Design Of Wavelength Division De-multiplexer Based On Two-dimensional Photonic Crystal

Photonic crystal is a kind of artificial material whose dielectric constant is arranged periodically. The most typical character of PCs is "band gap", that means the propagation of electromagnetic wave is highly prohibited in the band gap. And because of this kind of feature, photonic crystals can control the transmission of light waves by introducing defects effectively. One of the most important applications of PCs is the realization of devices for use in Wavelength Division de-multiplexing (WDDM), which is useful to divide and combine different wavelength channels each carrying an optical data signal. In this paper, we proposed two kinds of Wavelength Division de-multiplexing based on the transfer property of the photonic crystal waveguides and resonant cavities.The key points of this paper are as follows:1. First, we discussed the coupling theory between waveguides. According to the coupling theory, we proved that the state of light output can be controlled by changing the length of the coupling area. In addition, the influence of different refractive indexes and the radius of the coupling rods on coupling property were studied, respectively. At last, we proved that we can design a directional coupler by changing the coulping length and rods’refractive indexes or radius.2. We studied the coupling relationship between resonate cavity and the waveguide. Then calculated the transmission expression equation for the structure of the channel drop filter based on a three-drop system. From the equation we learned that we can get higher transmission rate by means of changing the distance between the cavity and the reflector which would have significant meanings.3. We designed a Wavelength Division de-multiplexing (WDDM) which combined the advantages of resonate cavities and folded directional coupler (FDC) based on the coupling relationship between resonate cavity and the waveguide. The union of waveguides coupling and cavities coupling which can get the wide bandwidth wavelength and narrow bandwidth wavelengths, make the applications become more widespread and flexible.4. Based on the evanescent coupling and guided-mode resonance theory, we calculated the central frequency of the cavity and the inherent frequency of the waveguide. Then we pictured the scatter between them. According to the coupling resonance characteristics, the curves of the modes in the waveguide and the resonant cavity can be intersected at point. And it is the point whose frequency can be energized. Thus, we can get the wavelength at that frequency. Then we designed a T-shaped wavelength division de-multiplexer. In this structure, we used a resonant cavity to select a channel with a5-nm bandwidth, and by changing the radius of rods as defects to change the propagation modes. As a result, we can get the wavelengths1310,1440, and1550nm, and the transmission rates of these three wavelengths are all reach up to95%.