Polarization-Controlled Switching of Dual-Wavelength Lines with Orthogonal Polarization in Erbium-Doped Fiber Ring Laser.

By incorporating an inline switching filter, which is comprised of a polarization-diversified loop (PDL), two fiber Bragg gratings (FBGs) with different resonances, and three quarter-wave plates (QWPs), we propose a dual-wavelength-switchable erbium-doped fiber (EDF) ring laser that can select and switch between two lasing lines with orthogonal polarization. The proposed laser is composed of EDF, a 980 nm laser diode, a wavelength-division-multiplexing coupler, a rotatable linear polarizer, an optical isolator, a 3 dB optical coupler, and the inline switching filter. At a special combination of the orientation angles of the three QWPs, the inline filter can offer a different transmittance according to input polarization, e.g., reflection spectra of one and the other of the two FBGs for linear horizontally and vertically polarized input light, respectively. At this special combination of the QWPs, one of two different resonances of the two FBGs can be selected by varying laser cavity polarization through the adjustment of the orientation angle of the rotatable linear polarizer. Consequently, switching operation between two laser lines with orthogonal polarization at the two FBG resonance wavelengths could be obtained by properly controlling cavity polarization. The polarization extinction ratio of each lasing line was measured as more than 19.9 dB.