The performance of the oxide-confined surface-relief(SR)structure vertical-cavity surface-emitting laser(VCSEL)is simulated and analyzed by using the three-dimensional finite-difference time-domain(FDTD)method.The imp...The performance of the oxide-confined surface-relief(SR)structure vertical-cavity surface-emitting laser(VCSEL)is simulated and analyzed by using the three-dimensional finite-difference time-domain(FDTD)method.The impacts of the device structure parameters on the far-field characteristics are researched.A single-fundamental-mode SR VCSEL with an oxide-aperture of 15μm is designed and produced.The single-mode power of the VCSEL is 5 mW,the threshold current is 2.5 mA,far-field divergent angles range from 7.8°to 10.8°and the side-mode suppression ratio is over 30 dB.The optical and electrical properties of the device are in agreement with the results of FDTD simulation,which shows that the SR technology can effectively suppress the higher-order-mode lasing,and make the SR VCSEL work in a single mode under a larger oxide aperture.展开更多
By introducing multi-leaf sectorial holes into an oxidation confined 850 nm vertical cavity surface emitting laser(VCSEL),the far-field divergence angle is reduced.The finite-difference time-domain method is used to s...By introducing multi-leaf sectorial holes into an oxidation confined 850 nm vertical cavity surface emitting laser(VCSEL),the far-field divergence angle is reduced.The finite-difference time-domain method is used to simulate the far-field pattern of the multi-leaf holey VCSEL with different etching depths and different shapes of the oxide aperture in diameter R.Based on the simulation result,we design and fabricate a multi−leaf holey VCSEL and its divergence angle is only 6°.The experimental results agree well with the theoretical predication.展开更多
The risk analysis of urban rainstorm water logging facing Tianjin city by using methods of probability, investigation and numerical simulation was carried out in this article. Firstly, a mathematical model for the urb...The risk analysis of urban rainstorm water logging facing Tianjin city by using methods of probability, investigation and numerical simulation was carried out in this article. Firstly, a mathematical model for the urban rainstorm water logging was established on the basis of one- and two-dimensional unsteady flow theory and the technique of non-structural irregular grid division, Secondly, the precipitation over heavy rain was divided into seven grades, the experiential expression of frequency and rain grades was got according to the observed rainfall from May 1918 to October 1998. Thirdly, the mathematical model was used to simulate various rain process according to the features of the rainstorm and the draining rule, based on the simulated maximum water depths, 3 class of disaster extents were established, the disaster risks were mainly in Class Ⅰ and Class Ⅱ, The risk analysis of water logging on traffic were primarily evaluated, and finally, some management and mitigation measures of the urban rainstorm water logging disaster were discussed.展开更多
基金Supported by the National High-Technology Research and Development Program of China under Grant No 2008AA03Z402the National Natural Science Foundation of China under Grant No 61076044the Natural Science Foundation of Beijing under Grant Nos 4092007,4102003 and 4112006.
文摘The performance of the oxide-confined surface-relief(SR)structure vertical-cavity surface-emitting laser(VCSEL)is simulated and analyzed by using the three-dimensional finite-difference time-domain(FDTD)method.The impacts of the device structure parameters on the far-field characteristics are researched.A single-fundamental-mode SR VCSEL with an oxide-aperture of 15μm is designed and produced.The single-mode power of the VCSEL is 5 mW,the threshold current is 2.5 mA,far-field divergent angles range from 7.8°to 10.8°and the side-mode suppression ratio is over 30 dB.The optical and electrical properties of the device are in agreement with the results of FDTD simulation,which shows that the SR technology can effectively suppress the higher-order-mode lasing,and make the SR VCSEL work in a single mode under a larger oxide aperture.
基金by the National High Technology Research and Development Program of China under Grant No 2008AA03Z402the National Natural Science Foundation of China under Grant No 61076044the Natural Science Foundation of Beijing under Grant Nos 4092007,4102003 and 4112006.
文摘By introducing multi-leaf sectorial holes into an oxidation confined 850 nm vertical cavity surface emitting laser(VCSEL),the far-field divergence angle is reduced.The finite-difference time-domain method is used to simulate the far-field pattern of the multi-leaf holey VCSEL with different etching depths and different shapes of the oxide aperture in diameter R.Based on the simulation result,we design and fabricate a multi−leaf holey VCSEL and its divergence angle is only 6°.The experimental results agree well with the theoretical predication.
文摘The risk analysis of urban rainstorm water logging facing Tianjin city by using methods of probability, investigation and numerical simulation was carried out in this article. Firstly, a mathematical model for the urban rainstorm water logging was established on the basis of one- and two-dimensional unsteady flow theory and the technique of non-structural irregular grid division, Secondly, the precipitation over heavy rain was divided into seven grades, the experiential expression of frequency and rain grades was got according to the observed rainfall from May 1918 to October 1998. Thirdly, the mathematical model was used to simulate various rain process according to the features of the rainstorm and the draining rule, based on the simulated maximum water depths, 3 class of disaster extents were established, the disaster risks were mainly in Class Ⅰ and Class Ⅱ, The risk analysis of water logging on traffic were primarily evaluated, and finally, some management and mitigation measures of the urban rainstorm water logging disaster were discussed.
