Increasing the operating distance of a phase-shift laser range-finding system by using an active reflector

A new phase-shift laser ranging method is developed by combining the conventional phase-shift ranging and the concept of transponder, in which the passive mirror in a phase-shift laser range-finding system is replaced with an active reflector whose light source power is the same as that at the measurement terminal. As a result, the power of the returned light is inversely proportional to the 2nd instead of the 4th power of the distance being measured. Section 3 indicate that by using the active reflector, the operating distance is dramatically increased without increasing the laser power or lens aperture. With a transmitted power of 20 mW and an aperture of 100 mm, the operating distance increased from 1.5 km to 9.4 km, and a 15-fold range gain can be forecasted for a transmitted power of 1 W. This strongly confirms the suitability of the developed phase-shift method with an active reflector for measuring longer distances.