Theoretical modelling of one dimensional photonic crystal based optical demultiplexer

An optical demultiplexer through one-dimensional Si–SiO₂ photonic crystal structure in the presence of air cavity with a single crystal PMN-0.38PT material is presented. The transmittance of this structure is obtained using the transfer matrix method. The transmittance of this structure shows a sharp passband in the band gap region. It is observed that by introducing PMN-0.38PT layer in both sides of the air cavity, the existing band gap region of Si–SiO₂ structure is slightly increased. Here, PMN-0.38PT material is working as a tunable element for passband. By applying some external potential on PMN-0.38PT crystal, the thickness of cavity layer can be tuned and the passband can be placed at any desired wavelength in the band gap region. Since the photonic band gap region contains a range of wavelengths which are not allowed to pass through the structure can be considered as a multiplex signal for the proposed demultiplexer. Therefore, any optical signal that lies in the band gap region of the structure can be separated into its components as a pass band. Hence, the proposed structure will work as an optical demultiplexer.     

Ordered Arrangement and Optical Properties of Silica‐Stabilized Gold Nanoparticle–PNIPAM Core–Satellite Clusters for Sensitive Raman Detection

Gold–polymer hybrid nanoparticles attract wide interest as building blocks for the engineering of photonic materials and plasmonic (active) metamaterials with unique optical properties. In particular, the coupling of the localized surface plasmon resonances of individual metal nanostructures in the presence of nanometric gaps can generate highly enhanced and confined electromagnetic fields, which are frequently exploited for metal‐enhanced light–matter interactions. The optical properties of plasmonic structures can be tuned over a wide range of properties by means of their geometry and the size of the inserted nanoparticles as well as by the degree of order upon assembly into 1D, 2D, or 3D structures. Here, the synthesis of silica‐stabilized gold–poly(N‐isopropylacrylamide) (SiO₂‐Au‐PNIPAM) core–satellite superclusters with a narrow size distribution and their incorporation into ordered self‐organized 3D assemblies are reported. Significant alterations of the plasmon resonance are found for different assembled structures as well as strongly enhanced Raman signatures are observed. In a series of experiments, the origin of the highly enhanced signals can be assigned to the interlock areas of adjacent SiO₂‐Au‐PNIPAM core–satellite clusters and their application for highly sensitive nanoparticle‐enhanced Raman spectroscopy is demonstrated.     

Consequences for Magnetic Properties of a Model to Explain Room-Temperature Superconductivity in Narrow Channels in Oxidized Polypropylene

There is published evidence suggesting that narrow channels through films of oxidized atactic polypropylene are superconducting at room temperature. Three properties combining to imply this are: (1) conductivity of channels at least several orders of magnitude higher than that of Cu at 300 K; (2) destruction of the high conductivity by nonthermal means when pulsed currents exceed a critical value; and (3) no observable electronic contribution to the thermal conductivity of the channels. Well-oxidized films also show unusual magnetic properties such as: (1) metamagnetism with transition fields in the range 0.1 to 0.2 T; (2) large diamagnetism at low fields in some films studied; and (3) occasional spontaneous forces tending to push samples toward lower fields in inhomogeneous magnetic fields. It will be shown that plausible explanations for these unusual magnetic properties can be found within the framework of a high-drift-velocity model introduced before to give a possible explanation for the electrical properties.     

Extreme narrow photonic bands and strong photonic localization produced by 2D defect two-segment-connected quadrangular waveguide networks

In this paper, we investigate the properties of optical transmission and photonic localization of two-dimensional (2D) defect two-segment-connected quadrangular waveguide networks (DTSCQWNs) and find that many groups of extreme narrow photonic bands are created in the middle of the transmission spectra. The electromagnetic (EM) waves in DTSCQWNs with the frequencies of extreme narrow photonic bands can produce strong photonic localizations by adjusting defect broken degree. On the other hand, we obtain the formula of extreme narrow photonic bands’ frequencies dependent on defect broken degree and the formula of the largest intensity of photonic localization dependent on defect broken degree, respectively. It may possess potential application for designing all-optical devices based on strong photonic localizations. Additionally, we propose a so-called defecton mode to study the splitting rules of extreme narrow photonic bands, where decomposition-decimation method is expanded from the field of electronic energy spectra to that of optical transmission spectra.     

Wide-field-of-view GaAs/AlxOy one-dimensional photonic crystal filter

The design, fabrication, and characterization of a one-dimensional photonic crystal optical filter that has a relatively narrow, flat-topped passband within a wide stop band and small angular sensitivity is presented. The filter is based on a one-dimensional photonic crystal structure that has multiple defects, facilitating simultaneous minimization of the angular sensitivity and optimization of the passband's characteristics. We use epitaxially grown and selectively oxidized GaAs/AlxOy multilayers to achieve a high-index-contrast material system and incorporate the experimentally determined optical and material properties into the design of the device. A flat-topped bandpass filter with a bandwidth of 65 nm and a wide field of view of 50 degrees is experimentally characterized and compared with the design predictions.     

Phase-Slip Phenomena in Proximitized NbN/NiCu Superconducting Nanostripes

Ultrathin superconducting/ferromagnet (S/F) nanostripes are very interesting systems to investigate both the physics involved on nanoscale size and as light sensitive elements for superconducting single photon detectors. The electrical transport properties of NbN(8 nm)/NiCu(10 nm) nanostripes are presented down to a temperature of 4.2 K. A number of voltage steps were observed on the current-voltage characteristics, and they were investigated at different temperatures. A possible explanation in terms of active phase-slip phenomena has been proposed on the basis of the time-dependent Ginzburg-Landau theory, leading to an estimation of the inelastic electron-phonon relaxation time around 0.8 ps. The latter value was found to be in good agreement with a relaxation time, independently measured by femtosecond transient optical reflectivity experiments performed on the same bilayer.     

Visibility of dichalcogenide nanolayers

Dichalcogenides with the common formula MX(2) are layered materials with electrical properties that range from semiconducting to superconducting. Here, we describe optimal imaging conditions for the optical detection of ultrathin, two-dimensional dichalcogenide nanocrystals containing single, double and triple layers of MoS(2), WSe(2) and NbSe(2). A simple optical model is used to calculate the contrast for nanolayers deposited on wafers with varying thicknesses of SiO(2). The model is extended for imaging using the green channel of a video camera. Using AFM and optical imaging we confirm that single layers of MoS(2) and WSe(2) can be detected on 90 and 270 nm SiO(2) using optical means. By measuring contrast under broadband green illumination we are also able to distinguish between nanostructures containing single, double and triple layers of MoS(2) and WSe(2.) We observe and discuss discrepancies in the case of NbSe(2).     

High‐Resolution 3D NIR‐II Photoacoustic Imaging of Cerebral and Tumor Vasculatures Using Conjugated Polymer Nanoparticles as Contrast Agent

Exogenous contrast‐agent‐assisted NIR‐II optical‐resolution photoacoustic microscopy imaging (ORPAMI) holds promise to decipher wide‐field 3D biological structures with deep penetration, large signal‐to‐background ratio (SBR), and high maximum imaging depth to depth resolution ratio. Herein, NIR‐II conjugated polymer nanoparticle (CP NP) assisted ORPAMI is reported for pinpointing cerebral and tumor vasculatures. The CP NPs exhibit a large extinction coefficient of 48.1 L g^?1 at the absorption maximum of 1161 nm, with an ultrahigh PA sensitivity up to 2 µg mL^?1. 3D ORPAMI of wide‐field mice ear allows clear visualization of regular vasculatures with a resolution of 19.2 µm and an SBR of 29.3 dB at the maximal imaging depth of 539 µm. The margin of ear tumor composed of torsional dense vessels among surrounding normal regular vessels can be clearly delineated via 3D angiography. In addition, 3D whole‐cortex cerebral vasculatures with large imaging area (48 mm²), good resolution (25.4 µm), and high SBR (22.3 dB) at a depth up to 1001 µm are clearly resolved through the intact skull. These results are superior to the recently reported 3D NIR‐II fluorescence confocal vascular imaging, which opens up new opportunities for NIR‐II CP‐NP‐assisted ORPAMI in various biomedical applications.     

Influence of monitor passband width on the layer thickness determination during deposition of a dense-wavelength-division-multiplexing filter

The monitor passband width of an optical monitor is an important parameter for the fabrication of a dense-wavelength-division-multiplexing (DWDM) filter. The peak insertion loss and transmittance of one-cavity narrow-bandpass filters (NBPFs) were analyzed by using different passband widths. The simulation monitoring curves of the last layer of the first, second, third, and fourth cavities of a five-cavity DWDM filter with different monitor passband widths were investigated. The last layer of each cavity is very sensitive to the monitor passband width, showing that the monitor passband width of an optical monitor should be less than half the designed passband width. This analysis demonstrates the successful fabrication of a five-cavity DWDM filter.     

Chalcogenide coatings of Ge15Sb20S65 and Te20As30Se50

Chalcogenide coatings are investigated to obtain either optical components for spectral applications or optochemical sensors in the mid-infrared. The deposition of Ge(15)Sb(20)S(65) and Te(20)As(30)Se(50) chalcogenide glasses is performed by two physical techniques: electron-beam and pulsed-laser deposition. The quality of the film is analyzed by scanning electron microscopy, atomic force microscopy, and energy dispersive spectroscopy to characterize the morphology, topography, and chemical composition. The optical properties and optical constants are also determined. A CF(4) dry etching is performed on these films to obtain a channeled optical waveguide. For a passband filter made by electron-beam deposition, cryolite as a low-refractive-index material and chalcogenide glasses as high-refractive-index materials are used to favor a large refractive-index contrast. A shift of a centered wavelength of a photosensitive passband filter is controlled by illumination time.     

The significance of carbon nanotubes on styrene butadiene rubber (SBR) and SBR modified mortar

A New approach is introduced to incorporate multi-walled carbon nanotubes (MWCNTs) in cementitious materials. The MWCNTs are dispersed in styrene butadiene rubber (SBR) matrix before mixing the matrix with cement. Surfactants have been successfully applied to enhance the dispersion and functionalization of MWCNTs in SBR. The significance of using this MWCNTs–SBR nanocomposite on the mechanical characteristics including compressive and tensile strengths and microstructural features of latex modified mortar (LMM) were examined. Subsequently, the significance of the functionalized MWCNTs on surface chemistry, microstructure and thermal stability of SBR were characterized. MWCNTs were found to be a useful additive for enhancing the mechanical response and thermal stability of SBR. MWCNTs–SBR nanocomposite was observed to be able to bridge micro-cracks in the LMM which helped enhancing its mechanical properties. The ability of MWCNTs to enhance the mechanical response of SBR polymer matrix might be attributed to chemical bond that functionalized MWCNTs can establish with the SBR polymer matrix. The enhanced MWCNTs–SBR nanocomposite gave rise to improved microstructural features of the LMM. Microstructural investigations showed MWCNTs were well dispersed in and bonded to the SBR matrix.     

Self-assembled one-dimensional nanostructure arrays

A range of proposed devices relies on the electronic, optical or magnetic properties of one-dimensional (1D) chains of nanoparticles. Here, well-controlled 1D arrays have been formed by templating a spherical-morphology block copolymer within a narrow groove. Significantly, the domains are distorted into ellipses with aspect ratio and major axis orientation controlled by the groove width. This technique gives unprecedented control over the period, particle size, aspect ratio, and orientation of nanoparticles in 1D arrays, making it valuable for creating self-assembled masks for the fabrication of novel devices.     

Monitoring thin films of the fence post design and its advantages for narrow bandpass filters

A fence post design, when viewed on a plot of index of refraction versus film thickness, has thin (usually of equal thickness) high-index posts that stand above a broad low-index ground. Monitoring fence post and related posthole designs offers error compensation and error reduction. There tend to be two or more extrema within the optical monitoring trace of each layer between the fence posts that aid in the calibration and control of film thickness. This also leads to a potentially improved control during deposition of narrow bandpass filters that have been designed with nonquarterwaves at the passband wavelength.     

Mechanical performance of styrene-butadiene-rubber filled with carbon nanoparticles prepared by mechanical mixing

Reinforcement of styrene-butadiene-rubber (SBR) was investigated using two different carbon blacks (CBs) with similar particle sizes, including highly structured CB and conventional CB, as well as multi-walled carbon nanotube (MWCNT) prepared by mechanical mixing. The attempts were made to examine reinforcing mechanism of these two different classes of carbon nanoparticles. Scanning electron microscopy and electrical conductivity measurement were used to investigate morphology. Tensile, cyclic tensile and stress relaxation analyses were performed. A modified Halpin-Tsai model based on the concept of an equivalent composite particle, consisting of rubber bound, occluded rubber and nanoparticle, was proposed. It was found that properties of CB filled SBR are significantly dominated by rubber shell and occluded rubber in which molecular mobility is strictly restricted. At low strains, these rubber constituents can contribute in hydrodynamic effects, leading to higher elastic modulus. However, at higher strains, they contribute in stress hardening resulting in higher elongation at break and higher tensile strength. These elastomeric regions can also influence stress relaxation behaviors of CB filled rubber. For SBR/MWCNT, the extremely great inherent mechanical properties of nanotube along with its big aspect ratio were postulated to be responsible for the reinforcement while their interfacial interaction was not so efficient.     

Metal Thio‐ and Selenophosphates as Multifunctional van der Waals Layered Materials

Since the discovery of Dirac physics in graphene, research in 2D materials has exploded with the aim of finding new materials and harnessing their unique and tunable electronic and optical properties. The follow‐on work on 2D dielectrics and semiconductors has led to the emergence and development of hexagonal boron nitride, black phosphorus, and transition metal disulfides. However, the spectrum of good insulating materials is still very narrow. Likewise, 2D materials exhibiting correlated phenomena such as superconductivity, magnetism, and ferroelectricity have yet to be developed or discovered. These properties will significantly enrich the spectrum of functional 2D materials, particularly in the case of high phase‐transition temperatures. They will also advance a fascinating fundamental frontier of size and proximity effects on correlated ground states. Here, a broad family of layered metal thio(seleno)phosphate materials that are moderate‐ to wide‐bandgap semiconductors with incipient ionic conductivity and a host of ferroic properties are reviewed. It is argued that this material class has the potential to merge the sought‐after properties of complex oxides with electronic functions of 2D and quasi‐2D electronic materials, as well as to create new avenues for both applied and fundamental materials research in structural and magnetic correlations.     

Superconductivity in the two-band hubbard model

We present a study of superconducting correlations in a two-band Hubbard model with a wide band strongly hybridized with a narrow band in which an attractive on-site interaction is operating. The narrow band pairs can induce superconducting correlations in the wide band through hybridization interaction. A generalized gap function for the induced wide-band pairing is obtained and its properties in the intermediate interaction region are analysed. Relevance of the results to high-T _c superconductors is briefly discussed.     

Structure and properties of fibrillar silicate/SBR composites by direct blend process

Silicate attapulgite(AT)/Styrene Butadiene rubber (SBR) composites with excellent properties and low cost were first prepared from a direct blending process (including polymer melt blending and emulsion co-coagulation). The structure and properties of above composites were carefully investigated. It was found that most AT separated into dispersed units with diameters less than 100 nm in SBR by the direct blend process. However, a few dispersion units as large as 0.2–0.5 m and a clear network structure of dispersion units in SBR was observed by TEM, SEM and RPA. AT can be purified, but purified AT cannot be easily dispersed in the rubber matrix by polymer melt blending. Siliane coupling agent Si69 can improve the dispersion of AT and enhance the chemical interfacial adhesion. At the same loading, AT (pretreated with Si69) was found to have better reinforcing effect on SBR than carbon black SRF with particle size 60–100 nm and even than N330 with particle size 26–30 nm to some extent. Meanwhile, the cost of AT/SBR composites is pretty low.     

Microstructure and superconducting properties of MgB2 films prepared by solid state reaction of multilayer precursors of the elements

Surface morphology and superconducting properties of MgB₂ superconducting thin films prepared by ex-situ annealing of multilayer Mg/B precursors in Mg vapor are studied.Depending on the precursor structure different physical and microstructural properties of the superconductor evolve. Structure and composition of the films are analyzed by scanning electron microscopy and wavelength dispersive x-ray spectroscopy. It is found that certain precursor structures can lead to high quality superconducting films, however, in specific precursor structures mechanical stress leads to the formation of wrinkles strongly affecting the superconducting homogeneity of the films. A correlation between microstructure and superconducting properties, such as pinning or critical current density, can be provided via magneto-optical Faraday microscopy.     

Link design for nondirected wireless infrared communications

We optimize the design of a short-range communication system using nondirected line-of-sight IR radiation. We propose a receiver structure comprising a spherical thin-film optical filter and a truncated spherical lens that can significantly outperform an optimized planar-filter system. We can make the passband of the spherical filter arbitrarily narrow without constraining the field of view by using an arbitrarily large filter radius. We argue that a truncation angle of 90° maximizes the receiver field of view when a spherical filter is used. We jointly optimize the transmitter radiation pattern and receiver optical components. Numerical results show that 269 mW of transmitted signal power is sufficient to achieve 100 Mbit/s throughout a 4-m-radius cell with high background irradiance.     

Multilayer bandstop filter for ultra wideband systems

A multilayer broadside-coupled microstrip-slot-microstrip structure is used to design a bandstop filter with a wide passband for ultra wideband (UWB) applications. The design procedure for the proposed filter is based on the conformal mapping technique and the even- and odd-mode analysis. The theoretical analysis indicates that value of the coupling factor between the top and bottom layers of the structure can be used to control the width of the stopband, whereas centre of that band can be controlled by the length of the coupled structure. To limit the passband of the proposed bandstop filter to 3.1 ?10.6 GHz, which is the specified bandwidth for UWB systems, a broadside-coupled bandpass filter is integrated with the proposed device. The simulated and measured results show that the proposed device achieve ,0.5 dB insertion loss across most of the passband and .20 dB insertion loss at the stopband. The device also shows a flat group delay across the passband with ,0.15 ns peak-to-peak variation. Hence, it is a suitable choice for the UWB systems that require a distortionless operation.