Narrow-linewidth Q-switched DBR laser on Ytterbium-doped glass

In this paper, an integrated passively Q-switched DBR laser made in glass integrated optics technology is designed, fabricated and investigated. The laser, operating at 1030 nm wavelength, is formed by an ion-exchanged single mode waveguide realized in an Ytterbium doped phosphate glass. The feedback is provided by a DBR structure made of a Fiber Bragg Grating and a dielectric mirror. The Q-switched behavior is obtained by hybridizing the saturable absorber on the waveguides, so that it interacts with the evanescent part of the guided field. The saturable absorber we use is a bis(4-dimethylaminodithiobenzil)nickel (BDN) dye incorporated in a polymeric film. Using this structure, we were able to demonstrate a Q-switched operation for several BDN concentrations, allowing to vary the pulse duration and the repetition rate of the device. Moreover, we report a very narrow 372 MHz wide emission spectrum while in Q-switched regime.     

Professional development to enhance teachers' practices in using information and communication technologies (ICTs) as cognitive tools: Lessons learned from a design-based research study

Technology integration in K-12 classrooms is usually overly teacher-centered and has insufficient impact on students' learning, especially in enhancing students' higher-order cognitive skills. The purpose of this project is to facilitate science teachers' use of information and communication technologies (ICTs) as cognitive tools to shift their practices from traditional teacher-centered methods to constructivist, student-centered ones. This paper describes the outcomes and lessons learned from an application of design-based research (DBR) in the implementation and refinement of a teacher professional development (PD) program that is a key component of the overall project. This DBR study involved 25 middle-school science teachers from 24 schools whose implementation of cognitive tools with their students in science classrooms and virtually through a social networking site were observed over four years. A mixed-methodology was utilized to examine the impact of the cognitive tools intervention on teachers' classroom practices and students' development of new literacy skills. Identifying reusable design principles related to technology integration was another focus of the DBR study. The results revealed teachers' positive changes in their classroom practices by gradually allowing students to take control over the use of technology, and positive impact on students' ICT skills and science learning. Design principles for future professional development programs aimed at preparing teachers to adopt a cognitive tools approach are described.     

光抽运垂直外腔面发射激光器特性与研究进展

介绍了光抽运半导体垂直外腔面发射激光器的结构特点、设计原理及其性能优势,综合评述该领域的最新研究进展,并探讨该类型激光器的发展前景和技术发展方向.     

用传输矩阵法分析取样光栅半导体激光器调谐特性

本文利用传输矩阵法分析了取样光栅DBR半导体激光器的调谐特性     

InGaN/GaN light-emitting diodes with a reflector at the backside of sapphire substrates

Nitride-based light-emitting diodes (LEDs) with a reflector at the backside of the sapphire substrates have been demonstrated. It was found that an SiO₂/TiO₂ distributed-Bragg reflector (DBR) structure could reflect more downward-emitting photons than an Al-mirror layer. It was also found that the 20-mA output power was 2.76 mW, 2.65 mW, and 2.45 mW for the DBR LED, Al-reflector LED, and conventional LED, respectively. With the same 50-mA current injection, the integrated-electroluminescence (EL) intensity of a DBR LED and an Al-reflector LED was 19% and 15% larger than that observed from a conventional LED.     

Operation and control of flow manufacturing based on constraints management for high-mix/low-volume production

The existing technology of flow manufacturing, which is mainly appropriate for high volume and repetitive production, is proven difficult to be applied in high-mix/low-volume environments. To adapt lean production into the latter, a new type of flow manufacturing is proposed based on flow path management technology. This paper first describes the general operation framework of the proposed new mode. The main idea is the dynamic formation of adaptable virtual production lines (called flow paths) corresponding to different product families. The application of different theories of constraints/drum-buffer-rope (TOC/DBR) control policies depends on the differences in scope of variety and scale of demand for these product families. The overall architecture of the proposed mechanism of constraint management-based operation and control is introduced. For the implementation, a mathematical programming method is suggested for the dynamic planning of flow paths, and a TOC/DBR ‘path-specific’ mechanism with group scheduling is used for the control over each flow path.We also study other critical issues including the identification and management of resource bottlenecks, and the setting of the buffer size in the deployment of the TOC/DBR mechanism.     

基于DBR的双馈风力机组低电压穿越方案设计

讨论了电网电压跌落下当前双馈风力发电机组各种LVRT技术拓扑方案及控制策略的优缺点,提出一种不同于常用Crowbar技术的低电压穿越技术方案。在基于DBR（Dynamic Brake Resistance）双馈风电机组新型LVRT拓扑结构及功能分析基础上,建立双馈风电机组在电网正常运行和发生低电压故障情况下发电系统的数学模型进行理论分析,提出了风电机组发生LVRT的控制策略。最后在此技术方案下进行20%电网故障下LVRT试验,试验实验数据充分证实了技术方案的正确性。     

基于DGS的微带DBR双工器的研究

提出了一种高隔离度的微带双工器结构.在微带双重行为谐振(DBR)滤波器中引入基于缺陷地结构(DGS)的低通滤波器,利用DGS的慢波特性减小DBR滤波器奇偶模之间的相速差,从而改善滤波器的上阻带特性.使用本文提出的微带滤波器结构设计并研制了一C波段的微带双工器,仿真和测试结果表明:微带双工器的插入损耗小于1.3dB,隔离度大于65dB.     

1.65 mm Three-Section Distributed Bragg Reflector (DBR) Laser for CH4 Gas Sensor

A 1.65-μm three-section distributed Bragg reflector (DBR) laser for CH₄ gas sensors is reported. The DBR laser has a wide tunable range covering the R3 and R4 methane absorption line manifolds. The wavelength tunability properties, temperature stability and laser linewidth are characterized and analyzed. Several advantages were demonstrated compared with traditional DFB lasers in harmonic detection.     

The analysis of light trapping and internal quantum efficiency of a solar cell with DBR back reflector

A theoretical analysis of the total internal quantum efficiency (IQE) of a flat-band p-n homo-junction silicon solar cell with back reflector using distributed Bragg reflectors to improve the light trapping is presented and contributions of different regions of the structure to IQEs are simulated. An optical model for the determination of generation profile of the cell is adopted and multiple light passes are considered and compared to previous single light pass approach. It is found that the spatial widths of the cell, the surface recombination velocities, the front surface transmittance and the back reflector have significant impacts on the IQEs. With two light passes and normal incident light, the simulation result shows the IQEs can be increased over the one pass value by 6.34% and with a 60° light reflection angle, the IQEs can be further increased by 9.01% while assuming the reflectance at back structure closed to 100%. The effect on IQEs by back reflectance is more significant than that by front transmittance. Under multiple light passes simulation, up to 51 light trapping passes have been considered at wavelength range 900-1100 nm, the cell IQEs can be enhanced by about 26.98%.