Remote lensless focusing of a light beam

TL;DR

This paper demonstrates remote, lensless focusing of light in a graded-index medium using mode interference, achieving super-resolution hot-spots and far-field imaging without evanescent waves, with potential applications in optical detection.

Contribution

It provides an exact analytical solution showing how to achieve long-distance, high-efficiency, subwavelength focusing and super-resolution imaging in graded-index waveguides.

Findings

Strong focusing occurs at long distances with periodic revivals.

Super-oscillatory hot-spots beyond diffraction limit are observed.

High-efficiency transfer of focused spots over large distances is demonstrated.

Abstract

Remote focusing of light in a graded-index medium via mode interference is demonstrated using exact analytical solutions of the wave equation. Strong focusing of light occurs at extremely long distances and it revivals periodically with distance due to mode interference. High efficiency transfer of a strongly focused subwavelength spot through optical waveguide over large distances takes place with a period of revival. Super-oscillatory hot-spots with the sizes which are beyond the conventional Abbe diffraction limit can be observed at large distances from the source. This can provide the possibility to detect optical super-resolution information in the far-field without any evanescent waves. Far-field super-resolution imaging capabilities of a graded-index waveguide are also analyzed.