Realization of sinusoidal transmittance with subwavelength metallic structures

We propose to use hybrid dielectric-metallic subwavelength structures to code complex transmittance (module and phase) in the mid-infrared wavelength range. As a demonstrator, we have designed and fabricated largearea (2mm×2mm) metallic gratings with transmittance levels ranging from 37% to 98%. Optical transmission measurements are in very good agreement with numerical computations. It demonstrates the ability to control the transmission intensity with high accuracy by the use of lateral structuration of metal at the nanoscale. A nonresonant process ensures a large spectral band. We discuss the integration of this concept to code a laterally modulated sinusoidal transmittance pattern. The phase shift induced by metal structures is analyzed. A technologically viable solution is proposed to reduce this parasitic effect in our application. Such devices allow one to obtain optical beams with a lateral, two-dimensional sinusoidal modulation and can answer the growing needs of optical wavefront analysis applications.