360° on Chip Optical Beam Steering Based on Superposition of Planar Spiral Orbital Angular Momentum Waves

Optical beam steering has been pursued in the past decade, largely motivated by its potential applications including optical communication and laser radar systems. Optical phased array (OPA) is a promising beam steering method, which has the potential advantages of low cost, chip scale, high resolution, high accuracy and fast scanning [1]. However, a main problem with current OPAs is the limited scanning angle. Steering angle of OP As based on out-of-plane emitting planar waveguide gratings is typically <; 50 degrees. End-fire OPA has a larger steering angle but still will be restricted to <; 180 degrees due to its geometry [2]. Circular OPA can provide 360-degree beam steering [3-4], but the existing proposals require large number of control elements which makes it very hard to realize.