Switchable Single-Polarization Dual-Wavelength Ring Laser Based on Structured PM-CFBG

A switchable single-polarization dual-wavelength single-longitudinal mode (SLM) erbium-doped fiber (EDF) ring laser is proposed and demonstrated. For the first time, the structured polarization-maintaining chirped fiber Bragg grating (PM-CFBG) filter, which has ultranarrow transmission band is created by tapering directly on the PM-CFBG. Then, the stable SLM operation of the fiber laser is guaranteed by the structured PM-CFBG filter and 20-cm unpumped EDF acting as a saturable absorber. Meanwhile, the stable dual-wavelength fiber laser with a wavelength spacing of ~0.41 nm and stable single polarization state is experimentally realized. The measured linewidth of the fiber laser for each wavelength is <;8 kHz with a 20-dB linewidth.