3D random-modulated pulse lidar based on a gain-switched semiconductor laser with a recirculating delay lines interferometer

This study presents the development of a 3D random-modulated pulse lidar based on a gain-switched semiconductor laser with a recirculating delay lines interferometer (RDLI). The random-modulated pulses are generated by homodyning the frequency-shifting gain-switched pulses with multiple self-delays. While they exhibit anti-interference characteristics similar to those in previously developed chaos-modulated lidar, there is no need for external pulse formation and wavelength-sensitive filtering components in the current configuration. By varying the injection currents in gain-switching and the delay lengths in the RDLI, we experimentally investigated the transient dynamics of the generated random-modulated pulses. We demonstrated how these operating parameters influence the modulation in their waveforms and spectra. The detection performance was quantified by calculating the effective bandwidths, signal-to-noise ratios, Cramér-Rao lower bounds, range precision, self-interference peaks, and detection probability. We identified two key operating conditions: the best-precision condition and the precision-interference balanced condition. Compared to a previously investigated delay self-homodyne interferometer (DSHI) scheme, which homodynes the gain-switched pulses with just a single delay, the RDLI scheme achieved a precision as low as 0.46 mm, approximately 1.5 times better than the DSHI scheme. To demonstrate its superior performance and feasibility for detection, we integrated the RDLI into a 3D lidar imaging system and compared its performance to the DSHI and chaos lidar schemes. To highlight its improved precision and robustness to temperature variations, we evaluated its precision under varying average output power and changes in laser temperature. With the developed lidar system, we successfully achieved high-quality face profiling of a person with millimeter-level precision.