High Spectral Purity Optical Source Stabilized on a Fiber Ring Resonator

This letter demonstrates the stabilization of an external cavity semiconductor laser at 1550 nm on an ultra-high Q factor fiber ring resonator (FRR). Based on a Pound-Drever-Hall technique, our system is optimized in order to take into account the properties of the FRR which features a large Q factor ($2\times 10^{9}$ ) but a relatively small free spectral range (2 MHz). The measured performances of the stabilized laser shows a frequency noise level as low as 0.4 Hz
²
/Hz in the 1 kHz to 10 kHz range and a linewidth lower than 30 Hz for 5 ms integration time.