Switchable multi-wavelength actively Q-switched erbium-doped fiber laser based on nonlinear polarization rotation and Sagnac filter

Abstract

This letter describes a switchable multi-wavelength actively Q-switched erbium-doped fiber (EDF) ring laser based on nonlinear polarization rotation (NPR) structure with Sagnac filter and electro-optic modulator (EOM). The intensity-dependent loss (IDL) generated by the constructed NPR structure can suppress the mode competition caused by EDF, combined with a comb filter Sagnac loop which composed of only 2-m-long polarization maintaining fiber (PMF), the constructed laser generates nine-wavelengths laser output with a constant wavelength interval of 3 nm. When the NPR structure is removed, the constructed laser generates quadruple-wavelengths laser output with 3 nm constant wavelength interval. It is proved that the effect of the NPR can suppress mode competition to achieve multi-wavelength laser output. In the laser with the constructed NPR structure, the nine-wavelengths laser output has a maximum wavelength shift of 0.21 nm and a maximum power fluctuation of 0.69 dB, while when the NPR structure is removed from the constructed laser, for the quadruple-wavelengths laser output, the maximum wavelength shift is 0.16 nm and the maximum power fluctuation is 0.29 dB. When the constructed laser with or without NPR structure, the minimum Q-switched pulse width and maximum average output power are 1.42 μs, 1.24 μs and 3.2μW, 10.2μW, respectively.