A Low-RIN Spectrally Pure Whispering-Gallery-Mode Resonator-Based Semiconductor Laser

We demonstrate a high-spectral-purity self-injection locked distributed-feedback semiconductor laser with relative intensity noise approaching -143 dB/Hz at 1 kHz and -160 dB/Hz at 100-kHz frequency offset. The frequency noise of the laser is 2 Hz/Hz
^1/2
at 1 kHz and 1 Hz/Hz
^1/2
at 100-kHz frequency offset. The fiber-pigtailed output power exceeds 70 mW. The low-intensity-noise performance is achieved due to the utilization of a low-noise current source feeding the laser chip and a saturated semiconductor optical amplifier reducing the technical amplitude noise of the laser. Reduction in the laser frequency noise results from the self-injection locking of the laser chip via a high-quality-factor whispering-gallery-mode resonator. The laser linewidth is less than 100 Hz.