We demonstrate the confinement of broadband optical energy in the visible to near-infrared regime in a threedimensional nanoscale volume with high energy efficiency in a nanostructure consisting of multiple nanoslits in dielectric chacolgenide material. We find that a broadband optical field can be confined down to the scale of 1 nm (λ∕650) with a confinement volume of λ3∕3 × 10The figure of merit of the nanostructure can be up to 10 times that achieved by plasmonic lensing and nanofocusing. Our
