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High-efficiency grating couplers for vertical coupling in thin-film silicon nitride technology
Francesca di Croce1, Valerio Vitali2,3, Thalía Domínguez Bucio4
1Electrical, Computer and Biomedical Engineering Department, University of Pavia, Pavia, 27100, Italy. francesca.dicroce01@universitadipavia.it.
Scientific Reports
|April 20, 2026
Summary
Researchers developed a novel grating coupler for silicon nitride photonics. This device achieves efficient fiber-to-chip coupling, overcoming previous limitations in thin-film platforms.
Area of Science:
- Integrated Photonics
- Materials Science
- Nanotechnology
Background:
- Silicon nitride (SiN) is a key material in integrated photonics due to its low propagation loss.
- Thin-film SiN platforms offer advantages but face challenges in efficient grating coupler realization.
- Poor grating scattering strength hinders efficient light coupling in SiN waveguides.
Purpose of the Study:
- To propose and experimentally demonstrate an efficient grating coupler for thin-film silicon nitride waveguides.
- To achieve perfectly-vertical fiber-to-chip coupling.
- To overcome fabrication challenges associated with existing grating coupler designs.
Main Methods:
- Fabrication of a silicon-rich silicon nitride apodized grating coupler.
- Integration with a 150 nm-thick silicon nitride waveguide.
- Experimental characterization of coupling efficiency at 1550 nm.
Main Results:
- A record coupling efficiency of -1.78 dB was achieved at 1550 nm.
- The device demonstrated efficient coupling without back-reflectors or index-matching fluid.
- The silicon-rich SiN grating offers improved fabrication tolerances compared to amorphous silicon layers.
Conclusions:
- The proposed grating coupler design is highly effective for thin-film silicon nitride photonics.
- This advancement enables efficient and fabrication-tolerant fiber-to-chip coupling.
- The use of silicon-rich SiN provides design flexibility and enhances performance.
