A Single-Chip Optical Phased Array in a Wafer-Scale Silicon Photonics/CMOS 3D-Integration Platform

• Published in: IEEE journal of solid-state circuits Vol. 54; no. 11; pp. 3061 - 3074
• Main Authors: Kim, Taehwan, Ngai, Tat, Timalsina, Yukta, Watts, Michael R., Stojanovic, Vladimir, Bhargava, Pavan, Poulton, Christopher V., Notaros, Jelena, Yaacobi, Ami, Timurdogan, Erman, Baiocco, Christopher, Fahrenkopf, Nicholas, Kruger, Seth
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.11.2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: 3-D integration; Apertures; CMOS; Density; Laser radar; LiDAR; Optical beams; optical phased array (OPA); Optical sensors; Optical variables control; Phase control; Phase shifters; Phased arrays; Photonics; Power consumption; Power efficiency; Silicon; silicon photonics; solid-state optical beam-steering; Steering; Wiring
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2019.2934601

With the growing demand for automotive LiDAR and the maturation of silicon photonics platforms, optical phased arrays (OPAs) have emerged as a key technology for solid-state optical beam-steering. In order to meet realistic automotive specifications with OPAs, >500 antenna elements should work reliably under tight power and cost budgets. Existing multi-chip solutions necessitate expensive packaging and assembly to achieve high interconnect density. Even with 2-D monolithic integration, high-voltage drivers to deliver sufficient power to resistive phase shifters typically result in significant overhead in die area and limited power efficiency. In this article, we introduce a single-chip OPA realized through wafer-scale 3-D integration of silicon photonics and CMOS. Flexible and ultra-dense connections with through-oxide vias (TOVs) in our platform resolve the I/O density issue. Moreover, low-voltage L-shaped phase shifters and compact, efficient switch-mode drivers, connected vertically using TOVs, remove wiring/placement overhead and achieve a large active array aperture within a compact die. Our OPA prototype achieves wide-range 2-D steering over 18.5°×16° by leveraging wavelength tuning and phase control, and array scaling up to 125 elements with a large aperture size of 0.5 mm×0.5 mm and 0.15°×0.25° beamwidth while consuming 20 mW/element average power. Since our system supports per-element independent phase control, increased sensitivity to process variations in L-shaped shifters is fully compensated by a simple calibration process.