Time-reversing a monochromatic subwavelength optical focus by optical phase conjugation of multiply-scattered light

TL;DR

This paper demonstrates the first experimental realization of subwavelength optical focusing beyond the diffraction limit using far-field time reversal through optical phase conjugation of multiply-scattered light.

Contribution

It introduces a novel method to regenerate a subwavelength focus by phase conjugating scattered light, enabling super-resolution focusing beyond the diffraction limit.

Findings

Successful subwavelength focusing via phase conjugation

First experimental demonstration of far-field time reversal at subwavelength scale

Achieved focus beyond the diffraction limit

Abstract

Due to its time-reversal nature, optical phase conjugation generates a monochromatic light wave which retraces its propagation paths. Here, we demonstrate the regeneration of a subwavelength optical focus by phase conjugation. Monochromatic light from a subwavelength source is scattered by random nanoparticles, and the scattered light is phase conjugated at the far-field region by coupling its wavefront into a single-mode optical reflector using a spatial light modulator. Then the conjugated beam retraces its propagation paths and forms a refocus on the source at the subwavelength scale. This is the first direct experimental realization of subwavelength focusing beyond the diffraction limit with far-field time reversal in the optical domain.