Phase laser ranger based on quadrature modem and frequency reduction

Abstract

A novel laser range finder method based on the quadrature modem and least square method was investigated to improve the accuracy and reliability of traditional portable phase laser range finders. A reflector was employed for inner and outer optical paths. After amplitude modulation of laser intensity by the quadrature modulation method, the echo signal was mixed with modulation signal and passed through a low-pass filter to reduce the frequency, thus simplifying phase detection and improving solution accuracies. The inner and outer phase shifts were used to eliminate the additional phase shift lead by the secondary mixing. The low frequency echo signal from the inner and outer optical path were sampled for analog to digital conversion respectively, then the phase was solved base on the least square method. Multi-frequency measurement was adopted to maintain the laser ranging range and measurement accuracy. Finally, the measured distance was obtained by solving the laser ranging ambiguity by overdetermined linear equation. The proposed range finder was experimented on the national standard baseline. The results show that the prototypes of those rangers exhibit an average measurement error less than 1.5 mm and an standard deviation less than 0.9 mm in the range of 0~60 m.