Efficient analysis of Gaussian pulse propagation along the synchronous and asynchronous directional couplers

In this paper, we use finite-difference time domain beam propagation method (FDTD-BPM) to analyze the pulse propagation in directional couplers. FDTD-BPM is an efficient method in numerical computation of optical passive components. The alternating-direction implicit method (ADIM) is applied to discretize the wave equation. The generalized Douglas (GD) scheme is used to the second order derivatives with respect to space coordinates. Required computer execution time and memory capacity of FDTD-BPM is less than those of conventional time domain method, FDTD. This method involves reflection and diffraction problems against well-known BPM. Design parameters can be manipulated easily by using this method. Non periodic grating-assisted directional coupler (GADC) cannot be treated by CMT or Bloch theory. Some weak periodic and non periodic GADCs can be analyzed by using time-domain FD-BPM.