研究目的
To reduce back reflection in grating couplers on silicon-on-insulator platforms by using a λ/4 offset at grating sub-teeth, improving performance for optical communication and sensing applications.
研究成果
The proposed grating coupler with λ/4 offset at sub-teeth effectively suppresses back reflection from ?12 dB to below ?25 dB, reducing spectral fluctuations in devices like ring resonators. This makes resonance wavelengths more distinguishable, beneficial for sensing applications. Future work could focus on optimizing coupling efficiency and fabrication precision.
研究不足
The fabrication process is imperfect, leading to slight deviations in offset and duty cycle from designed values. There is an extra loss of about 1 dB due to the λ/4 offset, and coupling efficiency could be further improved with methods like apodization.
1：Experimental Design and Method Selection:
The study uses a focusing grating coupler design with each grating tooth divided into multiple sub-teeth with a λ/4 offset to induce destructive interference of reflected light, reducing back reflection. 3D-FDTD simulations are employed for design and analysis.
2：Sample Selection and Data Sources:
SOI wafers with a 250 nm thick top silicon layer and 3 μm thick buried oxide layer are used. Samples include straight waveguides and add-drop ring resonators fabricated with the proposed grating couplers.
3：List of Experimental Equipment and Materials:
Equipment includes e-beam lithography system, RIE-ICP etcher, STS-PECVD for deposition, tunable laser source (Agilent 81600B), polarization controller, power sensor (Agilent 81635A), and single-mode fibers. Materials include photoresist ma-N-2403, SF6 and C4F8 gases for etching, H2SO4 and H2O2 for cleaning, and silicon dioxide for cladding.
4：Experimental Procedures and Operational Workflow:
Fabrication involves cleaning SOI chip, spin-coating photoresist, e-beam lithography for patterning, development, RIE-ICP etching, photoresist removal, and PECVD deposition of silicon dioxide. Characterization involves coupling light from tunable laser through fibers to the grating couplers, adjusting polarization, and measuring transmission spectra and back reflection levels.
5：Data Analysis Methods:
Data is analyzed using simulations (3D-FDTD) and experimental measurements to calculate back reflection levels, coupling efficiencies, and spectral responses, with comparisons to conventional designs.
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tunable laser source
81600B
Agilent
Provides tunable laser light for coupling into the optical fibers and waveguides during characterization.
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power sensor
81635A
Agilent
Measures the optical power output from the waveguides after coupling.
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photoresist
ma-N-2403
Used in the e-beam lithography process for patterning the grating couplers.
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RIE-ICP etcher
Used for etching the silicon layer with a mixture of SF6 and C4F8 gases.
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STS-PECVD
Deposits a layer of silicon dioxide as the upper cladding on the SOI chip.
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single-mode fiber
Used to couple light into and out of the waveguides, placed at a 10° angle to the grating surface.
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polarization controller
Adjusts the polarization of the input light to achieve maximal power coupling.
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