High-Extinction-Ratio Multipassband Filter With Flat-Top and Low-Dispersion

This paper proposes a novel structure to realize a high-extinction-ratio multipassband filter (HERMPF) with flat-top, low dispersion, and large passband and stopband bandwidths. Spectrum and chromatic dispersion of the HERMPF are given under ideal conditions, which show that such a filter has excellent performance. Analysis on fabrication tolerances is given as well, focusing on factors such as the length mismatch and loss which degrade the spectral and chromatic dispersion performances of HERMPF in practice. A single-cavity ring resonator is inserted into either arm of a Mach-Zehnder interferometer to form a Mach-Zehnder ring resonator interferometer (MZRRI), which is an infinite-impulse- response half-band filter with two complementary channels (even and odd channels). MZRRI is the core element of HERMPF which determines the spectral performance. A set of multicavity Gires-Tournois etalon composed of cascaded Sagnac loop mirrors is proposed as the tunable dispersion compensator and fully reflective mirror in HERMPF. The third main part of HERMPF is a 1 × 2 switch, which is used to select the even/odd channel of MZRRI. Thus, HERMPF can be used as an even/odd channel switch.