Switchable 0.612-nm-Spaced Dual-Wavelength Fiber Laser With Sub-kHz Linewidth, Ultra-High OSNR, Ultra-Low RIN, and Orthogonal Polarization Outputs

A high-performance switchable 0.612-nm-spaced dual-wavelength erbium-doped fiber (EDF) laser is proposed and experimentally demonstrated. For the first time, we combine a compound-cavity structure (CCS) and an enhanced polarization hole burning (PHB) effect in laser cavity to obtain stable dual-wavelength lasing (λ1 and λ2) and single-longitudinal-mode (SLM) operation at each wavelength without mode hopping. In the CCS, a high-quality triple-ring passive resonator is employed to achieve SLM lasing and a high-birefringence fiber Bragg grating combined with a three-loop polarization controller made with a length of EDF is used to establish a strong PHB effect. Easy switch between dual- and single-wavelength lasing modes is achieved. At a pump power of 150 mW, we obtain dual-wavelength lasing with optical signal-to-noise ratios (OSNRs) of >84 dB for both wavelengths and linewidths of 663 Hz for λ1 and 768 Hz for λ2, respectively; we also obtain single-wavelength lasing at λ1 with an OSNR of >86 dB and a linewidth of 687 Hz or at λ2 with an OSNR of >88 dB and a linewidth of 678 Hz. For both dual- and single-wavelength operations, the two lasing wavelengths are orthogonally polarized, with a degree of polarization of ~100%, and their relative intensity noises are <;-155 dB/Hz at frequencies over 3 MHz. In addition, the dependence of wavelength, OSNR, and linewidth on pump power and wavelength-tunability on temperature for the proposed fiber laser are also investigated in detail.