Quadruple-Wavelength EDF Laser Based on Chirped Fiber Grating and 62.5 μm Multimode Fiber

We propose and experimentally demonstrate a novel switchable quadruple-wavelength CW erbium-doped fiber laser, using a linear cavity structure. It is composed of two Sagnac loops that act as cavity mirrors in the resonant cavity. The left loop consists of a 3 dB fiber coupler (FC), a squeezed polarization controller (PC), and a chirped fiber grating. The right loop consists of a 10 dB FC, the same PC and a length multimode fiber with a core diameter of 62.5 mu m. The two loops based on different operation principles become two comb filters to jointly excite the multiwavelength output. On the role of the polarization hole burning effect, after adjusting the two PCs, the laser can switch flexibly to output fourteen kinds of different modes from a single wavelength to the quadruple wavelength. All lasing lines, with a narrow linewidth less than 0.28 nm, have the optical signal-to-noise ratio of more than 20 dB. The laser with good power uniformity shows better stabilities of the wavelength and peak power.