摘要： 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, fast scanning [1]. However, a main problem with current OPAs is the limited scanning angle. Steering angle of OPAs 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. We report a silicon based OPA which is built on our previous works on orbital angular momentum (OAM) [5-6]. The OPA consists of N concentric micro-ring OAM emitters that, when injected with a transverse magnetic (TM) polarized mode, are capable of emitting ‘sideways’ – a planar spiral orbital angular momentum (PS-OAM) beam whose phase fronts spiral outwards in the micro-ring plane with li number of arms, as given by the dipole model [7-9], by superposition of such PS-OAM waves or azimuthal Fourier harmonics, ∑Ni=1aiexp(jliφ)exp(jφi),. The superposition of such PS-OAM waves is capable of providing a practical realization of beamforming in radiofrequency and optical domain [7-9], by controlling their amplitude ai, phase φi, and topological charge li. A narrow beam can be rotated 360 degrees easily by adjusting the phase shifters, and with its 3 dB beamwidth decreases with higher number of PS-OAM modes.