Characterization of Si₃N₄ Grating Couplers for Trapped Ion Applications

¹ Physikalisch-Technische Bundesanstalt, Bundesallee 100, Braunschweig, 38116, Germany
² Technische Universität Braunschweig, Institute of Semiconductor Technology, Hans-Sommer-Str. 66, Braunschweig, 38106, Germany
³ Laboratory for Emerging Nanometrology (LENA), Langer Kamp 6a/b, Braunschweig, 38106, Germany
⁴ AMO GmbH, Otto-Blumenthal-Straße 25, 52074 Aachen, Germany
⁵ Chair of Electronic Devices, RWTH Aachen University, Otto-Blumenthal Str. 25, Aachen 52074, Germany
⁶ Leibniz Universität Hannover, Institut für Quantenoptik, Welfengarten 1, Hannover, 30167, Germany
⁷ Leibniz Universität Hannover, Laboratorium für Nanound Quantenengineering, Welfengarten 1, Hannover, 30167, Germany

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Published online: 22 September 2025

Abstract

Integrating grating outcouplers into ion traps offers a promising approach for efficient optical addressing of trapped ions. However, most existing implementations utilize only transverse-electric (TE) mode grating outcouplers, where the emitted light is polarized in the plane of the chip. This restriction imposes constraints on beam geometry and limits the placement flexibility of grating couplers within the ion trap architecture. In this work, we present the characterization of a Si₃N₄ grating coupler with TE and transverse-magnetic (TM) modes. The grating enables efficient outcoupling for both polarizations, albeit with different emission angles. Integrating TM-mode grating couplers into ion traps expands polarization control by enabling out-of-plane polarization, allowing for more flexible waveguide routing and grating placement, and thereby relaxing constraints on beam geometry design. This polarization demultiplexing also allows for new functionality by allowing interacting with the same ion using different polarizations by shuttling it between beam spots.