Analysis of frequency characteristics of dielectric waveguide discontinuities using finite difference-time difference method

The frequency characteristics of several discontinuous shapes in a dielectric slab waveguide have been studied numerically by means of the finite difference-time difference (FD-TD) method. First, an excitation method of the incident mode field suitable for the FD-TD calculations is presented in detail and the numerical accuracy of the method is discussed. For the step and bent discontinuities, the transmission and reflection coefficients derived by the FD-TD method are compared with rigorous values. It is confirmed that sufficient accuracy is guaranteed. Next, for the discontinuities such as step, gap, slope, crank, axial offset, and sharp bend, the frequency dependence of the transmission coefficient is studied; both amplitude and phase are investigated. Finally, with a simple model of the quadriphase-shift keying (QPSK) modulated wave, the discontinuity transmission characteristics are examined.