Cascaded One-Dimensional Liquid Crystal OPAs for 2-D Beam Steering

Beam steering in two dimensions can be achieved using a reflection-mode liquid crystal optical phased array (OPA) with a backplane that has a twodimensional pixel structure. However, current lithographic constraints require a relatively large pixel pitch, limiting two-dimensional OPAs to steering only to milliradian angles. Moderate to large angle two-dimensional steering can also be readily achieved by placing two onedimensional OPAs in series. After a brief introduction to liquid crystal beam steering, we discuss the coupled wave analysis, with which the modulation depth can be determined from the wave vector components along the direction of propagation. It can be shown that the minimum off-axis effects occur when the orientation of the liquid crystal extraordinary axis is perpendicular to the plane of incidence. This is followed by experimental demonstration of the change in phase modulation depth for the cases of normal incidence and a 45 degree angle of incidence. Two-dimensional beam steering using two one-dimensional reflective liquid crystal electrode arrays is reported on for the first time. The paper ends with conclusions drawn from this research.