Design and numerical studies of composite defect photonic crystal optical filter

To eliminate the multimode property of the photonic crystal ring cavity filter,a composite defect photonic crystal filter structure combined point defect with ring cavity is proposed,in which the line defect is taken as the main waveguide and the load waveguide combining the point defect with the ring cavity is adopted to achieve the filtering for the certain wavelength.By changing the refractive index of the rods in the general photonic crystal structure,the refractive index of the point defect or the size of the point defect,the influences on the filtering property is analyzed.Mis regarded as m=r-point/r,the numerical simulation result shows that the filtering wavelength will remain the same the filtering characteristic when mis varied from 0to 0.6,while mis in the reasonable range from 0.6to 1.8,the single longitudinal mode filtering characteristic and its tunability can be achieved by changing the point defect radius,which can make the effective theoretical reference for the design of multi-channel filter.