All-Fiber 3>tex<$times$>/tex<3 Interleaver Design With Flat-Top Passband

In this letter, a three-port all-fiber flat-top optical interleaver is developed by using a new configuration of cascading three 3 /spl times/ 3 directional fiber couplers. An approach that is based on the maximally flat principle is used to design the interleaver with a flat-top transmission. The proposed design approach also allows one to design interleavers with certain passband ripples in order to obtain a wider passband bandwidth. A 100/300-GHz three-port interleaver with a passband bandwidth of 40 GHz at 0.5 dB is demonstrated by experiment.