On-Chip Planar Lens Architectures for Optical Beam Steering

Abstract

Free-space optical beam steering is an important technological capability because of its applications in optical communication links and sensing such as light detection and ranging (lidar). Over the past decade, there has been significant efforts to develop a beam steering architecture that can lead to solid-state lidar with lower size, weight, power consumption, and cost (SWaP-C) while still meeting a high level of sensing performance and reliability. Herein, is the experimental demonstration of two novel planar lens-based architectures for optical beam steering in two dimensions. The first experimental demonstration is an aplanatic lens designed via the paraxial ray approximation and ray tracing. The second experimental demonstration is a Luneburg lens that is designed with a gradient in the refractive index along the radius of the lens. This second system uses a circularly symmetric grating to emit the optical beam over a wide field of view. Both planar lens architectures leverage a near-infrared tunable laser, a Mach-Zehnder interferometer switch tree, the lens that collimates and steers an optical mode in-the-plane of the chip, and a wavelength dependent grating for out-of-plane coupling. Various grating designs are presented towards the improvement of the effective aperture length and optical power emitted from the grating including double-layer grating designs and apodization schemes for the grating fill-fraction. Both devices are fabricated using a wafer-scale fabrication process and pave the way for two-dimensional optical beam steering with low electronic complexity and a large field of view. Lastly, remaining architecture challenges for a high performance lidar-on-a-chip system are discussed.