The Structures And Characteristics Of Optical Communication Devices Based On Two Dimensional Photonic Crystals

The complete photonic crystals exhibit photonic band gaps, within which no modes are allowed and the density of states is zero. Introducing defect into complete photonic crystal can produce some defect modes in photonic band gap and form some localized mode because the defect modes are trapped into the defect position. Removing a row of rods, a photonic crystal waveguide formed and in the waveguide, the line-defect modes can propagate without loss; removing a single rod, we get a photonic crystal micro-cavity where some point-defect modes may be trapped into the defect position tightly. Photonic crystal have attracted more and more attentions because of its photonic band gap and strong photon confinement effect, the two characteristics can be used for controlling light to propagate in dielectric material.Based on the resonant coupling principle, a novel coupled-cavity waveguide based on two-dimensional triangular lattice photonic crystals was proposed. This structure was composed of a line-defect waveguides, a resonant microcavity and ellipse-holes which are located between line-defect waveguide and resonant micro-cavity. The band structure of line-defect waveguide was simulated by the plane-wave expansion method. The transmission characteristics and quality factor of the coupled-cavity waveguides were investigated by the finite-difference time-domain (FDTD) method. By optimizing the structural parameters such as amount, size and arrangement of ellipse-holes between the resonant micro-cavity and the line-defect waveguide, a 90% transmission efficiency was obtained with a Q-factor of 104. Then at optimum parameters, a high Q-factor of 107 was achieved and at the corresponding resonance frequency, the transmission efficiency is still above 60%.Based on the resonant coupling principle, a four-channel wavelength division multiplexing (WDM) system that is made of 2D triangular lattice photonic crystal was designed. This system was composed of a line-defect waveguide, four ring resonators and four 60° bend waveguides. The band structure of line waveguide was investigated by the plane-wave expansion method. The transmission characteristics of light wave with different frequencies in the system were simulated by the finite-difference time-domain method, the effects of factors on output efficiency were distinguished and the system was improved. The analysis shows that the resonance frequencies depend on the radius of the dielectric rods. It is demonstrated that the transmission efficiency of the system is improved greatly by changing the shape of dielectric rods in the coupling region and by adding the reflection dielectric rods at end of the bus waveguide. The numerical results indicate that the transmission efficiency of the WDM system can be above 90% at all different resonance wavelengths.