Fig. 4: Visible frequency comb generation from the integrated optical parametric oscillator chip.
From: Visible-to-mid-IR tunable frequency comb in nanophotonics
a The complete emission spectrum of an OPO (Spectra obtained from different optical spectrum analyzers/ spectrometers are stitched together). Apart from the emission of the signal and the idler waves, the OPO also produces output in the visible spectra owing to the auxiliary nonlinear processes, namely the second-harmonic generation (SHG) and the sum-frequency generation (SFG). Schematic representations of the different nonlinear processes are shown. The processes marked by solid black arrows are initiated first, followed by the ones marked in gray. b Optical microscope image capturing the visible light emission from various regions of the periodically poled section of the OPO device, c Tunable visible frequency comb generation from the integrated OPO chip, where different colors indicate spectra obtained from OPOs with distinct poling periods.
