[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - 360° on Chip Optical Beam Steering Based on Superposition of Planar Spiral Orbital Angular Momentum Waves

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.