IMPURITY MODES IN 1-D PERIODIC OPTICAL-SYSTEMS

A one-dimensional periodic structure composed of an alternating array of dielectric slabs is considered for the case in which an impurity is introduced substitutionally into the array by replacing one of the di electric slabs with an impurity slab. Two types of impurities are cons idered: (1) impurities obtained by changing the dielectric constant of one of the dielectric slabs in the periodic system from that of its f ellows; (2) impurities obtained by changing the width of one of the di electric slabs in the periodic system from that of its fellows. The de pendence of the gap impurity mode frequencies as functions of either i mpurity dielectric constant or impurity width is studied for a fixed b ackground dielectric constant in the periodic array. The computations for the impurity mode frequencies are performed numerically using tran sfer matrix techniques in conjunction with the supercell method for tr eating impurity modes in otherwise periodic arrays.