3.8-octave broadband nearfield generation with high stability and high tolerance using a gradually varying thickness thin-film waveguide

The generation of an optical near-field spot through a gradually varying thickness waveguide composed of metallic and dielectric thin films was comprehensively analyzed by the finite element method. The incident angle of the excitation beam, excitation wavelength, and material dependent strength of the near-field hotspot were evaluated using three different material combinations. The analysis showed that the waveguide can generate a near-field spot with an electric field stronger than that of the excitation beam in the wide spectral range, reaching from visible 488 nm to mid-infrared 7000 nm (3.8-octave). From the wedge angle and excitation position dependency, the thin-film waveguide with varying thickness indicated the high stability, high freedom of design, and high tolerance to process precision. These manifold advantages progress optoelectronics, plasmonics, and nanotechnologies, including nanometric spectroscopy.