FMCW laser ranging method based on a frequency multiplier.

A reference interferometer is often introduced into the frequency-modulated continuous wave (FMCW) ranging system to deal with nonlinear laser modulation. In this system, the beat signal of the reference interferometer is regarded as the system clock to resample the measurement signal. According to Nyquist sampling theorem, the optical path difference (OPD) of the reference interferometer should be more than twice the target distance. We propose a resampling method that uses a frequency multiplier to help shorten the OPD of the reference interferometer. A quadruple frequency circuit board with two multipliers is added into the system to generate a new clock for this system. Results show that a target at a distance of 6.4 m can be measured when the OPD of the reference interferometer is provided by a 3 m delay fiber, and the ranging standard deviation of 9.4 µm is achieved.