Widely-tunable optical bandpass filter based on long-range surface plasmon polaritons

Abstract

We report that unique properties of long-range surface plasmon polaritons (LR SPP) allow one to produce optical components with very wide tuning range using small variations in the refractive index of the dielectric layer. Our filter is based on integration of a thin metal film between two dielectrics with dissimilar refractive index dispersion. In this configuration, the filter only has low insertion loss at a wavelength for which the refractive indices of the top and bottom dielectrics are the same, leading to a bandpass filter. As a proof-of-principle demonstration, we present operation of LR-SPP- based bandpass optical filters with refractive index matching fluids on an Au/SiO2 surface in which a 0.004 variation in the refractive index of the top dielectric translates into 210nm of bandpass tuning at telecom wavelengths. To make a more practical solid-state device, thermo-optic polymer can be used as a top dielectric and we expect that only 8°C of temperature variation translates into 200nm. The tuning mechanism proposed here may be used to create monolithic filters with tuning range spanning over more than an optical octave, compact and widely-tunable laser systems, multi-spectral imagers, and other plasmonic components with broadly-tunable optical response.