Eight-Wavelength-Switchable Narrow Linewidth Erbium-Doped Fiber Laser Based on Cascaded Superimposed High-Birefringence Fiber Bragg Grating

A narrow-linewidth eight-wavelength-switchable erbium-doped fiber laser is proposed, and its performance is demonstrated. A cascaded superimposed high-birefringence fiber Bragg grating is used to determine the lasing wavelengths. The combination of a Fabry-Perot filter and a single-coupler ring is adopted to achieve the single-longitudinal-mode (SLM) oscillation. By introducing the enhanced polarization-hole-burning effect to suppress the gain competition between different wavelength lasers, the stable lasing output is guaranteed. When the pump power is 200 mW, by adjusting the polarization controller to balance the gain and loss in the laser cavity, 24 switchable lasing modes are achieved, including 8 single-wavelength operations and 16 dual-wavelength operations with orthogonal polarization states. For single-wavelength operations, every laser is in the SLM lasing state, with a high stabilized optical spectrum, a linewidth of approximately 1 kHz, an optical signal-to-noise ratio (OSNR) as high as 73 dB, a relative intensity noise of less than -150 dB/Hz, and very good polarization characteristics. For dual-wavelength operations, the lasers also have a stable spectrum and an OSNR as high as 65 dB. The proposed fiber laser has a wide range of applications, including long-haul coherence optical communication, optical fiber sensing, and dense wavelength-division-multiplexing.