Microcomb Source Based on InP DFB / Si3N4 Microring Butt-Coupling

In this article, we demonstrate an integrated Kerr frequency comb source based on the butt-coupling between a III-V (InGaAsP/InP) DFB laser and a silicon nitride (Si
₃
N
₄
) microresonator. The maturity of our silicon platforms permits the fabrication of high-quality factor microresonators with parametric oscillation threshold as low as 300 μW. Combined with a high optical power semiconductor chip, it enables to build an integrated comb source that consumes less than 3 W of electrical power, in less than one cm
³
. Our source emits an optical comb centered at 1576 nm with a 30 dB bandwidth measured to be 13.6 THz, and a repetition rate of 113.5 GHz. The radio frequency (RF) spectrum associated to the global 10 mW output optical power is characterized both at low frequency and at the beat note frequency, in order to distinguish unstable comb generation from stable comb generation. Finally, we reveal how our hybrid compact source can be used to generate 17-soliton crystal state that is a comb with a 2.04 THz line spacing.