Optical phased arrays (OPA) developed by Raytheon and Air Force Research Lab is a versatile device for laser beam steering, adaptive optics, electronic lens, and network switching. Fig. 1 shows the OPA device structure and its operating principle. The applied stepwise voltages create a phase grating inside the liquid crystal (LC) media that deflects the incoming laser beam to a programmable angle with high precision and high energy efficiency. To steer a λ=1.55μm laser beam, the required 2π phase change (δ=2πdΔn/λ) leads to dΔn～1.6; d is the LC cell gap and An is the birefringence. A thick LC layer would lead to a large phase shift, however, its response time is sluggish because the LC response time is proportional to d{sup}2. In order to achieve fast response time while keeping high manufacturing yield, the cell gap is normally kept at d～4μm. Thus, LC mixtures with Δn≥O.4 and low viscosity, wide nematic range, low operating voltage and good IW stability are particularly desirable.
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