limitations and possible enhancements of the presented method were also discussed. The presented technique reduces complexity and cost of adaptive optics systems. It opens the door to new experiments by allowing dynamic modulation of aberrations and apertures of any shape.

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.

LCoS SLM Study and Its Application in Wavelength Selective Switch

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

Sub-GHz Resolution Photonic Spectral Processor and Its System Applications

A record performance metric waveguide grating router (WGR) design with a 200 GHz free spectral range (FSR) capable of resolving sub-GHz resolution spectral features is developed for a fine resolution photonic spectral processor (PSP). The WGR's FSR was designed to support subchannel add/drop from a superchannel of 1 Tb/s capacity. Due to fabrication imperfections, we introduce phase corrections to the light beams emerging from the 250 waveguides of the WGR output using a liquid crystal on silicon (LCoS) phase spatial light modulator (SLM) placed in an imaging configuration. A second LCoS SLM is located at the Fourier plane, for arbitrary spectral amplitude and phase manipulations. The PSP is utilized in multiple system transmission experiments, such as flexible spectral shaping and subcarrier drop demultiplexing with sub-GHz spectral resolution.

Resolution enhancement using simultaneous couple illumination

A super-resolution technique based on structured illumination created by a liquid crystal on silicon spatial light modulator (LCOS-SLM) is presented. Single and simultaneous pairs of tilted beams are generated to illuminate a target object. Resolution enhancement of an optical 4f system is demonstrated by using numerical simulations. The resulting intensity images are recorded at a charged couple device (CCD) and stored in the computer memory for further processing. One dimension enhancement can be performed with only 15 images. Two dimensional complete improvement requires 153 different images. The resolution of the optical system is extended three times compared to the band limited system.

Non-uniform spatial response of the LCoS spatial light modulator

Liquid crystal on silicon (LCoS) spatial light modulators have been considered for a wide variety of scientific applications, due to their phase modulation capability and high spatial resolution. Nevertheless, their intrinsic characteristics, like the extensively studied depolarization and phase shift fluctuations, can make their behavior significantly distant from the ideal and somewhat unpredictable. Here, we present the characterization of a different source of uncertainty: the non-uniform spatial response of the LCoS, which is fundamentally different to the static aberrations of the panel. We measured local deviations of ±22% from the expected phase shift, resulting in non-negligible effects for phase modulation measurements, phase shifting interferometry, wavefront correction, and speckle interferometry.

Evaluation and Calibration of LCoS SLM for Direct Laser Structuring with Tailored Intensity Distributions

Tailored intensity distribution enables efficient microstructuring as the maximum pulse energy of an ultrashort-pulsed laser can be applied. Dynamic adaptation of the intensity profile can be realized by holographic laser beam shaping using phase-only liquid crystal on silicon (LCoS) displays as a spatial light modulator (SLM). To achieve the desired intensity profile at the focal plane an accurate phase retardation of the SLM's liquid crystals has to be guaranteed. In this publication we present the phase calibration of three LCoS SLM from different manufacturers. Each system is evaluated for direct laser structuring applications. As one of the tested SLM show a spatially nonlinear behavior, a compensation method proposed by Engström et al. in 2013 is applied. Finally, the necessity of this phase calibration is presented and discussed by applying a squared flat-top profile.

Optimization of the Liquid Crystal on Silicon Technology for Laser Microprocessing Applications

Phase-only spatial light modulators (SLMs) allow to bring adaptive optics and diffractive optics methods into laser material processing. We focus our research on the liquid crystal on Silicon (LCOS) technology, which is known from display and photonic applications for its high resolution, flexibility, technological and economical feasibility.The broad range of applications in laser material processing imposes various requirements on such dynamic components.Most important is the ability of the SLM to withstand the higher intensities and energies over the long time. This requires better understanding of the laser induced damage threshold (LIDT) levels of these devices on system and component level as well as long term performance degradation, especially if ultra-short pulse (USP) light sources are used. The measures to improve LIDT and other important parameters while keeping the economically feasible wafer-scale fabrication of LCOS SLMs will be discussed.

Fine Resolution Photonic Spectral Processor Using a Waveguide Grating Router With Permanent Phase Trimming

Spectrally dispersed light from a fine resolution waveguide grating router (WGR) of 25-GHz free spectral range that radiates to free space is spatially filtered at ~1 GHz optical resolution and 50 MHz spectral addressability using a liquid crystal on Silicon (LCoS) spatial light modulator (SLM). Fabrication imperfections leading to phase errors on the 32 waveguide arms of the WGR are corrected using a UV pulsed laser to inscribe permanent optical path changes to the waveguides. WGR phase errors are permanently trimmed waveguide-by-waveguide with an excimer laser by inducing stress in the glass cladding above the waveguide for coarse setting and using the photosensitivity effect for fine setting. The WGR was then mated with an LCoS SLM located at the Fourier plane to form a photonic spectral processor, for arbitrary spectral amplitude and phase manipulations.

Digital holography with multidirectional illumination by LCoS SLM for topography measurement of high gradient reflective microstructures

In this paper we present a method for topography measurement of high gradient reflective microstructures that overcomes the limited numerical aperture (NA) of a digital holographic (DH) system working in reflection. We consider a case when a DH system is unable to register the light reflected from the full sample area due to insufficient NA. To overcome this problem, we propose digital holography in a microscope configuration with an afocal imaging system and a modified object arm in the measurement setup. The proposed modification includes application of a spatial light modulator (SLM) based on liquid crystal on silicon (LCoS) technology for multidirectional plane wave illumination. The variable off-axis illumination enables characterization of the sample regions that cannot be imaged by the limited NA of a classical DH system utilizing on-axis illumination. In the proposed method, the final object topography is merged from a set of captured object waves corresponding to various illumination directions using a novel automatic algorithm. The proposed technique is experimentally validated by full-field measurement of a silicon mold with a high gradient of shape.

Dual-plane in-line digital holography based on liquid crystal on silicon spatial light modulator.

A dual-plane in-line digital holographic method is proposed with a liquid crystal on silicon (LCOS) spatial light modulator (SLM) for recording holograms at two slightly displaced planes. The computer-generated chirp-like complex reflectance is displayed on the LCOS SLM to adapt the object beam at two planes for recording two holograms processed to eliminate the DC term and twin image accurately; no mechanical components or manual operation during data acquisition is required. The proposed approach improves the speed, accuracy, and stability of the experiment. Computer simulation and experiments for both amplitude and phase objects are carried out to validate the proposed method.

Self-distortion compensation of spatial light modulator under temperature-varying conditions.

Conventional methods of compensating for self-distortion in liquid-crystal-on-silicon spatial light modulators (LCOS-SLM) are based on aberration correction, where the wavefront of the incident beam is modulated to compensate for aberrations caused by the imperfect optical flatness of the LCOS-SLM surface. However, the phase distribution of an LCOS-SLM varies with changes in ambient temperature and requires additional correction. We report a novel phase compensation method under temperature-varying conditions based on an orthonormal Legendre series expansion of the phase distribution. We investigated the temperature dependency by controlling the ambient temperature with an incubator and successfully corrected for self-distortion in a temperature range of 20 °C to 50 °C. Our approach has the potential to be adopted in tight-focusing applications which require wavefront modulation with very high accuracy.

39.3: Invited Paper: Advances in Application of Liquid Crystal on Silicon Spatial Light Modulator (LCOS‐SLM)

AbstractA high quality and high performance 2D Spatial Light Phase Modulator has been developed for wide range of basic and practical applications. We will discuss how LCOS micro‐display device is developed into LCOS‐SLM for various important non‐display applications ranging from basic and applied researches such as singular optics and fluorescence microscopy to industrial applications in laser processing and machining.

Adaptive Generation and Diagnostics of Linear Few-Cycle Light Bullets

Recently we introduced the class of highly localized wavepackets (HLWs) as a generalization of optical Bessel-like needle beams. Here we report on the progress in this field. In contrast to pulsed Bessel beams and Airy beams, ultrashort-pulsed HLWs propagate with high stability in both spatial and temporal domain, are nearly paraxial (supercollimated), have fringe-less spatial profiles and thus represent the best possible approximation to linear “light bullets”. Like Bessel beams and Airy beams, HLWs show self-reconstructing behavior. Adaptive HLWs can be shaped by ultraflat three-dimensional phase profiles (generalized axicons) which are programmed via calibrated grayscale maps of liquid-crystal-on-silicon spatial light modulators (LCoS-SLMs). Light bullets of even higher complexity can either be freely formed from quasi-continuous phase maps or discretely composed from addressable arrays of identical nondiffracting beams. The characterization of few-cycle light bullets requires spatially resolved measuring techniques. In our experiments, wavefront, pulse and phase were detected with a Shack-Hartmann wavefront sensor, 2D-autocorrelation and spectral phase interferometry for direct electric-field reconstruction (SPIDER). The combination of the unique propagation properties of light bullets with the flexibility of adaptive optics opens new prospects for applications of structured light like optical tweezers, microscopy, data transfer and storage, laser fusion, plasmon control or nonlinear spectroscopy.

Wavefront pre-compensation for thermal deformations in a high power inner optical system

The phase aberration caused by thermal deformations in a high power inner optical system is simulated and the wavefront pre-compensation for correcting the aberration is studied experimentally. Choosing Strehl ratio (SR) and the root-mean-square (RMS) of distorted phase as the characteristic parameters, the beam quality of outgoing laser is calculated when the wavefront of incident laser is compensated. Based on the computed results, the laboratory experiment is designed to model the thermal deformations aberration and the correction process by using two Liquid Crystal on Silicon Spatial Light Modulators (LCoS-SLM). The negative influence of astigmatism and defocusing on laser beam quality in far field is obvious and the astigmatism induces the non-axisymmetrical divergence of intensity distribution. After wavefront pre-compensation the power in the bucket (PIB) value of outgoing laser beam is close to the flat wavefront laser source. Both simulated and experimental results indicate that the method of wavefront pre-compensation can greatly correct the aberrations caused from thermal deformation, and the laboratory experiment is a feasible method to modeling the inner optical system with phase aberration.