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This paper reports a complete solution for short-acquisition-time, flood-illumination, and non-scanning 3D imaging. Based on an InGaAs/InP 64×64 Geiger-mode avalanche photodiode array, we developed a single-photon imaging Lidar with a field of view of 19.2 mrad. A spatiotemporal dominant imaging method was also applied for depth estimation under high daytime background noise conditions. In the field tests, 3D imaging information was effectively extracted from objects with strong solar background light. An acquisition time of only 0.5 ms to 4 ms was needed for a building target approximately 1300 m away. The experimental results show that the Lidar and its data processing method have the potential for dynamic scenarios that require high performance 3D imaging, such as vehicle navigation, airborne mapping, and moving target monitoring.

Photon-counting detectors can increase the range of underwater optical wireless communication (UWOC) by enhancing the detection sensitivity and have thus become an active research area in recent years. However, system performance still needs to be improved in the reported underwater photon-counting communication (UPCC) experiments. In this study, a real-time, high-speed UPCC system was designed and experimentally validated based on a single-photon avalanche diode (SPAD). A reliable symbol synchronization method based on pulse-position modulation (PPM) was developed. This method achieved slot synchronization by using a narrow-pulse-width laser and a simple matched filter and realizes frame synchronization through an improved synchronization sequence. In addition, channel errors were corrected by serially concatenated convolutionally coded PPM (SCPPM), and digital signals were processed in real time based on field-programmable gate arrays (FPGAs). Finally, desktop communication experiments were completed at a slot frequency of 25 MHz and a communication rate of 6.21 Mbps. The system exhibited a bit error rate (BER) of less than 10–7, a received optical power of only −84.3 dBm, and an efficiency of 1.35 photons per bit.

We report a pulsed wavelength-agile laser near 765 nm, which was frequency doubled from an erbium-doped fiber amplifier for oxygen A-band spectroscopy. A single frequency distributed feedback laser around 1529.6 nm was employed as the seed. After three stages of amplification, its average power was boosted to 610 mW and was then frequency doubled via a 15-mm-long MgO:PPLN crystal with the highest conversion efficiency of 34%. Thanks to the short crystal length expanding the acceptance bandwidth, a power difference of only 36% for the second harmonic output was achieved within the whole wavelength tuning range benefitting low-noise remote sensing. The measured oxygen transmission spectra using a 0.5-meter-long gas cell with multiple passes were mostly in good agreement with the calculations from HITRAN 2012 database indicating the capability of our laser for oxygen A-band related remote sensing.

We report the optimization of tunable nanosecond cascaded optical parametric oscillators (COPOs) based on monolithic tandem lithium niobate superlattices. The nonlinear crystal is designed with a uniform grating section for the optical parametric oscillation process and a linearly chirped grating section for the different frequency generation process. By employing couplers with proper reflectivities and crystals with optimized structures, such tunable COPOs can generate idler waves more efficiently than conventional optical parametric oscillators. It is concluded that higher pump pulse energy and tighter pump beam focus can further improve the pump-to-idler conversion efficiency of such tunable COPOs, particularly for those with wider idler wavelength tuning ranges.