Octave bandwidth 3D-Printed Couplers for Low-Loss Thin-Film Lithium Tantalate Circuits

Erik Jung; Xinyu Ma; Jan Brandes; Caghan Ünlüer; Shabnam Taheriniya; Seongmin Jo; Philipp Schmidt; Eric Biedert; Liam McRae; Julian Rasmus Bankwitz; Frank Brückerhoff-Plückelmann; Wolfram Pernice

arXiv · 2606.16398

Octave bandwidth 3D-Printed Couplers for Low-Loss Thin-Film Lithium Tantalate Circuits

Erik Jung·Xinyu Ma·Jan Brandes·Caghan Ünlüer·Shabnam Taheriniya·Seongmin Jo·Philipp Schmidt·Eric Biedert·Liam McRae·Julian Rasmus Bankwitz·Frank Brückerhoff-Plückelmann·Wolfram Pernice

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Abstract

Low-loss, broadband photonic integrated circuits (PICs) are critical enablers for optical communications, photonic computing, and quantum applications. Lithium tantalate on insulator (LTOI) is an emerging photonic platform offering a wide transparency window and strong Pockels effect, and thereby enabling efficient electro-optic modulation and high data rates. Here, we present the first implementation of efficient out-of-plane polymer coupling interfaces fabricated via 3D direct laser writing for both fully etched strip and partially etched rib LTOI waveguides, achieving ultra-low coupling losses of 0.9 dB (strip) and 1.25 dB (rib) per interface. Both coupler types exhibit a 3 dB optical bandwidth spanning more than an octave from 850 nm to 1740 nm and maintain stable operation under 1 W optical input power. Combined with on-chip waveguides exhibiting propagation losses below 0.1 dB/cm, these characteristics represent a key step toward unlocking the full potential of LTOI for high-speed optical signal processing with an unprecedented degree of parallelism. In addition, the octave-spanning bandwidth enables efficient interfacing of both the fundamental and second-harmonic signals, making the platform highly attractive for second harmonic generation based quantum squeezing applications.

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Erik Jung, Xinyu Ma, Jan Brandes, Caghan Ünlüer, Shabnam Taheriniya, Seongmin Jo, Philipp Schmidt, Eric Biedert, Liam McRae, Julian Rasmus Bankwitz, Frank Brückerhoff-Plückelmann, Wolfram Pernice. 2026-06-15. Octave bandwidth 3D-Printed Couplers for Low-Loss Thin-Film Lithium Tantalate Circuits. https://arxiv.org/abs/2606.16398

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