Photoconductively Loaded Plasmonic Nanoantenna as Building Block for Ultracompact Optical Switches

Abstract

We propose and explore theoretically a new concept of ultrafast optical switches based on nonlinear plasmonic nanoantennas. The antenna nanoswitch operates on the transition from the capacitive to conductive coupling regimes between two closely spaced metal nanorods. By filling the antenna gap with amorphous silicon, progressive antenna-gap loading is achieved due to variations in the free-carrier density in the semiconductor. Strong modification of the antenna response is observed both in the far-field response and in the local near-field intensity. The large modulation depth, low switching threshold, and potentially ultrafast time response of antenna switches holds promise for applications ranging from integrated nanophotonic circuits to quantum information devices.KEYWORDS Plasmonics, nanoantennas, nanoparticles, ultrafast switches P lasmonics has emerged recently as an extremely promising technological research area, owing to rapid advances in nanofabrication and modeling.1-3 Miniaturized nanoplasmonic devices hold the potential to become one of the key nanotechnologies capable of combining electric and photonic components on the same chip.2 Of special interest for nanoscale control over light are metal nanoantennas, capable of concentrating optical fields into a subwavelength volume. [4][5][6][7] Analogous to their radiowave counterparts, nanoantennas support standing-wave electromagnetic resonances at visible and infrared wavelengths. Nanoantennas of various geometries have been applied successfully in nonlinear optics, 4,5,8,9 nanoscale photodetectors, 10 fluorescence enhancement, 11-14 high-harmonic generation, 15 and single-molecule detection. 16Active control over subwavelength optical fields is of importance for optical communication, sensing, and quantum information technology. In the terahertz range, the conductivity of semiconductors has been used recently to control the transport of terahertz waves using coupling to plasmonic modes on surfaces and nanostructures.17,18 Alloptical control over plasmons in the optical range has recently been demonstrated using planar metal films, 20,21 hole arrays, 22 and waveguided gold gratings. 23 For single small metal nanoparticles, ultrafast heating, and coherent vibrations of the metal particle give rise to broadening and a spectral shift of its plasmon resonances. [24][25][26] These effects are however not large enough for full optical control at the single-particle level for practical pump powers. In this communication, we explore the functionality of plasmonic nanoantennas as novel building blocks for ultracompact nonlinear photonic devices. We propose that the small footprint, large light-matter interaction strength, and fast dynamics of single plasmonic nanoantennas can be used to design a new type of optical switch for controlling both the far-field and near-field distribution of light. Tunability of the antenna by impedance loading of its nanogap using a dielectric medium has recently been described theoretically 27 and experimentally. 28 In th...

All-Optical Control of a Single Plasmonic Nanoantenna–ITO Hybrid

“…A variety of schemes have been proposed and developed to control plasmonic modes using optical, electrical, magnetic, thermal, or mechanical means [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. While propagating surface plasmon polaritons provide a long interaction length, allowing switching at modest intensities [9][10][11][12][13], localized mode switching may benefit from the design of nanoplasmonic modes with strong local field enhancement and high sensitivity to refractive index changes [14][15][16][17][18][19][20]. Large modulation has been obtained recently for plasmonic nanoantennas using an electrically-controlled liquid crystal [18,19].…”

Hotspot-mediated ultrafast nonlinear control of multifrequency plasmonic nanoantennas

“…Subwavelength focusing of energy is of enormous interest for many applications including coupling of light to single molecules [3,4], field-enhanced spectroscopy and sensing [5][6][7][8][9], photochemistry [10], nonlinear frequency conversion [11,12], and all-optical switching [13][14][15][16]. In analogy with radiowave antennas, plasmonic nanoantennas are designed to optimize the coupling between far-field light and near-field 'hotspots' [5,[17][18][19].…”

“…In order to successfully achieve effective optical control at the single nanoantenna level, new types of nanoscale hybrid nonlinearities have to be devised [11,[14][15][16]. One of the largest optical nonlinearities in nanoplasmonics is generated by the metal itself, through a combination of interband excitations [13,20], hot-plasma effects [16,[21][22][23] and electronic charging [24].…”

Interference, Coupling, and Nonlinear Control of High-Order Modes in Single Asymmetric Nanoantennas

“…11 Plasmonics holds promise as a new paradigm for achieving truly nanoscale, ultrafast optical devices in integrated photonic circuits. [12][13][14] Active control of the properties of electromagnetic resonances in nanoantennas is generally considered as an important landmark toward the development of transistor-type nanodevices capable of manipulating the flow and emission of light.…”