(3+1)D Printing of Low-Loss Core-Clad Waveguide by Two-Photon Polymerization

Three-dimensional printing using two-photon polymerization (TPP), is nowadays a powerful technique for the fabrication of photonic components including optical waveguides. Numerous publications have demonstrated 3D printing of clad-less guiding structures in polymer materials [1], [2]. These waveguides, printed in a single step, result from a simple manufacturing method that has enabled advances and breakthroughs for the production of photonic integrated circuits (PICs). However, these waveguides have inherent losses related to the printing process, such losses predominantly resulting from scattering. A major cause of scattering losses arises from the surface roughness of the waveguide, which is detrimental to the quality of printed components by 3D TPP. In the case of femtosecond laser inscription in bulk glasses, the multi-laser-pass approach has already shown to homogenize the waveguide structure and thus to reduce the associated losses [3]. However, in 3D printing, few studies have referred yet on the multipass approach for the single-step direct printing of photonic structures. To produce coreclad waveguides, it is necessary to tune locally the index variation within the printed object. Recently, the ability to modify the laser power during the printing process has been demonstrated, referenced as (3+1)D multiphoton printing, leading to the realization of core-cladding waveguides and −6.2 dB.mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> losses [4].