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TOF LiDAR with SiPM technology


LiDAR (Light Detection And Ranging) systems measures the distance from the sensor to the target by determining the time between the release of the laser pulse to the receiving of the backscattered pulse. The interest in LiDAR technology has exploded in recent years since the applications are numerous. Here, we would highlight the Advanced Driver Assistance Systems (ADAS) and for rendezvous & docking operations between spacecraft. We built two LiDAR systems differing for the detector: a Silicon Photomultiplier (SiPM) and an Avalanche Photodiode (APD). The advantages of the SiPM approach has been extensively discussed in [1]. The comparison between these systems has been performed in terms of Time Of Flight (TOF) measurements varying the distance of the target at different intensities of ambient light and at various weather conditions. The APD, specifically designed for LiDAR applications, was chosen for its high performances at 905nm, the emission wavelength of our laser diode. The SiPM, fabricated by STMicroelectronics, was selected for its high responsivity, high gain, high fill factor with very low breakdown voltage (28V vs. 175V of the APD), low operating bias (30V vs. 164V of the APD) and low price. Both the LiDARs (Fig. 1) are battery-operated (supply voltage = 5V) and exhibit the same optical system with separated lenses for emission (2 glass lenses that behave as a collimator with an equivalent focal length of 110 mm) and receiving (a 100-mm focal length lens). The SiPM or the APD, that triggers the pulse stopping the time count, is placed behind the receiving lens. The laser diode is pulsed at 35ns with a pulse repetition frequency <20kHz and a peak optical power of 70W at 905nm. A board containing a filtering and peak detection system and a time-to-digital converter is employed in order to detect the start and the stop pulses and perform the time count. The result of the measurement is displayed on a PC connected to the LiDAR via a USB cable. TOF measurements were performed both indoor and outdoor (where the difference of the performances of the two photodetectors is much more evident) at midday and in the evening after sunset, with clear and rainy weather. The SNR for each measurement was calculated and it was not significantly influenced by the rain. Outdoor, the LiDAR with SiPM was able to detect the target up to a distance of 360m, with a SNR of 22 while, the system based on the APD detected the target up to 36m exhibiting a SNR of 8. Targets were detected with a maximum resolution of a few centimeters (indoor) and the SNR of the SiPM was higher at least one order of magnitude than the SNR of the APD in every condition (Table 1). In the next step, we will fabricate a standalone LiDAR with a deep integration to achieve better results in terms of performance, minimum encumbrance and cost. In particular, we will implement a waveguide light source with integrated optics and MEMS mirrors in order to perform scans. Furthermore, the photonic integration involves the SiPM provided with narrow band (10nm) filters and optics included in its package.