Study of a Novel All-Fiber 3 $,\times,$ 3 Interleaver With a Dual-Eight-Shaped Ring Resonator

A three-channel all-fiber flat-top optical interleaver is developed by using a new configuration of a dual-eight-shaped ring resonator used as an input device. An approach that is based on the maximally flat principle is used to design the interleaver with a flat-top transmission. The optimum values of structural parameters, such as splitting ratios of the couplers and the physical length differences of the interferometer arms, are chosen. The results of the analysis show that with the proposed configuration, the transmission spectrums of the three channels of the interleaver can be controlled to have an identical shape but with 2π/3 a phase shift between them in frequency. Compared with the three-port interleaver based on two-stage cascaded Mach-Zehnder interferometer, the passband/stopband and channel isolation of the proposed interleaver are improved remarkably, which has an ideal rectangular spectral response.