Plasmonic antennas can enhance the intensity of a nanojoule laser pulse by localizing the electric field in their proximity 1 . It has been proposed that the field can become strong enough to convert the fundamental laser frequency into high-order harmonics through an extremely nonlinear interaction with gas atoms that occupy the nanoscopic volume surrounding the antennas [2][3][4] . However, the small number of gas atoms that can occupy this volume limits the generation of high harmonics [5][6][7] . Here we use an array of monopole nano-antennas to demonstrate plasmon-assisted high-harmonic generation directly from the supporting crystalline silicon substrate. The high density of the substrate compared with a gas allows macroscopic buildup of harmonic emission. Despite the sparse coverage of antennas on the surface, harmonic emission is ten times brighter than without antennas. Imaging the high-harmonic radiation will allow nanometre and attosecond measurement of the plasmonic field 8 thereby enabling more sensitive plasmon sensors 9 while opening a new path to extreme-ultraviolet-frequency combs 10

Nanoantennas are key optical components for several applications including photodetection and biosensing. Here we present an array of metal nano-dipoles supporting surface plasmon polaritons (SPPs) integrated into a silicon-based Schottky-contact photodetector. Incident photons coupled to the array excite SPPs on the Au nanowires of the antennas which decay by creating "hot" carriers in the metal. The hot carriers may then be injected over the potential barrier at the Au-Si interface resulting in a photocurrent. High responsivities of 100 mA/W and practical minimum detectable powers of -12 dBm should be achievable in the infra-red (1310 nm). The device was then investigated for use as a biosensor by computing its bulk and surface sensitivities. Sensitivities of ∼ 250 nm/RIU (bulk) and ∼ 8 nm/nm (surface) in water are predicted. We identify the mode propagating and resonating along the nanowires of the antennas, we apply a transmission line model to describe the performance of the antennas, and we extract two useful formulas to predict their bulk and surface sensitivities. We prove that the sensitivities of dipoles are much greater than those of similar monopoles and we show that this difference comes from the gap in dipole antennas where electric fields are strongly enhanced.

Optical nanoantennas have raised much interest during the past decade for their vast potential in photonics applications. This thesis investigates the response of periodic arrays of nanomonopoles and nanodipoles on a silicon substrate, covered by water, to variations of antenna dimensions. These arrays are illuminated by a plane wave source located inside the silicon substrate.Modal analysis was performed and the mode in the nanoantennas was identified. By characterizing the properties of this mode certain response behaviours of the system were explained. Expressions are offered to predict approximately the resonant length of nanomonopoles and nanodipoles, by accounting for the fringing fields at the antenna ends and the effects of the gap in dipoles. These expressions enable one to predict the resonant length of nanomonopoles within 20% and nanodipoles within 10% error, which significantly facilitates the design of such antennas for specific applications.ii

Articles you may be interested inHigh-responsivity plasmonics-based GaAs metal-semiconductor-metal photodetectors Appl. Phys. Lett. 99, 133112 (2011); 10.1063/1.3625937 Strain-driven alignment of In nanocrystals on InGaAs quantum dot arrays and coupled plasmon-quantum dot emission Appl. Phys. Lett. 96, 113101 (2010); 10.1063/1.3358122 Modulating emission polarization of semiconductor quantum dots through surface plasmon of metal nanorod Appl. Phys. Lett. 92, 162107 (2008); 10.1063/1.2916826 Wavelength selective quantum dot infrared photodetector with periodic metal hole arraysWe propose and investigate a surface plasmon photodetector concept, based on the enhancement of electrical near-field in low-defect, low-doped In 0.53 Ga 0.47 As detection volumes located in the gaps of an array of metal nanodipole antennas. We report enhancement in responsivity in the presence of nanodipoles and predict a maximum responsivity of $100 mA/W at wavelengths near 1550 nm. The 3 dB electrical bandwidth of the device is estimated based on its RC rise time and the hole transit time through the detection volume for the cases of conventional and ballistic transport in InGaAs and is found to range from $0.7 to 4 THz. Also, trends are observed relating the responsivity to the gap dimensions, revealing a trade-off between the field-enhancement in the gap and its volume, and leading to an optimum gap length producing the maximum responsivity. V C 2014 AIP Publishing LLC. [http://dx.

The fabrication of a high-speed plasmonic reflection/transmission modulator for operation at λ0 = 1550 nm is presented and described in detail. Front-side ground and signal contacts provide easy electrical probe access to the device, while allowing the transmission of light through the substrate. Modulation is based on enhanced perturbation of the effective refractive index of grating-coupled surface plasmon polaritons propagating along a metal–oxide–semiconductor structure on silicon. Fabrication steps include deposition of a plasmonic metal patch, deposition of Ohmic contacts, deposition of an Au nanograting coupler overlaid by e-beam lithography, and the application of an intermetal dielectric layer with metalized vias and metal electrical contacts. Current–voltage and capacitance–voltage characteristics verify the electrical integrity of the structure.