Epsilon-Near-Zero Supercoupling

An epsilon-near-zero (ENZ) channel is a slice of material whose permittivity is tuned to sit right at zero, which sends its refractive index toward zero and its phase velocity toward infinity. This simulator builds a real wide–narrow–wide waveguide in 3D, computes exact Fabry–Pérot transfer-matrix transmission and reflection for the narrow throat, and animates wavefront markers squeezing through it. Drag the channel's permittivity through zero and watch the reflection collapse and stay collapsed even as you pinch the throat down to a sliver or bend it sideways — the shape-independent "supercoupling" signature first predicted by Silveirinha and Engheta. Push permittivity negative and the same channel flips into a plasmonic barrier that reflects almost everything regardless of thickness.