研究目的
To investigate the feasibility of using multimode Bragg gratings for refractive index sensing applications by experimentally characterizing their sensitivities and comparing them to single mode devices.
研究成果
Multimode Bragg gratings show lower sensitivity than single-mode devices, with the highest sensitivity of 120 nm/RIU achieved for single-mode TM polarization. However, multimode gratings have potential for mode multiplexing applications, enabling higher data transfer and more complex sensing experiments through mode conversion.
研究不足
The sensitivity of multimode devices is lower compared to single-mode counterparts due to reduced evanescent field extension with higher order modes. The study is limited to specific device geometries and materials, and no additional cladding was used, which might affect performance in other environments.
1：Experimental Design and Method Selection:
The study involves designing and fabricating various Bragg gratings on a Silicon-On-Insulator (SOI) platform, including single-mode and multimode configurations, to assess their sensitivity to refractive index changes. Theoretical models based on phase matching conditions are used for design.
2：Sample Selection and Data Sources:
Devices are fabricated on SOI wafers with specific dimensions (e.g., 250 nm thick Silicon layer, 2 μm buried SiO2). Liquids with different refractive indices (1.333, 1.342, 1.351, 1.360) are used as cladding for sensitivity testing.
3：2). Liquids with different refractive indices (333, 342, 351, 360) are used as cladding for sensitivity testing. List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: SOI wafer, Electron-Beam Lithography system, positive resist ZEP520-A, ICP-RIE with SF6 gas, tunable laser (1440 nm – 1640 nm range), alignment stages, single-mode fiber, polarization controller, photo diode, microfluidic channel made of soft silicon resin.
4：Experimental Procedures and Operational Workflow:
Fabrication involves E-beam lithography and etching. Experimental setup includes coupling light via diffraction grating couplers, controlling polarization, and measuring transmitted spectrum with a photo diode. Devices are exposed to liquids, and wavelength shifts are measured.
5：Data Analysis Methods:
Transmission spectra are normalized using a straight waveguide. Sensitivity is calculated from Bragg wavelength shifts with varying refractive indices.
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Electron-Beam Lithography system
Used for patterning the devices on the SOI wafer during fabrication.
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ICP-RIE
Used for etching the silicon with SF6 gas to create smooth sidewalls.
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tunable laser
Provides light source with a wavelength range of 1440 nm to 1640 nm for experimental characterization.
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photo diode
Detects the power of transmitted light for spectrum measurement.
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polarization controller
Selects TE or TM polarization for the input light.
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microfluidic channel
Made of soft silicon resin to expose devices to liquids without immersing grating couplers.
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SOI wafer
Substrate for device fabrication, with 250 nm thick Silicon layer and 2 μm buried SiO2.
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positive resist
ZEP520-A
Used in Electron-Beam Lithography for patterning.
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