Stable single-longitudinal-mode erbium-doped fiber laser with narrow linewidth utilizing parallel fiber ring resonator incorporating saturable absorber and fiber Bragg grating

A stable, single-frequency, narrow linewidth ring erbium-doped fiber laser (EDFL) is proposed and demonstrated experimentally. The main ultranarrow filter of the ring cavity EDFL is realized by an improved Mach-Zehnder interferometer, which consists of two parallel optical fiber ring resonators (FRRs). The FRRs share a saturable absorber and a fiber Bragg grating. Attributed to the Vernier effect, the single longitudinal mode operation is successfully obtained. The output of the EDFL can present good performance with a narrow linewidth of 1.09 kHz at 1549.57 nm and a high optical signal-to-noise ratio of 68 dB. Meanwhile, the laser has a relatively low threshold of 10.7 mW. In addition, the central wavelength variation and power fluctuation of the laser are less than 0.002 nm and 0.2 dB, respectively, showing favorable stability.