Compact, Low Noise, Dual FP Etalons Based External Cavity Diode Laser for Micro-Vibration Sensing Systems

Fiber interferometer based on low noise lasers are crucial to the micro-vibration sensing systems. Laser noise is a key factor impacting the detection resolution of such systems. To enhance the minimum measurable acceleration of the micro-vibration sensing system, a compact external cavity diode laser (ECDL) is designed and fabricated to reduce the frequency/phase noise and the relative intensity noise (RIN) of the laser source. The ECDL is composed of a gain chip and an external cavity based on two high-Q Fabry-Perot (FP) etalons with small FSR differences. The two FP etalons enable a narrowband filtering response that selects a single longitudinal mode in the laser cavity, resulting in a single-frequency laser output with low noise. In this way, the intrinsic linewidth of less than 400 Hz with the RIN of −153 dBc/Hz@10 MHz and the output power of 9.5 mW are realized. The ECDL is employed in the micro-vibration sensing system, the noise evaluation experiment results reveal that the overall noise floor is 21.47 ng/Hz^1/2 with an average sensitivity of 43.5 dB re rad/g.