A fiber loop mirror (FLM) with two-stage high birefringence (Hi-Bi) fibers is theoretically and experimentally studied for various rotation angles and Hi-Bi fiber lengths. The experimental spectra are observed to be in good agreement with the theoretical spectra, verifying our theoretical model. The wavelength interval of the comb filter depends on the Hi-Bi fiber lengths and rotation angles. By varying the rotation angle from 0ο to 90ο, a comb-like transmission spectrum with small wavelength spacing is evolving into an exotic but periodic transmission spectrum and eventually become a larger wavelength spacing transmission spectrum. The FLM is useful in many applications such wavelength division multiplexing power equalization and management, switchable multi-wavelength fiber laser, optical switch and etc.
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