Design analysis of flattop all-fiber asymmetric interleaver

A novel all-fiber interleaver consisting of a three-stage cascaded Mach-Zehnder interferometer (MZI) is presented. Based on a comprehensive analysis, a mathematical description is provided. To achieve a flattop wavelength response, a design process is adopted to determine the optimum coupling-coefficient-angle values according to finite impulse response (FIR) digital filter theory. A set of coupling-coefficient-angles of fiber couplers were obtained. Furthermore, these optimum coupling-coefficient-angle values were exploited to fabricate an interleaver with flattop response within the passband in the experimental, so these optimum values are validated. The theoretic analysis and the experimental results indicate that the flattop passband in odd channels and even channels could be obtained. 3 dB passband in odd channels and in even channels are asymmetric, and the 3 dB passband is more than the 60 GHz passband and 30 GHz passband, for transmission speed of 40 Gb/s and 10 Gb/s, respectively. The channel isolation of the interleaver is more than 35 dB. The tolerance characteristics of the splitting ratios are favorable. Our design and analysis should be useful in the realization of flattop all-fiber asymmetric interleaver for deployment in dense wavelength division multiplexing (DWDM) networks of high spectral efficiency.