Nanofocusing in laterally tapered plasmonic waveguides.

Center for Nanophotonics, FOM-Institute for Atomic and Molecular Physics (AMOLF), Kruislaan 407, 1098 SJ Amsterdam, The Netherlands.
Optics Express (Impact Factor: 3.53). 01/2008; 16(1):45-57. DOI: 10.1364/OE.16.000045
Source: PubMed

ABSTRACT We investigate the focusing of surface plasmon polaritons (SPPs) excited with 1.5 microm light in a tapered Au waveguide on a planar dielectric substrate by experiments and simulations. We find that nanofocusing can be obtained when the asymmetric bound mode at the substrate side of the metal film is excited. The propagation and concentration of this mode to the tip is demonstrated. No sign of a cutoff waveguide width is observed as the SPPs propagate along the tapered waveguide. Simulations show that such concentrating behavior is not possible for excitation of the mode at the low-index side of the film. The mode that enables the focusing exhibits a strong resemblance to the asymmetric mode responsible for focusing in conical waveguides. This work demonstrates a practical implementation of plasmonic nanofocusing on a planar substrate.


Available from: Laurens Kuipers, Jan 28, 2014
  • [Show abstract] [Hide abstract]
    ABSTRACT: Plasmonic waveguides supporting gap surface plasmon (GSP) modes localized in a deep subwavelength dielectric gap between a metal strip and underlay film are investigated numerically and experimentally at telecom wavelengths. Particularly, we demonstrate that GSP waveguides with only the top metal layer structured to form the waveguide, including nanoantenna couplers optimized for normal incident Gaussian beam excitation, can be fabricated in a single lithography step leading to 15% experimental coupling efficiency of GSP modes with ∼10 μm propagation length when the gap size is 10 times smaller than the free-space wavelength.
    Journal of the Optical Society of America B 03/2015; 32(3). DOI:10.1364/JOSAB.32.000462 · 1.81 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this review, we show that by designing the metallic nanostructures, the surface plasmon (SP) focusing has been achieved, with the focusing spot at a subwavelength scale. The central idea is based on the principle of optical interference that the constructive superposition of SPs with phase matching can result in a considerable electric-field enhancement of SPs in the near field, exhibiting a pronounced focusing spot. We first reviewed several new designs for surface plasmon focusing by controlling the metallic geometry or incident light polarization: We made an in-plane plasmonic Fresnel zone plates, a counterpart in optics, which produces an obvious SP focusing effect; We also fabricated the symmetry broken nanocorrals which can provide the spatial phase difference for SPs, and then we propose another plasmon focusing approach by using semicircular nanoslits, which gives rise to the phase difference through changing refractive index of the medium in the nanoslits. Further, we showed that the spiral metallic nanostructure can be severed as plasmonic lens to control the plasmon focusing under a linearly polarized light with different angles.
    Plasmonics 08/2014; 9(4):879-886. DOI:10.1007/s11468-014-9692-5 · 2.74 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The enhancement and confinement of electromagnetic radiation to nanometer scale have improved the performances and decreased the dimensions of optical sources and detectors for several applications including spectroscopy, medical applications, and quantum information. Realization of on-chip nanofocusing devices compatible with silicon photonics platform adds a key functionality and provides opportunities for sensing, trapping, on-chip signal processing, and communications. Here, we discuss the design, fabrication, and experimental demonstration of light nanofocusing in a hybrid plasmonic-photonic nanotaper structure. We discuss the physical mechanisms behind the operation of this device, the coupling mechanisms, and how to engineer the energy transfer from a propagating guided mode to a trapped plasmonic mode at the apex of the plasmonic nanotaper with minimal radiation loss. Optical near-field measurements and Fourier modal analysis carried out using a near-field scanning optical microscope (NSOM) show a tight nanofocusing of light in this structure to an extremely small spot of 0.00563(Lambda/(2n(r_max)))^3 confined in 3D and an exquisite power input conversion of 92%. Our experiments also verify the mode selectivity of the device (low transmission of a TM-like input mode and high transmission of a TE-like input mode). A large field concentration factor (FCF) of about 4.9 is estimated from our NSOM measurement with a radius of curvature of about 20nm at the apex of the nanotaper. The agreement between our theory and experimental results reveals helpful insights about the operation mechanism of the device, the interplay of the modes, and the gradual power transfer to the nanotaper apex.
    Nano Letters 01/2015; 15(2). DOI:10.1021/nl503409k · 12.94 Impact Factor