Tunable, multiwavelength Tm-doped fiber laser based on polarization rotation and four-wave-mixing effect

We propose and demonstrate a tunable multiwavelength fiber laser employing polarization-maintaining Tm-doped fiber based on polarization rotation and four-wave-mixing effect. Polarization-maintaining Tm-doped fiber and polarization controllers were employed to manipulate the polarization modes in the laser, and 400 m long single-mode passive fiber was used to enhance the four-wave-mixing effect and suppress the polarization mode competition. Stable fiber laser operation of 1-6 wavelengths around 1.9 μm was achieved at room temperatures. The wavelengths can be tuned through adjusting the polarization controllers. The optical signal-to-noise ratio of the laser is more than 31 dB. The wavelength shift is less than 0.05 nm and the peak fluctuation of each wavelength is analyzed. For most of the wavelengths the peak fluctuations are less than 3 dB and the peak fluctuations of wavelengths with more stability are below 1.5 dB.