Coupled Plasmonic Nanowires: Dual-Channel Fourier Microscopy Studies

Abstract

Transmission and localization of light at subwavelength scale has direct relevance in the nanophotonic-circuits of light. Usage of dielectric materials hampers nanophotonic operations due to diffraction limit of light. To overcome this problem, plasmonic nanostructures made of metals such as silver and gold have been utilized. They show unique optical properties at subwavelength scales, such as enhanced localization of electric fields, sub-diffraction limit light propagation, directional emission and optical antenna effects, which can be harnessed in chip-scale integrated photonics and optoelectronics. This has motivated research in identifying novel optical nanostructures that can efficiently perform optical operations at sub-wavelength scale. With this hindsight, we have experimentally developed and studied unique nanophotonic architecture: seriallycoupled plasmonic nanowires, and observed the capability of light transmission and polarized emission beyond diffraction limit of light. In order to control the light transmission and emission, the geometry of coupled nanowire system were optimized. The optimization parameters were bending angle between nanowires, excitation profile and coupling geometry. Upon optimization, we tested the capability of routing the light as a function of polarization of incident light and showcased the ability of polarization beam splitting at sub-wavelength scale. In order to further understand the light emission characteristics from such nanowire systems, it was important to develop advanced optical microscopy methods to probe angular scattering and emission characteristics. To fulfill this requirement, we have designed and developed an advanced dual-channel Fourier optical microscopy and spectroscopy system to study the directional optical emission from individual plasmonic nanowires and nanoparticle-nanowire system. An important aspect of our microscope is the measurement of k-vector distribution of light emanating from an individual, supported nanowire through the substrate and superstrate. I have explained how our home-built optical microscope can probe far-field directional emission properties of an individual nanowire and nanoparticle-coupled nanowire architectures resting on a dielectric substrate. I have emphasized upon the ability to capture optical images in Fourier-plane and spectroscopic signatures in real-plane through a substrate and superstrate. Our work pushes the limit of optical characterization of nanoscale structures, and can be utilized to address relevant questions pertaining to interaction of