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.Comment: 18 pages, 6 figure

Mesoscopic light transport by very strong collective multiple scattering in nanowire mats

Under the extreme condition of the scattering length being much shorter than the wavelength, light transport in random media is strongly modified by mesoscopic interference, and can even be halted in an effect known as Anderson localization. Anderson localization in three dimensions has recently been realized for acoustic waves and for cold atoms. Mats of disordered, high-refractive-index semiconductor nanowires are one of the strongest three-dimensional scattering materials for light, but localization has not been shown. Here, we use statistical methods originally developed for microwave waveguides to demonstrate that transport of light through nanowire mats is strongly correlated and governed by mesoscopic interference contributions. Our results confirm the contribution of only a few open modes to the transmission

Observation of Intensity Statistics of Light Transmitted Through 3D Random Media

We experimentally observe the spatial intensity statistics of light transmitted through three-dimensional isotropic scattering media. The intensity distributions measured through layers consisting of zinc oxide nanoparticles differ significantly from the usual Rayleigh statistics associated with speckle, and instead are in agreement with the predictions of mesoscopic transport theory, taking into account the known material parameters of the samples. Consistent with the measured spatial intensity fluctuations, the total transmission fluctuates. The magnitude of the fluctuations in the total transmission is smaller than expected on the basis of quasi-one-dimensional (1D) transport theory, which indicates that quasi-1D theories cannot fully describe these open three-dimensional media.Comment: 4 pages 3 figure

Mesoscopic transport and control of light through disordered nanowire mats

In this thesis the transport of light through disordered, densely packed semiconductor nanowire mats is studied. It is found that the extremely high photonic strength of these samples leads to corrections to the traditional diffusion picture of light transport due to mesoscopic interference. Such effects are characterized by large intensity fluctuations and correlations, and it is found the transport is dominated by only a few independent transmission channels, close to the Anderson localisation regime. In addition to the strongly scattering nanowire samples, comparatively weakly scattering samples of ZnO are investigated, demonstrating mesoscopic effects in a less exotic, isotropic multiple scattering material. Control is obtained over the transmission by a combination of shaping the incident wavefront and harnessing the intrinsic nonlinearity of the semiconductor with ultrafast optical excitation. Through these techniques, a bright focus at an arbitrary point through the nanowires is created which can be modulated by up to 60% in a demonstration of a reconfigurable photonic switch

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

Wavefront shaping of light fields has opened up a wealth of new applications in imaging and communication in highly multimode environments [1-11]. By mixing of the modes with optimized phases and amplitudes it is possible to focus light through - or even inside - opaque scattering media [1,2]. Here we present work demonstrating ultrafast control of such an optimized wavefront transmitted through a dense disordered mat of semiconductor nanowires by exploiting their inherent nonlinearity. Modulations of the peak intensity of up to 63% (4.3 dB) are induced by optical pumping as a result of a combination of multimode dephasing and induced absorption. Next to ultrafast dephasing of the shaped field, we show that it is possible to dynamically rephase the light fields into an optimized spot by means of pulsed nonlinear excitation of the medium. We obtain an enhancement of the peak to background ratio of the optimized spot resulting from rephasing of up to 18%. While our results are obtained for three dimensional media, the concepts of multimode nonlinear switching are generally extendable to other systems, including plasmonic and photonic waveguides, thus enabling new avenues for ultrafast and reconfigurable nanophotonic devices

Optical transmission matrix as a probe of the photonic strength

We demonstrate that optical transmission matrices (TMs) provide a powerful tool to extract the photonic strength of disordered complex media, independent of surface effects. We measure the TM of a strongly scattering GaP nanowire medium and compare the singular value density of the measured TM to a random-matrix-based wave transport model. By varying the transport mean free path and effective refractive index in the model, we retrieve the photonic strength. From separate numerical simulations we conclude that the photonic strength derived from TM statistics is insensitive to the surface reflection at rear surface of the sample

Measurements on the optical transmission matrices of strongly scattering nanowire layers

\u3cp\u3eLight incident on a scattering medium is redistributed over transport channels that either transmit through or reflect from the medium. We perform experiments aiming at finding individual transport channels of extremely strongly scattering materials. A small number of transport channels in a scattering sample are open with transmission coefficient close to 1; field transmission mainly takes place through these channels [1-3]. This means that, even if two very different incident fields are sent to the sample, the corresponding transmitted fields are correlated. As the scattering becomes stronger, these correlations become more pronounced.\u3c/p\u3