And in the standard silica based fibers the Brillouin frequency shift is approximately
10 GHz. Various efforts have been made to increase the frequency spacing or realize the spacing tunable to make demultiplexing process easily. Wang-Yuhl Oh et al. has realized 10 and 20 GHz
optical combs generation in MBEFL by the adjustment of polarization controllers in the Sagnac reflector [16]. The optical comb generation with 20 GHz spacing in their work is demonstrated by
discrimination of the even-order and the odd-order Stokes waves. But the signal-to-noise ratio (OSNR) of the multi-wavelength operation of 10 GHz spacing is very small. The output spectrum is not stable. The generation of switchable dual-wavelength Brillouin ring-cavity fiber laser is described in Ref.[17]. Incorporating the FBG filter only realizes that the spacing of dual-wavelength can be tuned at an interval of about 0.084N nm (N¼1, 2, …, 13).