Solving 2pi ambiguity problem of a laser scanner based on phase-shift measurement method or long distances measurement

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. The maximum unambiguous range for a laser scanner based on phase-shift measurement method is inversely proportional to the modulation frequency of the signal. When the modulation frequency is increased for high distances resolution, the unambiguous range will be decreased. In this paper we describe a method to solve the 2pi ambiguity problem of a laser scanner based on phase shift measurement method. In addition, we propose a method for implementing two frequencies modulation technique.