Abstract
The limited resolution of a conventional optical imaging system stems from the fact that the fine feature information of an object is carried by evanescent waves, which exponentially decays in space and thus cannot reach the imaging plane. We introduce here an adiabatic lens, which utilizes a geometrically conformal surface to mediate the interference of slowly decompressed electromagnetic waves at far field to form images. The decompression is satisfying an adiabatic condition, and by bridging the gap between far field and near field, it allows far-field optical systems to project an image of the near-field features directly. Using these designs, we demonstrated the magnification can be up to 20 times and it is possible to achieve sub-50 nm imaging resolution in visible. Our approach provides a means to extend the domain of geometrical optics to a deep sub-wavelength scale.
Highlights
The limited resolution of a conventional optical imaging system stems from the fact that the fine feature information of an object is carried by evanescent waves, which exponentially decays in space and cannot reach the imaging plane
As the surface plasmon waves originated from an object in the gap region propagate along the curved interface, from the gap to the upper hemisphere, they experience adiabatic decompression; the effective wavelength continuously increases from single nanometres in the gap region to the vacuum wavelength of hundreds of nanometres
A possible method to further circumvent this limit could be by using active materials that uses gain media to compensate the loss[20,21,22,23,24]. Transformation optics provides another angle to understand the origin of the super-resolution in this adiabatic lens[25,26]
Summary
The limited resolution of a conventional optical imaging system stems from the fact that the fine feature information of an object is carried by evanescent waves, which exponentially decays in space and cannot reach the imaging plane. The decompression is satisfying an adiabatic condition, and by bridging the gap between far field and near field, it allows far-field optical systems to project an image of the near-field features directly Using these designs, we demonstrated the magnification can be up to 20 times and it is possible to achieve sub-50 nm imaging resolution in visible. Adiabatic concentration of plasmon polaritions has been proposed and demonstrated in tapered plasmonic wave guides, which utilize the proximity effects of a second surface near the plasmon-guiding interface to stop light and asymptotically compress the wavelength to near zero[2,3,6,8,15] None of these schemes lends itself to imaging applications. Notice that the required slow variation of the effective index implies that the plasmonic structures considered here must be large in terms of wavelengths, as opposed to other systems[5], which are sub-wavelength and described electrostatically
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