In the phase-shift measurement method, the distance traveled by light can be obtained on the basis of the phase difference between the reference signal and the measured signal. When a different colored object is measured, the intensity of the measured signal varies greatly, even at the same distance, which causes a different phase delay owing to the wide dynamic range input into the signal processing circuit. In this study, an intensity control method is proposed to solve this phase delay problem.

Time-of-flight-based two-dimensional and three-dimensional light detection and ranging (LiDAR) applications have recently been implemented in several industries because of their high-precision measuring capabilities over long distances in outdoor environments. Avalanche photodetectors (APDs) are commonly used for LiDARs because of their high internal gain that significantly amplifies a measured signal. However, the magnitude of the measured signal changes significantly with temperature variations, owing to the temperature dependent characteristics of the APD. In this study, a temperature compensation method, in which a bias voltage of the APD is adjusted for temperature changes using signal-to-noise ratio feedback control, is proposed to solve the problem. This method has the advantage of a simple hardware configuration, without using a conventionally considered cooler.

To utilize a time-of-flight-based laser scanner as a distance measurement sensor, the measurable distance and accuracy are the most important performance parameters to consider. For these purposes, the optical system and electronic signal processing of the laser scanner should be optimally designed in order to reduce a distance error caused by the optical crosstalk and wide dynamic range input. Optical system design for removing optical crosstalk problem is proposed in this work. Intensity control is also considered to solve the problem of a phase-shift variation in the signal processing circuit caused by object reflectivity. The experimental results for optical system and signal processing design are performed using 3D measurements.

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