Heterodyne multi-wavelength absolute interferometry based on cavity-enhanced electro-optic frequency comb pair

We present a heterodyne absolute distance interferometer with a macroscopic range, based on a promising optical source. The basis of the heterodyne measurement principle, a frequency comb pair with slightly different repetition rates and offset frequencies, is realized coherently by synchronized cavity-enhanced electro-optic frequency comb generators. The unknown distance is determined absolutely from the interferometric phases of distinct comb modes, by a parallel digital lock-in scheme. Comparison experiments with a reference HeNe incremental interferometer show an agreement well within 15 μm, for a range up to 10 m.