Nanowire waveguide made from extremely anisotropic metamaterials

TL;DR

This paper derives exact solutions for wave modes in an extremely anisotropic cylindrical nanowire waveguide, revealing unique propagation characteristics including backward waves and zero group velocity modes, with potential applications in photonic devices.

Contribution

It provides closed-form solutions for all modes in anisotropic waveguides and characterizes their unique propagation behaviors, especially for extremely anisotropic materials.

Findings

Only TM and hybrid modes propagate in the extremely anisotropic waveguide.

Most TM modes are backward waves with large effective indices.

Zero group velocity modes occur at a critical radius, enabling light trapping.

Abstract

Exact solutions are obtained for all the modes of wave propagation along an anisotropic cylindrical waveguide. Closed-form expressions for the energy flow on the waveguide are also derived. For extremely anisotropic waveguide where the transverse permittivity is negative while the longitudinal permittivity is positive, only transverse magnetic (TM) and hybrid modes will propagate on the waveguide. At any given frequency the waveguide supports an infinite number of eigenmodes. Among the TM modes, at most only one mode is forward wave. The rest of them are backward waves which can have very large effective index. At a critical radius, the waveguide supports degenerate forward- and backward-wave modes with zero group velocity. These waveguides can be used as phase shifters and filters, and as optical buffers to slow down and trap light.