Enhancement of defect mode transmission peaks in thermally tunable filter with graded thickness: a comparative study between different gradation functions

Abstract A ternary photonic crystal of the structure (ABC)N (CBA)N is treated as a thermally tunable filter. Layers A, B and C are silver (Ag), silicon dioxide (SiO2) and Silicon (Si), respectively. The low-index layer (SiO2) is assumed to have a graded thickness according to four different functions. The thickness gradation functions are considered exponential, linear, quadratic and cubic. The transmission peaks at defect modes and their wavelength positions are investigated as functions of temperature and incident angle. The performance of each gradation function is investigated. Many findings are obtained. With the increase in temperature, the transmission peaks shift toward longer wavelengths. Transmissions at defect modes of TM polarization have higher values than those of TE polarization for the same incidence angle. The cubic function showed a transmission peak of 0.897 which is the highest among all functions.