Title: Achromatic super-oscillatory lenses with sub-wavelength focusing,
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 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 (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.