Dual-Frequency Laser Range Finder with Coherent Detection

The precise range measurement is a fundamental component of reliable Internet of Things (IoT) applications. Conventional phase-shifted laser ranging architectures have been demonstrated to exhibit deterioration in modulation depth and frequency stability with increasing frequency, which leads to decreased accuracy. In this context, we propose a novel architecture for implementing a Dual-Frequency Laser Range Finder (DF-LRF) based on the phase-shift range measurement. With optical frequency modulation technology, which guarantees high frequency modulation depth and stability, a dual-frequency laser with a difference of 200MHz is obtained. As a result, the Signal-to-Noise Ratio (SNR) of the backscattered signals is improved, and the ranging accuracy and detection sensitivity of the DF-LRF are enhanced. The SNR and ranging results of the DF-LRF are experimentally measured and analyzed. When the dual-frequency laser heterodyne is used in the DF-LRF, the SNR of the beat signal is improved by 3.67dB. With the aggravation of phase jitter, the absolute and relative ranging accuracy deteriorates compared with those without heterodyne in the DFLRF, which provides a reference for integrating DF-LRF into the IoT system.