Nonlinear error correction for FMCW ladar by the amplitude modulation method.

FMCW ladar is a kind of absolute distance measurement technology with high spatial resolution. However, the advantage of high spatial resolution is significantly covered up by the non-linearity of laser frequency sweep. One of the typical approaches for the nonlinearity is resample technology, which has residual phase error from the sample time delay mismatch between the clock signal and the measurement signal. We have proposed and demonstrated a novel amplitude modulation method for correcting the nonlinear error of FMCW technology. The optical structure of the method is comprised of two tandem fiber interferometers. The first interferometer is used to produce a carrier signal and the second one is used to load the range information on the amplitude of the carrier signal. In the end, the experimental result verifies that the nonlinear error can be suppressed effectively, the phase error from the mismatch has been eliminated observably, and the range resolution can be notably improved to 69μm; the stability is 2.9μm and the measurement precision is 4.3μm.