Analytical computation of transmittivity of double-defected layer 1D photonic crystal for bandpass filter applications

Transmittivity of one-dimensional defected photonic crystal is analytically computed for normal and oblique incidences of electromagnetic wave. Presence of defect is considered in both the layers of unit cell (GaN/AlxGa1-xN), and result is compared with that obtained for ideal structure. Transfer matrix technique is used for computation purpose, and structural parameters are varied within practical limit. Following Adachi's model, refractive index of AlxGa1-xN is considered as a function of mole fraction and operating wavelength. Numerical calculation reveals that appropriate choice of design parameters can tune the position of bandwidth along central wavelength. Comparative studies of TE and TM mode of incidences along with normal incidence are carried out for filter performance. Result shows that suitable introduction of defect along with variation of incident angle makes the structure as efficient bandpass filter by tailoring the width of passband at 1550 nm for the sole purpose of optical communication.