Design of periodic bandpass filters based on a multi-reflector Gires-Tournois resonator for DWDM systems

For applications in dense wavelength-division-multiplexing (DWDM) systems, optical periodic filters with a rectangular spectral response are highly desirable to maximize system performance. In this paper, optical periodic filters using a multi-reflector Gires-Tournois resonator (MRGTR) in a Michelson interferometer (MI), are theoretically investigated. We derive the general optimum conditions that enable us to choose proper reflection coefficients to ensure flattop spectral responses for the MRGTR-based filters. Detailed discussions for the MRGTR-based filters with a maximum of five reflectors (four coupled cavities) are considered. The results show that as the number of reflectors increases, the ripple-free spectral response approaches the ideal rectangular profile. For example, with a five-reflector Gires-Tournois resonator based filter, the flattop bandwidth with a ripple less than 0.004 dB can reach more than 90% of that for an ideal case, i.e., a rectangular profile. The group delay response and chromatic dispersions of the MRGTR-based filters are also examined. It is found that such filters have nearly constant group delays or near-zero dispersion within the passband regions when more reflectors are used; with increase of the number of reflectors, the range of near-zero dispersion is enhanced.