Silica layer drives frequency combs
Researchers have used the silica cladding of a silicon nitride photonic circuit to generate Raman lasing and broadband frequency combs, demonstrating a new approach to increasing functionality in integrated photonic devices.
Researchers have demonstrated an integrated photonic device that combines silicon nitride and silica to generate Raman lasing and broadband optical frequency combs on-chip.
The device uses a silicon nitride ring resonator surrounded by silica. Rather than treating the silica cladding as a passive layer, the researchers exploited the portion of the optical field extending into it to generate Raman gain.
The device produced a Raman-shifted signal approximately 11 THz from the pump wavelength.
At higher optical powers, four-wave mixing in the silicon nitride generated additional frequencies around the pump and Raman-shifted signals. By optimising the waveguide geometry and dispersion, the resulting frequency comb extended across more than 400 nm.
The measured Raman lasing threshold was 143 mW, closely matching the predicted 140 mW, while more than 32% of the input optical power was converted into newly generated frequencies.
The approach could enable compact integrated light sources for applications including spectroscopy, optical communications, precision metrology and astronomical instrumentation.
