Nearly perfect routing of chiral light by plasmonic grating on slab waveguide

TL;DR

This paper demonstrates a plasmonic grating on a silicon nitride waveguide that efficiently couples circularly polarized light to specific waveguide modes, enabling advanced polarization control and routing functionalities.

Contribution

It introduces a novel plasmonic grating design that achieves high-efficiency coupling of circularly polarized light to waveguide modes with controllable directionality.

Findings

Coupling efficiency up to 95% for normally incident light.

Achieves up to 97% circular polarization degree in outcoupled light.

Enables polarization-division multiplexing and integrated polarization devices.

Abstract

Grating couplers are widely used to couple waveguide modes with the far field. Their usefulness is determined not only by energy efficiency but also by additional supported functionality. In this paper, we demonstrate a plasmonic grating on a silicon nitride slab waveguide that couples both TE and TM waveguide modes with circularly polarized light in the far field. Specifically, we experimentally confirmed that circularly polarized light excites TE and TM modes propagating in opposite directions, and the direction is controlled by the handedness. The routing efficiency for normally incident light reaches up to 95%. The same structure operates in the outcoupling regime as well, demonstrating up to 97% degree of circular polarization, where the handedness is determined by the polarization and propagation direction of outcoupled modes. Our results pave the way for the realization of polarization-division multiplexers and demultiplexers, integrated circular polarization emitters, as well as detectors of the polarization state of the incident optical field.