Large scale indium tin oxide (ITO) one dimensional gratings for ultrafast signal modulation in the visible spectral region

Indium tin oxide (ITO) is a heavily doped semiconductor with a plasmonic response in the near infrared region. When exposed to light, the distribution of conduction band electron induces a change in the real and imaginary parts of the dielectric permittivity. The coupling of the electromagnetic waves with the electrons in the conduction band of metallic nanostructures with ultrashort light pulses results in a nonlinear plasmonic response. Such optical modulation occurring on ultrafast time scales, e.g. picosecond response times, can be exploited and used to create integrated optical components with terahertz modulation speed. Here, we present a photophysical study on a one dimensional ITO grating, realized using a femtosecond micromachining process, a very industrially accessible technology. The geometries, dimensions and pitch of the various gratings analyzed are obtained by means of direct ablation in a controlled atmosphere of a homogeneous thin layer of ITO deposited on a glass substrate. The pitch has been selected in order to obtain a higher order of the photonic band gap in the visible spectral region. Femtosecond micromachining technology guarantees precision, repeatability and extreme manufacturing flexibility. By means of ultrafast pump-probe spectroscopy, we characterize both the plasmon and inter-band temporal dynamics. We observe a large optical nonlinearity of the ITO grating in the visible range, where the photonic band gap occurs, when pumped at the surface plasmon resonance in the near infrared (1500 nm) region. All together, we show the possibility of all-optical signal modulation with heavily doped semiconductors in their transparency window with a picosecond response time through the formation of ITO grating structures

Light Transmission Properties and Shannon Index in One-Dimensional Photonic Media With Disorder Introduced by Permuting the Refractive Index Layers

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Fully direct written organic micro-thermoelectric generators embedded in a plastic foil

Organic materials have attracted great interest for thermoelectric applications due to their tuneable electronic properties, solution processability and earth-abundance, potentially enabling high-throughput realization of low-cost devices for low-power energy harvesting applications. So far, organic thermoelectricity has primarily focused on materials development, with less attention given to integrated generators. Yet, future applications will require the combination of efficient generators architectures and scalable manufacturing techniques to leverage the advantages of such promising materials. Here we report the realization of a monolithic organic micro-thermoelectric generator (μ-OTEG), using only direct writing methods, embedding the thermoelectric legs within a plastic substrate through a combination of direct laser writing and inkjet printing techniques. Employing PEDOT:PSS for the p-type legs and a doped fullerene derivative for the n-type ones, we demonstrate a μ-OTEG with power density of 30.5 nW/cm2 under small thermal gradients, proving the concrete possibility of achieving power requirements of low-power, distributed sensing applications

Low-Voltage Tuning in a Nanoparticle/Liquid Crystal Photonic Structure

In this study, we propose the fabrication and characterization of nanoparticle based multilayer photonic crystals infiltrated with a nematic liquid crystal. We show a very simple infiltration of the liquid crystal in the porous structure, controlled by monitoring the photonic band gap during the infiltration process. Tunability with electric field (by aligning the liquid crystal director) has been observed at very low applied voltage, with a blue shift of the photonic band gap of 8 nm at only 8 V. The presented results could be very interesting for realization of low cost and portable switching devices for high density integrated optics

Infiltration of E7 Liquid Crystal in a Nanoparticle-Based Multilayer Photonic Crystal: Fabrication and Electro-optical Characterization

In this study, we propose the fabrication and the electro-optical characterization of nanoparticle-based multilayer photonic crystals infiltrated with a nematic liquid crystal. Two methods of the photonics band gap tunability have been proposed. In the first, we have observed an aligning of the liquid crystal director along the external electric field vector at very low applied voltage, with a blue shift of the photonic band gap of 8nm at only 8Vrms. In the second, we put forward the possibility of tuning the photonic band gap of the porous multilayer just by infiltration of appropriate liquid crystals, in accordance with results carried out by a custom simulation software. The presented device could be very interesting for applications where high sensitivity sensor and selective color tunability is needed with the use of cheap and low-voltage power supplies