We report on an integrated plasmonic ultraviolet (UV) photodetector composed of aluminum Fano-resonant heptamer nanoantennas deposited on a Gallium Nitride (GaN) active layer which is grown on a sapphire substrate to generate significant photocurrent via formation of hot electrons by nanoclusters upon the decay of nonequilibrium plasmons. Using the plasmon hybridization theory and finite-difference time-domain (FDTD) method, it is shown that the generation of hot carriers by metallic clusters illuminated by UV beam leads to a large photocurrent. The induced Fano resonance (FR) minimum across the UV spectrum allows for noticeable enhancement in the absorption of optical power yielding a plasmonic UV photodetector with a high responsivity. It is also shown that varying the thickness of the oxide layer (Al₂O₃) around the nanodisks (tox) in a heptamer assembly adjusted the generated photocurrent and responsivity. The proposed plasmonic structure opens new horizons for designing and fabricating efficient opto-electronics devices with high gain and responsivity.

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We report on photo-thermal modulation of thin film surface plasmon polaritons (SPP) excited at telecom wavelengths and traveling at a gold/air interface. By operating a modulated continuous-wave or a Q-switched nanosecond pump laser, we investigate the photo-thermally induced modulation of SPP propagation mediated by the temperature-dependent ohmic losses in the gold film. We use a fiber-to-fiber characterization set-up to measure accurately the modulation depth of the SPP signal under photo-thermal excitation. On the basis of these measurements, we extract the thermo-plasmonic coefficient of the SPP mode defined as the temperature derivative of the SPP damping constant. Next, we introduce a figure of merit which is relevant to characterize the impact of temperature onto the properties of bounded or weakly leaky SPP modes supported by a given metal at a given wavelength. By combining our measurements with tabulated values of the temperature-dependent imaginary part of gold dielectric function, we compute the thermo-optical coefficients (TOC) of gold at telecom wavelengths. Finally, we investigate a pulsed photo-thermal excitation of the SPP in the nanosecond regime. The experimental SPP depth of modulation obtained in this situation are found to be in fair agreement with the modulation depths computed by using our values of gold TOC.

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International audienceDielectric loaded gratings (DLGs) comprised of polymer gratings lying on a thin gold film are used to couple light at telecommunication frequencies in and out of plasmonic waveguides featuring sub-micron cross-sections. The grating couplers are found to be efficient and easy to implement to perform direct fiber-to-fiber telecommunication characterizations of dielectric loaded surface plasmon polariton waveguide (DLSPPW) components. By analyzing the dispersion of the plasmonic Bloch modes supported by DLGs as a function of the period and the filling factor of the gratings, efficient couplers comprised of gratings with a filling factor around 0.5 are designed and fabricated by a simple one-step electron beam lithography process. Typical losses in the range of dB per coupler are obtained for gratings designed to operate at normal and 30 -tilted incidence. The performance of the couplers for normal incidence can be further improved by adding a back-reflecting Bragg mirror. We demonstrate the transmission of a 10 Gbits/s signal along a 75 m-long DLSPPW by using DLG couplers for light injection and extraction. A power penalty below below 0.4 dB on the bit-error-rate has been measured over the entire C-band demonstrating the suitability of DLSPPWs for Wavelength-Division-Multiplexed high bit rate traffic and the efficiency of DLG couplers for fiber-to-fiber characterizations of stand alone DLSPPW components

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The thermo-optical dynamics of polymer loaded surface plasmon waveguide (PLSPPW) based devices photo-thermally excited in the nanosecond regime is investigated. We demonstrate thermo-absorption of PLSPPW modes mediated by the temperature-dependent ohmic losses of the metal and the thermally controlled field distribution of the plasmon mode within the metal. For a PLSPPW excited by sub-nanosecond long pulses, we find that the thermo-absorption process leads to modulation depths up to 50% and features an activation time around 2 ns whereas the relaxation time is around 800 ns, four-fold smaller than the cooling time of the metal film itself. Next, we observe the photo-thermal activation of PLSPPW racetrack shaped resonators at a time scale of 300 ns followed however by a long cooling time (18 μs) attributed to the poor heat diffusivity of the polymer. We conclude that nanosecond excitation combined to high thermal diffusivity materials opens the way to high speed thermo-optical plasmonic devices.

We report on numerical study of dispersion properties and frequency dependent absorption characteristics of asymmetric dual grating gate terahertz (THz) plasmonic crystals. The study shows that the dispersion relations of plasmons in a two‐dimensional electron gas (2DEG) capped with asymmetric dual grating gates have energy band gaps in the Brillion zones. Depending on the wave vector, the plasmons can have symmetrical, anti‐symmetrical, and asymmetrical charge distributions that are different from the ones for uniform gratings case. Plasmons in the studied plasmonic crystal exhibit both tightly confined/weakly coupled behavior and propagating/strongly coupled behavior depending on the plasmonic modes. The responsivity of the plasmonic detector based on asymmetric dual grating gate does not monotonically decrease with the frequency, which is in contrast to the responsivity of uniform grating THz detectors. The cross‐section of an asymmetric dual grating gate terahertz plasmonic device under THz illumination is represented, where excited plasmons are shown in red.