All-fiber tunable bandpass filter based on cascaded twin-core fiber

An all-fiber tunable bandpass filter (TBPF) based on cascaded twin-core fiber (TCF) is theoretically analyzed and experimentally demonstrated. The spectrum of this proposed TBPF can be easily adjusted by bending, twisting, stretching, or changing the length of TCF to achieve the required filter parameters. In the example of a TBPF fabricated with TCF, the center wavelength can be tuned from 1540.8 to 1557.8 nm, while the full width at half-maximum bandwidth of the filter maintains around 6.5 nm.