LIMITS ON QUALITY FACTORS OF LOCALIZED DEFECT MODES IN PHOTONIC CRYSTALS DUE TO DIELECTRIC LOSS

The spectral widths of defect modes localized at line defects formed i n a two-dimensional photonic crystal composed of a square lattice of d ielectric cylinders were analyzed theoretically. The transmission spec tra calculated by the layer-doubling method based on the vector-cylind rical- wave expansion of the internal field showed a rapid decrease of the spectral width with increasing number of the lattice layers when the dielectric loss is absent. Quality factors larger than 10(7) were predicted for the total lattice layers of 18. However, the numerical e valuation of the decay constant of the defect modes due to the imagina ry part of the dielectric constant showed that the actual quality fact or is limited by the dielectric loss. The calculated widths agreed qua litatively with the experimental observations by Lin et al. [Appl. Phy s. Lett. 68, 3233 (1996)]. (C) 1998 American Institute of Physics. [S0 021-8979(98)07623-3].