May 2016
Spotlight Summary by Parinda Vasa
Broadband efficient directional coupling to short-range plasmons: towards hybrid fiber nanotips
Metal nanostructures supporting surface plasmon polaritons (SPPs) carry significant potential for guiding and manipulating light on the nanoscale. SPPs are spatially confined electromagnetic field modes at a metal-dielectric interface capable of generating intense optical near-fields on sub-wavelength length scales. Recent advances in nanotechnology have enabled fabrication of high quality metal-dielectric hybrid nanostructures for launching, guiding and focusing SPPs. Subsequent studies have demonstrated that these hybrid nanostructures open up exciting possibilities in realizing novel applications in super-resolution microscopy and sensing.
Due to their relatively large wave vector, SPP modes generally cannot be excited via free space excitation. The large momentum mismatch is a key problem in realizing SPP based devices demanding sophisticated coupling schemes. One of the techniques for efficient excitation of SPPs is based on directional plasmonic coupling, which relies on phase-matching of neighbouring metal-dielectric waveguides. Extending the idea of integrating increasingly sophisticated nanophotonic functionality into optical fibers, a hybrid waveguide can be fabricated in which closely spaced metal and dielectric cores are integrated into a single fiber using a variety of processing techniques. One such all-in-fiber design is proposed by Alessandro Tuniz and Markus Schmidt in this Optics Express paper. Their design consists of a step-index fiber with a central dielectric core and a closely spaced gold nanowire running parallel, resulting in a plasmonic coupler with a nanotip protruding from the fiber. Light launched into the dielectric core is efficiently coupled to the strongly spatially confined mode of the gold nanowire. The protruding gold nanotip allows nanofocusing of SPPs on the ~10 nm lengthscale by adiabatic reduction in the metal core diameter.
The authors carry out a detailed but straightforward analytical formulation of a proof-of-principle planar design to demonstrate the enhanced performance of the all-in-fiber SPP coupler. They estimate higher than 50% transfer efficiency over more than 800 nm spectral bandwidth for NIR spectral range. Their detailed analysis reveals that such an all-in-fiber superfocussing coupler is realistic to implement and can have important applications in all-fiber plasmonic superfocussing, nanoscale sensing and nonlinear plasmonics.
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Due to their relatively large wave vector, SPP modes generally cannot be excited via free space excitation. The large momentum mismatch is a key problem in realizing SPP based devices demanding sophisticated coupling schemes. One of the techniques for efficient excitation of SPPs is based on directional plasmonic coupling, which relies on phase-matching of neighbouring metal-dielectric waveguides. Extending the idea of integrating increasingly sophisticated nanophotonic functionality into optical fibers, a hybrid waveguide can be fabricated in which closely spaced metal and dielectric cores are integrated into a single fiber using a variety of processing techniques. One such all-in-fiber design is proposed by Alessandro Tuniz and Markus Schmidt in this Optics Express paper. Their design consists of a step-index fiber with a central dielectric core and a closely spaced gold nanowire running parallel, resulting in a plasmonic coupler with a nanotip protruding from the fiber. Light launched into the dielectric core is efficiently coupled to the strongly spatially confined mode of the gold nanowire. The protruding gold nanotip allows nanofocusing of SPPs on the ~10 nm lengthscale by adiabatic reduction in the metal core diameter.
The authors carry out a detailed but straightforward analytical formulation of a proof-of-principle planar design to demonstrate the enhanced performance of the all-in-fiber SPP coupler. They estimate higher than 50% transfer efficiency over more than 800 nm spectral bandwidth for NIR spectral range. Their detailed analysis reveals that such an all-in-fiber superfocussing coupler is realistic to implement and can have important applications in all-fiber plasmonic superfocussing, nanoscale sensing and nonlinear plasmonics.
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Article Information
Broadband efficient directional coupling to short-range plasmons: towards hybrid fiber nanotips
Alessandro Tuniz and Markus A. Schmidt
Opt. Express 24(7) 7507-7524 (2016) View: Abstract | HTML | PDF