Low Intensity Noise Ring-Cavity Single-Frequency Fiber Laser Using Filter Characterizing Technique

We demonstrate a single-frequency fiber laser (SFFL) with sub-kHz linewidth and ultra-low intensity noise, which is realized by a ring configuration. A newly generalized method to characterize ultra-narrow bandwidth filters and thus avoid mode hopping is proposed, which involves the Kramers-Kronig relation and I-Q demodulation. The resulting SFEL exhibits a narrow linewidth of 0.6 kHz at the wavelength of 1545.35 nm. Also, the mode-hopping-free operation is verified by a scanning F-P interferometer and self-heterodyne method, respectively. The time trace and power monitor present the power variations of 0.02 dB @ 400 ms and 0.05 dB @ 1 h, respectively. The relative intensity noise base caused by shot noise is −147dBc/Hz (>100kHz). The relaxation oscillation peak reaches −130dBc/Hz, which is 30 dB lower than that of commercial SFFL.