Anomalous reflection coefficient underlying experimentally validated outstanding transmission through metal–dielectric–metal microcavities

Analytical modelling of light transmission through a metal-insulator-metal geometry embedded in a coupling glass surrounding medium is possible through an extended Fabry-Pérot formula. Two distinct coupled surface plasmon resonance branches are allowed inside such microcavity, where two thin metallic layers act as mirrors delimiting an inner dielectric material. In agreement with transfer-matrix method simulations, the resulting theoretical expressions predict a large and almost constant transmittance even for intracavity thicknesses greater than light’s penetration depth. Results at λ = 800 nm have been validated experimentally and show optical transmittance over 10% until nearly 3 μm. This high transmittance under such unexpected conditions, related to an anomalously high mirror reflection coefficient, sheds light on new possibilities for the design of optical devices. The experimental setup successfully used to corroborate the validity of the transmittance formula over different angular, spectral and geometrical conditions is also presented.