Design And Research Of High Efficiency Multifunctional Photonic Crystal Filter

Photonic crystals were first proposed by Yablonovitch and John in 1987;which are periodic structures comprising two or more dielectric materials.The two most important features of photonic crystals are “photonic band gap” and “photonic local,” which enable the introduction of linear and point defects to form waveguides,microcavities,and ring cavities in the photonic crystal bandgap frequency range.Photonic crystals can then be coupled to design a photonic crystal optical device with high integration,small size,and low loss.Herein,waveguide and microcavity coupling is used to design a photonic crystal filter having high output efficiency and a one-way transmission function.This study adopts a two-dimensional square lattice photonic crystal structure,designs and simulates the photonic crystal filter structure using the COMSOL multiphysics finite element software,and thus creates the distribution diagram of filter output efficiency.First,a novel photonic crystal wavelength division multiplexer is designed.Point defect microcavities are widely used in photonic crystal filters because they are useful in selecting frequencies.By coupling waveguides with microcavities of four different types,wavelengths of 1530,1555,1580,and 1605 nm are demultiplexed.The results show that multi-wavelength transmittance of approximately 93% can be achieved by adjusting the radius of the microcavity medium.This design has potential applications in small and selective optical communication devices.Second,a novel one-way transmission device based on symmetry matching between the defect and waveguide modes is designed and evaluated.The device comprises one elliptical defect and two wire defect waveguides,with a single-mode and dual-mode waveguide each.Because the point defect state has four different resonant frequencies and four corresponding types of mode field symmetries,the proposed design uses the match or mismatch between the defect and waveguide modes to realize the symmetric/antisymmetric optical signal with frequency 0.4171 c/? of one-way transmission with a transmittance >90%.This design can be applied to devices with one-way optical signal transmission such as an optical diode.Finally,based on the photonic crystal having one-way transmission,a single-mode waveguide is added to the design.Similarly,according to the symmetric match between the point defect and waveguide modes,the design achieves two resonant frequencies,0.4332 c/? and 0.4380 c/?,with single waveguide filter outputs of 84% and 96% respectively.