Using periodic metallic nanostructure for compact optical sensor to detect refractive index change

Abstract

We demonstrate a compact optical transducer (~50μm) based on a gold film perforated with a square array of square holes. The lattice constant (separation between nearest holes) is chosen to be a ~ 1μm to detect refractive index change around ( n~ 1.4) with resonant wavelength (λ~1.5μm). Both reflectance measurement and finite difference time domain (FDTD) simulations are performed to evaluate the performance of the sensors. The responsivity of the resonant wavelength is measured to be Δλ/Δ n ~835nm RIU -1 (RIU= refractive index unit). The linewidth and contrast of resonance are compared with different size of holes from experimental measurement and FDTD simulations. Coupled mode theory analysis is also used to understand the change reflectance spectrum as a function of hole width.