Abstract
Lenses are crucial to light-enabled technologies. Conventional lenses have been perfected to achieve near-diffraction-limited resolution and minimal chromatic aberrations. However, such lenses are bulky and cannot focus light into a hotspot smaller than a half-wavelength of light. Pupil filters, initially suggested by Toraldo di Francia, can overcome the resolution constraints of conventional lenses but are not intrinsically chromatically corrected. Here we report single-element planar lenses that not only deliver sub-wavelength focusing, thus beating the diffraction limit of conventional refractive lenses, but also focus light of different colors into the same hotspot. Using the principle of super-oscillations, we designed and fabricated a range of binary dielectric and metallic lenses for visible and infrared parts of the spectrum that are manufactured on silicon wafers, silica substrates and optical fiber tips. Such low-cost, compact lenses could be useful in mobile devices, data storage, surveillance, robotics, space applications, imaging, manufacturing with light and spatially resolved nonlinear microscopies.
Highlights
Chromatic aberration and the resolution limit are two major challenges for high-performance optical imaging
Near-IR achromatic fiberized amplitude mask SOL A sub-wavelength focusing, near-IR lens on a fiber tip would be valuable in many applications, most notably imaging through silicon wafers and substrates inside silicon chips, diagnostics of optoelectronic devices, high-resolution two-photon-polymerization nano-fabrication, non-destructive imaging of in vitro biomedical samples, microspectrometry of molecular vibrational modes, and an interconnect element of silicon photonic devices
We experimentally demonstrated that chromatic aberration and the optical diffraction limit can be simultaneously overcome using an SOL consisting of a single planar optical element
Summary
Chromatic aberration and the resolution limit are two major challenges for high-performance optical imaging. It results from dispersion of the lens material. Chromatic aberration results from the accumulated wavelength-dependent phase delay of the electromagnetic waves that form the focus. Complex optical elements such as achromatic doublet, triplet and diffractive-refractive hybrid lenses have been built[1,2] with components of opposing dispersion properties[3]. Such lenses are inevitably bulky, which complicates integration. Chromatism remains a key challenge, which has been tackled using dielectric metasurfaces[13,14] and wavelength-independent geometric phases[15] and by exploiting the inherent dispersion in diffractive optics[16]
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