Doctor of Philosophy (PhD)
Electrical and Computer Engineering
In 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 ¡ 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 ¡ 3.3 times coupling enhancement compared to the optimized single-slit structure. In all cases the coupler response is broadband.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Huang, Yin, "Plasmonic devices for manipulating light at the nanoscale: slow-light waveguides and compact couplers" (2012). LSU Doctoral Dissertations. 1341.