Behavior Of Waveguides Research Articles

Statistical Patterns of Transmission Losses of Low-Frequency Sound in Shallow Sea Waveguides with Gaussian and Non-Gaussian Fluctuations

Based on the local mode method, the problem of the average intensity (transmission loss) behavior in shallow waveguides with losses in the bottom and fluctuations of the speed of sound in water is considered. It was previously shown that the presence in a waveguide with absorbing penetrable bottom of 2D random inhomogeneities of the speed of sound leads to the appearance of strong fluctuations in the acoustic field already at relatively small distances from the sound source. One of the most important and interesting manifestations of this is the slowing down of the average intensity of the acoustic field compared with a waveguide, which has no such random inhomogeneities of the speed of sound. This paper presents the results of a numerical analysis of the decay of the average field intensity in the presence of both Gaussian and non-Gaussian fluctuations in the speed of sound. It is shown that non-Gaussian fluctuations do not fundamentally change the conclusion about reducing losses during the propagation of a sound signal but can enhance this effect.

Elastic organic crystals of π-conjugated molecules: anisotropic densely packed supramolecular 3D polymers exhibit mechanical flexibility and shape tunability

π-Conjugated molecules have attracted much attention over recent years and have applications in various organic devices. Single crystals of these molecules are attractive materials for developing unique and/or high-performance devices owing to their anisotropic densely packed supramolecular 3D polymer structures. However, they are not flexible and are therefore not suitable for wearable devices. In this focus review, the author’s recent work on flexible crystals involving designing fibril lamella of slip-stacked molecular wires based on planar π-conjugated molecules and their applications is summarized. Unlike common organic crystals, 1,4-bis[2-(4-methylthienyl)]-2,3,5,6-tetrafluorobenzene exhibits elastic bending flexibility with π-functionality. This supramolecular 3D polymer design concept offers top–down synthesis of crystalline fibers and films. Moreover, the functionality and flexibility of such a crystal realizes both high-performance flexible fluorescent waveguide and reversible mechanofluorochromic behavior. Finally, the interesting shape-tunable supramolecular formation of a fluorescent π-conjugated polymer containing a 1,4-bis[2-(4-hexylthienyl)]-2,3,5,6-tetrafluorobenzene repeating unit is described. This focus review describes that “elastic organic crystals of π-conjugated molecules”. The author developed the field of innovative materials for flexible optoelectronics. Intentional design of intramolecular interaction in π-system furnish the flexible crystals. These crystals show not only elastic bending flexibility and shape tunability but also functionality for mechanical sensors and flexible optical waveguide.

Behavior of waveguide scattering matrices in a neighborhood of thresholds

Behavior of waveguide scattering matrices in a neighborhood of thresholds

Tunable Locally Resonant Surface-Acoustic-Waveguiding Behavior by Acoustoelectric Interaction in ZnO -Based Phononic Crystal

The authors consider the guiding of surface acoustic waves by the local resonance band gap of a ZnO pillar-based phononic crystal, by introducing a hollow-cylindrical linear defect. Such a defect can be structurally engineered to yield narrow-band guiding modes near the middle of the gap. Moreover, the authors point out the frequency tunability of this waveguiding behavior, thanks to the acoustoelectric response of ZnO to ultraviolet illumination. This approach is attractive for designing reconfigurable, high-$Q$ surface-acoustic-wave devices, such as filters and duplexers for wireless communication.

Sub-wavelength waveguide properties of 1D and surface-functionalized SnO2 nanostructures of various morphologies.

One-dimensional (1D) SnO2 sub-wavelength waveguides are a critical contribution to advanced optoelectronics. Further understanding of the surface defects and role of morphology in 1D SnO2 nanowires can help to better utilize these nanostructures more efficiently. For this purpose, three different nanowires (NWs), namely belts, cylindrical- and square-shaped structures were grown using SnO2 quantum dots as a precursor material. The growth process of these NWs is discussed. The nanobelts were observed to grow up to 3 mm in length. Morphological and structural studies of the nanostructures were also carried out. All NWs showed waveguide behavior with visible photoluminescence (PL) upon excitation with a 325 nm laser. This behavior was also demonstrated in tapered and surface-functionalized SnO2 NWs. While the tapered waveguide can allow for easy focusing of light, the simple surface chemistry offers selective light propagation by tuning the luminescence. Defect-related PL in NWs is studied using temperature-dependent measurements and a band diagram is proposed.

Efficient Plasmonic 2D Arrangement and Manipulation System, Suitable for Controlling Particle–Particle Interactions

Investigating interactions between biological or artificial micro and nanoparticles (NPs) are vital for understanding processes such as intercellular communications, and quantum and optical effects in an array of NPs. In this line of research, methods to precisely trap and manipulate NPs are essential to investigate such inter-particle interactions. Exciting higher order counter-propagating leaky surface plasmon modes (LSPMs) of a thin gold stripe, we present a simple and efficient method to arrange NPs into a two-dimensional (2D) periodic pattern, allowing precise control over inter-particle interactions. We demonstrate that the 2D lattice of traps is generated by interference of totally reflected surface plasmons from the gold stripe edges and also interference of two counter-propagating LSPMs. Analytical calculations and numerical simulations are in good agreement with the observed modal behavior of LSPMs. Due to the modal dependency of LSPMs on the incident wavelength, we show that in this system different inter-particle distance with nanometer resolution can be achieved by adjusting the wavelength of the incident laser beams. Moreover, we show that the trapped NP array shows waveguiding behavior, enhances the mode intensities and the resulted potential wells consequently. We expect that this self-induced enhancement of trapping efficiency is beneficial for the periodic arrangement of NPs and array formation. The proposed approach implemented in a simple plasmonic optophoresis system, opens the possibility to develop integrated optical manipulation chips, which allows simple and low-cost approach for controlling and studying the inter-particle interactions. Furthermore, the proposed approach is also promising for controllable assembling of NPs without the need for complicated and time consuming nano-lithography techniques.

Modulation of waveguide behaviour of an ICT 2H-Benzo[d][1,2,3]Triazole derivative with graphene

Abstract Needle-like supramolecular structures prepared by the organized aggregation of a 2H-benzo[d][1,2,3]triazole derivative with few-layer graphene using the slow diffusion technique are described. The as-prepared aggregate shows, by using scanning electron microscopy (SEM), the formation of needles with graphene attached on the surface, which was corroborated by Raman spectroscopy and optical microscopy. The graphene-modified aggregate acts as a selective optical waveguide for green light, in contrast to the pristine aggregate which emits green and red light. These new materials may be of crucial importance for the development of high-performance optoelectronic devices.

Eu-based coordination polymer microrods for low-loss optical waveguiding application.

Lanthanide-based coordination polymers (CPs) have received great attention due to their tuneable structures and excellent luminescence properties. However, limited by the stability and micro/nanoscale morphology, a very small number of lanthanide-based CPs have been used for photonic applications. Herein, we present the synthesis of Eu-based CPs (compound 2) with highly regular one-dimensional (1D) microrod morphology by in situ structure transformation from compound 1. Moreover, the Eu-based CP microrods have an excellent stability and a high photoluminescence quantum yield (PLQY), and the distance-dependent PL spectra also exhibited typical characteristics of photoactive waveguides with a low optical-loss coefficient (0.00894 dB μm-1) during propagation. These intriguing behaviors not only extend the research field of optical waveguides through lanthanide-based CPs, but also provide an opportunity for further application in optical communication systems.

Topological Waveguiding near an Exceptional Point: Defect-Immune, Slow-Light, and Loss-Immune Propagation.

Electromagnetic waves propagating in conventional wave-guiding structures are reflected by discontinuities and decay in lossy regions. In this Letter, we drastically modify this typical guided-wave behavior by combining concepts from non-Hermitian physics and topological photonics. To this aim, we theoretically study, for the first time, the possibility of realizing an exceptional point between coupled topological modes in a non-Hermitian nonreciprocal waveguide. Our proposed system is composed of oppositely biased gyrotropic materials (e.g., biased plasmas or graphene layers) with a balanced distribution of loss and gain. To study this complex wave-guiding problem, we put forward an exact analysis based on classical Green's function theory, and we elucidate the behavior of coupled topological modes and the nature of their non-Hermitian degeneracies. We find that, by operating near an exceptional point, we can realize anomalous topological wave propagation with, at the same time, low group velocity, inherent immunity to backscattering at discontinuities, and immunity to losses. These theoretical findings may open exciting research directions and stimulate further investigations of non-Hermitian topological waveguides to realize robust wave propagation in practical scenarios.

Self‐Assembled Alkynyl Azoles and Benzoazoles as Colored Optical Waveguides

AbstractDifferent alkynyl azoles and benzoazoles have been synthesized in good yields by carbon‐carbon coupling reactions. The self‐assembly of some of these compounds by the slow diffusion technique led to well‐defined ribbons and needle‐like aggregates. The X‐ray study of some materials showed that the CH‐π interactions involving the C≡C triple bond and the heteroatoms induce aggregation along with H‐bonds due to the methoxy groups. A fluorescence and confocal optical microscopy study of most of the aggregates indicated optical waveguide behavior with different colors.

Waveguiding behavior of VLS-grown one-dimensional Ga-doped In2O3 nanostructures

Highly crystalline undoped and Ga-doped indium oxide nanorods with square-shaped faceted morphology were fabricated through the vapor-liquid-solid process at moderate temperature. Effects of Ga incorporation on the growth rate, morphology, and crystallinity of the nanostructures were evaluated by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. Defect structure and waveguiding behavior of the 1-D In2O3 nanostructures have been studied using microRaman and micro photoluminescence spectroscopies. The appearance of several resonant modes superposed over the broad room temperature micro-photoluminescence spectra of the nanostructures demonstrates their waveguiding behaviors. While the pristine or undoped In2O3 nanostructures of 20–150 nm widths revealed Fabry-Pérot resonance modes, the Ga-incorporated nanostructures of 20–100 nm width revealed whispering gallery modes due to their smaller widths. The quality factor (Q) of the resonators was estimated to be about 20.86 and 188.79 for the pristine and Ga-incorporated nanostructures, respectively, indicating a huge enhancement due to Ga incorporation. The increment in the Q factor on Ga incorporation in In2O3 nanorods opens up the possibility of their utilization for the development of new optical transmitters and resonators, and fabrication of nanoscopic lasing devices.

Electrically pumped Fabry-Perot microlasers from single Ga-doped ZnO microbelt based heterostructure diodes.

Semiconducting micro/nanostructures possessing naturally optical waveguiding behaviors and Fabry-Perot (F-P) like resonances are emerging as versatile building blocks for the assembly of photonic and optoelectronic devices, such as photodetectors, light-emitting diodes, lasers and so on. Individual ZnO micro/nanowires with a rectangular cross-section, such as microwires and microbelts possessing naturally smooth facets along both sides for good optical feedback, can be employed as an underlying F-P mode microcavity whilst as the gain medium for light amplification. In this context, electrically pumped F-P mode microlasers comprising a single ZnO:Ga microbelt and p-GaN substrate have been realized. By treating as the precondition, electrically driven exciton-polariton light-emitting behavior was achieved from the heterojunction diodes, which could be ascribed to strong exciton-photon coupling and waveguided nature of the synthesized microbelts. Once the applied bias exceeded the threshold value, an electrically pumped F-P mode lasing behavior could be observed, the lasing peaks centered at 410.5 nm and 450.5 nm respectively, accompanied with a dramatic narrowing of the spectral line-width to be around 1.0 nm emerging on the waveguided emission spectrum. Therefore, the realization of electrically pumped F-P mode lasing using single microbelt based heterojunction diodes opens the door not only to the fabrication of coherent light sources and model systems for waveguided resonators, but also affords a competitive candidate to develop electrically pumped and ultralow threshold polariton lasers.

Optical Waveguide of Buckled CdS Nanowires Modulated by Strain-Engineering

The optical waveguides under subwavelength scale are highly desirable for on-chip photonics to link various optical elements or to realize logical operations. In this work, the optical waveguiding along a single buckled CdS (cadmium sulfide) nanowire is comprehensively investigated at room temperature. By carefully scanning excitation along buckled nanowire with fixed PL detection at nanowire end, we present unique waveguide propagation loss strongly modulated by strain effect, which is distinct from the waveguide behavior of straight nanowires. When laser spot moves to buckling part, the light waveguide propagation loss is significantly reduced because band-to-band reabsorption effect during light propagation is greatly suppressed by tensile strain-induced bandgap shrinking. In addition, a dynamic manipulating waveguide propagation based on a controllable buckling of nanowires is also carried out; the solely strain-dependent waveguiding intensity loss and intensity modulation nearly 400% are clearly demonstrated. Our results indicate that strain-modulated semiconductor nanowires would pave new way to develop multifunctional optical elements and interconnects for integrated and flexible nanophotonic devices.

Surface-Guided CsPbBr3 Perovskite Nanowires on Flat and Faceted Sapphire with Size-Dependent Photoluminescence and Fast Photoconductive Response.

All-inorganic lead halide perovskite nanowires have been the focus of increasing interest since they exhibit improved stability compared to their hybrid organic-inorganic counterparts, while retaining their interesting optical and optoelectronic properties. Arrays of surface-guided nanowires with controlled orientations and morphology are promising as building blocks for various applications and for systematic research. We report the horizontal and aligned growth of CsPbBr3 nanowires with a uniform crystallographic orientation on flat and faceted sapphire surfaces to form arrays with 6-fold and 2-fold symmetries, respectively, along specific directions of the sapphire substrate. We observed waveguiding behavior and diameter-dependent photoluminescence emission well beyond the quantum confinement regime. The arrays were easily integrated into multiple devices, displaying p-type behavior and photoconductivity. Photodetectors based on those nanowires exhibit the fastest rise and decay times for any CsPbBr3-based photodetectors reported so far. One-dimensional arrays of halide perovskite nanowires are a promising platform for investigating the intriguing properties and potential applications of these unique materials.

Tailoring optical resonant cavity modes in SnO2 microstructures through doping and shape engineering

Optical resonances are effectively tailored by engineering size, morphology and doping in tin oxide microstructures. The use of Cr shifts the light confinement to the near-infrared region, as compared to the undoped microstructures, while achieving good Q and F factors. Other issues, such as appropriate thickness to width ratio, allow the selection of Fabry–Pérot or Whispering Gallery modes, or the appearance of a combination of both kinds of resonances in the same microstructure. Morphology variability would contribute with flexibility in the design of systems for different applications, while combining the observed waveguiding behavior with the optical resonances in the same material is an advantage for applications based in a monolithic design. Refraction index of Cr doped tin oxide has been obtained.

Submillimeter Wavelength 2-D Frequency Scanning Antenna Based on Slotted Waveguides Fed Through a Phase Shifting Network

This paper describes a 2-D frequency scanning array, operating in the 240–310-GHz frequency range, which is intended to be used in electromagnetic imaging applications. The proposed antenna combines eight slotted waveguides that are parallel fed through a frequency-dependent phase shifting network. As the working frequency is swept in the considered range, the inherent frequency-dependent behavior of the slotted waveguide causes beam scanning in one plane, while the progressive phase shift introduced by the feeding network provides beam steering in the perpendicular direction. The influence of the particular negative effects that suffer the employed structures on the array performance is carefully analyzed to determine the viability of this approach. A prototype has been implemented and experimentally characterized. The manufactured antenna presents a measured 20-dBi minimum gain and it is able to scan a $60 {^{\circ }}\times 20 {^{\circ }}$ space region, which would be large enough for a great number of imaging applications.

A New Benzodithiophene‐Based Cruciform Electron‐Donor–Electron‐Acceptor Molecule with Ambipolar/Photoresponsive Semiconducting and Red‐Light‐Emissive Properties

AbstractThe rational design of multifunctional materials with both emissive and semiconducting properties remains a challenge. A multifunctional cruciform donor–acceptor (D–A) molecule, 2,2′‐(((4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl)bis(thiophene‐5,2‐diyl))bis(methanylylidene))dimalononitrile (BDTTM), which contains a benzodithiophene as the central core, has been synthesized and, based on the output and transfer characteristics of the corresponding FETs, thin films of BDTTM exhibited ambipolar semiconducting behavior. Notably, FETs with thin films of BDTTM showed a photoresponse in both p‐ and n‐channels, and drain‐source‐current enhancement under white‐light irradiation could be detected, even at a low light intensity of 0.1 mW cm−2. Furthermore, BDTTM exhibited red‐light emission both in solution and as a crystalline solid. A microplate of BDTTM with red‐light emission displayed typical optical waveguiding behavior.

Dynamic performance of detuned ridge waveguide AlInGaAs distributed feedback laser diodes

The dynamic behavior of AlInGaAs ridge waveguide distributed feedback lasers is reported in this work covering five detuned wavelengths between 1291 nm and 1326 nm for a laser active layer optical peak gain design centered at 1310 nm at room temperature. The detuning is achieved by modifying the laser grating pitch that performs the mode selection within the laser cavity simultaneously across a single processed wafer. The dynamic behavior is evaluated using the resonance frequencies of the detuned lasers measured at a range of injection currents for heatsink temperatures of 25°C and 85°C. The results confirm that a speed improvement can be achieved at 25°C by detuning the laser to shorter wavelengths. However, the results also show that a lower direct modulation bandwidth at 85°C makes the shorter wavelength design less attractive. For communications applications such as 10 Gbps uncooled operation, this trade-off between detuning and modulation bandwidth imply an optimum around −2 nm to +8 nm detuning (measured at 25°C). © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1468–1470, 2017

Tunable emission in aggregated T-Shaped 2H-Benzo[d][1,2,3]triazoles with waveguide behaviour

Symmetrical Donor-Acceptor-Donor (D-A-D) 2H-benzo[d][1,2,3]triazole derivatives have been designed by DFT calculations and prepared by a multistep synthetic protocol. The design strategy involved the identification of a suitable acceptor benzotriazole core and modification of the steric volume and donor strength of the branches in order to modulate the Intramolecular Charge Transfer (ICT) process and, consequently, the band gap. Self-assembly of the reported triazoles afforded organized supramolecular structures, the morphologies of which were visualized by SEM imaging. The outcomes demonstrated the effect that the donor moiety has on the emission properties and the morphologies of the aggregates. The aggregates that had a crystal-like structure, with smooth surfaces and flat end facets, exhibited optical waveguide behaviour with tunable colour emission. Depending on the initial design, the different emission wavelengths are related to the band gap of the benzotriazole derivatives.

Early detection of first-time slope failures using acoustic emission measurements: large-scale physical modelling

Early warning systems for slope instability need to alert users of accelerating slope deformation behaviour to enable safety-critical decisions to be made. This study shows that acoustic emission (AE) monitoring of active waveguides (i.e. a steel tube with a granular backfill surround installed through a slope) can both detect shear surface development and quantify increasing rates of movement during slope failure, thereby providing an early detection of slope instability. A large-scale physical model was designed and built to simulate slope failures on elements of soil, through which full-scale active waveguides were installed. A shear surface develops in each test and the sliding mass accelerates during failure, reaching velocities greater than 300 mm/h and shear deformations of 50 mm. Continuous measurements were obtained to examine the behaviour of active waveguides subjected to first-time slope failure dynamics (i.e. development of new shear surfaces and accelerating deformation behaviour). Comparisons with continuous subsurface deformation measurements show that AE detection began during shear surface formation, and AE rates increased proportionally with displacement rates as failure occurred. Empirical AE rate–slope velocity relationships are presented for three granular backfill types, which demonstrate that generic AE rate–slope velocity relationships can be obtained for groups of backfill types; these relationships allow displacement rates to be quantified from measured AE rates to provide early detection of slope instability.