Performance metrics and active temperature control of spatial light modulators

Surface-stabilized antiferroelectric liquid crystals (AFLCs) and V-shape smectics share the spontaneous generation of intermediate transmission states, i.e. analogue grayscale. On the other hand, liquid crystal on silicon (LCOS) appears to be a promising alternative to thin-film transistors (TFTs) in the preparation of reflective microdisplays and spatial light modulators (SLMs). The feasibility of preparing LCOS SLMs using AFLC and V-shaped LCs has been analyzed. A comparative study of a number of AFLC and V-shape materials as candidates for LCOS SLMs has been carried out. Test cells below 1 µm have been prepared using an ITO-coated transparent glass plate and an aluminized silicon back plate mimicking the actual LCOS device. AFLC waveforms compatible to low-voltage operation of the silicon backplane have been demonstrated. V-shape waveforms have been designed and demonstrated as well. The results show that both LC families may be employed in this specific application. Dynamic behavior, with frame rates over 200 Hz, is especially remarkable.

In 3‐D display system based on opto‐electronic reconstruction of digitally recorded hologram, the field of view of such a system is limited by the spatial resolution of the liquid crystal on silicon (LCOS) spatial light modulator (SLM) used to perform the opto‐electronic reconstruction. In this article, the spatial resolution limitation of LCOS SLM associated with fringe field effect and interpixel coupling is determined by liquid crystal director simulation and Finite Difference Time Domain (FDTD) simulation. The diffraction efficiency loss associates with the imperfection in phase profile is studied with an example of opto‐electronic reconstruction of an amplitude object. A high spatial resolution LCoS SLM with wide reconstruction angle is proposed.

The cavity supports the orthogonal reference beam families as its eigenmodes while enhancing the reference beam power. Such orthogonal eigenmodes are used as additional degree of freedom to multiplex data pages, consequently increase storage densities for volume Holographic Data Storage Systems (HDSS) when the maximum number of multiplexed data page is limited by geometrical factor. Image bearing holograms are multiplexed by orthogonal phase code multiplexing via Hermite-Gaussian eigenmodes in a Fe:LiNbO3 medium with a 532 nm laser at multiple Bragg angles by using Liquid Crystal on Silicon (LCOS) spatial light modulators (SLMs) in reference arms. Total of nine holograms are recorded with three angular and three eigenmode.

We have developed a high-resolution, multi-color retinal imaging system using liquid crystal adaptive optics. A liquid crystal on silicon (LCOS) spatial light modulator (SLM) is used to correct ocular aberrations. In order to compensate for the dependency of an LCOS SLM on optical wavelength and acquire aberration-corrected images at different color, we apply an open-loop technique. In the open-loop technique, the imaging light is separated from the sensing light and the optimal phase modulation is applied only to the imaging light while the sensing light is not phase-modulated. With the system, in vivo imaging of the human retina is achieved by using illumination light at wavelength of 655nm and 593nm and sensing light at 780nm. Photoreceptors are clearly revealed at each illumination wavelength with the liquid crystal adaptive optics.

2-D optical phased array (OPA) antenna based on a liquid crystal on silicon (LCOS) spatial light modulator is introduced. Diffraction efficiency of the 1-D OPA for fine angle beam steering and 2-D OPA for aberration correction is characterized experimentally and by computer simulation. Excellent agreement between the simulation, measurement and empirical model is observed. Large aperture transmitter for long distance free space communication is analyzed by wave optics simulation. The system performance for beam steering and correction for wavefront aberration in large aperture transmitter is discussed.

Linear structured illumination microscopy (SIM) is a super-resolution microscopy technique that does not impose photophysics requirements on fluorescent samples. Multicolor SIM implementations typically rely on liquid crystal on silicon (LCoS) spatial light modulators (SLM's) for patterning the excitation light, but digital micromirror devices (DMD's) are a promising alternative, owing to their lower cost and higher speed. However, existing coherent DMD SIM implementations use only a single wavelength of light, limited by the lack of efficient approaches for solving the blazed grating effect for polychromatic light. We develop the requisite quantitative tools, including a closed form solution of the blaze and diffraction conditions, forward models of DMD diffraction and pattern projection, and a model of DMD aberrations. Based on these advances, we constructed a three-color DMD microscope, quantified the effect of aberrations from the DMD, developed a high-resolution optical transfer function measurement technique, and demonstrated SIM on fixed and live cells. This opens the door to applying DMD's in polychromatic applications previously restricted to LCoS SLM's.

A novel imaging technique that produces accurate amplitude and phase images of an optical fiber facet using only a phase-only liquid-crystal on silicon (LCOS) spatial light modulator (SLM) and a single-pixel detector is presented. The system can take images in two orthogonal polarizations and so provides a powerful tool for modal characterization of multimode fibers, which is of increasing importance due to their burgeoning use in telecommunications and medical applications. This technique first uses a simulated annealing algorithm to compute a hologram that collects light from a small region of the fiber facet. Next, the fiber facet is automatically brought into focus using adaptive aberration correction on the SLM. Finally, a common-path interferometer is created using the SLM, and the phase of the optical field at each pixel is determined. Finally, high-definition amplitude and phase images of a ring-core refractive index fiber are presented as a proof-of-principle demonstration of the technique.

We present a method for reducing the phase flicker originated by the pulsed modulation of a Liquid Crystal on Silicon (LCoS) Spatial Light Modulator (SLM). It consists in reducing the temperature of the LCoS in a controlled way, in order to increase the viscosity of the liquid crystal. By doing this, we increase the time response of the liquid crystal, and thus reduce the amplitude of phase fluctuations. We evaluate the efficacy of this method quantifying the temporal evolution of phase shift using an experiment that is insensitive to optical polarization fluctuations. Additionally, we determine the effect of the temperature reduction on the effective phase modulation capability of the LCoS. We demonstrate that a reduction of up to 80% of the flicker initial value can be achieved when the LCoS is brought to -8 °C.

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.

A liquid crystal panel for a video projector is often used for holographic television. However, its pixel size and pixel number are not enough for practical holographic 3-D display. Therefore, a multipanel configuration is generally used to increase the viewing window and displayed image size, and many spatial light modulators should be used in them. We propose a novel method to increase the viewing window of a holographic display system. The proposed method, which is implemented by using a mirror module and 4-f lens set, is to reconfigure the beam shape reflected by a spatial light modulator. The equipment is applied to a holographic display system, which has only a single spatial light modulator; a hologram could be displayed in a wider viewing window by the equipment than that of the conventional method. By the proposed method, the resolution of the reconfigured spatial light modulator has double resolution in the horizontal direction. Inversely, the vertical resolution is decreased. Even if the vertical resolution is decreased, a viewer could get 3-D effect because humans get more 3-D information in the horizontal direction. We have experimented using a liquid crystal on silicon (LcOS), whose resolution is 4096×2160 pixels. The reconfigured resolution by the mirror module is 8192×1080 pixels. From the experiments, the horizontal viewing window is almost two times wider than that without the mirror module. As a result, the hologram can be observed binocularly.

Liquid Crystal on Silicon (LCoS) Spatial Light Modulators (SLMs) are used as programmable adaptive optical elements1,2,3 in many applications involving high power lasers. In some cases, LCoS SLMs may be exposed to laser radiation that can cause permanent, irreparable damage to the SLM. The damage arises from a number of parameters including laser wavelength, pulse duration, pulse repetition rate, beam diameter, spatial profile, temporal profile, and even angle of incidence. This paper is an introduction and practical guide to understanding laser damage mechanisms and expected damage threshold levels for LCoS SLMs.

An autostereoscopic display system was designed and constructed. The design, which uses pupil imaging with a curved mirror, is described. It employs a monocentric configuration to enable a wide field of view and large pupils while keeping the lens diameters small to fit them within the interoccular separation. For each eye, image formation was accomplished using 1920 x 1200 liquid crystal on silicon (LCOS) spatial light modulators in a 3-panel configuration. The design employs custom curved diffusers, which were developed to optimize throughput, contrast, and pupil illumination uniformity.

Spatial light modulators (SLMs) are the most relevant technology for dynamic wavefront manipulation. They find diverse applications ranging from novel displays to optical and quantum communications. Among commercial SLMs for phase modulation, Liquid Crystal on Silicon (LCoS) offers the smallest pixel size and, thus, the most precise phase mapping and largest field of view (FOV). Further pixel miniaturization, however, is not possible in these devices due to inter-pixel cross-talks, which follow from the high driving voltages needed to modulate the thick liquid crystal (LC) cells that are necessary for full phase control. Newly introduced metasurface-based SLMs provide means for pixel miniaturization by modulating the phase via resonance tuning. These devices, however, are intrinsically monochromatic, limiting their use in applications requiring multi-wavelength operation. Here, we introduce a novel design allowing small pixel and multi-spectral operation. Based on LC-tunable Fabry-Perot nanocavities engineered to support multiple resonances across the visible range (including red, green and blue wavelengths), our design provides continuous 2π phase modulation with high reflectance at each of the operating wavelengths. Experimentally, we realize a device with 96 pixels (~1 μm pitch) that can be individually addressed by electrical biases. Using it, we first demonstrate multi-spectral programmable beam steering with FOV~18° and absolute efficiencies exceeding 40%. Then, we reprogram the device to achieve multi-spectral lensing with tunable focal distance and efficiencies ~27%. Our design paves the way towards a new class of SLM for future applications in displays, optical computing and beyond.

We demonstrate that layered spatial light modulators (SLMs), subject to fixed lateral displacements and refreshed at staggered intervals, can synthesize images with greater spatiotemporal resolution than that afforded by any single SLM used in their construction. Dubbed cascaded displays , such architectures enable superresolution flat panel displays (e.g., using thin stacks of liquid crystal displays (LCDs)) and digital projectors (e.g., relaying the image of one SLM onto another). We introduce a comprehensive optimization framework, leveraging non-negative matrix and tensor factorization, that decomposes target images and videos into multi-layered, time-multiplexed attenuation patterns---offering a flexible trade-off between apparent image brightness, spatial resolution, and refresh rate. Through this analysis, we develop a real-time dual-layer factorization method that quadruples spatial resolution and doubles refresh rate. Compared to prior superresolution displays, cascaded displays place fewer restrictions on the hardware, offering thin designs without moving parts or the necessity of temporal multiplexing. Furthermore, cascaded displays are the first use of multi-layer displays to increase apparent temporal resolution. We validate these concepts using two custom-built prototypes: a dual-layer LCD and a dual-modulation liquid crystal on silicon (LCoS) projector, with the former emphasizing head-mounted display (HMD) applications.

Phase-only liquid crystal spatial light modulator (SLM) has been widely used for accurate phase-manipulation in holographic display, optical tweezers, lithography, etc. Due to the nonlinear optical response of liquid crystal and manufacturing defects, the grayscale-phase response could be different for every single SLM device. The calibration for phase modulation is needed for improving the performance of the SLM involved system. The principles of phase-only SLM are reviewed. The main phase calibration methods for SLM are discussed and compared.