Multifunctional Optical Filter Using Direct-Coupled and Cross-Coupled All-Pass Filters

We present a multifunction optical filter that operate as: 1) symmetric interleaver (SI); 2) asymmetric interleaver (AI); 3) dual-wavelength, channel passing add-drop filter (ADF); and 4) dual-wavelength, channel dropping ADF. The new filter is a pair of direct-coupled all-pass-filter (APF) and cross-coupled APF positioned in each of the two arms of a Mach-Zehnder interferometer (MZI). Depending on the MZI's path length difference and the values of the coupler's coefficients, these four functions are demonstrated. The interleaver has a superior flat-top profile, low ripple value (-0.095 dB for SI, -0.075 dB for AI), and high extinction ratio (<-60dB). The effect on waveguide losses on flat-top, ripple, slope, and SNR are also investigated.