Injection Locked Low Noise Chip-Based Silica Soliton Microwave Oscillator

Microsonator-based photonic microwave oscillators can deliver ultralow phase noise with a compact form factor and a low power consumption. Here, we report on a low noise microwave oscillator at 10 GHz using a chip-based silica wedge soliton microcomb. By operating in a quiet point, the phase noise at the offset frequency of 100 kHz (10 kHz) can reach −143 dBc/Hz (−132 dBc/Hz). By measuring the phase noise under different amplified microcomb powers, we find that the phase noise at the offset frequencies above 1 MHz are limited by the photodetector, instead of shot noise. The phase noise for low offset frequencies is suppressed by injection locking to a high quality commercial electric oscillator. When locked, the soliton microcomb oscillator can purify the electric oscillator more than 10 dB at the offset frequency of hundreds of kHz. Different from previous results in a MgF
$_{2}$
microcavity, no deterioration of the phase noise at high offset frequencies due to injection locking is observed. The injection locking is relatively loose for the silica mcirocomb operating in the quiet point, with phase noise reduction only observed below an offset frequency of kHz. Our measurements show how the injection locking impacts the low noise silica soliton oscillators.