In this paper

the ring resonator-based photonic crystal T-shaped channel-drop filter is investigated by the finite element method

in which the effects of the refractive index of the dielectric rods on the resonant frequency and normalized transmission are analyzed.On this basis

a filter model for the narrowband photonic crystal filter is designed.The numerical simulation results demonstrate the approximately linear dependence of the inner dielectric rods refractive index on the central wavelength of the drop waveguide output of the narrowband filter

which presents theoretical reference for the design and manufacture of photonic crystal filter.