The stressed liquid-crystal (SLC) electro-optic effect promises fast electro-optic response times even for design wavelengths
in the infrared (IR). Here we report characteristics of SLC devices appropriate for use as liquid-crystal-onsilicon
(LCOS) spatial light modulators (SLMs) in the near ( λ = 1.8-2.5 μm), mid (3-5.5 μm) and far (8-14 μm) IR
bands. For these three bands we fabricated SLC devices with 5, 10, and 20 μm thicknesses; at drive voltages of 25, 50,
and 125 V respectively these devices gave half-wave modulation with response speeds in the 1.3-1.6 ms range. Visiblelight
measurements on a 20-μm-thick SLC device between crossed polarizers gave a contrast ratio of 360:1 which
improved to nearly 18,000:1 with a Babinet-Soleil compensator offsetting residual SLC retardance. Widely available
high-voltage options in standard CMOS processes offer sufficient drive for near- and mid-IR SLCOS devices; with
modest increase of SLC material birefringence Δn and dielectric anisotropy Δε far-IR devices would be feasible, too.
Pixel drivers utilizing these options have pitches less than 24 μm, making 1000 ×1000 SLMs feasible.
Stressed liquid crystals (SLCs) have been applied in fields such as optical phase array non-mechanical beam steering applications, adaptive optical tip-tilt correction, and fast displays because SLCs are capable of switching large phase shift in sub-millisecond time ranges. SLCs consist of liquid crystal micro-domains dispersed in a stressed polymer matrix. In this paper, we propose a model of close-packed, shaped liquid crystal droplets inside a sheared polymer matrix based upon the measurements of polarizing microscopy, fluorescence confocal microscopy, and visible-near-infrared spectroscopy. The light scattering of SLC films results mostly from the index mismatch between adjacent liquid crystal domains instead of the index mismatch between polymer matrices and liquid crystals as in traditional polymer dispersed liquid crystals. We show how the light scattering of SLC cells is greatly reduced upon shearing because the liquid crystal domains are aligned along the direction of shearing. The stretching of polymer matrices and the reshaping of liquid crystal domains upon shearing are confirmed by fluorescence confocal microscopy. The calculations of the electro-optic responses are based on the balance between the elastic torque and the electric field torque. Our experimental results support the calculations.
Recently discovered stressed liquid crystals (SLCs) are of a great interest because they provide largest phase retardation shift achievable within shortest time interval. This effect was accomplished by decoupling the speed of a liquid crystal layer from its thickness. SLCs easily switch 5 microns of the phase retardation at sub-millisecond speeds while 50 microns requires only several milliseconds. SLCs are therefore able to modulate the IR light with the frequencies higher than 10 kHz. The SLCs are polymer/liquid crystal composites; however, their electro-optic properties differ significantly from previously developed polymer dispersed liquid crystals and polymer network/stabilized liquid crystals. The applied stressed force aligns the domains, eliminating scattering and hysteresis at the same time. The phase shift is highly linear with the applied voltage, greatly simplifying the drive electronics. The SLCs pose intriguing basic scientific questions and may be used in a lot of new electro-optical applications (micro-displays, diffractive optical elements, beam steering devices).
The recently discovered stressed liquid crystals (SLCs) are of a great interest because they provide the largest phase retardation shift achievable within the shortest time interval. This was accomplished by decoupling the speed of a liquid crystal layer from its thickness. SLCs easily switch 5 microns of phase retardation at sub-millisecond speeds. We have produced phase shifts as large 50 microns in several milliseconds. SLCs are therefore able to modulate IR light with response frequencies higher than 10 kHz. The SLCs are polymer/liquid crystal composites; however, their electro-optic properties differ significantly from previously developed polymer dispersed liquid crystals and polymer network/stabilized liquid crystals. An applied mechanical stress aligns the liquid crystal domains, eliminating scattering and hysteresis at the same time. The phase shift is highly linear with the applied voltage, greatly simplifying the drive electronics. The SLCs pose intriguing basic scientific questions and may be used in a host of new electro-optical applications (micro-displays, diffractive optical elements, beam steering devices).
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