A tunable polarization-independent comb filter based on high-order mode fiber

This paper presents an all-fiber tunable comb filter based on high-order mode fiber (HOMF). The filter is constructed by splicing a segment of HOMF between two sections of conventional single-mode fibers (SMFs), with an intentionally introduced offset at the first joint between the SMF and HOMF, and without an offset at the second joint between the HOMF and SMF, to optimize the visibility of the transmission spectrum. The optimal transverse offset of the fibers at the first joint and the tunable polarization-independent properties of the filter were studied theoretically and experimentally. An example of using this tunable comb filter in the application of a sensor, based on demodulating the wavelength shift of a fiber Bragg grating, has also been demonstrated. The particular advantages of this all-fiber tunable filter make it valuable in various applications.