We present a comb calibrated frequency-modulated continuous wave (FMCW) LADAR system for absolute distance measurements to diffuse or specular surfaces. The FMCW LADAR uses a MEMS-based external cavity laser that is swept quasi-sinusoidally over 1 THz at a 1 kHz rate. The system simultaneously records the heterodyne FMCW LADAR signal and the instantaneous laser chirp of up to 3500 THz/sec, as measured against a free-running frequency comb (femtosecond fiber laser). Demodulation of the LADAR signal against the instantaneous laser chirp yields the range to the target with sub-millisecond update rates, bandwidth-limited 130-m resolution, precision as low as ~6 nm, and accuracy of ~ 100 ppb. The basic approach is compatible with operation at even faster update rates and with future chip-based coherent FMCW LADAR systems.
Citation: Optics Letters
Pub Type: Journals
ranging, frequency modulated CW ladar, comb