Fiber-to-Waveguide and 3D Chip-to-Chip Light Coupling Based on Bent Metal-Clad Waveguides

TL;DR

This paper introduces a novel bent metal-clad waveguide coupler, called 'L-coupler', that efficiently couples light from fibers into on-chip waveguides with over 80% efficiency, enabling compact and 3D chip-to-chip optical interconnections.

Contribution

The paper presents a new L-shaped fiber-to-waveguide coupler using bent metal-clad waveguides, achieving high efficiency and enabling 3D chip-to-chip optical coupling.

Findings

Coupling efficiency exceeds 80% in near-infrared wavelengths.

The coupler is polarization-dependent, with low efficiency for TM waves.

It enables efficient 3D chip-to-chip optical interconnections.

Abstract

Efficient fiber-to-waveguide light coupling has been a key issue in integrated photonics for many years. The main challenge lies in the huge mode mismatch between an optical fiber and a single mode waveguide. Herein, we present a novel fiber-to-waveguide coupler, named "L-coupler", through which the light fed from the top of a chip can bend 90{\deg} with low reflection and is then efficiently coupled into an on-chip Si waveguide within a short propagation distance (<20{\mu}m). The key element is a bent metal-clad waveguide with a big matched input port. According to our finite-difference time-domain (FDTD) simulation, the coupling efficiency is over 80% within a broad range of working wavelengths in the near-infrared regime for a transverse electric input Gaussian wave. The coupler is polarization-dependent, with very low coupling efficiency (6%-9%) for transverse magnetic waves. The coupler can also be used for three-dimensional (3D) chip-to-chip optical interconnection by efficiently coupling light into an integrated photonic chip from a vertical-cavity surface-emitting laser (VCSEL), or Si waveguide on another chip. The work presented in this Arxiv article has been filed as a patent. Detailed description of this work may be published in future papers.