Temperature tunable multiwavelength fiber laser by using compounded filter

A stable multiwavelength erbium-doped fiber laser was proposed and experimentally demonstrated by using a compounded fiber filter, which was composed of a Mach-Zehnder interferometer(MZI) and a birefringence fiber filter-Lyot filter. The MZI was fabricated by using the fiber fusion splicer to splice a section of SMF to form two cascaded spherical structures. The Lyot filter was incorporating a segment of polarization maintaining fiber(PMF) and two polarization controllers(PCs), which provided nonlinear polarization rotation(NPR) and birefringent filter effect to suppress the mode competition and generate multiwavelength. Using cascaded spherical-shape structures MZI and the Lyot filter as mode restricting elements respectively, the transmission spectrum of cascaded spherical-shape structures MZI was modulated by the Lyot filter, which determined the period of the compounded structure. In the experiments, 9-wavelength operation with a side-mode suppression ratio (SMSR) of~40 dB was achieved, and the space of wavelength was 0.68 nm defined by the Lyot filter. When the stability of proposed structure was observed for 2 hours every 10 minutes, the fluctuation of the central wavelength's output power was less than 0.67 dB. Furthermore, when the two spherical-shape structures MZI was fixed on a furnace and the temperature varied from 30℃ to 110℃, the spectrum of output wavelength can be tuned within the range of 6.69 nm.