STUDY ON X-SHAPED PHOTONIC CRYSTAL WAVEGUIDE IN 2D TRIANGULAR LATTICE FOR WDM SYSTEM

摘要

For wavelength division multiplexing system, X-shaped waveguide situated in two dimensional pillar type photonic crystal structure was studied in this paper. Propagation and filtering characteristics of some types of the waveguide 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 0=7.5 mm and its dielectric constant ε_r=36.0. First, symmetric X waveguide was measured to show its basic transmission characteristics. After the measurement, three cavities with a pair of dielectric rods were situated in each output waveguide to perform a filtering function. Next, asymmetric X waveguide 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 waveguide was compared with the result of Y-shaped cascaded waveguide with 4 outputs. The asymmetric X-shaped waveguide showed better results with higher resonant peak amplitude than that of Y-shaped waveguide. Applying good resolution characteristics of 40MHz with respect to input frequency, proposed asymmetric X-branch circuit is available for signal add/drop device for wavelength division multiplexing (WDM) system.