High-precision absolute distance measurement by cascaded synthetic wavelength interferometry using a single electro-optic frequency comb.

We demonstrate high-precision absolute distance measurement through cascaded synthetic wavelength interferometry (SWI) based on a single GHz-rate electro-optic frequency comb (EO comb). For this purpose, 3 of its discrete comb modes are selectively filtered by cascaded dense wavelength division multiplexers to serve as phase-linked continuous-wave (CW) lasers with relative frequency stability inherited from the microwave frequency reference. We vary the frequencies of these comb modes to generate a series of synthetic wavelengths by periodically switching the EO comb repetition rate. This allows us to obtain a maximum non-ambiguity range (NAR) of ∼3.74 m accompanied by the instrument's ± 4 µm precision validated by a commercial HeNe interferometer. In addition to static targets, a velocity measurement with < ±15 µm/s residual compared to the HeNe interferometer is also shown. Our simple and robust technique for high-precision absolute distance and velocity measurement is well-suited for many industry-relevant problems requiring the combination of micrometer precision with a meter-scale NAR.