Based on vector diffraction theory and inverse Faraday effect, we report on the generation of optical needle and magnetization needle with tunable longitudinal depth by focusing a narrow annulus of azimuthally polarized beams using optmagnetic materials and an elliptical mirror. In this paper, we present the expression of the approximate result between the angular thickness Δθ and the longitudinal depth when the annulus is assumed to be sufficiently narrow (Δθ<<π/2). We theoretically demonstrate that the induced magnetization needle has the same longitudinal depth as optical needle, but with different distributions. The results are applied to the specific cases of the elliptical mirror and the parabolic mirror, then we further theoretically demonstrate that the longitudinal depth is equally long in the elliptical mirror focusing system and the parabolic mirror focusing system.
As a national pilot institute of the educational reform on practical teaching, an integrative and continuous practical teaching was established and implemented through four measures: promote a practical teaching system that is available for every undergraduate throughout their whole bachelor program; integrate the design of theoretical the practical teaching to closely associate the theoretical course with practical teaching; construct a complete practical teaching system by including experiment teaching, course design, project practice and extracurricular innovative practice; improve the level of practical teaching by appropriately allocating scientific research team, relevant personnel and resource. Based on the exploration and practice of this kind of practical teaching system, the integrative competence and quality of the undergraduates and graduates are both improved.
In this paper we proposed a new approach to design a telecommunication satellite constellation for regional coverage and
aiming at determining the best trade-off between maximal earth coverage and minimum delay of the satellite
communication. In this work, the nondominated sorting genetic algorithm 2 (NSGA-II) is used to generate sets of
constellation designs (Pareto fronts) that show the tradeoff for two pairs of conflicting metrics. A thorough parameter
analysis is performed on the NSGA-II for the constellation design problem so that the utility of the approach may be
assessed and general guidelines for use established. The results reported include the approximated Pareto fronts obtained
by the NSGA-II for the tradeoffs are discussed.
LEO(Low Earth Orbit) satellite network is more suitable for multimedia communication than GEO(Geosynchronous
Earth Orbit) and MEO(Medium Earth Orbit) satellite network because of short propagation delay. Routing computation
in communication network with several constraint factors has been proved to be a NP-C problem. Ant colony algorithm
as a bionics algorithm has good performances on solving NP-C problem. Existing research about ant colony algorithm
mainly concentrates on Ad hoc network, and application in satellite network is not completely developed. According to
the characteristics of LEO satellite network, this paper presents a new routing method based on ant colony algorithm
with forecast strategy and elitist strategy. Generally each satellite establishes two intra-ISLs with forward and backward
neighbors in the same orbit, and two inter-ISLs with left and right neighbors in the adjacent orbits. Thus the topology of
satellite network consists of many grids. According to the specific topology, forecast strategy is introduced to reduce
redundant information. On the other hand, pheromone is updated continuously to ensure elitist path chosen. Assuming a
reference satellite network model is given, the simulation results show that the improved algorithm converges more
quickly than basic ant colony algorithm.
Mobile terminals in a mobile satellite communication system cause the radio propagation channel to vary with time. So it is necessary to study the channel models in order to estimate the behavior of satellite signal propagation. A lot of research work have been done on the L- and S- bands. With the development of gigabit data transmissions and multimedia applications in recent years, the Ka-band studies gain much attention. Non-geostationary satellites are also in research because of its low propagation delay and low path loss. The future satellite mobile communication systems would be integrated into the other terrestrial networks in order to enable global, seamless and ubiquitous communications. At the same time QoS-technologies are studied to satisfy users' different service classes, such as mobility and resource managements. All the above make a suitable efficient channel model face new challenges. This paper firstly introduces existed channel models and analyzes their respective characteristics. Then we focus on a general model presented by Xie YongJun, which is popular under any environment and describes difference through different parameter values. However we believe that it is better to take multi-state Markov model as category in order to adapt to different environments. So a general model based on Markov process is presented and necessary simulation is carried out.
Mobile satellite network with Inter Satellite Links (ISLs), which consists of non-geostationary satellites, has the characteristic of network topology's variability. This is a great challenge to the design and management of mobile satellite network. This paper analyzes the characteristics of mobile satellite network, takes multimedia Quality of Service (QoS) as the chief object and presents a reference model based on Geostationary Earth Orbit (GEO)/ Low Earth Orbit (LEO) satellite constellation which adapts to the design and management of mobile satellite network. In the reference model, LEO satellites constitute service subnet with responsibility for the access, transmission and switch of the multimedia services for mobile users, while GEO satellites constitute management subnet taking on the centralized management to service subnet. Additionally ground control centre realizes the whole monitoring and control via management subnet. Comparing with terrestrial network, the above reference model physically separates management subnet from service subnet, which not only enhances the advantage of centralized management but also overcomes the shortcoming of low reliability in terrestrial network. Routing of mobile satellite network based on GEO/LEO satellite constellation is also discussed in this paper.
Raman Fiber Amplifier is the important component in the next generation optical network. High power Raman Fiber Laser is kinds of selection of the pumping source for Raman Amplifier. In the paper, we theoretically emulating the Fiber Raman Laser and optimizing the Raman Fiber Laser parameters for the output power, experimentally analyzes the device. The analyzing is based on the Raman Fiber Laser's model and doing the simulation with four-order Runge-Kutta arithmetic. The experiment set gave more than 500mw output Laser at 1428nm which is based on a Raman resonator using the high nonlinear efficient fiber, Fiber Bragg Gratings, and pumped by the 1342nm solid state Laser.
Pumping source is the key technology of fiber Raman amplifiers (FRA) which are important for ultra long haul and high bit rate dense wavelength division multiplexing (DWDM) systems. In this paper the research work of the project, "Fiber Raman Laser and Amplifier pumped by Nd3+:YVO4 Solid State Laser", supported by the National High-tech Program (863-program) of China is introduced, in which a novel 14xx nm pump module with fine characteristics of high efficiency, simplicity, compactness and low cost is researched and developed. A compact 1342 nm Nd3+:YVO4 diode pumped solid state laser (DPSSL) module is developed with the total laser power of 655mW and the slope efficiency of 42.6% pumped by a 2W 808nm laser diode (LD). A special C-lens fiber collimator is designed to couple the 1342nm laser beam into a piece of single mode fiber (SMF) and the coupling efficiency of 80% is reached. The specific 14xx nm output laser is generated from a single stage Raman resonator which includes a pair of fiber Bragg gratings and a piece of Germanic-silicate or Phospho-silicate fiber pumped by such DPSSL module. The slope efficiency for conversion from 1342 to 14xx nm radiation is 75% and the laser power is more than 300mW each. Finally, Raman gain experiments are carried out with 100km SMF. 100 nm bandwidth with 10dB on-off Raman gain and 1.1dB gain flatness is achieved by pumped at 1425, 1438, 1455 and 1490nm.
Very high-efficiency, simple, continuous-wave different material-doped Raman fiber lasers are presented. With 1 W Nd:YV04 laser at wavelength 1342 nm pumping, single mode output power above 500 mW (optical-to-optical conversion efficiency of 50%) is simulated operating at l4xx nm. Using high-germanium, high-phosphate and high-borate silicate fiber as the gain medium, and using different geometries, output wavelengths of 1420, 1450, 1480, 1495 nm can be produced respectively, which arejust adapt to pump the C-band and L-band distributed Raman fiber amplifiers.
The technique of support vector machines (SVM's) has been used as a new method for solving classification, regression, time series prediction and function estimation problems with many successful applications. In this paper, we use SVM to solve the problem of classification for ultrasonic medicine image. We use statistical characteristics of the interesting part in an ultrasonic image to aid a doctor to give a correct diagnosis. The procedure is: first, to extract a number of small sampling regions in the interesting part; second, to calculate a series of moments about those sampling regions; third, to decide whether the interesting part of the organ is normal or abnormal according to the analyses of the series of moments based on SVM. SVM's structural risk minimization principle is the guarantee that the diagnosis has the minimum mistake probability. The diagnosis based on SVM is optimal from the viewpoint of structural risk minimization principle. It is hoped that the results presented here will be helpful to the diagnosis based on ultrasonic medicine image.
The major limitation of flashlamp-pumped solid-state lasers is the low overall efficiency. Replacing flashlamps with high power laser diodes allows an increase of system efficiency by over an order of magnitude. Because of the thermally induced stress fracture of the laser materials, power-scaling possibilities of end-pumped configurations are limited. Therefore side pump geometry has to be used for high power laser. The theory and the design of high power diode side-pumped Nd:YAG laser system is described. The Nd:YAG rod is side-pumped by diode laser arrays with wavelength at 808 nm. We analyze the result of our experiments and make some conclusions about the design of side-pumped laser.