Synthesis of optical filter composed of cascaded sagnac circuits

We propose using a novel multifunction optical filter with cascaded sagnac circuits for future smart wavelength division multiplexed network system applications. The coupling coefficients of the couplers in cascaded sagnac circuits are apodized according to the Gaussian function. By properly adjusting only two parameters, the coupling coefficients are convex-apodized or concave-apodized. For the former, we can obtain passband filter and improve response functions such as flatness and steepness; for the latter, it is possible to gain comb-like transmitted responses.