On tailoring of the flat-top response of photonic crystal based optical filter

In this paper, the flat top spectral characteristic of a photonic crystal based optical filter is tailored through proper insertion of defects within the crystal structure. Such tailoring is essential for accommodating the shift in channel wavelength. Estimated defects are incorporated here through proper extension in dielectric layers of specific unit cells. The distribution of such defect regions within the filter structure is crucial in determining the flatness of the filter pass band. Performance of the flat top filter is analyzed using transfer matrix method and a condition regarding distribution of defects within the filter is derived. The flat top pass band, provided by our proposed model, can support the shifts of signal wavelength in an allotted channel within its permissible limit, which is specified as 12-14 nm by ITU-T Recommendation G.694.2 for a coarse wavelength division multiplexing (CWDM) system.