Impact of the silicon layer thickness to the optical property of sandwich photonic crystal structure

One hexagonal lattice sandwich structure Al/SiO₂/Si has been fabricated with different thickness of silicon layer based on Silicon-On-Insulator (SOI) wafer. The transmission spectrum in mid-infrared range is extremely sensitive to the variety of the thickness of silicon layer. An important characteristic is that the number of the coupled modes corresponding to the surface plasmon polaritons (SPPs) model is different with each thickness, especially at 4.08 micrometer, only one coupled mode emerged. This experiment result shows that Localized surface plasmon (LSP) coupled mode and quasi-cylindrical wave (Quasi-CW) resonant mode all have been involved in the enhanced optical transmission phenomenon (EOT), and different coupled mechanisms have strong interaction with each other. The experiment result further reveals the deeper underlying physics of the EOT phenomenon, and is significant to new design of some optical sensor devices based on enhanced optical transmission phenomenon.