Wave propagation in ordered, disordered, and nonlinear photonic band gap materials

Photonic band gap materials are artificial dielectric structures that give the promise of molding and controlling the flow of optical light the same way semiconductors mold and control the electric current flow. Their basic property is the photonic gap, a frequency range in which wave propagation is not allowed in any direction, in a close analogy with the electronic energy band gap in semiconductors;In this dissertation we study two areas of photonic band gap materials. The first area is focused on the properties of one-dimensional PBG materials doped with Kerr-type nonlinear material. Such systems have been shown to exhibit bistability, an essential feature for an all-optical switching mechanism. Here, we will study an approximate structure model, in which the nonlinear material is concentrated in very thin, or delta-function, layers. We will derive analytical solutions, and compare with the finite-width nonlinear layer case, in order to find it\u27s limitations and the physical mechanisms behind them. Also, by using numerical simulations, we will study the dynamics of an externally-controlled switching mechanism for such systems, which is pulse injection while they are illuminated by a constant wave. Finally, we will develop a model for the nonlinear response of colloidal crystals, which will reveal a light-lattice coupling similar to the electron-phonon in semiconductors;The second area of study is focused on the mechanisms responsible for the gap formation, as well as other properties of two-dimensional PBG materials. We will show that in one case, the dominant gap-forming mechanism is the excitation of single scatterer Mie resonances and not Bragg-like multiple scattering, and that the photonic states are analogous to the localized atomic orbitals in semiconductors. We will develop a tight-binding model based on a linear combination of Mie resonances, that will successfully reproduce the photonic band structure of any lattice arrangement, with and without defects, thus proving the validity of a strongly localized photon picture. Then, using ab initio numerical techniques, we will study the effects of disorder for various realizations of two-dimensional photonic band gap materials, and identify the cases for which the strongly localized photon picture applies, and those for which a nearly free photon picture is a more proper one

Flat-band localization and self-collimation of light in photonic crystals

We investigate the optical properties of a photonic crystal composed of a quasi-one-dimensional flat-band lattice array through finite-difference time-domain simulations. The photonic bands contain flat bands (FBs) at specific frequencies, which correspond to compact localized states as a consequence of destructive interference. The FBs are shown to be nondispersive along the $\Gamma\rightarrow X$ line, but dispersive along the $\Gamma\rightarrow Y$ line. The FB localization of light in a single direction only results in a self-collimation of light propagation throughout the photonic crystal at the FB frequency.Comment: 18 single-column pages, 7 figures including graphical to

Laser Annealing as a Platform for Plasmonic Nanostructuring

Nanoconstruction of metals is a significant challenge for the future manufacturing of plasmonic devices. Such a technology requires the development of ultra‐fast, high‐throughput and low cost fabrication schemes. Laser processing can be considered as such and can potentially represent an unrivalled tool towards the anticipated arrival of modules based in metallic nanostructures, with an extra advantage: the ease of scalability. Specifically, laser nanostructuring of either thin metal films or ceramic/metal multilayers and composites can result on surface or subsurface plasmonic patterns, respectively, with many potential applications. In this chapter, the photo‐thermal processes involved in surface and subsurface nanostructuring are discussed and processes to develop functional plasmonic nanostructures with pre‐determined morphology are demonstrated. For the subsurface plasmonic conformations, the temperature gradients that are developed spatially across the metal/dielectric structure during the laser processing can be utilized. For the surface plasmonic nanoassembling, the ability to tune the laser\u27s wavelength to either match the absorption spectral profile of the metal or to be resonant with the plasma oscillation frequency can be utilised, i.e. different optical absorption mechanisms that are size‐selective can be probed. Both processes can serve as a platform for stimulating further progress towards the engineering of large‐scale plasmonic devices

Surface-Enhanced Raman Spectroscopy of Graphene Integrated in Plasmonic Silicon Platforms with Three-Dimensional Nanotopography

Integrating graphene with plasmonic nanostructures results in multifunctional hybrid systems with enhanced performance for numerous applications. In this work, we take advantage of the remarkable mechanical properties of graphene to combine it with scalable three-dimensional (3D) plasmonic nanostructured silicon substrates, which enhance the interaction of graphene with electromagnetic radiation. Large areas of femtosecond laser-structured arrays of silicon nanopillars, decorated with gold nanoparticles, are integrated with graphene, which conforms to the substrate nanotopography. We obtain Raman spectra at 488, 514, 633, and 785 nm excitation wavelengths, spanning the entire visible range. For all excitation wavelengths, the Raman signal of graphene is enhanced by 2–3 orders of magnitude, similarly to the highest enhancements measured to date, concerning surface-enhanced Raman spectroscopy of graphene on plasmonic substrates. Moreover, in contrast to traditional deposition and lithographic methods, the fabrication method employed here relies on single-step, maskless, cost-effective, rapid laser processing of silicon in water, amenable to large-scale fabrication. Finite-difference time-domain simulations elucidate the advantages of the 3D topography of the substrate. Conformation of graphene to Au-decorated silicon nanopillars enables graphene to sample near fields from an increased number of nanoparticles. Due to synergistic effects with the nanopillars, different nanoparticles become more active for different wavelengths and locations on the pillars, providing broad-band enhancement. Nanostructured plasmonic silicon is a promising platform for integration with graphene and other 2D materials, for next-generation applications of large-area hybrid nanomaterials in the fields of sensing, photonics, optoelectronics, and medical diagnostics

Fast and sensitive terahertz detection using an antenna-integrated graphene pn-junction

Although the detection of light at terahertz (THz) frequencies is important for a large range of applications, current detectors typically have several disadvantages in terms of sensitivity, speed, operating temperature, and spectral range. Here, we use graphene as photoactive material to overcome all of these limitations in one device. We introduce a novel detector for terahertz radiation that exploits the photo-thermoelectric effect, based on a design that employs a dual-gated, dipolar antenna with a gap of ~100 nm. This narrow-gap antenna simultaneously creates a pn-junction in a graphene channel located above the antenna, and strongly concentrates the incoming radiation at this pn-junction, where the photoresponse is created. We demonstrate that this novel detector has excellent sensitivity, with a noise-equivalent power of 80 pW/√Hz at room temperature, a response time below 30 ns (setup-limited), a high dynamic range (linear power dependence over more than 3 orders of magnitude) and broadband operation (measured range 1.8 - 4.2 THz, antenna-limited), which fulfils a combination that is currently missing in the state of the art. Importantly, based on the agreement we obtain between experiment, analytical model, and numerical simulations, we have reached a solid understanding of how the PTE eect gives rise to a THz-induced photoresponse, which is very valuable for further detector optimization.Peer ReviewedPostprint (author's final draft

Plasmonic antenna coupling to hyperbolic phonon-polaritons for sensitive and fast mid-infrared photodetection with graphene

Integrating and manipulating the nano-optoelectronic properties of Van der Waals heterostructures can enable unprecedented platforms for photodetection and sensing. The main challenge of infrared photodetectors is to funnel the light into a small nanoscale active area and efficiently convert it into an electrical signal. Here, we overcome all of those challenges in one device, by efficient coupling of a plasmonic antenna to hyperbolic phonon-polaritons in hexagonal-BN to highly concentrate mid-infrared light into a graphene pn-junction. We balance the interplay of the absorption, electrical and thermal conductivity of graphene via the device geometry. This novel approach yields remarkable device performance featuring room temperature high sensitivity (NEP of 82 pW-per-square-root-Hz) and fast rise time of 17 nanoseconds (setup-limited), among others, hence achieving a combination currently not present in the state-of-the-art graphene and commercial mid-infrared detectors. We also develop a multiphysics model that shows excellent quantitative agreement with our experimental results and reveals the different contributions to our photoresponse, thus paving the way for further improvement of these types of photodetectors even beyond mid-infrared range

Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.Peer ReviewedPostprint (published version

Wave propagation in ordered, disordered, and nonlinear photonic band gap materials

Photonic band gap materials are artificial dielectric structures that give the promise of molding and controlling the flow of optical light the same way semiconductors mold and control the electric current flow. Their basic property is the photonic gap, a frequency range in which wave propagation is not allowed in any direction, in a close analogy with the electronic energy band gap in semiconductors;In this dissertation we study two areas of photonic band gap materials. The first area is focused on the properties of one-dimensional PBG materials doped with Kerr-type nonlinear material. Such systems have been shown to exhibit bistability, an essential feature for an all-optical switching mechanism. Here, we will study an approximate structure model, in which the nonlinear material is concentrated in very thin, or delta-function, layers. We will derive analytical solutions, and compare with the finite-width nonlinear layer case, in order to find it's limitations and the physical mechanisms behind them. Also, by using numerical simulations, we will study the dynamics of an externally-controlled switching mechanism for such systems, which is pulse injection while they are illuminated by a constant wave. Finally, we will develop a model for the nonlinear response of colloidal crystals, which will reveal a light-lattice coupling similar to the electron-phonon in semiconductors;The second area of study is focused on the mechanisms responsible for the gap formation, as well as other properties of two-dimensional PBG materials. We will show that in one case, the dominant gap-forming mechanism is the excitation of single scatterer Mie resonances and not Bragg-like multiple scattering, and that the photonic states are analogous to the localized atomic orbitals in semiconductors. We will develop a tight-binding model based on a linear combination of Mie resonances, that will successfully reproduce the photonic band structure of any lattice arrangement, with and without defects, thus proving the validity of a "strongly localized" photon picture. Then, using ab initio numerical techniques, we will study the effects of disorder for various realizations of two-dimensional photonic band gap materials, and identify the cases for which the "strongly localized" photon picture applies, and those for which a "nearly free" photon picture is a more proper one.</p