Simple method of carrier-envelope-offset locking with f-3f self-referencing solely by a dispersion-controlled silicon-nitride waveguide

On-chip carrier-envelope-offset (CEO)-locked frequency combs are very attractive for many applications. They can achieved with simplicity by using CMOS compatible materials because the supercontinuum (SC) spectrum can be broadened and a CEO signal generated with a single miniaturized device. A very simple and attractive method for f -3 f self-referencing directly from a SiN waveguide has been reported [1] . However, the CEO signal with a low signal-to-noise ratio (SNR) could not be stabilized since it was detected by the interference between the dispersive wave and third-harmonic generation (THG) light. To overcome this problem, we show that a simple fully stabilized frequency comb can be achieved with f -3 f self-referencing through the simultaneous generation of high-intensity visible components of SC light with THG light from a dispersion-controlled SiN waveguide. For this purpose, we fabricated low-loss 5-mm-long SiN waveguides (n=1.87@λ=632 nm) with spot-size converters. We controlled the dispersion of the SiN waveguides by varying their width from 1.3 to 2.0 µm.