Binary zero-order diffractive and anti-reflective optical elements in silicon for the mid-infrared

We propose a novel method for the design of binary 2-level diffractive optical elements that provide an efficient diffractive function while reducing the reflectivity of a high-index interface. The structure can be fabricated with a single patterning step and is particularly useful for the mid-infrared spectral range. The concept is based on zero-order transmission gratings using subwavelength micro-structures. To demonstrate the concept a Dammann grating has been realized in silicon and characterized in the mid-infrared by scanning the far-field intensity distribution.