Silica-Based Arrayed Waveguide Grating with Flattened Spectral Response Using a Multimode Interference Coupler

We designed and fabricated an arrayed waveguide grating based on silica-on-silicon materials with flattenedspectral response by adding a multimode interference coupler in the input region. The theoretical analysis andcalculation are given. The device has worked effectively and has been tested with the passband 0.43 nm at I dB,0.72nm at 3dB and 1.56nm at 20dB respectively, at a cost of power penalty of about 1.5dB. The crosstalk isless than -30 dB, owing to the high-resolution photomask and well-controlled fabrication processes.     

Ⅲ–Ⅴ/Si Hybrid Laser Array with DBR on Si Waveguide

We report an eight-channel silicon evanescent laser array operating at continuous wave under room temperature conditions using the selective-area metal bonding technique.The laser array is realized by evanescentl.y coupling the optical gain of InGaAsP multi-quantum wells to the silicon waveguides of varying widths and patterned with distributed Bragg reflector gratings.The lasers have emission peak wavelengths in a range of 1537-1543 nm with a wavelength spacing of about 1.0 nm.The thermal impedances Z_T of these hybrid lasers are evidently lower than those DFB counterparts     

4 × 4 Plastic Optical Fiber Star Coupler Incorporated with a Common Polymer Waveguide Optical Power Distribution Region

Abstract

Two types of 4 × 4 plastic optical fiber star couplers incorporated with a polymer waveguide as the optical power distributor are proposed, and their high performances are demonstrated. The characteristics of the proposed star coupler are investigated based on ray optics, and its power distribution performance is evaluated in terms of the flatness of the coupling ratio and the amount of the excess loss. Under the best conditions, the flatness of the coupling ratio and the excess loss of the fabricated device have been obtained as 2.0 dB and 2.5 dB, respectively.     

Development of the physical principles of the design and implementation of a 500–700 GHz spectrometer with a superconducting integrated receiver

A spectrometer based on the effect of freely decaying polarization in the frequency range 500–700 GHz has been designed. Radiation sources are harmonics from a quantum semiconductor superlattice frequency multiplier. The receiving system of this spectrometer is constructed using a superconducting integrated receiver based on a superconductor-insulator-superconductor mixer and a flux-flow oscillator operating as a heterodyne oscillator. The spectrometer has been used to measure absorption lines of NH₃ in a sample of expired air (572 GHz).     

Conceptual Design of a Hybrid Fusion–Fission Power Reactor with a Tokamak and a Depleted Uranium Blanket

Physics of Atomic Nuclei - We assess the viability of energy generation with depleted uranium irradiated with fast neutrons from the reaction of DT fusion driven by a tokamak reactor. Since...     

Hybrid organic–inorganic nanocomposites fabricated with a novel biocompatible precursor using sol-gel processing

The synthesis of hybrid organic–inorganic nanocomposite materials containing biopolymers by the sol-gel processing is often faced with severe difficulties owing to their poor compatibility with the common precursors. The problem was solved when tetrakis(2-hydroxyethyl) orthosilicate (THEOS) was recently suggested for the preparation of sol-gel derived nanocomposites. This article summarizes recent data on novel types of hybrid polysaccharide-silica nanocomposite materials fabricated with the help of THEOS. Their formation, properties and structure as well as features and possible mechanism for the sol-gel processes are considered. It is demonstrated that the novel approach is particularly suitable in situations where others are unsatisfactory. This includes systems of which supramolecular organization or phase state is sensitive to the pH of solutions, temperature and addition of organic solvents. One example of a successful application is the immobilization of labile enzymes. The biocompatibility of THEOS allows their activity to be retained, thereby enhancing long-term and thermal stabilities.     

Metallic hydrogen with a strong electron–phonon coupling at a pressure of 300–500 GPa

Atomic metallic hydrogen, which has a lattice with the FDDD unit cell symmetry, has been shown to be a stable phase at a hydrostatic pressure of 350–500 GPa. The found structure has a phonon spectrum which is stable with respect to decay. The structural, electronic, phonon, etc., characteristics of normal metallic phases of hydrogen at a pressure of 350–500 GPa have been ab initio calculated.     

Microwave Impedance of Thin-Film Superconductor–Normal Metal Hybrid Structures with a High Conductivity Ratio

Physics of the Solid State - The temperature dependence of the linear electrodynamic response of thin-film superconductor (MoN)–normal metal (Al) hybrid structures with a high conductivity...     

A Femtosecond Pulse Train with a Selectable Carrier–Envelope Offset Phase

Optics and Spectroscopy - A method and a scheme of obtaining a femtosecond pulse train without frequency comb offset and selectable carrier–envelope offset phase are proposed.     

Hybrid fusion–fission reactor with a thorium blanket: Its potential in the fuel cycle of nuclear reactors

Discussions are currently going on as to whether it is suitable to employ thorium in the nuclear fuel cycle. This work demonstrates that the ²³¹Pa–²³²U–²³³U–Th composition to be produced in the thorium blanket of a hybrid thermonuclear reactor (HTR) as a fuel for light-water reactors opens up the possibility of achieving high, up to 30% of heavy metals (HM), or even ultrahigh fuel burnup. This is because the above fuel composition is able to stabilize its neutron-multiplying properties in the process of high fuel burnup. In addition, it allows the nuclear fuel cycle (NFC) to be better protected against unauthorized proliferation of fissile materials owing to an unprecedentedly large fraction of ²³²U (several percent!) in the uranium bred from the Th blanket, which will substantially hamper the use of fissile materials in a closed NFC for purposes other than power production.     

A study of an exciton in a quantum dot with Woods–Saxon potential

A theoretical study of an exciton confined in a quantum dot with the Woods–Saxon potential is presented. The great advantage of our methodology is that it enables confinement regimes by varying two parameters in the model potential. Calculations are made by using the method of the numerical diagonalization of the Hamiltonian matrix within the effective-mass approximation. The binding energies of the ground (L=0$L=0$) and first excited (L=1$L=1$) states are obtained as functions of the dot radius. Based on the computed energies and wave functions, the linear, the third-order nonlinear and the total optical absorption coefficients have been examined between the ground and the first excited states. The results are presented as a function of the incident photon energy for the different values of the dot radius and the barrier slope. It is found that the binding energy and the optical properties of the excitons in a quantum dot are strongly affected by the dot radius and the barrier slope of the confinement potential.     

A Bandpass Filter–Polarizer Based on a Dielectric Multilayer with Strip Conductor Gratings

Doklady Physics - A new design of a multilayer bandpass filter is proposed, in which each resonator consists of two identical dielectric layers with parallel strip conductor gratings on their outer...     

A Swept-Frequency Wideband Channel Sounding System at the 63.4–64.4?GHz Band with 1?ns Time-Resolution

A Versatile channel sounding impulse response identification system using the swept-frequency method is designed at the 63.4–64.4 GHz band. The swept-frequency channel sounder offers high time and frequency resolution of 1 ns and 625 KHz respectively. The high dynamic range (70 dB) and constant power enable non-linearities to be overcome in the measurement areas lying with the coverage range of the order of a picocell.     

A neutral spinning particle in interaction with a magnetic field and Poschl–Teller potential

The problem of a neutral spinning particle in interaction with a linear increasing rotating magnetic field and a Poschl–Teller potential is considered via path integrals. The calculations are carried out explicitly using an external current source. The problem is then reduced to that of a spinning forced Poschl–Teller oscillator whose spin is coupled to external derivative current sources. The result of the propagator is given as a series. The relative propagator of this forced oscillator is converted to that of an angular momentum via an extension of the dimension. Next, the series is exactly summed by means of a Laplace transformation and the orthonormalization relation of the eigenfunctions of the angular momentum. Received: 29 June 2001 / Published online: 23 November 2001     

A quantum efficiency analytical model for complementary metal–oxide–semiconductor image pixels with a pinned photodiode structure

A quantum efficiency analytical model for complementary metal–oxide–semiconductor（CMOS） image pixels with a pinned photodiode structure is developed. The proposed model takes account of the non-uniform doping distribution in the N-type region due to the impurity compensation formed by the actual fabricating process. The characteristics of two boundary PN junctions located in the N-type region for the particular spectral response of a pinned photodiode, are quantitatively analyzed. By solving the minority carrier steady-state diffusion equations and the barrier region photocurrent density equations successively, the analytical relationship between the quantum efficiency and the corresponding parameters such as incident wavelength, N-type width, peak doping concentration, and impurity density gradient of the N-type region is established. The validity of the model is verified by the measurement results with a test chip of 160×160 pixels array,which provides the accurate process with a theoretical guidance for quantum efficiency design in pinned photodiode pixels.     

Hybrid nanofluid flow over two different geometries with Cattaneo–Christov heat flux model and heat generation: A model with correlation coefficient and probable error

The authors scrutinize the steady, MHD flow of SiO₂−MoS₂/water hybrid nanofluid towards two different geometries i.e. a wedge and a cone. The Tiwari and Das model is implemented with a generalized–Fourier's model, popularized as Cattaneo-Christov heat flux model. Analysis of heat transfer also incorporates the effects of suction, heat generation and thermal radiation. To showcase the relationship between engineering quantities and pertinent parameters involved in the study, the correlation coefficient for heat transfer coefficient and the skin friction coefficient is computed followed by the computation of probable error and statistical declaration. Similarity transformations are utilized to remodel the constitutive laws of flow in non-dimensional form. Numerical computation of non-linear, coupled O.D.E.’s is performed with the support of the Runge-Kutta-Fehlberg scheme and shooting method. Graphical and tabular illustrations of computed results are provided to report the variation in flow properties with the fluctuation in physical parameters. In both cases, i.e. flow close to a wedge and a cone, the temperature of hybrid nanofluid enhances on intensifying the thermal radiation and experiences a decrement with thermal relaxation parameter and magnetic field. Rising values of the suction parameter, thermal relaxation parameter, and thermal radiation cause increment in heat transfer coefficient. Interestingly, it was spotted that the heat generation parameter has contrary effects on temperature distribution over the two geometries.     

A Chebyshev–Lagrangian method for acoustic analysis of a rectangular cavity with arbitrary impedance walls

A general Chebyshev–Lagrangian method is proposed to obtain the analytical solution for a rectangular acoustic cavity with arbitrary impedance boundary conditions. The originality of the present paper is the successful attempt of applying orthogonal polynomials, such as Chebyshev polynomials of the first kind, to the analysis of a rectangular sound field with general wall impedance. The sound pressure is uniformly expressed as triplicate Chebyshev polynomial series which is independent in each direction. The Chebyshev polynomial series solution is obtained using the Rayleigh–Ritz procedure after considering the influence of boundary impedance on the cavity as the work done by the impedance surfaces in the Lagrangian function. The accuracy and reliability of the proposed method are validated against the analytical solutions and some numerical results available in the literature. Excellent orthogonality and complete properties of the Chebyshev polynomials ensure the rapid convergence, numerical stability, high accuracy of the current solution. The simplicity and low computational cost of the present approach make it preferable to obtain the results of complex models even in the relative high frequency range by choosing enough truncated terms in the sound pressure expression. Numerous cases with various uniform or non-uniform impedance boundary conditions are analyzed numerically and some of the results can be used as benchmark. It is shown that the impedance boundary condition can effectively influence or modify the acoustic characteristics and response of a cavity.     

A reduced gradient description of stochastic-resonant spatiotemporal patterns in a FitzHugh–Nagumo ring with electric inhibitory coupling

We study the synchronization (sync) properties of a ring of N units with excitable FitzHugh–Nagumo dynamics, when the inhibitor fields of nearest-neighbor units are coupled diffusively (electric coupling). The system is submitted to a common subthreshold adiabatic signal $S(t)$, and independent Gaussian white noises with common variance η. By running numerical integrations with increasing η, we observe the excitation activity to become spatiotemporally self-organized, until η is so strong that spoils sync. By means of a two-cell model and projecting the dynamics along the slow manifolds, we obtain a (signal-dependent) potential landscape which explains qualitatively the sync regime, and whose barrier heights give a good estimate of the optimal noise intensity.