High-Efficiency Beam Steering LCOS for Wavelength Selective Switch

Abstract

A liquid crystal on silicon (LCOS) device exhibiting high diffraction efficiency at a large deflection angle is demonstrated. An LC mixture with a large birefringence ( $\Delta \text{n}\,\,=0.25$ at $\lambda =1550$ nm) and a large dielectric constant ( $\Delta \varepsilon = 10.4$ ) is developed to obtain the high-phase retardation, more than $4\pi $ , at 1550 nm within a relatively low operation voltage of 5.5 V on LCOS. When compared with the conventional modulation method of $2\pi $ phase retardation, both grating period and phase retardation are doubled in $4\pi $ modulo modulation. Using the high-phase retardation modulation method, the LCOS may achieve high diffraction efficiency more than 56.6% at 4.5° deflection angle of C-band wavelength with an optimized phase retardation profile. The high diffraction efficiency phase modulator shows the great potential application of beam steering for the wavelength selective switch and the holographic display.