Electronics Weekly Electronics Design & Components Tech News
PH18 uses silicon and silicon nitride waveguides to create and link optical building blocks including couplers, interferometers, radiators, modulators and photodetectors. Its low-loss silicon nitride waveguides are capable of handling the optical powers necessary for lidars.
The IC was designed by researchers from the University of Southern California led by SungWon Chung, and was first quietly revealed at the IEEE International Solid-State Circuits Conference in February.
It can build a 3D image of the surrounding environment without moving parts. Instead, it employs an optical phased array, along with amplitude and phase modulators on the silicon chip. “Additionally, the field of view, resolution, scanning pattern, and scanning speed are all programmable, meaning that cars outfitted with this system can respond better to real-world scenarios,” according to Tower.
The chip uses a single 256 element optical phased array for both transmit and receive, and works with a pair of identical electronic ICs (180nm CMOS from TSMC), each with 136 Class-D PWM drivers that power heaters on the optical chip to thermally tune a 32 x 8 photonic phase and amplitude shifter array (see diagram). Optical transmit power comes from an external laser diode and chirp modulator.
This system is self-calibrating without interaction with an external object. It has a closed-loop scheme to allow an algorithm monitoring samples of the transmit signals (picked off at the antenna elements), aided by a pre-stored fingerprint, to offset the phase modulation signals. “Instead of using external detectors at the far-field distance, self-calibration is performed by exploiting an integrated FMCW receiver and a star coupler that provide internal optical feedback paths,” said the team at ISSCC 2021.
Operation is FMCW (continuous wave frequency modulation) at 1,550nm, and it produces a 3dB beam width is 0.3° horizontally and ~1° vertically, and the beam can be steered ±33.6° horizontally and ±2.5° vertically.
More information is available from ISSCC 2021 Digest paper 19.1 ‘Optical phased-array FMCW lidar with on-chip calibration’.
The work by USC and Tower was also funded by Toyota Central R & D Corporation (TCRDL), Samsung Advanced Institute of Technology (SAIT) and the USC Pratt and Whitney Institute for Collaborative Engineering.
ISSCC is an annual showcase for the cream of on-chip circuitry, selected from commercial and university development teams all over the world.
