Experimental Study on X-shaped Photonic Crystal Waveguide in 2D Triangular Lattice for Wavelength Division Multiplexing System

For wavelength division multiplexing system, X-shaped wave guide situated in two dimensional pillar type photonic crystal structure was studied in this paper. Propagation and filtering characteristics of some types of the wave guide were experimentally investigated. Measurement was done by using a model in microwave frequency around 4 GHz with lattice period P=26.5 mm, diameter of pillar φ=7.5 mm and its dielectric constant ε_r=36.0. First, symmetric X wave guide was measured to show its basic transmission characteristics. After the measurement, three cavities with a pair of dielectric rods were situated in each output wave guide to perform a filtering function. Next, asymmetric X wave guide with cavities was examined to improve filtering characteristics in each output port. For the asymmetric structure, higher extinction ratio and higher Q-factor were obtained, compared to symmetric structure. Finally, filtering characteristics of the asymmetric X-shaped wave guide was compared with the result of Y-shaped cascaded wave guide with 4 outputs. The asymmetric X-shaped wave guide showed better results with higher resonant peak amplitude than that of Y-shaped wave guide. Applying good resolution characteristics of 40MHz with respect to input frequency, proposed asymmetric X-branch circuit is available for signal drop device for wavelength division multiplexing (WDM) system.