光纤光栅外腔半导体激光器的实验研究

利用光纤光栅作为选频元件的外腔半导体激光器具有波长稳定性和可控性好等优点。报道了该激光器的关键工艺 ,主要是光纤光栅制备、芯片的腔面增透和光纤耦合封装等。报道了初步的实验结果。     

基于光纤Bragg光栅的掺铒光纤激光器

研制了基于光纤Bragg光栅的掺铒单模光纤激光器。用 980nmLD作抽运源 ,在 1 56 μm波段获得了谱线宽为 0 1nm的激光输出。最大输出光功率为 1 73mW。输出功率稳定性为± 0 .0 2dB ,波长稳定性为 0 0 5dB。阈值抽运光功率为 7mW ,斜率效率为 3%。     

Optical fibre sensors for health monitoring of bonded repair systems

In the aircraft industry the use of externally bonded composite repairs has become an accepted way of repairing fatigue, or corrosion, damaged metallic structural components. However, current NDI and damage assessment techniques for composite repairs are passive and generally performed on ground. The challenge is to develop new techniques utilising recent analytical and experimental tools. This report examines the use of optical fibre sensors. Optical fibres offer a means of monitoring the load transfer process in these repairs, and can therefore be used to provide an indication of the integrity of the repair. This paper describes the use of an array of fibre Bragg grating strain sensors (FBGs) for the in situ monitoring of bonded repairs to aircraft structures and, in particular, the monitoring of crack propagation beneath a repair. In this work the FBGs have been multiplexed using a combination of wavelength and spatial techniques employing a tunable Fabry–Pérot (FP) filter to track individual gratings. The multiplexed FBGs were then surface-mounted on a boron–epoxy unidirectional composite patch bonded to an aluminium component. The sensors were located so as to monitor the changing stress field associated with the propagation of a crack beneath the patch. The ability of relating experimental results to sensor readings is then confirmed using both a thermo-elastic scan of the patch and 3D finite element analysis.     

Wideband constant beamwidth coplanar waveguide‐fed slot antennas using metallic strip loadings and a widened tuning stub with shaped reflectors

Sectored antennas with wideband operation for wireless communication systems are presented. The proposed configurations are based on a coplanar waveguide fed slot antenna using metallic strip loadings and a widened tuning stub above various reflector shapes. By shaping the reflector, noticeable enhancements in both unidirectional radiation pattern and beamwidth can be achieved while maintaining the simple fabrication and installation. Based on the results obtained, three sector antennas covering 72°, 90°, and 120° beamwidths suitable for five, four, and three sectors, respectively, have been proposed and designed. The simple structural configurations, low cost, and ease of half power beamwidth control of the proposed antennas make the design very attractive for practical implementation. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Influence of differential settlement on pavement structure of widened roads based on large-scale model test

This study introduced at first the background of numerous highway widening projects that have been developed in recent years in China.Using a large ground settlement simulator and a fiber Bragg grating (FBG) strain sensor network system,a large-scale model test,with a similarity ratio of 1:2,was performed to analyze the influence of differential settlement between new and old subgrades on pavement structure under loading condition.The result shows that excessive differential settlement can cause considerabl...     

Optimization of parabolic bars for maximum Bragg resonant reflection of long waves

This paper presents an analytical solution for the problem of the long wave reflection by a series of artificial bars with parabolic configuration in terms of the associated Legendre functions. It is shown that both the reflection and transmission coefficients depend solely upon the number of bars, the dimensionless bar height, the dimensionless bar width and the dimensionless bar distance. Particularly, under the Bragg resonance condition, i.e., the distance between two adjacent bars is about half of the wavelength of the normal incident waves, the analytical solution for the peak Bragg resonant reflection is obtained, which reveals that the peak Bragg resonance depends upon the number of bars, the dimensionless bar height and the dimensionless bar width. Based on this solution, the optimization of the parabolic bars is made to obtain the maximum Bragg resonance and a group of optimal curves, which may be very useful in the design of Bragg breakwaters with parabolic bars.     

Polarimetric distributed Bragg reflector fiber laser sensor array for simultaneous measurement of transverse load and temperature

A polarimetric fiber laser sensor array based on wavelength/beat frequency hybrid interrogation approach for simultaneous measurement of transverse load and temperature is presented and experimentally demonstrated. Operation principle of the hybrid interrogation approach has been theoretically analyzed, which is validated by our experimental results. The shift of beat frequency and laser wavelength in response to the change of transverse load and temperature allows for simultaneous dual-parameter discrimination. Experimental results indicate that laser beat frequency is highly sensitive to transverse load and temperature while laser wavelength is insensitive to transverse load. And the temperature sensitivities of laser wavelength have the same magnitude as common FBG sensors. The proposed active sensor array with simple configuration has considerable potential applications for future fiber sensor networks.     

Design and application of the ice force sensor based on fiber Bragg grating

Ice load is one of the most dangerous factors which threaten the health of offshore structures in cold area. The ice-loading model experiment is an effective method to identify the ice load and to evaluate its influence towards structures. Fiber Bragg grating (FBG) with advantages of reliability, durability and high accuracy, has become one of the most popular sensing element for structural health monitoring and intelligent materials system. In this paper, a novel FBG ice force sensor is presented and applied in the tests of ice loading on bridge pier model. Its sensing property is theoretically analyzed and calibration experiments are conducted. The research results demonstrate that the FBG-based ice force sensor has advantages of small size, high precision and low influence on the structure, showing great prospect for measurement of ice force in model test.     

新型坡度同轴布喇格反射器数值模拟比较研究

将一种新型加坡度方式同轴布喇格反射器的多模耦合理论与电磁仿真软件(CST)进行了数值模拟比较研究.结果表明:两者吻合较好,但多模耦合理论方法计算编程容易,运算速度快,参数调整非常方便;具有正圆锥形坡度的同轴布喇格反射器的带宽随着所加坡度角的增大而变窄,具有倒圆锥形坡度的同轴布喇格反射器的带宽随着所加坡度角的增大而变宽;...     

Depth-dose distribution of proton beams using inelastic-collision cross sections of liquid water

Complete physical processes contributing to the shape of the depth-dose distribution and the so-called Bragg peak of proton beams passing through liquid water are given. Height, width and depth of the Bragg peak through investigation of collisions of the projectile, nuclear processes and stochastic phenomena are discussed. Different analytical models for stopping cross sections which lead to Bragg peak are contrasted. Results are also compared with GEANT4 package simulation.