Mainz 2026 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 40: Poster – Photonics

Q 40.22: Poster

Wednesday, March 4, 2026, 17:00–19:00, Philo 1. OG

Simulating Surface Roughness Effects on TIR Coupling Losses in Thermally Annealed SLE Structures — •Thilo Danner, Veronica Montoya, Patrick Hildebrand, Yassin Nasr, Andreas Michalowski, and Tobias Menold — Institut für Strahlwerkzeuge (IFSW), Pfaffenwaldring 43, 70569 Stuttgart, Germany

Femtosecond laser-written structures in fused silica offer a versatile platform for integrated photonic devices, leveraging their 3D processing capabilities to enable integrated light handling, including guiding, reflecting, and focusing. Integrated light reflection is achieved via Selective Laser Etching (SLE) on a specific surface, where light is reflected through total internal reflection (TIR). Unfortunately, the SLE process inherently yields a rough surface, introducing scattering losses that degrade performance and cause unwanted mode distortion. Thermal annealing is a common method of reducing surface roughness. Using experimental roughness data, we simulated the influence of roughness after various annealing times to obtain the resulting coupling losses of a Gaussian beam into a waveguide. Various design parameters are simulated using electromagnetic solvers, specifically the Finite-Difference Time-Domain (FDTD) and Finite Difference Eigenmode (FDE) methods, to evaluate how much annealing is required to approach the surface quality demanded for low-loss coupling.

Keywords: Femtosecond-laser writing; Photonic integrated circuits; FDTD Simulation; Fused silica