Abstract

Subwavelength high-contrast gratings (sub-$\lambda$ HCGs) were pursued to design mid-IR optical devices based on wavefront engineering. Unlike metallic counterparts, dielectric and semiconductors offer low-loss operation over a wide spectral range. Silicon gratings on sapphire substrate are proposed here as the device platform due to their transparency at near-IR to mid-IR wavelengths. The proposed generic methodology manipulates the wavefront of the reflected wave based on the phase and magnitude of reflectivity for unit cells with different dimensions. To demonstrate the capability of generating an arbitrary wavefront profile, several design examples are shown: (1) a reflective mirror with $\sim 100\%$ power efficiency and broad bandwidth of $>1\mathrm{\mu m}$ as reflectivity $>90\%$; (2) a blazed grating with a reflection peak automatically aligned with its $+1\mathrm{st}$ diffraction order at 19.5°; (3) a focusing mirror with a focal length of 35 μm and diffraction-limited focus; (4) a sinusoidal phase profile with a periodicity of 8860 nm.

© 2016 Optical Society of America

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