Type of Document Dissertation Author Huang, Yin Author's Email Address email@example.com URN etd-11122012-124413 Title Plasmonic Devices for Manipulating Light at the Nanoscale: Slow-light Waveguides and Compact Couplers Degree Doctor of Philosophy (Ph.D.) Department Electrical & Computer Engineering Advisory Committee
Advisor Name Title Veronis, Georgios Committee Chair Daniels-Race, Theda Committee Member Dowling, Jonathan Committee Member Lee, Hwang Committee Member Rose, Kenneth Dean's Representative Keywords
- compact couplers
- slow light waveguides
Date of Defense 2012-10-30 Availability unrestricted AbstractIn this dissertation, I explore new plasmonic structures and devices for manipulating light at the nanoscale: slow-light waveguides and compact couplers. I ﬁrst introduce a plasmonic waveguide system, based on a plasmonic analogue of electromagnetically induced transparency (EIT), which supports a subwavelength slow-light mode, and exhibits a small group velocity dispersion. The system consists of a periodic array of two metal-dielectric-metal (MDM) stub resonators side-coupled to a MDM waveguide. Decreasing the frequency spacing between the two resonances increases the slowdown factor and decreases the bandwidth of the slow-light band.
I also show that there is a trade-oﬀ between the slowdown factor and the propagation length of the slow-light mode. I next consider Mach-Zehnder interferometer (MZI) sensors in which the sensing arm consists of a slow-light waveguide based on a plasmonic analogue of EIT. I show that a MZI sensor using such a waveguide leads to approximately an order of magnitude enhancement in the refractive index sensitivity, and therefore in the minimum detectable refractive index change, compared to a MZI sensor using a conventional MDM waveguide.
I also introduce compact wavelength-scale slit-based structures for coupling free space light into MDM subwavelength plasmonic waveguides. I ﬁrst show that for a single slit structure the coupling eﬃciency is limited by a trade-oﬀ between the light power coupled into the slit, and the transmission of the slit-MDM waveguide junction. I next consider a two-section slit structure, and show that for such a structure the upper slit section enhances the coupling of the incident light into the lower slit section. The optimized two-section slit structure results in бн 2.3 times enhancement of the coupling into the MDM plasmonic waveguide compared to the optimized single-slit structure. I ﬁnally consider a symmetric double-slit structure, and show that for such a structure the surface plasmons excited at the metal-air interfaces are partially coupled into the slits. Thus, the coupling of the incident light into the slits is greatly enhanced, and the optimized double-slit structure results in бн 3.3 times coupling enhancement compared to the optimized single-slit structure. In all cases the coupler response is broadband.
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