Abstract

We demonstrate a comb-calibrated frequency-modulated continuous-wave laser detection and ranging (FMCW ladar) system for absolute distance measurements. The FMCW ladar uses a compact 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 frequency at sweep rates up to $3400\mathrm{THz}/\mathrm{s}$, as measured against a free-running frequency comb (femtosecond fiber laser). Demodulation of the ladar signal against the instantaneous laser frequency yields the range to the target with 1 ms update rates, bandwidth-limited 130 μm resolution and a $\sim 100\mathrm{nm}$ accuracy that is directly linked to the counted repetition rate of the comb. The precision is $<100\mathrm{nm}$ at the 1 ms update rate and reaches $\sim 6\mathrm{nm}$ for a 100 ms average.

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