Linear and nonlinear infrared optical properties of subwavelength coaxial metallic arrays.

摘要

The objective of this work is to explore the linear and nonlinear optical properties of metallic annular coaxial arrays and elucidate the physical origin of enhanced transmission and its applicability. A single step interferometric lithography patterning technique and self-aligned processing are used to make large area metallic coaxial arrays on different substrate materials.; We report the first experimental demonstration of the enhanced transmission through such arrays, which is the result of unit coax cell supporting attenuated guided coax mode---TE11 coaxial mode. Polarization and angle-dependent transmission measurements clearly demonstrate the coupling between this localized mode and delocalized surface plasmon modes associated with the metal film and the periodicity of the array. A generalized, multiple discrete states Fano lineshape analysis provides a good fit to the experimental results. Detailed study is done theoretically and experimentally to better understand the physical origin of transmission spectra. By proper design of coaxial array parameters, 5x improvement peak transmission is realized on coaxial array compared to a hole array on a GaAs substrate with the same fractional opening area percentage.; By adding the nonlinear material inside the gap area of the coax unit cell, we demonstrate an important application of the metallic coax array---second harmonic generation (SHG) on isotropic crystalline material (GaAs), where phase matching is not required due to the nanoscale interaction length infrared wavelength. We show that the enhanced field intensity in the coax cell is responsible for the non-linear interaction. This is the first study to utilize a dipole-allowed nonlinear material in the active region, rather than using quadrupole of higher-order surface nonlinear effects. The second harmonic signal strength from the sample is comparable to that of z-cut unphasematched LiNbO3---not just an arbitrary unit for the SHG strength, but a direct comparison to a well-known SHG nonlinear crystal.; This dissertation concludes with the future research topics, such as plasmonic antenna detectors with coaxial aperture and SHG optical signal processing applications without phase matching.