Design And Optimization Of Optical Filter Based On Photonic Crystals

Photonic crystal (PhC) structure, whose dielectric constant varies periodically in space, possesses a photonic band gap in which electromagnetic wave cannot propagate. Great attention was paid to research on PhC-based optical devices due to their compactness and the potential application in photonic integrated circuits and all-optical communication network. Optical filters are key components to access signals on a particular channel or multiple channels in wavelength division multiplexed optical communication system. Therefore, research on Phc-based filter is also critical. In this paper, researches are given on the design of reflection filter based on multiple resonators side coupled to PhC waveguide. They are summerized in the following.One kind of transfer matrix method is derived from coupled mode theory in time. It is successfully applied to analyze the coupling between periodically distributed resonators embedded in the PhC waveguide as well as placed on the two sides of the waveguide. And phase response of the reflection filter is also demonstrated by this kind of transfer matrix method.Chirp and apodization techniques are firstly introduced to suppression of sidelobes in the reflection response of optical system composed of multiple resonators periodically placed on the two sides of the PhC waveguide. To remove sidelobes, a linearly chirped or symmetrically chirped system is realized in the considered optical system with non-continuously distribution of dielectric constant. However, the bandwidth of the resulted reflection spectrum is twice or more of that of the uniform system. The apodization technique, which modulates the coupling coefficients between the resonators and the waveguide, is also proved to be efficient to suppress sidelobes. Reflection power can be decreased by 25dB at the nearest sidelobe of the reflection peak. Furthermore, good agreements are obtained between theoretical analysis using the derived transfer matrix method and first-principle finite-difference time-domain experiment.The phase response of the reflection filter composed of periodically distributed resonators side coupled to PhC waveguide is considered by using derived transfer matrix method. The impact of phase response on Gaussian pulse transmission is demonstrated. It is confirmed that phase response cannot be ignored in the design and optimization of the reflection filter. As for optical system composed of five resonators, apodized system results in severe inter-symbol interference when parameter G is increased to 0.3. And output pulse remains its shape as long as G is less than 0.2.Furthemore, the tuning of silica-based reflection filter composed of side-coupled resonators is analyzed by applying plasma dispersion effect. The resonance frequency of the resonator is changed from 193.5THz to 217.2 THz when the refractive index of the central rod of the resonator decreases by 0.4. The fabrication design, in which different coupling waveguides are considered, is also given. This kind of coupling waveguides can decrease the coupling loss between the optical fiber and photonic crystal structure.