Investigation and compensation of distance error caused by avalanche gain of a photodetector in an infrared laser rangefinder

The avalanche photodetector (APD) has promising prospects among available optical sensors in time-of-flight (ToF) infrared laser rangefinder applications due to its ability to improve the signal-to-noise ratio and long-range object detection by internal gain through the avalanche process. However, the avalanche process requires a specific amount of time, resulting in a phase delay in the ToF infrared laser rangefinder. Meanwhile, the measured distance in the ToF infrared laser rangefinder is determined by the phase shift between the received and reference signals, which leads to an error measurement due to an extra phase shift from phase delay when using the avalanche gain. For this reason, we propose a simple technique that introduces a compensated offset error into the algorithm used to correct the measured distance. To determine the value of the compensated offset error, we first investigated the effect of the avalanche gain of the APD in range measurement using a ToF infrared laser rangefinder by involving two targets with different reflectance. Subsequently, we applied the proposed technique to validate the ToF infrared laser rangefinder by measuring two targets again, and this shows that the error can be suppressed from 0.330 m to less than 0.060 m within the coverage range of 30-60 m. Given that accuracy and precision can be improved on the order of centimeters over tens of meters of coverage, the ToF infrared laser rangefinder using the proposed technique has good potential for middle-range applications.