  Dual-comb interferometry is a measurement technique that uses two laser
frequency combs to retrieve complex spectra in a line-by-line basis. This
technique can be implemented with electro-optic frequency combs, offering
intrinsic mutual coherence, high acquisition speed and flexible repetition-rate
operation. A challenge with the operation of this kind of frequency comb in
dual-comb interferometry is its limited optical bandwidth. Here, we use
coherent spectral broadening and demonstrate electro-optic dual-comb
interferometry over the entire telecommunications C band (200 lines covering ~
40 nm, measured within 10 microseconds at 100 signal-to-noise ratio per
spectral line). These results offer new prospects for electro-optic dual-comb
interferometry as a suitable technology for high-speed broadband metrology, for
example in optical coherence tomography or coherent Raman microscopy.
