Spectral dynamics of broadband optical frequency comb

Optical frequency combs are key to optical precision measurements and nonlinear effects enable their broadband generation. Here we show, experimentally and numerically, that overlapping harmonics can have profound impact on the entire comb spectrum, leading to multiple interleaved combs across the entire spectrum. With the pump arranged to be offset-free, the entire spectrum can form an evenly spaced multi-octave frequency comb.

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Picture: Frequencz comb (TBA)

Optical frequency combs are essential to modern time and frequency metrology with their evenly spaced discrete spectral lines. Recently, it has been demonstrated that efficient nonlinear broadening in integrated photonic waveguides enables extending an initially narrowband frequency comb to multi-octave bandwidth. Here, we study the nonlinear dynamics in the generation of such ultra-broadband spectra where different harmonics of the comb can overlap. The experiment results, together with offset frequency resolved numerical simulations, demonstrate that a set of interleaved combs with different offset frequencies extending across the entire spectrum can emerge. When the initial comb is offset-free, the generated spectrum be arranged into a practically evenly spaced ultra-broadband frequency comb.