Design And Research Of Narrow Band Filter Based On Photonic Crystal

Filter is a kind of device to eliminate interference in communication field, and it can filter out some specific frequency points or frequency beside some points. At present, the widely used filter in the market is crystal filter, which is composed of crystal resonator. Compared with the early LC resonance circuit filter, crystal filter has a further development in the frequency selectivity, frequency stability, loss, etc. But crystal filter still can’t meet the high integration and high speed signal processing requirements, so a narrow band filter based on photonic crystal is designed in the thesis. An adjustable band gap is the most important characteristics of a photonic crystal. Photonic crystal will function as reflection when point defect or line defect has been intriduced, which will has advantages of low loss, high transmission rate. In addition, the photonic crystal-based device has the advantages of flexible design, small size, high speed, etc. So the photonic crystal filter has a good prospect for development.COMSOL Multiphysics4.3b software is used in this thesis to design and study narrow-band filter based on square lattice and triangular lattice two-dimensional photonic crystals respectively, which have the common characteristics of 1.5 um wavelength communication,8um*8um size, air background, silicon column and 11.4 dielectric constant. Firstly, COMSOL Multiphysics4.3b built-in S parameter is used to analysis reflection and transmission spectrum to confirm the band gap range of complete photonic crystal, and the effect of various structural parameters (lattice constant, dielectric column radius, dielectric constant) to band gap range is studied. The optimized results of above structure parameters are used in the subsequent design of narrow-band filter. Secondly, a medium Si column is taken out to introduce a point defect in the complete photonic crystal structure to form a resonance cavity with higher quality factor, and two line defect waveguides are introduced in upper right and lower left of the cavity to form two waveguids. And after those design, filtering process is realized with the couple between the cavity and waveguide. Thirdly, as we know, the structural parameters (lattice constant, Si column radius, number of Si columns, line defect size of the two structures) have effects to the characteristics (the resonance frequency, transmission coefficient, the change trend of quality factor and so on) of the designed structure. As the research wavelength is 1.5 um, the resonance frequencies of the narrow-band filter should be 2e14Hz. And after our study, for narrow-band filter based on square lattice photonic crystal, when the resonant frequency is 2e14Hz, the optimized structural parameters are as below: lattice constant a1 is 0.6384um, dielectric column radius r1 is 0.1159*a1, dielectric constant ε1 is 11.4, the number and radius of dielectric column in the reflector N1 is 7, the radius of dielectric column in the reflector rr1 is 1.5*r1, the filter sizeS1 is 13*13(13 is the rod number in x,y direction of the narrow-band filter), transmission coefficient is 0.953 and the quality factor is 1330. And for narrow-band filter based on triangular lattice photonic crystal, when the resonant frequency is 2e14hz, the optimized structural parameters are as below:lattice constant a2 is 0.6518um, dielectric column radius r2 is 0.1316* a2, dielectric constantε2 is 11.4, the number and radius of dielectric column in the reflector N2 is 6, the radius of dielectric column in the reflector rr2 is 0.6* r2, the filter sizeS2 is 11*12*13(11 and 12 are the rod number in even column and odd column of the narrow-band filter,13 is the rod number in y direction), transmission coefficient is 0.87, the quality factor is 1428. In this thesis, the design of narrow-band filter resonant frequency is in 2el4Hz place, and size is in micron, which is ease of integration. And this thesis has provided a certain theory basis for the research of infrared communication and large optical integrated circuits.