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Fabrication and Characterization of High-Q Silicon Nitride Membrane Resonators
Published on: August 8, 2025
Embedded metallic focus grating for silicon nitride waveguide with enhanced coupling and directive radiation
Lingyun Wang1, Youmin Wang, Xiaojing Zhang
1Department of Electrical and Computer Engineering, University of Texas at Austin, 2501 Speedway, Austin, Texas 78712, USA.
Optics Express
|October 6, 2012
Summary
Researchers developed a compact metallic elliptical grating coupler for efficient free space to silicon nitride waveguide coupling. This device offers high directivity and transmission efficiency, enhancing biosensor applications.
Area of Science:
- Photonics and Nanotechnology
- Optoelectronics
- Integrated Optics
Background:
- Efficiently coupling light between free space and integrated photonic circuits is crucial for advanced optical systems.
- Existing grating couplers often face limitations in directivity and efficiency, hindering device performance.
- Silicon nitride (SiN) waveguides offer low propagation loss and a broad transparency window, making them suitable for various photonic applications.
Purpose of the Study:
- To design and demonstrate a compact, embedded metallic elliptical focus grating coupler.
- To achieve efficient free space to silicon nitride waveguide coupling at 632.8 nm wavelength.
- To enhance performance metrics such as directivity, gain, and transmission efficiency compared to traditional etched gratings.
Main Methods:
- Design of a metallic elliptical focus grating coupler using gold or silver.
- Simulation and analysis of the 3D far-field radiation pattern.
- Characterization of free space transmission efficiency and diffraction angles.
- Evaluation of potential applications in fluorescence signal detection and biosensing.
Main Results:
- The proposed grating coupler exhibits significantly higher gain and directivity for free space coupling compared to etched gratings.
- A free space transmission efficiency of up to 65% was achieved with the silver grating coupler.
- The device enables isolation of the peak diffraction angle at 10°, enhancing fluorescence signal detection for Cy-5 fluorophores.
- Demonstrated potential for dense system integration in sub-wavelength light processing and near-field fluorescent biosensors.
Conclusions:
- The compact embedded metallic elliptical focus grating coupler provides superior performance for free space to waveguide interfacing.
- The high directivity and coupling efficiency make it suitable for advanced photonic applications, including biosensing.
- This technology facilitates the integration of on-chip optical circuits with far-field detection systems.
