Fast multi-spectral liquid-crystal-on-silicon spatial light modulators

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 (lambda = 1.8-2.5 mu m), mid (3-5.5 mu m) and far (8-14 mu m) IR bands. For these three bands we fabricated SLC devices with 5, 10, and 20 pm 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. Visible-light measurements on a 20-mu m-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 An and dielectric anisotropy Delta epsilon far-IR devices would be feasible, too. Pixel drivers utilizing these options have pitches less than 24 mu m, making 1000 x 1000 SLMs feasible.