Photonic bandgap microcavities with flat-top response

In this paper, the analysis and the design of a photonic handgap (PBG) microcavity waveguide filter with flat-top spectral characteristics are theoretically presented. The split filter analysis and the bidirectional eigenmode propagation method are applied to the investigation of this waveguide structure to obtain the design parameters of the filter with nearly unity transmittance and a squared passband. It shows that the radiation loss in the PBG mirrors diminishes the transmittance of the filter, and a mirror with anomalous dispersion region in reflection phase could be used to assemble an optical filter with the flat-top passband. A 1-D PBG monorail waveguide microcavity filter centered at 1554 nm with a maximum transmission of -0.55 dB and full-width at half-maximum (FWHM) of 13.6 nm is numerically carried out by using 3-D finite-difference time-domain method.