Generation of broadband near-field optical spots using a thin-film silicon waveguide with gradually changing thickness.

We developed a thin-film silicon waveguide with gradually changing thickness for generating a near-field optical spot. Theoretical studies show that the surface plasmons that are resonantly excited on the waveguide generate a hot spot with a wide spectral range. We experimentally confirmed generation of the near-field hot spot using continuous waves at 850 and 660 nm wavelengths. This waveguide, which can generate the enhanced electric field by normal incident of the excitation beam under situations of the practical use, is promising for broadband near-field optical technologies.