Thermo-optic switching and beam-steering structures for widening 2D field-of-view of silicon optical phased array

Abstract

As the need for 3D image sensors in unmanned vehicles, robots and drones increases, LiDAR (light detection and ranging) technology capable of acquiring 2D images and depth information using light is attracting attention. In the conventional LiDAR technique, a mechanical spinning method is mainly used, but these methods are difficult to miniaturize and have low durability. In order to solve such problems, researches on a semiconductor-based solid-state optical phased array (OPA) have been actively conducted. In most optical phase arrays, beam-steering in the transversal direction is achieved by electrically controlling the phase of each channel. In the case of beam-steering in the longitudinal direction, it is achieved by using a phased array using a 2D array, or by changing the wavelength of light and controlling the Bragg-condition of the radiator. In the case of using a 2D array, it is difficult to obtain a wide beam-steering range because it is physically difficult to reduce the gap between the radiators which determine the transversal beam-steering range. In the method of changing the wavelength of light, it is difficult to integrate a laser capable of wavelength modulation into a chip, Are sensitive to wavelengths, it is difficult to ensure the consistency of light emitted from the optical phase array. In order to solve this problem, this paper proposes an optical phased array capable of steering a beam in a longitudinal direction using a thermo-optic effect of silicon by placing a silicon-based heater of n-i-n structure in the radiator region. In this structure, a wider longitudinal beam-steering can be achieved by arranging a multiple optical phase arrays and sequentially operating them. Silicon-based optical switches are needed to operate the optical phased array sequentially. In this paper, I also propose a compact thermo-optic switch based on silicon MMI (Multi-mode interferometer) as well as an optical phase array capable of vertical radiation angle control. The MMI optical switch is an element that operates the optical switching by using the 1x2 MMI and the n-i-n heater to adjust the interference mode of the MMI asymmetrically and using the phase difference generated therefrom. In this paper, I examine performance of individual devices of optical phased array and MMI or MZI switch. In addition, I proposed the wide angle beam-steering optical phased array by combining two devices.