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.