Bianisotropic Effective Parameters of Optical Metamagnetics and Negative-Index Materials

Approaches to the adequate homogenization of optical metamaterials are becoming more and more complex, primarily due to an increased understanding of the role of asymmetric electrical and magnetic responses, in addition to the nonlocal effects of the surrounding medium, even in the simplest case of plane-wave illumination. The current trend in developing such advanced homogenization descriptions often relies on utilizing bianisotropic models as a base on top of which novel optical characterization techniques can be built. In this paper, we first briefly review general principles for developing a bianisotropic homogenization approach. Second, we present several examples validating and illustrating our approach using single-period passive and active optical metamaterials. We also show that the substrate may have a significant effect on the bianisotropic characteristics of otherwise symmetric passive and active metamaterials

All-dielectric planar chiral metasurface with gradient geometric phase

Planar optical chirality of a metasurface measures its differential response between left and right circularly polarized (CP) lights and governs the asymmetric transmission of CP lights. In 2D ultra-thin plasmonic structures the circular dichroism is limited to 25% in theory and it requires high absorption loss. Here we propose and numerically demonstrate a planar chiral all-dielectric metasurface that exhibits giant circular dichroism and transmission asymmetry over 0.8 for circularly polarized lights with negligible loss, without bringing in bianisotropy or violating reciprocity. The metasurface consists of arrays of high refractive index germanium Z-shape resonators that break the in-plane mirror symmetry and induce cross-polarization conversion. Furthermore, at the transmission peak of one handedness, the transmitted light is efficiently converted into the opposite circular polarization state, with a designated geometric phase depending on the orientation angle of the optical element. In this way, the optical component sets before and after the metasurface to filter the light of certain circular polarization states are not needed and the metasurface can function under any linear polarization, in contrast to the conventional setup for geometry phase based metasurfaces. Anomalous transmission and two-dimensional holography based on the geometric phase chiral metasurface are numerically demonstrate as proofs of concept

Co-design of Reconfigurable and Multifunction Passive RF/Microwave Components

In order to meet the market demands, multi-band communication systems that are able to accommodate different wireless technologies to be compatible with different wireless standards should be investigated and realized. Multifunction and multi-band RF front-end components are promising solutions for reducing the size and enhancing the performance of multi-band communication systems. This dissertation focuses on the design and implementation of different multifunction and tunable microwave components for use in multi-standard, flexible transceiver. For frequency-domain duplexing (FDD) communication systems, in which the uplink and downlink channels are carried on different RF frequencies, a diplexer is an essential component to separate the transmitting and receiving signals from the antenna. Electrically tunable diplexers simplify the architecture of reconfigurable RF-front end. Moreover, in modern communication systems, the crowding of the spectrum and the scaling of electronics can result in higher common-mode interference and even-order non-linearity issues. In this dissertation, three tunable compact SIW-based dual-mode diplexers, with various SE (single-ended) and BAL (balanced) capabilities, are introduced for the first time. The dual-mode operation results in a dependent tuning between the two ports. The presented designs are for SE-SE, SE-BAL, and BAL-BAL. However, based on the presented design concepts, any combination of the diplexer ports can be achieved in terms of supporting the balanced and single-ended system interface. The fabricated diplexers show low insertion loss, high isolation, good tuning range and high common mode rejection. Tunable bandstop filter (BSF) is one of the essential components in the design of RF front-ends that require wide-band operations. A wide-open front-end leaves the receiver vulnerable to jamming by high-power signals. As a result, this type of front-ends requires dynamic isolation of any interfering signal. Realization of such filters in a balanced configuration, as a second function, is an important step in the realization of full-balanced RF front-ends. Balanced (differential) circuits have many important advantages over unbalanced (single-ended) circuits such as immunity to system noise, reduction of transient noise generation and inherent suppression of even-order nonlinearities. All reported balanced filters are bandpass filters that target wide pass-bands and high common-mode rejection. These filters are necessary for wide-band RF front-ends but, as mentioned above, leave the system open to interferers and jammers. In this dissertation, a new differential coupling structure for evanescent-mode cavity resonators is developed, enabling the design of fully-balanced tunable BSF. The proposed filter is tunable from 1.57-3.18 GHz with 102% tuning range. In addition, over the full range, the measured 10-dB fractional bandwidth ranges from 1-2.4%, and the attenuation level is better than 47 dB. Lastly, Substrate Integrated Waveguide (SIW) evanescent-mode cavity resonators (EVA) are employed in the design of RF couplers, quadrature hybrid and rat-race couplers. These couplers are used in the design of numerous RF front-end components such as power amplifiers, balanced mixers, and antenna array feeding networks. Utilizing such resonators (EVA) in the design allows the couplers to have wide spurious-free range, low power consumption, high power handling capability and both tunability and filtering capabilities. The proposed quadrature hybrid coupler can be tuned starting from 1.32–2.22 GHz with a measured insertion loss range from 1.29 to 0.7 dB. The measured reflection and isolation are better than 12 dB and 17 dB, respectively. Moreover, the coupler has a measured spurious free range of 5.1–3fo (lowest–highest frequency). Regarding rat-race coupler, two designs are introduced. The first design is based on a full-mode cavity while the second one is more compact and based on a half-mode cavity. Both designs show more than 70% tuning range, and the isolation is better than 30 dB

Photonic Metasurfaces for Spatiotemporal and Ultrafast Light Control

The emergence of photonic metasurfaces - planar arrays of nano-antennas - has enabled a new paradigm of light control through wave-front engineering. Space-gradient metasurfaces induce spatially varying phase and/or polarization to propagating light. As a consequence, photons propagating through space-gradient metasurfaces can be engineered to undergo a change to their momentum, angular momentum and/or spin states

Manipulating Electromagnetic Fields with Advanced Metamaterials

In almost any scientific experiment, we take into account some particular properties of materials, e.g. electromagnetic, mechanical, thermal, etc. These properties determine a majority of the physical phenomena that arise from the interaction with matter, and thus restrict potential applications of natural materials. The discovery and subsequent development of novel materials regularly boost the standards of living through new technological progress and cutting-edge research. One of the very recent and promising discoveries is related to the field of metamaterials - artificially structured media with subwavelength patterning. These artificial materials offer a unique platform with large flexibility and unusual properties for tailoring acoustic and electromagnetic waves, including novel ways for the manipulation of light. In this thesis, I employed the concept of metamaterials for both the study of new physical phenomena related to the emerging field of topological photonics and also develop innovative applications of specific metamaterials for the advancing the magnetic resonance imaging (MRI) machines. Chapter 1 provides an introduction to the field of metamaterials and their unusual properties, starting from the definition of meta-atoms and expanding to more complex structures, including one-dimensional meta-chains and metasurfaces. This is followed by an introduction to the fields of topological photonics and magnetic resonance imaging techniques. The experimental approaches based on a microwave platform are also described. Finally, the thesis motivation and structure are summarized. Chapter 2 presents experimental studies of topological features of zigzag arrays of dielectric particles. It includes the first experimental observation of the subwavelength photonic topological edge states, topological phase transition in the chains of dielectric particles, as well as, the study of the specific features of the photonic spin Hall effect mediated by the excitation of the subwavelength topological edge states. Chapter 3 describes the study of bianisotropic metasurfaces and metamaterials. The experimental designs of bianisotropic metallic and dielectric metasurfaces are presented, with a direct observation of topologically nontrivial edge states. Further, it is revealed how to couple topologically protected metasurfaces to form three-dimensional all-dielectric topologically nontrivial bianisotropic metamaterials and metacrystals. Chapter 4 focuses on the study metasurfaces based on resonant arrays of metallic wires used for advancing magnetic resonance imaging (MRI) characteristics. A new conceptual idea for the substantial enhancement of signal-to-noise ratio of a 1.5T MRI is presented. This approach is further developed and extended to ultra-high field MRI (7T) where a direct evaluation of the metasurface properties is examined during in-vivo human brain imaging. Chapter 5 summarizes the results and concludes the thesis