Tricontrollable pixelated metasurface for absorbing terahertz radiation

The incorporation of materials with controllable electromagnetic constitutive parameters allows the conceptualization and realization of controllable metasurfaces. With the aim of formulating and investigating a tricontrollable metasurface for efficiently absorbing terahertz radiation, we adopted a pixel-based approach in which the meta-atoms are biperiodic assemblies of discrete pixels. We patched some pixels with indium antimonide (InSb) and some with graphene, leaving the others unpatched. The bottom of each meta-atom was taken to comprise a metal-backed substrate of silicon nitride. The InSb-patched pixels facilitate the thermal and magnetic control modalities, whereas the graphene-patched pixels facilitate the electrical control modality. With proper configuration of patched and unpatched pixels and with proper selection of the patching material for each patched pixel, the absorptance spectrums of the pixelated metasurface were found to contain peak-shaped features with maximum absorptance exceeding 0.95, full-width-at-half-maximum bandwidth of less than 0.7~THz, and the maximum-absorptance frequency lying between 2~THz and 4~THz. The location of the maximum-absorptance frequency can be thermally, magnetically, and electrically controllable. The lack of rotational invariance of the optimal meta-atom adds mechanical rotation as the fourth control modality

Metasurfaces Based on Phase-Change Material as a Reconfigurable Platform for Multifunctional Devices

Integration of phase-change materials (PCMs) into electrical/optical circuits has initiated extensive innovation for applications of metamaterials (MMs) including rewritable optical data storage, metasurfaces, and optoelectronic devices. PCMs have been studied deeply due to their reversible phase transition, high endurance, switching speed, and data retention. Germanium-antimony-tellurium (GST) is a PCM that has amorphous and crystalline phases with distinct properties, is bistable and nonvolatile, and undergoes a reliable and reproducible phase transition in response to an optical or electrical stimulus; GST may therefore have applications in tunable photonic devices and optoelectronic circuits. In this progress article, we outline recent studies of GST and discuss its advantages and possible applications in reconfigurable metadevices. We also discuss outlooks for integration of GST in active nanophotonic metadevices.1115sciescopu

A Tunable Terahertz Metamaterial Perfect Absorber Based on Vanadium Dioxide

In this paper, a tunable metamaterial perfect absorber based on vanadium dioxide (VO2) is designed in the terahertz frequency range. The proposed structure is simulated by the numerical method of three-dimensional Finite Difference Time Domain (FDTD). Simulation results show that the absorption spectrum of the device in the normal incidence of a plane wave light in the range of 1 THz to 12 THz, has three polarization-insensitive resonance peaks whose amplitude changes for the different conductivities of VO2 and shifts in a certain frequency range. This device also having a tolerance of 6 degrees of incidence angle can provide a relatively stable absorption spectrum.Comment: 5 pages, 6 figure

Nonlinear and wavelength-tunable plasmonic metasurfaces and devices

textWavelength-tunable optical response from solid-state optoelectronic devices is a desired feature for a variety of applications such as spectroscopy, laser emission tuning, and telecommunications. Nonlinear optical response, on the other hand, has an important role in modern photonic functionalities, including efficient frequency conversions, all-optical signal processing, and ultrafast switching. This study presents the development of optical devices with wavelength tunable or nonlinear optical functionality based on plasmonic effects. For the first part of this study, widely wavelength tunable optical bandpass filters based on the unique properties of long-range surface plasmon polaritons (LR SPP) are presented. Planar metal stripe waveguides surrounded by two different cladding layers that have dissimilar refractive index dispersions were used to develop a wide wavelength tuning. The concept was demonstrated using a set of index-matching fluids and over 200nm of wavelength tuning was achieved with only 0.004 of index variation. For practical application of the proposed concept, a thermo-optic polymer was used to develop a widely tunable thermo-optic bandpass filter and over 220 nm of wavelength tuning was achieved with only 8 ºC of temperature variation. Another novel approach to produce a widely wavelength tunable optical response for free-space optical applications involves integrating plasmonic metasurfaces with quantum-electronic engineered semiconductor layers for giant electro-optic effect, which is proposed and experimentally demonstrated in the second part of this study. Coupling of surface plasmon modes formed by plasmonic nanoresonators with Stark tunable intersubband transitions in multi-quantum well structures induced by applying bias voltages through the semiconductor layer was used to develop tunable spectral responses in the mid-infrared range. Experimentally, over 310 nm of spectral peak tuning around 7 μm of wavelength with 10 ns response time was achieved. As the final part of this study, highly nonlinear metasurfaces based on coupling of electromagnetically engineered plasmonic nanoresonators with quantum-engineered intersubband nonlinearities are proposed and experimentally demonstrated. In the proof-of-concept demonstration, an effective nonlinear susceptibility over 50 nm/V was measured and, after further optimization, over 480 nm/V was measured for second harmonic generation under normal incidence. The proposed concept shows that it is possible to engineer virtually any element of the nonlinear susceptibility tensor of the nonlinear metasurface.Electrical and Computer Engineerin

Recent progress in terahertz metamaterial modulators

The terahertz (0.1–10 THz) range represents a fast-evolving research and industrial field. The great interest for this portion of the electromagnetic spectrum, which lies between the photonics and the electronics ranges, stems from the unique and disruptive sectors where this radiation finds applications in, such as spectroscopy, quantum electronics, sensing and wireless communications beyond 5G. Engineering the propagation of terahertz light has always proved to be an intrinsically difficult task and for a long time it has been the bottleneck hindering the full exploitation of the terahertz spectrum. Amongst the different approaches that have been proposed so far for terahertz signal manipulation, the implementation of metamaterials has proved to be the most successful one, owing to the relative ease of realisation, high efficiency and spectral versatility. In this review, we present the latest developments in terahertz modulators based on metamaterials, while highlighting a few selected key applications in sensing, wireless communications and quantum electronics, which have particularly benefitted from these developments

Dynamic metamaterials towards terahertz applications

Metamaterials (MMs) and metasurfaces (MSs) as artificially engineered materials have revolutionized research for efficient manipulation of electromagnetic waves. Recent trends in MMs and MSs research have advanced towards the realization of modulated MMs and MSs that enable real-time control, thereby creating exceptional opportunities in the field of active and dynamic MMs and MSs via external stimulus such as electrical control, thermal gradient, optical excitations among others. In this work, fundamental physics and engineering applications have been investigated in several dynamic THz metamaterial designs. An optically tunable broadband silicon membrane metasurface absorber is introduced at first with the effective medium theory (EMT) analysis to explain the broadband absorption. The optical tunability is further acheived by optical pump, providing a promising platform to realize compact terahertz devices including detectors, modulators, and switches. Then, a vanadium dioxide (VO2)-integrated metamaterial is investigated with enhanced amplitude modulation upon traversing the insulating-to-metal transition (IMT). Neither Maxwell-Garnett nor Bruggeman EMT adequately describes the observed frequency shift and amplitude decrease during the phase transition. However, a Drude model incorporating a significant increase of the effective permittivity does describe the experimentally observed redshift. Our results highlight that symbiotic integration of metamaterial arrays with quantum materials provides a powerful approach to engineer emergent functionality. Finally, dynamic bound states in the continuum (BIC) is achieved from both a thermally-actuated bi-layer metamaterial and an optically tunable all-silicon metamaterial. Coupled mode theory (CMT) is implemented in both designs to explain the dynamic BIC responses. Both designs provide potential applications for nonlinear optics and light-matter control at terahertz frequencies. This thesis work demonstrates several potential methods towards functional terahertz devices through integration of metamaterials with MEMS technology for dynamic light-matter interactions

Topological Materials for Near-Field Radiative Heat Transfer

Topological materials provide a platform that utilizes the geometric characteristics of structured materials to control the flow of waves, enabling unidirectional and protected transmission that is immune to defects or impurities. The topologically designed photonic materials can carry quantum states and electromagnetic energy, benefiting nanolasers or quantum photonic systems. This article reviews recent advances in the topological applications of photonic materials for radiative heat transfer, especially in the near field. When the separation distance between media is considerably smaller than the thermal wavelength, the heat transfer exhibits super-Planckian behavior that surpasses Planck's blackbody predictions. Near-field thermal radiation in subwavelength systems supporting surface modes has various applications, including nanoscale thermal management and energy conversion. Photonic materials and structures that support topological surface states show immense potential for enhancing or suppressing near-field thermal radiation. We present various topological effects, such as periodic and quasi-periodic nanoparticle arrays, Dirac and Weyl semimetal-based materials, structures with broken global symmetries, and other topological insulators, on near-field heat transfer. Also, the possibility of realizing near-field thermal radiation in such topological materials for alternative thermal management and heat flux guiding in nano-scale systems is discussed based on the existing technology

A MAGNETO-THERMALLY CONTROLLABLE MICROSTRIP-PATCH ANTENNA FOR LOW RCS APPLICATIONS

This research focuses on the development of a novel technique for reducing the Radar Cross Section (RCS) of a microstrip antenna operating in the terahertz spectral regime. This can be accomplished by loading the antenna with Indium Antimonide (InSb); a thermally-magnetically controllable semi-conductor. The low-RCS feature of the antenna implies that it becomes hardly detectable by detecting radars; a desired feature in stealthy applications. For an optimal operation beside low RCS, the other antenna parameters (e.g., radiated power, gain, standing-wave ratio, and reflection coefficient) must be within tolerable ranges. Thus, a study on the effects of the temperature and the static magnetic field of the InSb on all antenna parameters has been conducted using the High-Frequency Structural Simulator (HFSS) software.A simple microstrip patch antenna loaded by InSb and fed by a coaxial cable has been simulated in HFSS. Plots of the various antenna parameters in relation to the temperature and the static magnetic field were obtained at some discrete frequency points; thereby revealing their effects on radiation characteristics. Furthermore, at each frequency point, the optimum values of the temperature and the static magnetic field were determined.Our proposed design provides means of controlling and modifying RCS in the terahertz regime; which may be varied depending on the specific application requirements, (i.e., military, medical, etc.)

Phase change materials for non-volatile photonic applications

Phase change materials (PCM) provide a unique property combination. Upon the transformation from the amorphous to the crystalline state, their optical properties change drastically. Short optical or electrical pulses can be utilized to switch between these states, making phase change materials attractive for photonic applications. We review recent developments of PCMs and evaluate the potential for all-photonic memories. Towards this goal, the progress as well as existing challenges to realize waveguides with stepwise adjustable transmission is presented. Colour-rendering and nano-pixel displays form another interesting application. Finally, nanophotonic applications based on plasmonic nanostructures are introduced. They provide reconfigurable, non-volatile functionality enabling manipulation and control of light. Requirements and perspectives to successfully implement PCMs in emerging areas of photonics are discussed