Visible blue-to-red 10 GHz frequency comb

A broadband 10 GHz frequency comb in the visible wavelength range is generated via triple-sum frequency mixing of a near-infrared electro-optic source. This approach provides a novel pathway to astronomical frequency combs in the visible domain.

TOP: Envelope of the optical spectrum (comb lines are unresolved). BOTTOM: Scattering of visible light generated on the photonic chip.

 

Broadband laser frequency comb spectra with large laser line spacing of >10 GHz can provide precision calibration of astronomical spectrographs for exoplanet detection and cosmological studies. As the required laser with >10 GHz pulse repetition rate provide only low pulse energy, commonly used techniques of nonlinear wavelength conversion and spectral broadening are challenging to apply. Here, we show that multi-mode phase matching in a highly nonlinear on-chip photonic waveguide enables triple-sum frequency and broadband spectral generation of visible 10 GHz frequency combs. Importantly, this approach relies on reliable telecom-wavelength laser technology and can work with pulse energies as low as 150 pJ.

Reference:

Visible blue-to-red 10 GHz frequency comb via on-chip triple-sum-frequency generation; Ewelina Obrzud, Victor Brasch, Thibault Voumard, Anton Stroganov, Michael Geiselmann, François Wildi, Francesco Pepe, Steve Lecomte, and Tobias Herr; Optics Letters, 2019; DOI:  10.1364/OL.44.005290