New Applications In Photonics Research Articles

Enhancement of second-harmonic generation in a lithium niobate metasurface by exploring the bound states in the continuum.

The nonlinear lithium niobate (LiNbO3), characterized by transparency across a broad spectral range from ultraviolet to mid-infrared, stands out as an ideal material for second-harmonic generation (SHG). The concept of bound states in the continuum (BIC) represents a non-radiative mode embedded within the radiation continuum, offering the capability to confine the electromagnetic field within the nanostructure. Here, we propose the design of a LiNbO3 metasurface utilizing the BIC mechanism to enhance SHG at fundamental wavelengths above 2 µm, which injects new thoughts into the field of integrated optics and on-chip photonics. Notably, we rigorously accounted for the influence of the side-wall angle θ and the corner rounding radius R of the LiNbO3 metasurface, which arises from fabrication tolerances. Considering those influences in the simulation, we achieved a quasi-BIC (q-BIC) with a quality factor (Q-factor) up to 1.44 × 105. Moreover, by considering the depleted pump model, the absolute efficiency of SHG reached 4.09% with a corresponding normalized efficiency of 8.19 × 10-10m2/W under a radiation intensity of 5 kW/cm2. Our research aims to establish a predictive framework through numerical simulations, specifically addressing realistic fabrication problems. This approach is intended to optimize the parameters for LiNbO3 metasurface fabrication, ensuring that the subsequent experiment efforts are efficient. Our findings provide an approach to predicting the optical response in actual structures and inspire new applications in photonics.

Modified Chalcogenide Glass Equations for the Activation Energy of Crystallization

For over six decades, chalcogenide glasses (ChGs) have played a pivotal role in the optical community, fostering innovations and new applications in photonics, electronics, and electro-optics. In the last decade, the exploration of novel applications, such as Gradient Index (GRIN) ChGs, has underscored the need for a nuanced comprehension and precise control of nucleation and crystallization kinetics in emerging infrared glass compositions. This article explores the activation energy of crystallization in amorphous materials, particularly focusing on ChGs. It identifies long-standing challenges associated with existing models used for crystal growth in nucleated glasses. Employing carefully outlined mathematical logic, our study critiques conventional models and introduces innovative equations centering around the need for balanced units and proper physical trends. These new models overcome some shortcomings of the established framework and provide a more accurate depiction of crystallization kinetics. To validate the efficacy of our proposed models, we conducted a comparative analysis using differential scanning calorimetry data from a recently published Sb-Te-Se chalcogenide glass composition. The numerical and graphical results clearly illustrate the improvements inherent in our models and their practical utility. Beyond ChGs, our models and equations have broader applications. They may extend to oxide, halide, oxy-halide, and fluoride glass compositions, as well as polymers, contributing new tools to the understanding of crystallization kinetics across diverse materials.

Temperature-dependent charge carrier behavior in phosphorene quantum dots probed by terahertz time-domain spectroscopy.

Although phosphorene quantum dots (PQDs) have gained significant attention in optoelectronics and physics due to their unique optical responses, the low-frequency electromagnetic properties of PQDs and the effects of temperature still remain largely unexplored. Herein, we investigate the temperature-dependent terahertz (THz) response of PQDs by using THz time-domain spectroscopy. Effective THz conductivity of the PQD sample is extracted based on THz measurements to analyze the charge carrier behavior. It is shown that the carriers in the PQDs can be approximated as a weakly confined Drude gas of classical and noninteracting charge particles, which are described by the modified Drude-Smith formula. Then, we also obtain the temperature dependences of the effective characteristic parameters for the charge carriers. As the temperature increases, the plasma frequency linearly enhances whereas both of the carrier diffusion time and the momentum scattering time decrease, which are akin to conventional semiconductors to a large extent. In addition, the confinement factor is closed to 1 and nearly insensitive to temperature. These results are helpful to gain an in-depth understanding of the low-frequency electromagnetic response of charge carriers in PQDs and to explore new applications in photonics and optoelectronics.

(Digital Presentation) Fabrication of Monolayer-Protected Gold Cluster Thin Films: Electrochemical and Optical Properties

Quantum-sized monolayer-protected gold clusters have captivated the imagination of scientists over the last two decades and show exciting optical, electrochemical and catalytic properties when compared to larger-sized plasmonic gold nanoparticles, making them useful for myriad new applications in photonics, catalysis and sensors. One interesting property is the photoluminescence (PL) of gold clusters making them suitable as biological imaging labels. However, the low PL Quantum Yields (QY) are a concern for these clusters and research is focused on improving the PL QYs. One strategy, our research group has worked on is the shell-gold rigidification via the use of surfactants and proteins. Shell ligand rigidification was achieved by ion pairing with bulky tertiary alkyl ammonium groups and aromatic chromophores. Another strategy to reduce the non-radiative deactivation pathways is by making the gold cluster thin films. In a recent study, it was shown that solid state films of clusters not only have manifold increase in PL quantum yield but also their luminescent lifetimes and two photon absorption cross-sections are greatly enhanced in comparison to their solution analogues. Researchers have worked on various strategies to make gold cluster thin films for device applications. One problem with thin films of gold clusters is that the clusters lose their interesting optical and electrochemical properties that were observed in solution phase. For making the clusters useful by enhancing PL for photonic device applications, it is important for the clusters to retain their properties in solid state, which is the main objective of the study carried out here. One problem is that drying intrinsic gold clusters results in crystallization whose optical properties are difficult to characterize. In this study, we have used Nafion and polyvinylpyrrolidone (PVP) to make thin films of water-soluble glutathione-protected gold clusters. Water soluble cluster Au22(SG)18 with reported PLQY of 8% were synthesized and characterized by UV-VIS absorption and PL measurements and thin films of these clusters were made using water soluble PVP and Nafion polymers via drop casting. Enhanced PL and electrochemical properties were observed for clusters in solid state. Similarly, non-polar gold cluster films are fabricated with Polystyrene and optical absorption and PL properties were retained in the solid state.Although drop casting with polymers was found to retain the optical properties, the uniformity of films is a problem. The uniformity of the film is dependent on solvent’s surface tension thus diminishing the quality of the film. Therefore, there is a need of depositing films of gold clusters in a controlled manner which governs their thickness and uniformity. Electropolymerization technique is known to make films during the polymerization of monomers possessing functional groups whose oxidation or reduction via anti-bonding or non-boding electrons on a heteroatom. In this study, we have used electropolymerization strategy to fabricate thin films of gold clusters on conducting substrates. The film is deposited at the working electrode during cyclic voltammetric (CV) sweep when passed through the required reduction or oxidation potential of the monomer under suitable conditions. This technique makes a uniform film throughout the exposed area of the working electrode active surface and the thickness of the film is often proportional to the number of sweep cycles employed. Therefore, introduction of gold clusters in this process with monomers which are previously known to bond with each other will incorporate clusters in the film during the polymerization process and will ease their film formation with uniform thickness. Amongst various size gold clusters, the one which shows good stability as a result of following the magic number series is Au25(SR)18 - . The stability of clustersis one of the important parameter required for practical applications. Aniline and other amine based monomers are used as precursors to make thin films of Au25 on conducting substrate such as Indium tin oxide. By solubilizing the gold clusters with the monomers they are deposited along with the polymers.

Defects and impurities in colloidal Ga2O3 nanocrystals: new opportunities for photonics and lighting

Defects, both native and extrinsic, critically determine functional properties of metal oxides. Gallium oxide has recently gained significant attention for its promise in microelectronics, owing to the unique combination of conductivity and high breakdown voltage, and solid-state lighting, owing to the strong photoluminescence in the visible spectral region. These properties are associated with the presence of native defects that can form both donor and acceptor states in Ga2O3. Recently, Ga2O3 nanocrystal synthesis in solution and optical glasses has been developed, allowing for a range of new applications in photonics, lighting, and photocatalysis. This review focuses on the structure and properties of Ga2O3 nanocrystals with a particular emphasis on the electronic structure and interaction of defects in reduced dimensions and their role in the observed photoluminescence properties. In addition to native defects, the effect of selected external impurities, including lanthanide and aliovalent dopants, and alloying on the emission properties of Ga2O3 nanocrystals are also discussed.

Switching resonance character within merocyanine stacks and its impact on excited-state dynamics

Summary In this study, the optical properties and excited-state dynamics of the unique self-assembled donor-acceptor (DA) merocyanine dye stacks from dimer up to octamer, prepared via dipole-dipole interactions, are reported in terms of coherent exciton dynamics and formation of an excimer-like state. Our findings are based on the steady-state absorption/emission, time-resolved fluorescence, and transient absorption (anisotropy) measurements, including wavepacket analysis and quantum mechanical calculations. Coherent exciton of torsional motions-restricted dye stacks rapidly localizes into the weakly emissive excimer-like state, by shortening the inter-moiety distance and changing the bond-length alternation pattern. The inner merocyanine moiety, having two neighboring units, has a reversed resonance character (non-polar (N) Z) in the ground state. This difference has led to two conclusions: (1) tetramers and octamers exhibit different features of excimer-like state than the dimer, and (2) octamers exhibit slower localization dynamics due to the enhanced homogeneity (six inner-moieties) compared with tetramers (two inner moieties).

Improved etching technique for creating sapphire nanostructures

Researchers experimented with multi-level etching masks and achieved a nine-fold increase in sapphire etching depth, which may lead to new applications in photonics, optoelectronics and other multifunctional materials.

Tungsten-disulphide-based heterojunction photodetector.

Two-dimensional (2D) materials have realized significant new applications in photonics, electronics, and optoelectronics. Among these materials is tungsten disulphide (WS2), which is a 2D material that shows excellent optoelectronic properties, tunable/sizable bandgap in the visible range, and good absorption. A polycrystalline WS2 thin film is successfully deposited on a substrate using radio frequency magnetron sputtering at room temperature. The x-ray diffraction pattern reveals two hexagonal structured peaks along the (100) and (110) planes. Energy-dispersive x-ray spectroscopy reveals a non-stoichiometric WS2 film with 1.25 ratio of S/W for a 156.3nm thick film, while Raman shifts are observed at the E2g1 and A1g phonon modes located at 350.70 cm-1 and 415.60 cm-1, respectively. A sandwiched heterojunction photodetector device is successfully fabricated and illuminated within the violet range at 441nm and 10V of bias voltage. The maximum photocurrent values are calculated as 0.95μA, while the responsivity is observed at 169.3 mA W-1 and detectivity 1.48×108 Jones at illuminated power of 0.6124μm. These results highlight the adaptability of the present technique for large-scale applications as well as the flexibility to promote development of advanced optoelectronic devices.

Subdiffraction Confinement in All-Semiconductor Hyperbolic Metamaterial Resonators

The strong optical anisotropy of hyperbolic metamaterials has enabled remarkable optical behavior such as negative refraction, enhancement of the photonic density of states, anomalous scaling of resonators, and super-resolution imaging. Resonators fashioned from these optical metamaterials support the confinement of light to dimensions much smaller than the diffraction limit. These ultrasmall resonators can be used to increase light–matter interactions for new applications in photonics. Here, we present subdiffraction mid-infrared resonators based on all-semiconductor hyperbolic metamaterials. Importantly, these resonators are fully compatible with epitaxial growth techniques and can be engineered to incorporate quantum well intersubband transitions that are degenerate with the mode of the resonators, enabling an entirely new generation of quantum optoelectronic devices. The strongest optical confinement achieved is λ/33 for a free-space wavelength of 10 μm, and the measured Q-factors are in the range of ...

Observation of optomechanical buckling transitions

Correlated phases of matter provide long-term stability for systems as diverse as solids, magnets and potential exotic quantum materials. Mechanical systems, such as buckling transition spring switches, can have engineered, stable configurations whose dependence on a control variable is reminiscent of non-equilibrium phase transitions. In hybrid optomechanical systems, light and matter are strongly coupled, allowing engineering of rapid changes in the force landscape, storing and processing information, and ultimately probing and controlling behaviour at the quantum level. Here we report the observation of first- and second-order buckling transitions between stable mechanical states in an optomechanical system, in which full control of the nature of the transition is obtained by means of the laser power and detuning. The underlying multiwell confining potential we create is highly tunable, with a sub-nanometre distance between potential wells. Our results enable new applications in photonics and information technology, and may enable explorations of quantum phase transitions and macroscopic quantum tunnelling in mechanical systems.

Generalized Brewster effect in dielectric metasurfaces.

Polarization is a key property defining the state of light. It was discovered by Brewster, while studying light reflected from materials at different angles. This led to the first polarizers, based on Brewster's effect. Now, one of the trends in photonics is the study of miniaturized devices exhibiting similar, or improved, functionalities compared with bulk optical elements. In this work, it is theoretically predicted that a properly designed all-dielectric metasurface exhibits a generalized Brewster's effect potentially for any angle, wavelength and polarization of choice. The effect is experimentally demonstrated for an array of silicon nanodisks at visible wavelengths. The underlying physics is related to the suppressed scattering at certain angles due to the interference between the electric and magnetic dipole resonances excited in the nanoparticles. These findings open doors for Brewster phenomenon to new applications in photonics, which are not bonded to a specific polarization or angle of incidence.

A review of progress in the physics of open quantum systems: theory and experiment

This report on progress explores recent advances in our theoretical and experimental understanding of the physics of open quantum systems (OQSs). The study of such systems represents a core problem in modern physics that has evolved to assume an unprecedented interdisciplinary character. OQSs consist of some localized, microscopic, region that is coupled to an external environment by means of an appropriate interaction. Examples of such systems may be found in numerous areas of physics, including atomic and nuclear physics, photonics, biophysics, and mesoscopic physics. It is the latter area that provides the main focus of this review, an emphasis that is driven by the capacity that exists to subject mesoscopic devices to unprecedented control. We thus provide a detailed discussion of the behavior of mesoscopic devices (and other OQSs) in terms of the projection-operator formalism, according to which the system under study is considered to be comprised of a localized region (Q), embedded into a well-defined environment (P) of scattering wavefunctions (with Q + P = 1). The Q subspace must be treated using the concepts of non-Hermitian physics, and of particular interest here is: the capacity of the environment to mediate a coupling between the different states of Q; the role played by the presence of exceptional points (EPs) in the spectra of OQSs; the influence of EPs on the rigidity of the wavefunction phases, and; the ability of EPs to initiate a dynamical phase transition (DPT). EPs are singular points in the continuum, at which two resonance states coalesce, that is where they exhibit a non-avoided crossing. DPTs occur when the quantum dynamics of the open system causes transitions between non-analytically connected states, as a function of some external control parameter. Much like conventional phase transitions, the behavior of the system on one side of the DPT does not serve as a reliable indicator of that on the other. In addition to discussing experiments on mesoscopic quantum point contacts that provide evidence of the environmentally-mediated coupling of quantum states, we also review manifestations of DPTs in mesoscopic devices and other systems. These experiments include observations of resonance-trapping behavior in microwave cavities and open quantum dots, phase lapses in tunneling through single-electron transistors, and spin swapping in atomic ensembles. Other possible manifestations of this phenomenon are presented, including various superradiant phenomena in low-dimensional semiconductors. From these discussions a generic picture of OQSs emerges in which the environmentally-mediated coupling between different quantum states plays a critical role in governing the system behavior. The ability to control or manipulate this interaction may even lead to new applications in photonics and electronics.

Reverse bistable effect in ferroelectric liquid crystal devices with ultra-fast switching at low driving voltage.

In this Letter, reverse bistable effect with deep-sub-millisecond switching time is first reported in ferroelectric liquid crystal (FLC) devices using a homogeneous photo-alignment technique. It is indicated by our experimental results that both the anchoring energy and the dielectric property of the FLC's alignment layer is critical for the existence of the reverse bistable effect. In addition, with the derived criteria of the reverse bistable effect, we quantitatively analyze the switching dynamics of the reverse bistable FLC and the transition condition between the traditional bistability and our presented reverse bistability. Moreover, the fabricated FLC device exhibits an ultra-fast switching of ∼160 μs and a high contrast ratio of 1000:1, both of which were measured at a low driving voltage of 11 V. The featured deep-sub-millisecond switching time is really advantageous for our presented reverse bistable FLC devices, which enables a significant quality improvement of the existing optical devices, as well as a wide range of new applications in photonics and display areas.

Energy transfer in supramolecular materials for new applications in photonics and electronics

Supramolecular materials use self-assembly of molecular components to form complex architectures that may otherwise be extremely difficult to prepare. One of the fundamental aspects of this approach is that relatively weak intermolecular forces are used to direct the assembly of the subcomponents. An important point is how to achieve strong electronic communication throughout the material in view of the ‘looseness’ of the molecular constituents, which interact only weakly. This is particularly important for applications in molecular electronics where exciton delocalization and charge transport generally limit the overall device performance. This review focuses on recent advances in supramolecular materials and architectures that are engineered to possess efficient energy transfer between the self-assembled component in view of new applications in photonics and electronics. Many biological functions are performed by molecules that self-assemble into large structures, and this concept is also used in supramolecular chemistry to design artificial single-molecule devices. Ken-Tsung Wong from National Taiwan University and Dario Bassani from the University of Bordeaux in France review efforts in supramolecular chemistry to achieve a strong electrical connection between different sections of such devices, even if they are only connected via weak chemical bonds. A strong energy transfer is important for electronic and photonic applications and can be achieved through the control of various intermolecular forces, such as hydrogen bonds. A further issue is the directionality of the energy transfer in a molecule. This poses a challenge for applications such as solar cells but can be mitigated though the use of appropriate molecular geometries such as tubes or nanowires. The scope and limitations of using supramolecular interactions to control and direct energy transfer processes in self-assembled materials are discussed with emphasis on recent developments in the field.

Domains stack up

Stacked bilayers can exhibit columnar alignment of phase-separated domains that propagates across hundreds of layers. The serial coupling of functionality that may result from such a long-range arrangement should lead to new applications in photonics and sensing.

Analogue of the Quantum Hanle Effect and Polarization Conversion in Non-Hermitian Plasmonic Metamaterials

The Hanle effect, one of the first manifestations of quantum theory introducing the concept of coherent superposition between pure states, plays a key role in numerous aspects of science varying from applicative spectroscopy to fundamental astrophysical investigations. Optical analogues of quantum effects help to achieve deeper understanding of quantum phenomena and, in turn, to develop cross-disciplinary approaches to realizations of new applications in photonics. Here we show that metallic nanostructures can be designed to exhibit a plasmonic analogue of the quantum Hanle effect and the associated polarization rotation. In the original Hanle effect, time-reversal symmetry is broken by a static magnetic field. We achieve this by introducing dissipative level crossing of localized surface plasmons due to nonuniform losses, designed using a non-Hermitian formulation of quantum mechanics. Such artificial plasmonic "atoms" have been shown to exhibit strong circular birefringence and circular dichroism which depends on the value of loss or gain in the metal-dielectric nanostructure.

Molecules of ruthenium-based olefin metathesis catalysts as two- and three-photon absorbers

Three ruthenium-based complexes exhibiting catalytic activity in olefin metathesis have been examined for the presence of interesting nonlinear optical (NLO) properties. Measurements were performed by the Z-scan technique using a tunable femtosecond laser system. This initial screening for potential new applications in photonics of complexes representative of a wide family of ruthenium-based olefin metathesis catalysts has found moderately strong two-photon and three-photon absorption properties in relatively simple molecules that may lead to the development of a new class of strong nonlinear absorbers.

Hollow ZnO Nano-cone Synthesis via Catalyst Free MOCVD

ABSTRACTZinc oxide is a wide band gap material with excellent semiconducting, photonic and piezoelectric properties. In the past ten years zinc oxide nano-structures such as nanowires and nanorods have received great interest due to their unique dimensional and material properties in the area of photonics, electronics, mechanics, energy recovery, etc. In this paper we report the manufacturing process of a new shape, i.e. hollow hexagonal ZnO nano-cones. We grew them on different kinds of substrate using a low pressure, catalyst free, metal organic chemical vapor deposition (MOCVD) process on a FirstNano EasyTube 3000™ MOCVD system. Nitrogen was used as carrier gas to bring the reactants, DEZ and H2O, to the substrate surface. At the right balance of process temperature and carrier/precursor gas flow rate the ZnO nano-structure transitioned into a hollow hexagonal cones growth mode. The both one and two dimensional aspects of these catalyst free hollow hexagonal ZnO nano-cones, which are novel to the best of our knowledge, could lead to new applications in photonics, near field probing, chemical sensors, quantum confinement, electronic, etc.

From Montpellier 1985 to Montpellier 2007

Since the pioneering meeting in 1981 in Padova, the international sol–gel community (now represented by the ISGS—International Sol–Gel Society) has celebrated advances in sol–gel science and technology in what has now become an important biannual conference series. The aim of the first meeting was to bring together eminent scientists working in this field throughout the world, to promote the exchange of ideas and the development of sol–gel materials with new potential applications. In September 1985, the third meeting in this series (the ‘‘Third International Workshop on Glasses and Glass Ceramics from Gels’’) was held in Montpellier (France). Twenty-two years later (in 2007), it returned to Montpellier as the ‘‘14th International Sol–Gel Conference’’. The outstanding success of this most recent meeting makes it tempting to offer a brief overview of the striking evolution of sol–gel science and technology over the past two decades. Thus, the original ‘‘workshop’’ has now become a ‘‘conference’’, with two parallel sessions featuring nearly 80 talks and more than 450 posters by delegates from 41 countries. This reflects the interest of the scientific community in the multidisciplinary field now simply referred to as ‘‘sol–gel’’, which has now grown well beyond its origins in traditional materials science underpinning development in glasses and ceramics. Historically the ninth workshop held in 1997 in Sheffield (England) was the first to extend the focus of the workshops to include ‘‘Hybrids and Nanocomposites from Gels’’, acknowledging the considerable developments in organic– inorganic materials. Combining organic and inorganic functionalities through a sophisticated ‘‘bottom up’’ approach, such hybrid materials considerably extended the range of accessible properties and inherent versatility of sol–gel materials. This approach led to new applications in photonics, sensing and electrochemistry. In the field of macromolecular chemistry, it led to hybrid nanocomposites, including polymers reinforced with inorganic nanofillers, as well as inorganic nanoparticles coated with an organic layer, and even systems with two interpenetrating continuous phases. The burst of research on nanoporous materials, synthesised by using self-assembling organic species as supramolecular templates stood out in the late nineties. It led to the development of materials with periodic porosity and hierarchical structures resulting in considerable technical developments, especially in the implementation of nanostructured films. In more recent times, the evolution of the field towards medical applications (drug delivery, bio-imaging etc.) and biomaterials is striking. Following the pioneering works of David Avnir and Jacques Livage, there is currently a growing interest in materials at the interface with biology such as those stemming from the encapsulation of enzymes and living cells in gels. This volume is the first of the Special Issues of the Journal of Sol–Gel Science and Technology devoted to the 14th International Sol–Gel Conference. It features work presented by Keynote and Invited speakers, including the work of the recipients of the Ulrich Awards and the Life Achievement Award. It is intended to provide an overview of the current state of—and key developments in—sol–gel science and technology and to illustrate the unique ‘‘melting pot’’ of knowledge, skills and concepts which will stimulate the development of tomorrow’s innovative technologies. We hope that you share our sense of excitement about the directions in which the field is evolving, as it continues to build up on its strong foundations in physics, biology and molecular chemistry. M. W. C. Man A. Vioux (&) Institut Charles Gerhardt, Montpellier, France e-mail: vioux@univ-montp2.fr

Direct‐Write Assembly of Three‐Dimensional Photonic Crystals: Conversion of Polymer Scaffolds to Silicon Hollow‐Woodpile Structures

Abstract : Impressive developments in silicon microfabrication are enabling new applications in photonics, microelectromechanical systems (MEMS), and biotechnology. Yet conventional Si microfabrication techniques require expensive masks and time-consuming procedures, including multiple planarization or bonding steps, to generate three-dimensional (3D) structures. In contrast, direct-write approaches, such as laser scanning and ink deposition, provide rapid, flexible routes for fabricating 3D micro-periodic structures. However, these approaches are currently limited to polymeric structures that lack the high refractive index contrast and mechanical integrity required for many applications. To take full advantage of these rapid, flexible assembly techniques, one must develop a replication (or templating) scheme that enables their structural conversion within the temperature constraints imposed by both the organic and inorganic components of the system. Here, we present a novel route for creating 3D Si hollow-woodpile structures that couples direct-write assembly of concentrated polyelectrolyte inks with a sequential silica/Si chemical vapor deposition (CVD) process. The optical properties of the 3D microperiodic woodpiles are characterized after each fabrication step. These interconnected, hollow structures may find potential application as photonic materials, low-cost MEMS, microfluidic networks for heat dissipation, and biological devices.