A tunable multiband chirped metasurface

AbstractWe numerically present a multiband double negative chirped metasurface (MS) in the near-infrared (N-IR) region. The MS was composed of a round nanoholes array (RNA) penetrating through metal/dielectric material/metal (AuAl2O3Au) trilayers. The chirp was excited by varying the positions of the RNA along the direction of incident electric (E) field vector inside the meta-atom. It is found that besides a multiband double negative refractive index (NRI), a spectral tuning of NRI is also unveiled by moving the neighbouring round holes closer to each other. Importantly, we also show that the chirped MS with large round hole resonators possesses a high value of the Figure-of-Merit (FOM) in the optical region

Phase Change Material Photonics

In the last decade phase change materials (PCM) research has switched from practical application in optical data storage toward electrical phase change random access memory technologies (PCRAM). As these devices are commercialised, we expect the research direction to switch once again toward electrical-photonic devices. The objective of this review is to introduce the concepts in PCM-tuned photonics. We will start by highlighting the key works in the field, before concentrating on PCM-tuned Metal-Dielectric-Metal (MDM) structures. We will discuss how to design tuneable-MDM photonics devices, their advantages, and their limitations. Finally we will discuss new materials for phase change photonics.Comment: 28 pages, 14 figures, adapted from a chapter to be published in the World Scientific Reference of Amorphous Material

Directive emission of red conjugated polymer embedded within zero index metamaterials

Abstract: We numerically demonstrate an impedance-matched multilayer stacked fishnet metamaterial that has zero index with flat high transmittance from 600nm to 620nm. The effective refractive index

Fast Tuning of Double Fano Resonance Using A Phase-Change Metamaterial Under Low Power Intensity

In this work, we numerically demonstrate an all-optical tunable Fano resonance in a fishnet metamaterial(MM) based on a metal/phase-change material(PCM)/metal multilayer. We show that the displacement of the elliptical nanoholes from their centers can split the single Fano resonance (FR) into a double FR, exhibiting higher quality factors. The tri-layer fishnet MMs with broken symmetry accomplishes a wide tuning range in the mid-infrared(M-IR) regime by switching between the amorphous and crystalline states of the PCM (Ge(2)Sb(2)Te(5)). A photothermal model is used to study the temporal variation of the temperature of the Ge(2)Sb(2)Te(5) film to show the potential for switching the phase of Ge(2)Sb(2)Te(5) by optical heating. Generation of the tunable double FR in this asymmetric structure presents clear advantages as it possesses a fast tuning time of 0.36 ns, a low pump light intensity of 9.6 μW/μm(2), and a large tunable wavelength range between 2124 nm and 3028 nm. The optically fast tuning of double FRs using phase change metamaterials(PCMMs) may have potential applications in active multiple-wavelength nanodevices in the M-IR region

Broadband polarization-independent perfect absorber using a phase-change metamaterial at visible frequencies

We report a broadband polarization-independent perfect absorber with wide-angle near unity absorbance in the visible regime. Our structure is composed of an array of thin Au squares separated from a continuous Au film by a phase change material (Ge(2)Sb(2)Te(5)) layer. It shows that the near perfect absorbance is flat and broad over a wide-angle incidence up to 80° for either transverse electric or magnetic polarization due to a high imaginary part of the dielectric permittivity of Ge(2)Sb(2)Te(5). The electric field, magnetic field and current distributions in the absorber are investigated to explain the physical origin of the absorbance. Moreover, we carried out numerical simulations to investigate the temporal variation of temperature in the Ge(2)Sb(2)Te(5) layer and to show that the temperature of amorphous Ge(2)Sb(2)Te(5) can be raised from room temperature to > 433 K (amorphous-to-crystalline phase transition temperature) in just 0.37 ns with a low light intensity of 95 nW/μm(2), owing to the enhanced broadband light absorbance through strong plasmonic resonances in the absorber. The proposed phase-change metamaterial provides a simple way to realize a broadband perfect absorber in the visible and near-infrared (NIR) regions and is important for a number of applications including thermally controlled photonic devices, solar energy conversion and optical data storage

Controlling Lateral Fano Interference Optical Force with Au-Ge2Sb2Te5 Hybrid Nanostructure

We numerically demonstrate that a pronounced dipole–quadrupole (DQ) Fano resonance (FR) induced lateral force can be exerted on a dielectric particle 80 nm in radius (Rsphere = 80 nm) that is placed 5 nm above an asymmetric bow-tie nanoantenna array based on Au/Ge2Sb2Te5 dual layers. The DQ-FR-induced lateral force achieves a broad tuning range in the mid-infrared region by changing the states of the Ge2Sb2Te5 dielectric layer between amorphous and crystalline and in turn pushes the nanoparticle sideways in the opposite direction for a given wavelength. The mechanism of lateral force reversal is revealed through optical singularity in the Poynting vector. A thermal–electric simulation is adopted to investigate the temporal change of the Ge2Sb2Te5 film’s temperature, which demonstrates the possibility of transiting the Ge2Sb2Te5 state by electrical heating. Our mechanism by tailoring the DQ-FR-induced lateral force presents clear advantages over the conventional nanoparticle manipulation techniques: it possesses a pronounced sideways force under a low incident light intensity of 10 mW/μm2, a fast switching time of 2.6 μs, and a large tunable wavelength range. It results in a better freedom in flexible nanomechanical control and may provide a new means of biomedical sensing and nano-optical conveyor belts

Microsphere femtosecond laser sub-50 nm structuring in far field via non-linear absorption

Creation of arbitrary features with high resolution is critically important in the fabrication of nano-optoelectronic devices. Here, sub-50 nm surface structuring is achieved directly on Sb2S3 thin films via microsphere femtosecond laser irradiation in far field. By varying laser fluence and scanning speed, nano-feature sizes can be flexibly tuned. Such small patterns are attributed to the co-effect of microsphere focusing, two-photons absorption, top threshold effect, and high-repetition-rate femtosecond laser-induced incubation effect. The minimum feature size can be reduced down to ~30 nm (λ/26) by manipulating film thickness. The fitting analysis between the ablation width and depth predicts that the feature size can be down to ~15 nm at the film thickness of ~10 nm. A nano-grating is fabricated, which demonstrates desirable beam diffraction performance. This nano-scale resolution would be highly attractive for next-generation laser nano-lithography in far field and in ambient air

Non-volatile dynamically switchable color display via chalcogenide stepwise cavity resonators

High-resolution multi-color printing relies upon pixelated optical nanostructures, which is crucial to promote color display by producing nonbleaching colors, yet requires simplicity in fabrication and dynamic switching. Antimony trisulfide (Sb2S3) is a newly rising chalcogenide material that possesses prompt and significant transition of its optical characteristics in the visible region between amorphous and crystalline phases, which holds the key to color-varying devices. Herein, we proposed a dynamically switchable color printing method using Sb2S3-based stepwise pixelated Fabry-Pérot (FP) cavities with various cavity lengths. The device was fabricated by employing a direct laser patterning that is a less time-consuming, more approachable, and low-cost technique. As switching the state of Sb2S3 between amorphous and crystalline, the multi-color of stepwise pixelated FP cavities can be actively changed. The color variation is due to the profound change in the refractive index of Sb2S3 over the visible spectrum during its phase transition. Moreover, we directly fabricated sub-50 nm nano-grating on ultrathin Sb2S3 laminate via microsphere 800-nm femtosecond laser irradiation in far field. The minimum feature size can be further decreased down to ~45 nm (λ/17) by varying the thickness of Sb2S3 film. Ultrafast switchable Sb2S3 photonic devices can take one step toward the next generation of inkless erasable papers or displays and enable information encryption, camouflaging surfaces, anticounterfeiting, etc. Importantly, our work explores the prospects of rapid and rewritable fabrication of periodic structures with nano-scale resolution and can serve as a guideline for further development of chalcogenide-based photonics components