Dual-wavelength single-longitudinal-mode erbium-doped fiber laser with Mach–Zehnder interferometer and saturable absorber loop

Abstract

A stable dual-wavelength erbium-doped fiber laser (DW-EDFL) in the single longitudinal mode (SLM) with a Mach–Zehnder interferometer (MZI) and a saturable absorber loop (SAL) is proposed and demonstrated experimentally. Dual wavelengths are obtained with different MZI arm lengths. After the first mode selection of the tunable fiber Bragg grating, SLM operation of the dual-wavelength is acquired by the SAL based on the Vernier effect and spatial hole burning, which induce an auto-tracking narrow bandwidth filter with an optical coupler and a 2 m unpumped erbium-doped fiber (EDF). The output of the DW-EDFL shows good performance, achieving 1.08 kHz at dual wavelengths of 1558.67 nm and 1558.77 nm. The interval of the dual wavelength is 0.1 nm, which has a good agreement with the theoretical value, and the peak powers are −5.508 dBm and −5.993 dBm, respectively under 170 mW pump power. Meanwhile, because of the automatic tracking of the wavelength of the SAL, the optical power instability and beating frequency fluctuation of the dual wavelength are less than 0.5 dB and 0.5 MHz, respectively, showing favorable stability.