Grating coupler is usually simulated in 2D FDTD instead of 3D FDTD to reduce the computational cost (both in time and memory). To perform the 2D FDTD simulation, the longitudinal cross section is considered only (see attached figure). However, the real grating coupler is 3D. Converting the result from 2D simulation to 3D is possible and it is well-known as Effective Index Method (EIM). But, how to achieve this in Optiwave? In the literature, people are talking about multiplying the 2D grating simulation by the lateral field. How to find out the lateral field in Optiwave?
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