Digital electric field induced switching of plasmonic nanorods using an electro-optic fluid fiber

Abstract

We demonstrate the digital electric field induced switching of plasmonic nanorods between "1" and "0" orthogonal aligned states using an electro-optic fluid fiber component. We show by digitally switching the nanorods, that thermal rotational diffusion of the nanorods can be circumvented, demonstrating an approach to achieve submicrosecond switching times. We also show, from an initial unaligned state, that the nanorods can be aligned into the applied electric field direction in 110 nanoseconds. The high-speed digital switching of plasmonic nanorods integrated into an all-fiber optical component may provide opportunities for remote sensing and signaling applications.In general, the permanent or induced dipole moment and resulting polarizability of a molecule is too small to couple to external electric fields to overcome disordering thermal forces, preventing alignment. If anisotropic molecules are condensed into a liquid crystal phase, then the additional van der Waal forces from the nearneighbor interactions increases the polarizability to enable alignment of the molecules and control the optical properties. The electric field induced alignment of anisotropic molecules in liquid crystal phases has enabled disruptive technologies such as smart phones and flat screen displays. 1,2The switching time of these materials depends on the sum of their on-and off -times. The on-time needed to align the molecules into the direction of the applied electric field is predominately set by the magnitude of the field applied, τ on ≈ γ/εE 2 , where γ is the viscosity, ε is the dielectric permittivity and E is the electric field. The off -time is related to the thermal rotational diffusion of the liquid crystal molecules and typically is the limiting factor to determine the overall switching time. In the case of liquid crystals, the near-neighbor interactions create strong electrohydrodynamic coupling, leading to a slow characteristic off -time, τ of f ≈ γd 2 /K ≈ ms, where d is the cell thickness and K is the elastic constant of the liquid crystal. This well-known limitation has constrained potential electro-optic applications for decades.A recent elegant approach avoided re-alignment of the molecules altogether by rapidly electrically inducing a change in the refractive index of the molecules in a liquid crystal phase.3 The response time of this system was 10 s of nanoseconds, yet the change in the optical properties was small and cannot be maintained for long times before a) Electronic mail: walter.margulis@ri.se b) Electronic mail: jake.fontana@nrl.navy.mil the usual electric field induced alignment of the molecules occurs.The electric field induced alignment of plasmonic nanorods is a paradigm to anisotropic molecules in liquid crystal phases.4 A key advantage of plasmonic nanorods is that the polarizibility of a single nanorod in a dilute suspension is adequately large to couple to an external electric field, enabling alignment and the ability to tune the optical properties at visible and near infrared wavelengths.4,5 A sig...

Dynamic Plasmonic Pixels

“…45 A key advantage of these NR suspensions over conventional LC devices is the decrease of switching time by at least 3 orders of magnitude due to the absence of nearneighbor interactions, establishing the effectiveness of this approach for high-performance optical devices with fast switching times. 46,47 Here, we demonstrate a dynamic plasmonic pixel that modulates the spatial, temporal, and spectral properties of light on demand. The pixel is composed of a suspension of colloidal NRs orientable by electric fields.…”

Resonant Optical Nonlinearity and Fluorescence Enhancement in Electrically Tuned Plasmonic Nanosuspensions

“…[ 22,23 ] Although such alignment of long nanorods (aspect ratio > 10) in aqueous suspensions has been reported before, [ 24 ] the alignment of short nanorods was demonstrated only recently in organic solutions, where absorption at the longitudinal surface plasmon resonance (LSPR) is shown to decrease with increasing e‐field when light propagates along the direction of the field. [ 25–27 ] In a similar experiment, the nonlinear refractive index of plasmonic suspensions is shown to be dynamically controlled in a Hartmann–Shack wavefront aberrometer. [ 28 ] By changing the relative orientation between the probe light polarization and plasmonic nanorods, tunable polarizability can be realized, which in turn leads to changes in their optical properties such as effective refractive indices, scattering and absorption cross‐sections, and the gradient and scattering optical forces.…”

Estudo Da Dinâmica De Alinhamento De Nanobastões De Ouro Sob Efeito De Um Campo Elétrico Externo

“…Na parte superior é apresentada a resposta do sistema com operação apenas do canal 0 (Curva azul), com operação apenas no canal 1 (curva vermelha), e com os dois canais operando alternadamente (curva verde). Na parte inferior, o sinal em cada canal (0azul, 1vermelho), e sinal do chaveador de alta tensão (preto) [14].…”

“…Figura 14 -Intensidade da luz transmitida pela fibra enquanto os nanobasstões se alinham e desalinham com o campo elétrico, tanto paralelamente (azul) e quanto perpendicularmente (vermleho) à polarização da luz incidente. (Preto) pulso de potencial retangular aplicado aos eletrodos para alinhar os nanobastões [14].…”

“…Estes resultados podem levar a novas oportunidades para a entrega ponto-a-ponto e modulação da luz. field induced switching of plasmonic nanorods using an electro-optic fluid fiber [14].…”