Low-Noise 770 nm VBG Laser via Fano Resonant Feedback in High-Q WGM Microresonators for Compact SERF Atomic Sensors

Low-noise laser sources are essential for advancing quantum metrology, optical atomic clocks, and cutting-edge quantum sensing technologies. While whispering gallery mode (WGM) resonators have revolutionized laser stabilization by enabling chip-scale devices with sub-Hertz line widths, their practical deployment in field-deployable quantum sensors remains hindered by their fundamental limitations. The Rayleigh scattering from the WGM microcavity is relatively weak and the feedback strength is uncontrollable. Moreover, the compression effect of intensity noise is limited due to the low feedback strength. In this paper, we demonstrated a 770 nm low-noise VBG laser based on Fano resonant optical feedback from a high-Q WGM microresonator. The results show significant frequency noise reduction performance from 1 Hz to 1 MHz. In the low-frequency range of 1–100 Hz, which is critical for SERF atomic comagnetometers, the frequency noise is reduced by up to 2 orders of magnitude, and the intrinsic frequency noise is also reduced by nearly 1 order of magnitude. In terms of intensity noise, the best suppression performance is achieved at 1–10 Hz, with a maximum reduction of about 16 dB, which is effective in suppressing the increased intensity noise due to temperature fluctuations and other environmental disturbances. It is significant for realizing a low-noise compact light source integrated in the SERF atomic comagnetometer and also suitable for on-chip light sources.