Cutoff-cladding waveguides: Subdiffraction guided modes near cutoff

TL;DR

This paper introduces cutoff-cladding waveguides that confine light below the diffraction limit by operating near cutoff, with energy mainly in the cladding, enabling applications in optoelectronic integration and uniform emission enhancement.

Contribution

The paper presents a novel waveguide design with subdiffraction confinement near cutoff, using uniaxial birefringent cladding to achieve slow divergence of modal length.

Findings

Effective modal length diverges slowly for thin cores

Mode confinement is comparable to plasmonic waveguides

Potential for uniform spontaneous emission enhancement

Abstract

We propose a class of waveguides operating near cutoff such that electromagnetic energy is mainly bound to the cladding rather than the dielectric core to achieve subdiffraction confinement of light. The cladding incorporates an alternating stack of thin films that exhibit uniaxial form birefringence with a high contrast between the effective principal dielectric constants. In contrast to conventional dielectric waveguides, the effective modal length for the fundamental mode of the proposed waveguide diverges at a much slower rate for core thicknesses less than a twentieth of the illumination wavelength, and is comparable to that attainable for plasmonic waveguides. The proposed waveguide can be exploited for important applications such as optoelectronic integration, and the fundamental mode exhibits a near-uniform spatial field distribution potentially allowing for position-independent spontaneous emission enhancement effects.