Pulsed TOF laser rangefinding with a 2D SPAD-TDC receiver

A pulsed time-of-flight laser radar based on a high speed/energy optical transmitter and a SPAD-TDC receiver is presented. The transmitter employs a bulk double heterostructure laser diode operating in enhanced gain switching mode at a wavelength of ~870nm, giving ~1nJ/125ps optical pulses. The receiver is a single CMOS chip consisting of a 9×9 CMOS SPAD array and a 10-channel 10ps precision TDC. The 2D detector array releases the required precision and tolerances of the opto-mechanics of the radar. Any of the 3×3 sub-arrays within the 9×9 array can be selected for simultaneous measurement, and the selection can be altered flexibly during measurements, e.g. to follow movements of the target image at the detector surface. Adjustable-width time-gating windows of down to ~5ns can be used to suppress background hits. A single shot precision of ~170ps (FWHM) and a measurement range of tens of metres with non-cooperative targets have been achieved with an 18mm receiver aperture.