Abstract
The enhancement of nonlinear optical effects via nanoscale engineering is a hot topic of research. Optical nanoantennas increase light–matter interaction and provide, simultaneously, a high throughput of the generated harmonics in the scattered light. However, nanoscale nonlinear optics has dealt so far with static or quasi-static configurations, whereas advanced applications would strongly benefit from high-speed reconfigurable nonlinear nanophotonic devices. Here we propose and experimentally demonstrate ultrafast all-optical modulation of the second harmonic (SH) from a single nanoantenna. Our design is based on a subwavelength AlGaAs nanopillar driven by a control femtosecond light pulse in the visible range. The control pulse photoinjects free carriers in the nanostructure, which in turn induce dramatic permittivity changes at the band edge of the semiconductor. This results in an efficient modulation of the SH signal generated at 775 nm by a second femtosecond pulse at the 1.55 μm telecommunications (telecom) wavelength. Our results can lead to the development of ultrafast, all optically reconfigurable, nonlinear nanophotonic devices for a broad class of telecom and sensing applications.
Highlights
The enhancement of nonlinear optical effects via nanoscale engineering is a hot topic of research
The optical Kerr effect in centrosymmetric nonlinear materials, such as silicon, has been enhanced by several orders of magnitude via nanoscale patterning.[9,10]. These advances were made possible by the capability of high-index nanostructures to simultaneously achieve intense local field enhancement and resonant light scattering, behaving as optical nanoantennas.[11−14] Research in the field has been so far developed along two distinct directions characterized by different aims:[4] (i) the enhancement of coherent harmonic generation for ultracompact nonlinear light sources;[6,7,15−19] (ii) the engineering of giant delayed nonlinearities, induced by photogenerated carriers, for ultrafast light-controlling-light devices.[20−23] Despite the huge efforts pursued on both topics, coherent nonlinear functionalities have been so far demonstrated only in static or quasi-static configurations, employing slow mechanical or electro-optical modulation schemes
We have demonstrated the possibility to reconfigure by all-optical means and at ultrahigh speed the second-harmonic generation (SHG) in a single nonlinear nanoantenna
Summary
The enhancement of nonlinear optical effects via nanoscale engineering is a hot topic of research. The capability to tailor the size and shape of high-index nanostructures has disclosed the opportunity to control light−matter interaction at the subwavelength scale, leading to the advent of nonlinear nanophotonics.[1−7] For example, nanoscale engineering can lift phase-matching constraints typical of the bulk and turn centrosymmetric materials, such as gold, into efficient second-harmonic generation (SHG) media.[8] the optical Kerr effect in centrosymmetric nonlinear materials, such as silicon, has been enhanced by several orders of magnitude via nanoscale patterning.[9,10] These advances were made possible by the capability of high-index nanostructures to simultaneously achieve intense local field enhancement and resonant light scattering, behaving as optical nanoantennas.[11−14] Research in the field has been so far developed along two distinct directions characterized by different aims:[4] (i) the enhancement of coherent harmonic generation for ultracompact nonlinear light sources;[6,7,15−19] (ii) the engineering of giant delayed nonlinearities, induced by photogenerated carriers, for ultrafast light-controlling-light devices.[20−23] Despite the huge efforts pursued on both topics, coherent nonlinear functionalities (such as second-/third-harmonic generation and, more generally, frequency conversion) have been so far demonstrated only in static or quasi-static configurations, employing slow mechanical or electro-optical modulation schemes. With the exception of a few works,[24−27] the ultrafast light-by-light reconfiguration of optical nanostructures has been so far limited to the switching of linear functionalities (e.g., light intensity modulation, polarization switching, and so on), mostly employing extended structures including metasurfaces[20,22,28] (see refs 29 and 30 for an overview)
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