RCWA-EIS method for interlayer grating coupling.

The grating coupling efficiencies for interlayer connection (overlaid chips) were previously calculated using the new rigorous coupled-wave analysis equivalent-index-slab (RCWA-EIS) method. The chip-to-chip coupling efficiencies were determined for rectangular-groove (binary) gratings. In the present work, the search algorithms used in the RCWA-EIS method are optimized giving rise to improved definition of equivalent indices. Further, the versatility of the RCWA-EIS method is demonstrated by extending it to (nonbinary) parallelogramic gratings, sawtooth gratings, and volume gratings. The finite-difference time-domain method is used to verify the results. This demonstrates the flexibility of the RCWA-EIS method in analyzing arbitrary 1D gratings.