Embedded silicon gratings for high-efficiency light-chip coupling to thin film silicon nitride waveguides

Rawat, P and Nambiar, S and Venkatachalam, P and Singh, R and Selvaraja, SK (2023) Embedded silicon gratings for high-efficiency light-chip coupling to thin film silicon nitride waveguides. In: Optics Express, 31 (18). pp. 29392-29402.

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Abstract

Thin film silicon nitride (<150 nm) waveguide has emerged as a dominant ultra-low-loss platform for many loss-critical applications. While thin-film silicon nitride propagation loss is a crucial characteristic, coupling light between an optical fiber and the waveguide is still challenging. While the larger mode size of the decoupled thin waveguide offers better coupling than a highly-confined waveguide, the coupling e�ciency is still sub-optimal. The poor diffraction e�ciency of such thin films limits the scope of implementing standalone surface gratings. We demonstrate an e�cient way to couple into thin film silicon nitride waveguides using amorphous silicon strip gratings. The high contrast gratings provide an e�cient means to boost the directionality from thin films leading to an enhanced coupling performance. In addition, we incorporate a bottom reflector to further improve the coupling. We present an optimal design for uniform strip gratings with a maximum coupling e�ciency of -1.7 dB/coupler. We achieved a maximum coupling e�ciency of -0.28 dB/coupler by engineering the scattering strength along the grating through apodization. We have experimentally shown the highest coupling e�ciency reported yet of -2.22 dB/coupler and -1.84 dB/coupler for uniform and apodized grating couplers in the C-L band. We present a detailed design strategy, simulation, fabrication and characterization data on the effect of various parameters on the coupling e�ciency. © 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement.

Item Type:	Journal Article
Publication:	Optics Express
Publisher:	Optica Publishing Group (formerly OSA)
Additional Information:	The copyright for this article belongs to authors.
Keywords:	Diffraction gratings; Optical fiber fabrication; Optical fibers; Silicon nitride; Waveguides, Chip coupling; Coupling efficiency; Critical applications; Higher efficiency; Low-loss; Propagation loss; Silicon gratings; Silicon nitride waveguides; Strip grating; Thin-films, Thin films
Department/Centre:	Division of Interdisciplinary Sciences > Centre for Nano Science and Engineering
Date Deposited:	14 Dec 2024 20:00
Last Modified:	14 Dec 2024 20:00
URI:	http://eprints.iisc.ac.in/id/eprint/85511

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