Miniature High-Power Nanosecond Laser Diode Transmitters Using the Simplest Possible Avalanche Drivers

Abstract

The state-of-the-art long-distance near-infrared optical radars use laser-diode-based miniature pulsed transmitters producing optical pulses of 3–10 ns in duration and peak power typically below 40 W. The duration of the transmitted optical pulses becomes a bottleneck in the task of improving the radar ranging precision, particularly due to the progress made in developing single photon avalanche detectors. The speed of miniature high-current drivers is limited by the speed of the semiconductor switch, either a gallium nitride field-effect transistor, the most popular alternative nowadays, or a silicon avalanche bipolar junction transistor (ABJT), which was traditional in the past. Recent progress in the physical understanding of peculiar 3-D transients promises further enhancement in speed and efficiency of properly modified ABJTs, but that is not the only factor limiting the transmitter speed. We show here that a low-inductance miniature transmitter assembly containing only a specially developed capacitor, a more advanced transistor chip than that used in commercial ABJTs and a laser diode, has allowed peak power from 40 to 180 W to be reached in optical pulses of 1–2 ns in duration without after-pulsing relaxation oscillations. This finding is of interest for compact low-cost, long-distance decimeter-precision lidars, particularly for automotive applications.