Digital multi-wavelength optical absolute ranging

Optical metrology underpins sensing applications that require extreme precision and accuracy. Optical metrology with a continuous-wave source is constrained by the near-ambiguous range of one optical wavelength, limiting the realization of full interferometric sensitivity. We present a digitally tunable, multi-wavelength continuous-wave optical phase measurement scheme, which can be used for absolute laser ranging. This system was demonstrated over a free-space link on an optical bench, with a distance uncertainty of, at best, 0.2 μm-sufficient to resolve the continuous-wave optical fringe. This design is flexible and can be applied to both coherent optical ranging and optical time and frequency transfer.