Tapering of fs Laser-written Waveguides

TL;DR

This paper presents tapered waveguide structures created by femtosecond laser writing that significantly improve coupling efficiency to standard fibers, advancing integrated quantum photonic device scalability.

Contribution

Introduction of tapered waveguides via femtosecond laser writing that enhance fiber coupling efficiency with minimal fabrication effort.

Findings

Coupling efficiency increased up to 77%.

Tapered waveguides maintain low fabrication complexity.

Enhancement supports multi-photon quantum state processing.

Abstract

The vast development of integrated quantum photonic technology enables the implementation of compact and stable interferometric networks. In particular laser-written waveguide structures allow for complex 3D-circuits and polarization-encoded qubit manipulation. However, the main limitation for the scale-up of integrated quantum devices is the single-photon loss due to mode-profile mismatch when coupling to standard fibers or other optical platforms. Here we demonstrate tapered waveguide structures, realized by an adapted femtosecond laser writing technique. We show that coupling to standard single-mode fibers can be enhanced up to 77% while keeping the fabrication effort negligible. This improvement provides an important step for processing multi-photon states on chip.