Antenna-assisted picosecond control of nanoscale phase transition in vanadium dioxide

Nanoscale devices in which the interaction with light can be configured using external control signals hold great interest for next-generation optoelectronic circuits.Materials exhibiting a structural or electronic phase transition offer a large modulation contrast with multi-level optical switching and memory functionalities.In addition,plasmonic nanoantennas can provide an efficient enhancement mechanism for both the optically induced excitation and the readout of materials strategically positioned in their local environment.Here,we demonstrate picosecond all-optical switching of the local phase transition in plasmonic antenna-vanadium dioxide(VO_(2))hybrids,exploiting strong resonant field enhancement and selective optical pumping in plasmonic hotspots.Polarization-and wavelength-dependent pump–probe spectroscopy of multifrequency crossed antenna arrays shows that nanoscale optical switching in plasmonic hotspots does not affect neighboring antennas placed within 100 nm of the excited antennas.The antenna-assisted pumping mechanism is confirmed by numerical model calculations of the resonant,antenna-mediated local heating on a picosecond time scale.The hybrid,nanoscale excitation mechanism results in 20 times reduced switching energies and 5 times faster recovery times than a VO_(2) film without antennas,enabling fully reversible switching at over two million cycles per second and at local switching energies in the picojoule range.The hybrid solution of antennas and VO_(2) provides a conceptual framework to merge the field localization and phase-transition response,enabling precise,nanoscale optical memory functionalities.

An ultrafast reconfigurable nanophotonic switch using wavefront shaping of light in a nonlinear nanomaterial

We demonstrate a new concept for reconfigurable nanophotonic devices exploiting ultrafast nonlinear control of shaped wavefronts in a multimode nanomaterial consisting of semiconductor nanowires.Femtosecond pulsed laser excitation of the nanowire mat is shown to provide an efficient nonlinear mechanism to control both destructive and constructive interference in a shaped wavefront.Modulations of up to 63%are induced by optical pumping,due to a combination of multimode dephasing and induced transient absorption.We show that part of the nonlinear phase dynamics can be inverted to provide a dynamical revival of the wavefront into an optimized spot with up to 18%increase of the peak to background ratio caused by pulsed laser excitation.The concepts of multimode nonlinear switching demonstrated here are generally extendable to other photonic and plasmonic systems and enable new avenues for ultrafast and reconfigurable nanophotonic devices.

All-silicon carrier accumulation modulator based on a lateral metal-oxide-semiconductor capacitor

In silicon photonics, the carrier depletion scheme has been the most commonly used mechanism for demonstrating high-speed electro-optic modulation. However, in terms of phase modulation efficiency, carrieraccumulation-based devices potentially offer almost an order of magnitude improvement over those based on carrier depletion. Previously reported accumulation modulator designs only considered vertical metal-oxidesemiconductor(MOS) capacitors, which imposes serious restrictions on the design flexibility and integratability with other photonic components. In this work, for the first time to our knowledge, we report experimental demonstration of an all-silicon accumulation phase modulator based on a lateral MOS capacitor. Using a Mach–Zehnder interferometer modulator with a 500-μm-long phase shifter, we demonstrate high-speed modulation up to 25 Gbit∕s with a modulation efficiency(V_πL_π) of 1.53 V·cm.