Femtosecond laser written low-loss multiscan waveguides in fused silica

TL;DR

This paper presents a femtosecond laser writing technique to create low-loss, high-quality waveguides in fused silica, achieving high mode overlap and low propagation and coupling losses suitable for advanced photonic applications.

Contribution

It introduces a multiscan laser writing method that optimizes waveguide fabrication in fused silica, significantly reducing losses and improving coupling efficiency for integrated photonics.

Findings

Mode overlap with standard fiber exceeds 98.8%

Coupling losses are as low as 0.2 dB/facet

Propagation losses are 0.07 dB/cm

Abstract

We report low-loss multiscan waveguides fabricated in fused silica using femtosecond laser writing technology. The multiscan principle allows to tailor the writing regime to excel at key features of any integrated photonic platform: coupling losses and propagation losses. We optimized the writing parameters for different sizes of square-shaped waveguides and reached the mode overlap value with a standard single-mode optical fiber of above 98.8\% and demonstrated very low coupling losses of 0.2 dB/facet on average. Propagation losses in the fabricated waveguides amounted to 0.07 dB/cm. We applied the developed recipe to the fabrication of a fiber-coupled 25-channel interferometer with total insertion losses below 1 dB. The findings of this work are of interest for broad range of applications and in particular for optical information processing and quantum photonics.