High-efficiency waveguide couplers via impedance-tunable transformation optics

TL;DR

This paper presents a method for designing highly efficient, compact waveguide couplers using impedance-tunable transformation optics, enabling reduced-parameter materials and near-perfect coupling efficiency.

Contribution

It introduces impedance-tunable transformation optics for waveguide couplers, allowing reduced-parameter materials and high efficiency in coupling different waveguides.

Findings

Near 100% efficiency in metallic waveguide couplers

Reduced-parameter transformation media are achievable

Numerical simulations confirm high performance

Abstract

We design compact waveguide couplers via impedance-tunable transformation optics. By tuning impedance coefficients in the original space, two-dimensional metallic and dielectric waveguide couplers are designed with a high efficiency. Through tuning refractive index simultaneously, we find that the transformation medium inside a designed metallic waveguide coupler can be a reduced-parameter material for coupling waves between waveguides with arbitrary different cross sections and embedded media. In the design of dielectric waveguide couplers, we apply two different schemes: one is that both core region and its cladding region are contained in a transformed space, the other is only core region contained in the transformed space. The former has a very high efficiency near 100%; the latter is less efficient with a very small decline which can be a simplified candidate in the design of near-perfect dielectric waveguide couplers. The transformation medium for dielectric waveguide couplers can also be reduced-parameter material by selecting appropriate refractive index coefficients. Two-dimensional numerical simulations confirm our design with good performances.