Double inverse nanotapers for efficient light coupling to integrated photonic devices

TL;DR

This paper introduces double inverse nanotapers that taper both height and width of waveguides, achieving efficient, polarization-independent light coupling suitable for nonlinear photonics and compatible with standard photolithography.

Contribution

The paper presents a novel double inverse taper design that improves coupling efficiency and fabrication practicality over traditional inverse tapers.

Findings

Achieves polarization-independent coupling

Enables larger taper dimensions for easier fabrication

Reduces coupling loss significantly

Abstract

Efficient light coupling into integrated photonic devices is of key importance to a wide variety of applications. "Inverse nanotapers" are widely used, in which the waveguide width is reduced to match an incident mode. Here, we demonstrate novel, "double inverse" tapers, in which we taper both the waveguide height, as well as the width. We demonstrate that in comparison to regular inverse tapers, the double inverse tapers have excellent polarization-independent coupling. In addition, the optimum coupling is achieved with much larger taper dimension, enabling the use of photolithography instead of electron beam lithography, relevant for applications at near-IR and visible wavelengths. The low coupling loss makes them particularly suitable for nonlinear photonics, e.g. supercontinuum and soliton micro-comb generation.