Laser polarization characteristics from phase-shifted grating inscribed by polarized ultraviolet Argon laser

Phase-shifted grating based distributed feedback fiber lasers with different polarization characteristics were made with Ppolarized and S-polarized 244nm Argon ion laser separately. In this paper, the laser polarization characteristics from the phase-shifted gratings were investigated experimentally. The narrow linewidth laser emitted from phase-shifted grating in Erbium doped fiber showed different polarization and wavelength characteristics for incident laser in different polarization states and in different doses. By high resolution spectrum analysis, the laser always had two close wavelengths with a gap of several pm which were in two orthogonal polarization states and had similar powers, if the phase-shifted grating was made with a P-polarized (which is paralleled to the the axial fiber) incident laser. The laser showed evidently different characteristics when the incident laser is in S-polarization (which is perpendicular to the axial fiber). Here, the laser operated in single wavelength mode when irradiated dose was in a range. However, the laser operated in dual-wavelength mode and dual polarization states when irradiated dose exceeded a threshold. The wavelength gap increased from several pm to more than 10 pm with the increasing irradiated dose. The power ratio of the two wavelengths changed simultaneously.