Carrier envelope offset detection via simultaneous supercontinuum and second-harmonic generation in a silicon nitride waveguide

We demonstrate a chip-scale f-2f interferometer for carrier-envelope-offset frequency (f_CEO) detection. This is enabled by simultaneously producing octave-spanning coherent supercontinuum generation and second-harmonic generation in a single dispersion-engineered silicon nitride waveguide. We measure the f_CEO beatnote of an 80 MHz modelocked pump source with a signal-to-noise ratio of 25 dB. Our simple approach for f-2f interferometry enables a straightforward route towards a chip-scale self-referenced frequency comb source that can operate at low pulse energies.