Fig. 3: Characteristics of the frequency comb generated from the synchronously pumped on-chip OPOs.
From: Visible-to-mid-IR tunable frequency comb in nanophotonics
a Resonance peak structure obtained by sweeping the pump central wavelength which is typical of doubly resonant OPO operation. A zoomed-in view of a single peak is shown in the inset, b Range of the existence of the synchronously pumped OPO for a fixed pump power as the pump repetition rate is varied, c An example of fine-tuning of a single OPO output by tuning the pump central wavelength (please see Supplementary Section 14 for more experimental results), d Spectral broadening of the OPO operating at degeneracy corresponding to a sub-picosecond transform-limited duration of ~400 fs. The spectrum for both the pump and the signal are normalized for the aid of visualization of the spectral broadening, e Verification of the coherence of the OPO output as evident from the existence of interference fringes (see inset) in the electric-field cross-correlation trace, f The close agreement between the spectra obtained from an optical spectrum analyzer measurement and that obtained by Fourier transforming the field cross-correlation corroborates the coherence of the OPO output.
