Abstract
We report the first demonstration of a mid-IR reflection-based flat lens with high efficiency and near diffraction-limited focusing. Focusing efficiency as high as 80%, in good agreement with simulations (83%), has been achieved at 45° incidence angle at λ = 4.6 μm. The off-axis geometry considerably simplifies the optical arrangement compared to the common geometry of normal incidence in reflection mode which requires beam splitters. Simulations show that the effects of incidence angle are small compared to parabolic mirrors with the same NA. The use of single-step photolithography allows large scale fabrication. Such a device is important in the development of compact telescopes, microscopes, and spectroscopic designs.
Highlights
The interest in the applications of mid-infrared (IR) light has recently increased in many areas, such as night vision, pharmaceutical quality monitoring, and homeland security
Since there is no spatial variation of the antenna array in the y-direction, only one row of disc antennas was simulated and Bloch boundary conditions were applied in the y-direction
We found that the effects of comatic aberrations on the focal length and focused beam size were small for a deviation of the incidence angle within ±15o, which compare favorably to an off-axis parabolic mirror with the same numerical aperture (NA)
Summary
The interest in the applications of mid-infrared (IR) light has recently increased in many areas, such as night vision, pharmaceutical quality monitoring, and homeland security. A new class of optical components based on metasurfaces has been developed [1]. These components control the wavefront of light using arrays of optical resonators with subwavelength dimensions, which are patterned on a surface to introduce a desired spatial distribution of optical phase. By tailoring the properties of each element of the array, one can spatially control the phase of the scattered light and mold the wavefront Based on this concept, various functionalities have been demonstrated including lenses [2, 3], axicons [2], blazed gratings [4], vortex plates [5] and wave plates [6]. Its material and processing requirements are minimal, requiring only a flat reflective substrate and one photolithography step using a high throughput deep-UV photolithography stepper, which enables largescale fabrication
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