Ultra broadband waveveguide coupler using an anisotropic sub-wavelength metamaterial

TL;DR

This paper presents a novel ultra broadband multimode interference coupler using anisotropic sub-wavelength metamaterials, achieving over 300nm bandwidth in experiments with a device three times shorter than traditional designs.

Contribution

The authors derive a semi-analytic design method for ultra broadband couplers using anisotropic metamaterials, demonstrating the most broadband MMI coupler to date.

Findings

Achieved over 300nm operational bandwidth experimentally.

Device length is three times shorter than conventional counterparts.

Demonstrated near-perfect performance across the bandwidth.

Abstract

Multimode interference couplers are a fundamental building block in many integrated photonic systems, ranging from high-speed coherent receivers to quantum splitters. However, their basic structure has remained fundamentally unchanged for almost four decades, limiting their size and operation bandwidth. Using sub-wavelength metamaterials, photonic devices with break-through size and performance have been recently reported. Leveraging the inherent anisotropy of these structures, here we derive a semi-analytic expression that enables the design of compact and ultra broadband multimode interference couplers. We experimentally demonstrate virtually perfect operation over a bandwidth in excess of 300nm (500nm in simulation), for a device three times shorter than its conventional counterpart, making this the most broadband multimode interference coupler reported to date. These results will enable ultra broadband integrated systems for applications in communications and sensing.