An all-fiber asymmetric optical interleaver of cascaded Mach-Zehnder interferometer using a 2×2 and two 3×3 fiber couplers is developed. Influences on its transmission characteristics by such factors as splitting ratio of the directional fiber couplers and the physical length differences of the interferometer arms are numerically analyzed in detail. One set of optimized data is validated in the experimental result. The results of numerical simulation and experiments show that all-fiber optical interleaver with -3 dB passband in odd channels and even channels can be obtained for transmission speed of 40 Gb/s and 10 Gb/s, respectively. Compared with all-fiber asymmetric optical interleaver of cascaded Mach-Zehnder interferometer using three 2×2 fiber couplers, the most advantage of the present method is that the coupling ratio of couplers can be controlled in the fabricating process accurately. Finally, a novel structure of interleaver is fabricated using fused biconical taper technics in experiment. The experimental results agree with the analytical ones well.