Strong Amplitude and Phase Modulation of Optical Spatial Coherence with Surface Plasmon Polaritons

TL;DR

This paper demonstrates how surface plasmon polaritons can be used to precisely control the spatial coherence of light at the micrometer scale, enabling dynamic modulation from incoherent to highly coherent states.

Contribution

It introduces a novel method to modulate optical spatial coherence using surface plasmon polaritons, surpassing traditional approaches in flexibility and tunability.

Findings

Achieved continuous modulation of spatial coherence from 0% to 80%.

Transformed incoherent light into highly coherent light.

Enabled control of coherence by varying slit separation.

Abstract

The degree of optical spatial coherence -a fundamental property of light that describes the mutual correlations between fluctuating electromagnetic fields- has proven challenging to control at the micrometer scale. Here we employ surface plasmon polaritons -evanescent waves excited on both surfaces of a thin metal film- as a means to entangle the random fluctuations of the incident electromagnetic fields at the slit locations of a Young's double-slit interferometer. Strong tunability of the complex degree of spatial coherence of light is achieved by finely varying the separation distance between the two slits. Continuous modulation of the degree of spatial coherence with amplitudes ranging from 0% up to 80% allows us to transform totally incoherent incident light into highly coherent light, and vice versa. These findings pave the way for alternative methods to engineer flat optical elements with multi-functional capabilities beyond conventional refractive- and diffractive-based photonic metasurfaces.