UC Berkeley

The superiority of lidar compared to radio-frequency and ultrasonic solutions in terms of depth and lateral resolution has been known for decades. In recent years, both application pull such as 3D vision for robotics, rapid prototyping, self-driving cars, and medical diagnostics, as well as technology developments such as integrated optics and tunable lasers have resulted in new activities.

Pulsed, amplitude-modulated continuous-wave (AMCW), and frequency-modulated continuous-wave (FMCW) lidars can all be used for ranging. The latter option enables excellent depth resolution at the micron level. Achieving this level of performance is contingent on a precision light source with accurate frequency modulation. This thesis presents a fully integrated solution realizing an electro-optical phase-locked loop (EO-PLL) fabricated on separate complementary metal-oxide-semiconductor (CMOS) and silicon-photonic wafers interconnected with through-silicon vias (TSVs).

The system performs 180,000 range measurements per second, with a root-mean square (RMS) depth precision of 8 μm at distances of ±5cm from the range baseline increasing to 4.2 mm RMS error at a range of 1.4 m, limited by the coherence length of the laser used in these experiments. Optical elements including input light couplers, waveguides, and photodiodes are realized on a 3 mm by 3 mm silicon-photonic chip. The 0.18 μm CMOS application-specific integrated circuit (ASIC) of the same area comprises the front-end trans-impedance amplifier, analog electro-optical PLL, and digital control circuitry consuming 1.7 mA from a 1.8-V supply and 14.1 mA from a 5-V supply. The latter includes 12.5 mA bias current for the distributed Bragg reflector (DBR) section of the tunable laser.

Also presented in the thesis is a novel dual mode lidar that combines FMCW and chirped-AMCW operation to simultaneously achieve precision depth resolution and a longer operating range not limited by Laser coherence length.