A wavelength spacing switchable and TUNABLE high-birefringence fiber loop mirror filter

We demonstrated an all-fiber birefringent comb filter with tunable and switchable wavelength spacing. The comb filter is based on a fiber loop mirror (FLM) with three sections of high-birefringence (HB) fibers and polarization controllers (PCs). The transmission characteristics of the birefringent FLM are dependent of the relative phase difference of the two orthogonal polarization modes and the rotational angles of the different HB fibers. By adjusting the PCs, four different wavelength spacings can be obtained; particularly, interleaving operation-halved and quartered wavelength spacing-can be effectively realized. By using a Jones matrix method, the transmission of the birefringent comb filter is analyzed. The theoretical analysis agrees with the experimental results. (c) 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1666-1670, 2014