Design And Study Of Ultracompact Triplexer Based On Photonic Crystal

Photonic crystals, as a new kind of artificial material, have been extensively concerned for the feature of photonic band gap (PBG). And they become the leading edge in optical communication area. As the period of photonic crystal is the magnitude of optical wavelength, the sizes of photonic devices are ultracompact. Photonic crystal waveguide (PCW) which is composed by introducing a line defect is one of the important components for constructing the future photonic integration circuits. This paper investigated the characteristics of two-dimensional PCWs and waveguide couplers theoretically. And based on the different theory we designed the triplexer, which has a significant applied prospect in fiber-to-the-home system.Firstly, we analyzed the coupling property of two waveguides couplers (2-CPCWs). Then, the coupled system which was composed of three parallel single-modes PCWs (3-CPCWs) was regarded as the multimode coupled system. According to the self-imaging effect, the numerical conditions of the direct and mirror replicas of the input field were obtained in this kind of system. And we also analyzed the decoupling property of the2-CPCWs and3-CPCWs; found that the decoupling frequency keep invariant.Based on the characteristic of the unchanged decoupling point for2-CPCWs and3-CPCWs, we designed a novel triplexer. The designed device realized the separation of the three wavelengths1310,1490and1550nm. Only by introducing a single defect rod can the three wavelengths be output with high extinction ratios. The present device has a simpler structure, and is more ultracompact with total size30μm×<11μm.The plane wave expansion method is used to compute and investigate the dispersion of PCW with an air holes array. The results indicate that the cutoff frequency of fundamental mode shifts to higher frequency as the radius of border holes adjacent to the PCW core. Due to the existence of PBG, only the frequency above the cutoff frequency can be transmitted, whereas the frequency below the cutoff frequency where no guided super modes exist is prohibited. Thus, we propose a triplexer based this property. The numerical results obtained by finite-difference time-domain method show that the introducing defect holes in the device can control the beam propagation and enhance the output efficiency. The designed device is compact and feasible for the practical application in the system of optical communication system.