Slow light, open cavity formation, and large longitudinal electric field on slab waveguide made of indefinite permittivity materials

TL;DR

This paper explores the unique optical properties of slab waveguides made from indefinite permittivity materials, revealing phenomena like slow light, open cavity formation, and large longitudinal electric fields, with potential applications in optical buffering and integrated circuits.

Contribution

It introduces the analysis of indefinite permittivity material waveguides, highlighting their support for diverse TM modes and potential for novel optical device functionalities.

Findings

Support for infinite TM modes with diverse phase indices

Existence of a critical thickness for mode degeneracy and zero group velocity

Potential for slow light, open cavities, and enhanced longitudinal electric fields

Abstract

The optical properties of slab waveguides made of indefinite permittivity ($\vep$) materials (IEM) are considered. In this medium the transverse permittivity is negative while the longitudinal permittivity is positive. At any given frequency the waveguide supports an infinite number of transverse magnetic (TM) eigenmodes. For a slab waveguide with a fixed thickness, at most only one TM mode is forward-wave. The rest of them are backward waves which can have very large phase index. At a critical thickness, the waveguide supports degenerate forward- and backward-wave modes with zero group velocity. Above the critical thickness, the waveguide supports complex-conjugate decay modes instead of propagating modes. The presence of loss in IEMs will lift the degeneracy, resulting in modes with finite group velocity. Feasible realization is proposed. The performance of IEM waveguide is analyzed and possible applications are discussed which are supported by numerical calculations. These slab waveguides can be used to make optical delay lines in optical buffers to slow down and trap light, to form open cavities, to generate strong longitudinal electric fields, and as phase shifters in optical integrated circuits.