Near-Field-Focusing Integrated Optical Phased Arrays

Abstract

Integrated optical phased arrays that focus radiated light to a tightly-confined spot in the near field are demonstrated for the first time. The element phase distributions necessary for generating and steering focused beams using phased arrays are developed. Discussion and simulations detailing the effects of the array aperture and focal length on the focal spot are included. Two focusing phased array architectures are presented: (1) a one-dimensional splitter-tree-based architecture with novel focusing antennas and inline phase bumps and (2) a two-dimensional large-scale pixel-based architecture. Both architectures are used to experimentally demonstrate a variety of aperture size and focal length passive focusing arrays in a CMOS-compatible platform, including (i) a 512-antenna splitter-tree-based array with a wavelength-steerable 7 µm spot at a 5 mm focal length, (ii) a 1024-antenna pixel-based array with a 21 µm spot at a 5 mm focal length, and (iii) a 10,000-antenna pixel-based array with a 21 µm spot at a 10 mm focal length. The demonstrated focusing phased arrays present a new functional modality compared to standard optical phased arrays that generate diffracting beams in the far field of the array. This new focusing modality has the potential to advance a number of important application areas at the cutting edge of lightwave technology, as it will enable future integrated optical phased array implementations for a wide range of applications that require focusing operation. Such areas include optical trapping for biological characterization, laser-based three-dimensional printing, short-range light detection and ranging, and short-range optical data communications.