Characteristics of mismatched twin-core fiber spectral filters

Both bandstop and bandpass filters can be easily implemented with mismatched twin-core fibers designed to phase-match at a certain wavelength. These filters are highly stable with very low temperature and strain sensitivity. We studied the spectral quality of these filters and that of cascaded filters designed to achieve improved bandpass response. We have also demonstrated the feasibility of achieving designed loss profile from these filters. This is very useful in gain spectrum flattening in Er-doped fiber amplifiers.