Past Achievements and Future Challenges in 3D Photonic Metamaterials

Photonic metamaterials are man-made structures composed of tailored micro- or nanostructured metallo-dielectric sub-wavelength building blocks that are densely packed into an effective material. This deceptively simple, yet powerful, truly revolutionary concept allows for achieving novel, unusual, and sometimes even unheard-of optical properties, such as magnetism at optical frequencies, negative refractive indices, large positive refractive indices, zero reflection via impedance matching, perfect absorption, giant circular dichroism, or enhanced nonlinear optical properties. Possible applications of metamaterials comprise ultrahigh-resolution imaging systems, compact polarization optics, and cloaking devices. This review describes the experimental progress recently made fabricating three-dimensional metamaterial structures and discusses some remaining future challenges

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 tunable terahertz polarization converter based on a sinusoidally-slotted graphene metamaterial

© 2018 Optical Society of Americaunder. A new wideband sinusoidally-slotted graphene-based cross-polarization converter (CPC) is proposed in this paper. The proposed polarization converter can realize a broadband terahertz polarization conversion from 1.28 to 2.13-THz with a polarization conversion ratio (PCR) of more than 0.85. Taking advantage of the gradient width modulation of the graphene-based unit structure, the continuous plasmon resonances are excited at the edges of the sinusoidal slot. Therefore, the proposed converter can achieve a broadband polarization conversion in a simplified structure. Furthermore, the polarization conversion characteristics of the CPC are insensitive to the incident angle. The PCR remains more than 0.85 with little bandwidth degradation even as the incident angle increases to as high as 50°. More importantly, the operating bandwidth and the magnitude of the PCR can be tuned easily by adjusting the chemical potential and the electron scattering times of the graphene. In a way, we believe this kind of graphene-based polarization converter can enrich the polarization conversion community for realizing broadband and tunable polarization conversion

Tunable compact THz devices based on graphene and other 2D material metasurfaces

Since the isolation of graphene in 2004, a large amount of research has been directed at 2D materials and their applications due to their unique characteristics. Compared with the noble metal plasmons in the visible and near-infrared frequencies, graphene can support surface plasmons in the lower frequencies of terahertz (THz) and midinfrared. Especially, the surface conductivity of graphene can be tuned by either chemical doping or electrostatic gating. As a result, the idea of designing graphene metasurfaces is attractive because of its ultra-broadband response and tunability. It has been demonstrated theoretically and experimentally that the third-order nonlinearity of graphene at the THz frequency range is exceptionally strong, and graphene has smaller losses with respect to noble metals. These features make graphene a promising candidate to enhance nonlinear effects at the far-infrared and THz frequencies. In this thesis, we present several designs to explore electromagnetic applications of graphene metasurface. Theoretical and simulation studies are carried out to design tunable THz polarizers, amplifiers, coherent perfect absorbers and to achieve enhanced nonlinear effect. These studies on the applications of monolayer graphene demonstrate prospective potentials of graphene in THz sensing, imaging, modulators, and nonlinear THz spectroscopy. Adviser: Christos Argyropoulo

Terahertz Technology and Its Applications

The Terahertz frequency range (0.1 – 10)THz has demonstrated to provide many opportunities in prominent research fields such as high-speed communications, biomedicine, sensing, and imaging. This spectral range, lying between electronics and photonics, has been historically known as “terahertz gap” because of the lack of experimental as well as fabrication technologies. However, many efforts are now being carried out worldwide in order improve technology working at this frequency range. This book represents a mechanism to highlight some of the work being done within this range of the electromagnetic spectrum. The topics covered include non-destructive testing, teraherz imaging and sensing, among others

Novel Metamaterials and Their Applications in Subwavelength Waveguides, Imaging and Modulation

The development of metamaterials has opened the door for engineering electromagnetic properties by subwavelength artificial atoms , and hence accessing new properties and functionalities which cannot be found among naturally occurring materials. In particular, metamaterials enable the flexibility of independently controlling the permittivity and permeability to be almost any arbitrary value, which promises to achieve deep subwavelength confinement and focusing of electromagnetic waves in different spectrum regimes. The next stage of this technological revolution will be focused on the development of active and controllable metamaterials, where the properties of the metamaterials are expected to be tuned by external stimuli. In this sense, some natural materials are also promising to provide the tunable capability, particularly in the near infrared and terahertz domains either by applying a voltage or shining light on the materials. The objective of this dissertation is to investigate novel metamaterials and explore three important applications of them: subwavelength waveguiding, imaging and modulation. The first part of this dissertation covers the theory, design and fabrication of several different types of metamaterials, which includes artificially designed metamaterials and some naturally existing materials. The second part demonstrates metal gratings functioning as designer surface plasmonic waveguides support deep subwavelength surface propagation modes at microwave frequency. The third part proposes multilayered metal-insulator stack as indefinite metamaterial that converts evanescent waves to propagating waves, hence deep subwavelength image can be observed. The fourth part explores the tunability of several natural materials - gallium (Ga), indium tin oxide (ITO) and graphene, and demonstrates electro-optical (EO) modulators based on these materials can be achieved on nano-scale. The final part summarizes the work presented in this dissertation and also discusses some future work for photodetection, photovoltaics, and modulation

All-optical metamaterial modulators : fabrication, simulation and characterization

Artificially structured composite metamaterials consist of sub-wavelength sized structures that exhibit unusual electromagnetic properties not found in nature. Since the first experimental verification in 2000, metamaterials have drawn considerable attention because of their broad range of potential applications. One of the most attractive features of metamaterials is to obtain negative refraction, termed left-handed materials or negative-index metamaterials, over a limited frequency band. Negative-index metamaterials at near infrared wavelength are fabricated with circular, elliptical and rectangular holes penetrating through metal/dielectric/metal films. All three negative-index metamaterial structures exhibit similar figure of merit; however, the transmission is higher for the negative-index metamaterial with rectangular holes as a result of an improved impedance match with the substrate-superstrate (air-glass) combination. In general, the processing procedure to fabricate the fishnet structured negative-index metamaterials is to define the hole-size using a polymetric material, usually by lithographically defining polymer posts, followed by deposition of the constitutive materials and dissolution of the polymer (liftoff processing). This processing (fabrication of posts: multi-layer deposition: liftoff) often gives rise to significant sidewall-angle because materials accumulate on the tops of the posts that define the structure, each successive film deposition has a somewhat larger aperture on the bottom metamaterial film, giving rise to a nonzero sidewall-angle and to optical bianisotropy. Finally, we demonstrate a nanometer-scale, sub-picosecond metamaterial device capable of over terabit/second all-optical communication in the near infrared spectrum. We achieve a 600 fs device response by utilizing a regime of sub-picosecond carrier dynamics in amorphous silicon and ~70% modulation in a path length of only 124 nm by exploiting the strong nonlinearities in metamaterials. We identify a characteristic signature associated with the negative index resonance in the pump-probe signal of a fishnet structure. We achieve much higher switching ratios at the fundamental resonance (~70%) relative to the secondary resonance (~20%) corresponding to the stronger negative index at the fundamental resonance. This device opens the door to other compact, tunable, ultrafast photonic devices and applications