Mainz 2026 – wissenschaftliches Programm

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Q: Fachverband Quantenoptik und Photonik

Q 40: Poster – Photonics

Q 40.21: Poster

Mittwoch, 4. März 2026, 17:00–19:00, Philo 1. OG

Simulations of inverse taper structures for efficient edge coupling in TFLN — •Micha Jonas, Filip Sosnicki, Laura Padberg, Harald Herrmann, and Christine Silberhorn — Paderborn University, Integrated Quantum Optics, Institute for Photonic Quantum Systems (PhoQS), Warburger Str. 100, 33098 Paderborn, Germany

Thin-film lithium niobate (TFLN) emerges as a promising platform for photonic integrated circuits due to notably electro-optic and nonlinear properties. It makes it particularly suitable for quantum photonics where one can apply frequency-mixing schemes or electro-optic modulation to single-photon pulses. Such applications require low losses within a broad spectral bandwidth. Currently, in- and out-coupling efficiencies are fundamental limitations due to the mode-mismatch of waveguide eigenmodes (MFD ca. 1µ m) and fiber mode (MFD ca. 10µ m). Here we investigate inverse tapers that enlarge the optical mode at the waveguide facet to match it to the fiber mode increasing coupling efficiency. We perform numerical simulations of taper structures in TFLN to optimize fiber in- and out-coupling of a waveguide. For this purpose, we use Eigenmode Expansion (EME) to calculate the optical mode distribution at the end of the taper while varying its dimensions, compatible with TFLN chip fabrication tolerances. We investigate impact of the inverse taper on the edge-coupling efficiency for various in-coupling optical beam dimensions as well as possible alignment tolerances and their spectral bandwidth. Our work will enable low-loss coupling into TFLN photonic integrated circuits paving the way for on-chip quantum photonics.

Keywords: Thin-film lithium niobate; edge coupling; inverse taper structures; Simulations