ANALYSIS OF DIELECTRIC OPTICAL WAVE-GUIDES USING THE NONORTHOGONAL FINITE-DIFFERENCE TIME-DOMAIN (FD-TD) METHOD

Research and development of optical circuit elements become important as the degree of integration of the optical circuit is advanced. Since the optical devices are integrated and become more complex and as optical circuit elements with high index difference begin to appear, the conditions of the weakly guided wave and of the reflectionless wave no longer hold rigorously. Hence, rigorous numerical analysis is needed. One of the analysis methods for the optical circuit elements is the finite-difference time-domain (FD-TD) method. Recently, as a generalization of the FD-TD method, the nonorthogonal FD-TD method has been proposed. In this paper, the optical circuit elements are analyzed by means of the nonorthogonal FD-TD method which is capable of analyzing optical circuit devices with various shapes. First, tapered waveguides are analyzed. The results are compared with those by the beam propagation method (BPM) and the characteristics with respect to the tapered angle are derived. Next, a directional coupler with a high refractive index difference is analyzed. The effectiveness of the present method for the coupling characteristics is presented.