Acoustooptic Coherent Mode Coupling in Polarization-Maintaining Fiber and Its Application as a Variable-Polarization-Dependent Loss Element

In this letter, we investigate coherent acoustooptic coherent mode coupling from the LP₀₁ core mode to LP_1m cladding mode of a polarization-maintaining fiber (PMF) induced by two acoustic gratings. We show narrowband variable attenuation along either birefringent axis of the PMF by varying the relative phase between the two acoustic gratings. By launching two acoustic gratings at different frequencies, variable attenuation and low crosstalk along either birefringent axis within the acoustooptic coupling bandwidth are demonstrated     

Noise Figure of Silicon Raman Amplifiers

The noise figure of silicon Raman amplifiers in the presence of nonlinear losses is calculated. The impact of two-photon absorption (TPA) and free-carrier scattering on the noise figure is quantified using the quantum formulation of the Langevin approach. It is found that TPA-induced free-carrier loss degrades the noise figure by an amount that depends on the carrier lifetime. For example, in a 1-cm-long waveguide pumped at 200 MW/cm², the noise figure is 5.2 dB for a lifetime of tau = 1.6 ns and is reduced to 3.7 dB for tau = 0.1 ns. The reduction in the noise figure along with a concomitant increase in Raman gain from 2 to 8 dB suggests that lifetimes on the order of 0.1 ns or less are needed to create a useful silicon Raman amplifier that operates in the continuous-wave mode. It is also shown that in devices that use a p-n junction for carrier sweep-out, the screening of the junction field by generated free carriers results in a sharp increase in the noise figure at high-pump intensities. These results apply to operation in the near-infrared communication wavelengths. For mid-infrared wavelengths above the two photon absorption band-edge (2.3 nm), the absence of TPA and pump-induced free-carrier absorption ensures that the amplifier has a low-noise figure.     

Object manipulation with a variable-stiffness robotic mechanism using deep neural networks for visual semantics and load estimation

Neural Computing and Applications - In recent years, the computer vision applications in the robotics have been improved to approach human-like visual perception and scene/context understanding....     

Gain enhancement in cascaded fiber parametric amplifier withquasi-phase matching: theory and experiment

We report a novel gain enhancement scheme for fiber-optic parametric amplifiers utilizing cascaded amplification and quasi-phase matching (QPM). The theory and method of QPM for four-wave mixing (FWM) are developed for the first time to our knowledge. In experimental implementations of the theory, we achieve >12 dB gain improvement in a three-stage dispersion-shifted (DS) fiber parametric amplifier. A 16-dB overall gain is obtained with 11 nm separation between zero-dispersion wavelength and pump wavelength. The experimental results show good agreement with theory and simulations. The influence of QPM on spectral characteristics of parametric gain is investigated with numerical simulations     

Negative Magnetization and Superconductivity in the (LaPt2Asx (x = 1, 2) and BaPt2As2 Compounds

Journal of Superconductivity and Novel Magnetism - We have investigated the electrical and magnetic properties of the compounds LaPt2As, LaPt2As2, and BaPt2As2 prepared by conventional solid-state...     

Rate-controlled optical burst switching for both congestion avoidance and service differentiation

Optical Burst Switching (OBS) has recently been proposed as a candidate architecture for the next generation optical Internet. Several challenging issues remain to be solved to pave the way for the OBS vision. Contention arises in OBS networks when two or more bursts are destined for the same wavelength, and a wide variety of reactive contention resolution mechanisms have been proposed in the literature. One challenging issue in OBS is proactively controlling the traffic flowing through the OBS network so that the network does not stay in a persistent state of contention, which we call the congestion avoidance problem. Another challenging issue is the need for service differentiation, which is common today in electronically switched networks via the use of advanced buffer management and scheduling mechanisms. However, such mechanisms cannot be used in OBS networks due to the limited use, or total absence, of buffering. One of the popular existing approaches to service differentiation in OBS networks is the use of larger offset times for high-priority bursts which, however, increases the delays and may adversely affect application-level performance. In this paper, we propose a feedback-based rate control protocol for the control plane of the OBS network to both address the congestion avoidance and service differentiation issues. Using this protocol, the incoming traffic is dynamically shaped at the edge of the OBS network in order to avoid potential congestion in the burst-switched core. Moreover, the traffic shaping policies for the low and high priority traffic classes are different, and it is possible using the proposed protocol to isolate high-priority and low-priority traffic almost perfectly over time scales on the order of a few round-trip times. Simulation results are reported to validate the congestion avoidance and service differentiation capabilities of the proposed architecture.     

Raman-based silicon photonics

This paper reviews recent progress in a new branch of silicon photonics that exploits Raman scattering as a practical and elegant approach for realizing active photonic devices in pure silicon. The large Raman gain in the material, enhanced by the tight optical confinement in Si/SiO2 heterostructures, has enabled the demonstration of the first optical amplifiers and lasers in silicon. Wavelength conversion, between the technologically important wavelength bands of 1300 and 1500 nm, has also been demonstrated through Raman four wave mixing. Since carrier generation through two photon absorption is omnipresent in semiconductors, carrier lifetime is the single most important parameter affecting the performance of silicon Raman devices. A desired reduction in lifetime is attained by reducing the lateral dimensions of the optical waveguide, and by actively removing the carriers with a reverse biased diode. An integrated diode also offers the ability to electrically modulate the optical gain, a unique property not available in fiber Raman devices. Germanium-silicon alloys and superlattices offer the possibility of engineering the otherwise rigid spectrum of Raman in silicon.     

Dynamic modeling of a horizontal washing machine and optimization of vibration characteristics using Genetic Algorithms

In this work, a 2D dynamic model of a horizontal axis washing machine is derived regarding the rotation plane in order to examine the vibration characteristics of the spin-cycle and improve the design proposing a new optimization scheme based on Genetic Algorithms (GA). The dynamic model is numerically simulated and the outputs are validated using experimental vibration data acquired from a test-rig including the drum and the motor of a horizontal-axis washing machine. The measurements are performed using piezo-transducers and a novel measurement scheme is used to obtain displacement values from acceleration data as well as estimating the instantaneous frequency of the rotation with appropriate signal processing. This study has two main contributions: (i) a new method for design improvement applying GA to optimization of vibration characteristics for the horizontal-axis washing machines, and (ii) a novel measurement method yielding the displacement in 2D and instantaneous frequency of vibration from acceleration data. While the GA is contributing to passive improvement methods in the field, the novel measurement method opens the way for low-cost diagnosis and active-vibration control of washing machines.     

Structural and Superconductivity Properties of BaFe<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Pt<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>As<Subscript>2</Subscript>

Extraordinary magnetic behaviors, resistivity properties, and lattice parameters of the main sample BaFe₂As₂ and BaFe_2?x Pt _x As₂ in the variation of x from 0 to 0.4 with the step of 0.1 were investigated. The bulk materials have been prepared by the solid-state reaction method and sealed into a quartz tube. The crystal structure of all samples exhibited the ThCr₂Si₂-type crystal structure which is in harmony with earlier studies in the literature. The superconducting states with magnetization measurements have been detailed in the wide temperature range 5–170 K, up to a field of 20 Oe. Increasing Pt and decreasing Fe elements in the BaFe_2?x Pt _x As₂ compound deteriorated superconductivity. Using magnetization measurement data, we present the variation of superconducting critical temperature (T _c) correlating with a Pt dopant rate from x = 0 to x = 0.4. The dopant rate of x = 0.3 exhibited the limit rate for maximum T _c; deterioration of superconductivity was revealed with a dopant rate of more than x = 0.3. This should be explained by varying T _c related to a lattice shrinking and pressure effect (geometric factor).     

Do positive thinking and meaning mediate the positive affect—Life satisfaction relationship?

The authors tested whether positive cognitions mediated the relationships between positive affect and both meaning in life and life satisfaction, and whether meaning in life partially mediated the relationship between positive cognitions and life satisfaction, among 232 students and community-dwelling adults. Also tested was an alternative model in which positive affect mediated the relationships between positive cognitions and both meaning in life and life satisfaction, and in which meaning in life partially mediated the relationship between positive affect and life satisfaction. Supporting hypotheses and the literature, positive cognitions mediated the relationship between positive affect and meaning in life, and meaning in life partially mediated the relationship between positive cognitions and life satisfaction. Together, positive affect and positive cognitions accounted for 48% of the variance in meaning in life, and the model accounted for 62% of the variance in life satisfaction. (PsycINFO Database Record (c) 2011 APA, all rights reserved)