In Fig.10, it is found that the symmetric MZ interferometer (MZI) shows maximum and minimum transmission at frequencies 3.816GHz and 4.196GHz, which are indicated by arrows and dots in the figure. Measurement of symmetrical MZI showed almost flat and relatively high transmission characteristics over same frequency range, comparing with result of asymmetrical one. Therefore, simulations by CIP method were demonstrated for these two frequencies and additional one frequency 4.006GHz as middle level of output. The electric field profiles by CIP method along with MZI are shown for these three frequencies in Fig.11. The electric field profile at output port is also indicated in Fig.12. From these figures, it is found that electric field propagated along with two arms comes to combining point with relatively small phase difference in Fig.11(a) and (b), while electric field become extinct for the two fields comes to combining point with out of phase in Fig.11(c) . In Fig.12(c), the maximum electric field is quite small compared with output with small phase difference in MZI as shown in Fig.12(a) and (b). From Fig.10 to 12, complicated output characteristics were qlearly interpreted by numerical results by CIP method. This is because CIP method provides more precise results of electromagnetic wave scattering compared with FDTD method, as we saw in subsection 3.1. From these results, it was shown that superiority and significance of the CIP method for designing photonic crystal structure which is composed of periodic structure with high contrast of material constant.