Wide Band Embedded Slot Antennas for Biomedical, Harsh Environment, and Rescue Applications

For many designers, embedded antenna design is a very challenging task when designing embedded systems. Designing Antennas to given set of specifications is typically tailored to efficiently radiate the energy to free space with a certain radiation pattern and operating frequency range, but its design becomes even harder when embedded in multi-layer environment, being conformal to a surface, or matched to a wide range of loads (environments). In an effort to clarify the design process, we took a closer look at the key considerations for designing an embedded antenna. The design could be geared towards wireless/mobile platforms, wearable antennas, or body area network. Our group at UT has been involved in developing portable and embedded systems for multi-band operation for cell phones or laptops. The design of these antennas addressed single band/narrowband to multiband/wideband operation and provided over 7 bands within the cellular bands (850 MHz to 2 GHz). Typically the challenge is: many applications require ultra wide band operation, or operate at low frequency. Low frequency operation is very challenging if size is a constraint, and there is a need for demonstrating positive antenna gain

Quantum dot plasmon coupling : Fundamental study and applications

The dissertation focuses on the engineering of light-matter interaction using plasmonic nanoparticles and metamaterials to achieve enhanced luminescence and based on which to improve the performance of biosensing and light-emitting technologies. We designed and fabricated a spectrum of nanostructures to exhibit particular dispersion relations capable of controlling the spontaneous emission properties of quantum emitters, such as quantum dots and organic fluorophores. To realize the concept, we developed a metal-assisted focused-ion beam nanopatterning technology to fabricate the plasmonic nanostructures with high-definition. We demonstrated a silver open-ring nanoarrays (ORA) for broadband enhancement of QD emission that was further exploited to demonstrate ultrasensitive DNA sensing. The ORA design offers multiple resonance peaks to support both Purcell effect and excitation enhancement, resulting in a maximal enhancement in QD emission of greater than 100 times and significant improvement in the limit-of-detection of DNA sensing by four orders of magnitude. Another plasmonic nanostructure, aluminum dimple array, was developed to take advantage of the inherent UV plasmonic property of aluminum for broadband enhancement of QD emission. The device may find major applications in optoelectronic devices. While the small-area plasmonic devices are suitable to enhance the fluorescence-based sensors on a chip, there exists a need for large-area enhancement for several applications. For this purpose, we developed multilayered hyperbolic metamaterials accompanied with an efficient light-extraction approach to achieve enhanced quantum dot emission over a large area. Lastly, we expanded the enhancement strategy using plasmonic nanoparticles to improve carbon dot-based microLEDs. The embedded plasmonic nanoparticles were utilized to enhance carbon dot emission while minimizing the UV excitation leak–age. This research provides a set of design rules for enhanced spontaneous emission and the demonstrated applications are expected to pave the way to advanced photonic, biosensing, and optoelectronic devices

Graphene-Assisted Integrated Nonlinear Optics

‎The unique linear and massless band structure of graphene in a purely two-dimensional Dirac fermionic structure has ignited intense research since the first monolayer graphene was isolated in the laboratory‎. ‎Not only does it offer new inroads into low-dimensional physics; graphene exhibits several peculiar properties that promise to widen the realm of opportunities for integrated optics and photonics‎. ‎This thesis is an attempt to shed light on the exceptional nonlinear optical properties of graphene and their potential applications in integrated photonics‎. ‎Following a theoretical exploration of light-graphene interaction‎, ‎disruptive new insight into the nonlinear optics of graphene was generated‎. ‎It now appears that graphene can efficiently enable photon-photon interaction in a fully integrated fashion‎. ‎This property‎, ‎taken together with ultrawideband tunability and ultrafast carrier dynamics could be fully exploited within integrated photonics for a variety of applications including harmonic generation and all-optical signal processing‎. ‎The multidisciplinary work described herein combines theoretical modeling and experimentation to proceed one step further toward this goal‎. ‎This thesis begins by presenting a semiclassical theory of light-graphene interaction‎. ‎The emphasis is placed on the nonlinear optical response of graphene from the standpoint of its underlying chiral symmetry‎. ‎The peculiar energy‎- ‎momentum dispersion of the quasiparticles in graphene entails a diverging field-induced interband coupling‎. ‎Following a many-body study of the carrier relaxations dynamics in graphene‎, ‎it will be shown that the charged carriers in the vicinity of the Dirac point undergo an unconventional saturation effect that can be induced by an arbitrarily weak electromagnetic field‎. ‎The perturbative treatment of the optical response of graphene is revisited and a theoretical model is developed to estimate the nonlinear optical coefficients including the Kerr coefficient of graphene‎. ‎The theoretical models are complimented by the experimental results‎. ‎The peculiar nonlinear optical properties of graphene together with its ablity to being integrated with optical platforms would render it possible to perform nonlinear optics in graphene integrated nanophotonic structures‎. ‎Here‎, ‎the suitability of graphene for nonlinear optical applications is investigated both theoretically and experimentally‎. ‎The emphasis is placed on an on-chip platform for ultrafast all-optical amplitude modulation‎. ‎The experimental results indicate strong all-optical modulation in a graphene-cladded planar photonic crystal nanocavity‎. ‎This development relies heavily on the unique properties of graphene‎, ‎including its fast carrier dynamics and the special phonon induced relaxation mechanism‎. ‎Finally‎, ‎the potential application of graphene based all-optical modulation in time resolved nonlinear spectroscopy is also discussed‎

Graphene-Assisted Integrated Nonlinear Optics

‎The unique linear and massless band structure of graphene in a purely two-dimensional Dirac fermionic structure has ignited intense research since the first monolayer graphene was isolated in the laboratory‎. ‎Not only does it offer new inroads into low-dimensional physics; graphene exhibits several peculiar properties that promise to widen the realm of opportunities for integrated optics and photonics‎. ‎This thesis is an attempt to shed light on the exceptional nonlinear optical properties of graphene and their potential applications in integrated photonics‎. ‎Following a theoretical exploration of light-graphene interaction‎, ‎disruptive new insight into the nonlinear optics of graphene was generated‎. ‎It now appears that graphene can efficiently enable photon-photon interaction in a fully integrated fashion‎. ‎This property‎, ‎taken together with ultrawideband tunability and ultrafast carrier dynamics could be fully exploited within integrated photonics for a variety of applications including harmonic generation and all-optical signal processing‎. ‎The multidisciplinary work described herein combines theoretical modeling and experimentation to proceed one step further toward this goal‎. ‎This thesis begins by presenting a semiclassical theory of light-graphene interaction‎. ‎The emphasis is placed on the nonlinear optical response of graphene from the standpoint of its underlying chiral symmetry‎. ‎The peculiar energy‎- ‎momentum dispersion of the quasiparticles in graphene entails a diverging field-induced interband coupling‎. ‎Following a many-body study of the carrier relaxations dynamics in graphene‎, ‎it will be shown that the charged carriers in the vicinity of the Dirac point undergo an unconventional saturation effect that can be induced by an arbitrarily weak electromagnetic field‎. ‎The perturbative treatment of the optical response of graphene is revisited and a theoretical model is developed to estimate the nonlinear optical coefficients including the Kerr coefficient of graphene‎. ‎The theoretical models are complimented by the experimental results‎. ‎The peculiar nonlinear optical properties of graphene together with its ablity to being integrated with optical platforms would render it possible to perform nonlinear optics in graphene integrated nanophotonic structures‎. ‎Here‎, ‎the suitability of graphene for nonlinear optical applications is investigated both theoretically and experimentally‎. ‎The emphasis is placed on an on-chip platform for ultrafast all-optical amplitude modulation‎. ‎The experimental results indicate strong all-optical modulation in a graphene-cladded planar photonic crystal nanocavity‎. ‎This development relies heavily on the unique properties of graphene‎, ‎including its fast carrier dynamics and the special phonon induced relaxation mechanism‎. ‎Finally‎, ‎the potential application of graphene based all-optical modulation in time resolved nonlinear spectroscopy is also discussed‎

Present and Future of Surface-Enhanced Raman Scattering.

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article