| Summary: | 碩士 === 國立臺灣科技大學 === 電子工程系 === 105 === The optical power splitters are widely utilized in photonic integrated circuits for optical signal transmission, optical switch, wavelength filter, and power monitoring. In this thesis, the novel couplers from MMI (multimode interference) and HPW (hybrid plasmonic waveguide) as well as the surface plasma biosensor, all constructed by the Mach-Zehnder interferometer (MZI), have been proposed, designed, and simulated on a 0.25-µm thick silicon-on-insulator platform. The numerical calculation was carried with the help of the OmniSim based on FDTD (Finite Difference Time Domain) and the FIMMWAVE based on FDM (Finite Difference Method) commercial software.
In this thesis, the S-bend MMI is utilized to adjust the output optical power. The S-bend MMI main function is combining the self-imaging and bend waveguide for mode redistribution to demonstrate a 2x2 broadband optical power splitter with any ratio. A 0.45-μm width and 0.25-μm depth are taken to be operated in the single-mode region of silicon wire for transmission. The multimode conditions of S-bend MMI are 3-μm width, 13.2-μm length, and 38-μm bend radius for the splitting ratio of 0.97±0.015 from 1520 to 1600 nm wavelength. And another 0.76±0.01 ratio comes from 3-μm width, 10.8-μm length, and 31-μm bend radius. Moreover, the S-bend MMI will be used to replace the wavelength sensitive directional coupler (DC) in delayed Mach-Zehnder interferometer (DMZI) wavelength filter for better extinction ratio. Finally a S-bend MMI composed of two bend radii will be theoretically studied for the phase and splitting ratio simultaneously.
Another broadband optical power splitter is the Mach-Zehnder directional coupler (MZDC) based hybrid plasmonic waveguide. Here, the surface plasma interference (SPI) is utilized to replace MZDC decoupled region. Moreover, the input and output bend effect on the splitting ratio will be further illustrated. In addition to the significant size reduction, the SPI splitter can be insensitive to the wavelength range between C and L-bands.
In this thesis, a MZI based silicon wire is utilized as the biological sensors through surface plasmon polaritons. The structure we propose different from the previous publication is the metal surrounding around the waveguide in the sensing area. The optical mode in the sensing region will be converted to the surface plasmon polariton between the silicon and metal. At the end of the surface plasma region, all the modes will interfere with each other to form MZI. The calculation shows that the sensitivity can achieve 2891 nm/Refractive Index Unit (RIU), the sensitivity increase is mainly from two interfered refractive indices of two surface plasma polaritons.
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