Study of All-Fiber Asymmetric Interleaver Based on Mach-Zehnder   Interferometer
  In order to improve the transmission efficiency of optical-fiber communication system with 10Gb/s+40Gb/s, an all-fiber interleaver with unequal passband is proposed and discussed, which is based on a two-stage cascaded Mach-Zehnder interferometer (MZI). The optimum value of structural parameters, such as splitting ratios of the couplers and the physical length differences of the interferometer arms, were chosen. One set of optimized data is validated in the experimental result.The experimental results and the theoretic analysis indicate that an all-fiber optical interleaver with -3dB passband width in odd channels and even channels could be obtained, which having more than 60GHz passband and 30GHz passband, for transmission speed of 40Gb/s and 10Gb/s, respectively.By assigning different portions of spectrum to the 10Gb/s and the 40 Gb/s channels, the bandwidth efficiency requirement of the 40 Gb/s channel is relieved, and therefore longer transmission distance can be achieved.Comparing with the conventional asymmetric interleaver, the most obvious benefit of the proposed interleaver is all-fiber structure. 
Lu Huaiwei, Wei Yun, Zhang Baoge, Wu Kaijun, Luo Guanwei
physics.optics