Reduction in Angular Dependence of Plasmon- Enhanced Transmission Through a Metal Layer

Angular responses of optical transmission enhanced by surface plasmon-polaritons (SPPs) in a metal layer are investigated. Propagating SPPs on a continuous metal layer with nanostructures depend on in-plane momentum; thus, transmission peaks associated with those SPPs are inherently affected by the incident angle. Here, we report that SPP-enhanced transmission peaks can become less dependent on the incident angle by introduction of deep nanoindentations, based on numerical simulations and experiments. Field localization at indentation patterns allows propagating-coupled SPPs to have properties of localized SPPs, which appears as a form of flattened SPP energy band. Spectral transmission in a fabricated silver layer with deep nanoindentations shows comparatively fixed peak positions when the incident angle increases.