光子晶体光纤带隙及模场的一种综合模拟分析方法

提出直接由MATLAB读入光纤端面图实现复杂结构光子晶体光纤(PCF)模型的快速建立,并综合平面波法(PWM)和频域有限差分(FDFD)法,模拟分析带隙型光子晶体光纤(PBG-PCF)的带隙和模场分布.利用PWM计算得到了在PBG-PCF中传输的光波频率及模式有效折射率范围;基于FDFD法在给定波长及模式有效折射率范围情况下,模拟得到了PBG-PCF中可能存在的模场分布及其他特性.以市售的PBG-PCF为例,验证了数值模拟的正确性,随后系统地分析了结构参数(晶格结构、"原子"占有率、背景材料折射率及"原子     

输出近百纳焦耳脉冲能量的光子晶体光纤锁模激光器

设计并搭建了一种支持百纳焦耳量级的单脉冲能量输出的锁模光纤激光器.激光器基于σ型腔结构,采用掺Yb偏振型大模场面积光子晶体光纤作为增益介质,利用半导体可饱和吸收镜实现自启动锁模.激光器内没有色散补偿机理,使其工作在全正色散锁模状态.通过在谐振腔内引入多通长腔使激光器的重复频率降低至11.1 MHz,直接获得了平均功率为1.08 W,单脉冲能量为 97 nJ,脉冲宽度为4.17 ps的稳定锁模脉冲输出,经腔外色散补偿,脉冲宽度压缩至740 fs.     

一种胶体光子晶体修饰的光纤

设计了一种胶体光子晶体修饰的光纤. 采用恒温快速蒸发法直接在经切割刀处理后的光纤端面生长胶体晶体,再与另一根切割后的光纤在毛细玻璃管中完成对接,制备成胶体光子晶体修饰的光纤. 用扫描电子显微镜和光谱分析仪对样品的形貌、结构以及光学特性进行分析. 实验结果表明,粒径为640 nm、体积分数约为0.5%的SiO₂胶体微球溶液在60 ℃的情况下沉积,大约12 h后可得到质量较高的胶体光子晶体. 在SEM下,观察到端面的胶体晶体为面心立方(fcc)结构. 透射光谱证明,该结构在(111)面上     

光子晶体光纤中孤子内拉曼散射的研究

利用快速分步傅里叶方法数值计算了孤子在光子晶体光纤中的传输。计算结果表明:光子晶体光纤中会产生较强的拉曼散射,非线性越强,孤子分裂得越快,同时分裂出更多孤子。而且,初始啁啾对光子晶体光纤中的拉曼散射有较大的影响,正初始啁啾会增大拉曼孤子的红移速度,而负初始啁啾则会减小拉曼孤子的红移速度。随着光子晶体光纤非线性加强,初始啁啾的作用减弱。     

光子晶体光纤中零色散点处超连续谱演变的研究

从非线性薛定谔方程出发,采用分步傅立叶分析方法数值模拟光子晶体光纤中超连续谱的产生,计算、模拟并分析初始啁啾在光子晶体光纤的零色散点对超连续谱演变和带宽的影响.结果表明,非线性作用使频谱分裂成多峰不对称的结构,初始啁啾C的引入能明显的改善超连续谱的带宽和平坦性.由于二阶色散β2=0,三阶色散猹对超连续光谱的展宽影响较大.当β3>0时,C取正值时,随着C的增大,带宽减小; C取负值时,带宽有所增大,平坦性也有改善;β3<0时,无论C取正取负,频谱带宽增大,且平坦性较好.     

中心外缺陷对带隙型光子晶体光纤色散特性的影响

利用时域有限差分法(FDTD)模拟仿真了在中心缺陷外出现点缺陷、空气柱位错和内层空气柱发生形变三种缺陷形态对光子带隙型光子晶体光纤(PBG-PCF)色散特性的影响.发现一方面缺陷的出现会使色散曲线趋于平坦,另一方面点缺陷和位错缺陷的出现会使零色散点向长波移动,内层空气柱的形变使零色散点向短波长移动.这对PBG-PCF的实际生产实践会有指导意义.     

高效异质结构四波长波分复用器的设计与优化

将两光子晶体单模波导平行、邻近放置构成一个光子晶体波导耦合结构.根据耦合和解耦合理论,设计了一种新型的高效异质结构四波长波分复用器.应用时域有限差分法模拟了该器件的效率,并通过改变一排介质柱的折射率,实现了较高的透射率.进一步发现在入射口处添加三对介质柱,可以有效地降低系统的反射,实现了四个波长的高效传输,四个波长的透射率均超过了90%.该器件不仅具有较高的透射率,而且其尺寸仅为36 μm×17 μm,在未来的光子集成回路中具有潜在的应用价值.     

二维GaAs 基光子晶体微腔的制作与光谱特性分析

研究了以InAs量子点为有源区的二维GaAs基光子晶体微腔的设计与制作,测试并分析了室温下微腔的光谱特性.观察到了波长约为1137 nm,谱线半高宽度约为1 nm的尖锐低阶谐振模式发光峰.我们比较了不同刻蚀条件下光子晶体微腔的发光谱线,结果表明空气孔洞截面的垂直度是影响光子晶体微腔发光特性的重要因素之一.通过调节干法刻蚀工艺,改变空气孔半径与晶格常数的比率,可以在较大范围内调节谐振模式发光峰位置,达到谐振模式与量子点发光峰调谐的目的.     

海冰厚度的微波辐射遥感模式研究

本文从电磁波在分层介质中的传播理论出发,导出了适合我国北部海区一年生海冰的微波辐射遥感三层介质模式.与实测数据对比表明,当微波波长为10cm时,相干模式在海冰厚度小于20 cm范围内、非相干模式在20～40 cm范围内分别给出较好的拟合结果.以这些理论模式为依据可建立海冰厚度的微波遥感反演软件.文中给出了利用这些理论模式和实测数据推算出的辽东湾不同类型海冰的相对复介电常数,其数值范围为(0.5～4.0)-j(0.07～0.19).     

各向异性光子晶体中二能级原子和自发辐射场间的纠缠

应用 Von Neumann熵 和 Schmidt number K两种纠缠度量讨论了各向异性光子晶体中二能级原子和自发辐射场间纠缠度的演化性质. 研究发现,原子-光场纠缠度的演化与原子上能级和光子晶体能带带边的相对位置有关,当原子上能级处于光子晶体禁带内,原子-光场纠缠度将保持稳定,当原子上能级处于光子晶体能带中,原子-光场纠缠度先增大后衰减到零. 纠缠度的大小还与原子的初态有关. 可以通过控制原子的初态和原子上能级与带边的相对位置来控制原子-光场纠缠度的演化特性.     

光纤传感腐蚀监测研究

通过化学、物理的方法用金属敏感膜取代光纤的原始包层监测海洋环境中金属结构物的腐蚀状况。通过腐蚀前后光功率的变化表征腐蚀的发生和发展。     

Modification of the spontaneous emission of quantum dots near the surface of a three-dimensional colloidal photonic crystal

This paper demonstrates experimentally and numerically that a significant modification of spontaneous emission rate can be achieved near the surface of a three-dimensional photonic crystal. In experiments, semiconductor core-shell quantum dots are intentionally confined in a thin polymer film on which a three-dimensional colloidal photonic crystal is fabricated. The spontaneous emission rate of quantum dots is characterised by conventional and time-resolved photoluminescence (PL) measurements. The modification of the spontaneous emission rate, which is reflected in the change of spectral shape and PL lifetime, is clearly observed. While an obvious increase in the PL lifetime is found at most wavelengths in the band gap, a significant reduction in the PL lifetime by one order of magnitude is observed at the short-wavelength band edge. Numerical simulation reveals a periodic modulation of spontaneous emission rate with decreasing modulation strength when an emitter is moved away from the surface of the photonic crystal. It is supported by the fact that the modification of spontaneous emission rate is not pronounced for quantum dots distributed in a thick polymer film where both enhancement and suppression are present simultaneously. This finding provides a simple and effective way for improving the performance of light emitting devices.     

Coherent reflection of acoustic plane wave from a rough seabed, with a random sediment layer overlying an elastic basement

The problem of coherent reflection of an acoustic plane wave from a rough seabed with a randomly inhomogeneous sediment layer overlying a uniform elastic basement is considered in this analysis. The randomness of the sound field is attributable to the roughness of the seabed and the sound-speed perturbation in the sediment layer, resulting in a joint rough surface and volume scattering problem. An approach based upon perturbation theory, combined with a derived Green's function for a slab bounded above and below by a fluid and an elastic half-space, respectively, is employed to obtain an analytic solution for the coherent field in the sediment layer. Furthermore, a boundary perturbation theory developed by Kuperman and Schmidt (1989) is applied to treat the problem of rough surface scattering. A linear system is then established to facilitate the computation of the coherent reflection field. The coherent reflection coefficients for various surface roughness, sediment randomness, frequency, sediment thickness, and basement elasticity have been generated numerically and analyzed. It was found that the higher/larger size of surface and/or medium randomness, frequency, thickness, and shear-wave speed, the lower the coherent reflection. Physical interpretations of the various results are provided.     

光纤光栅称重传感器在大型海上浮吊中的应用

为了实现大型海上浮吊臂架结构健康状态监测,开发了大型海上浮吊光纤光栅称重传感器系统,提出了光纤光栅称重传感器设计理论,建立了传感器设计框架。通过悬臂梁理论,借助于有限元分析软件,提出了悬臂梁和受压弹性体复合结构;通过温度补偿理论与对比,提出了滤波温度补偿方案;通过迟滞效应原理,提出了双光栅式迟滞效应消除方案。进行光纤光栅称重传感器性能实验、反复性实验和稳定实验,讨论了系统的性能和可行性。并将大型海上浮吊光纤光栅实时称重系统应用于实际工程项目,成功实现了大型海上浮吊负重状况监测。     

Coherent reflection of an acoustic plane wave from a random sediment layer over an elastic sea floor

The problem of coherent reflection of an acoustic plane wave from a seabed consisting of a randomly inhomogeneous sediment layer overlying a uniform elastic sea floor is considered in this analysis. The random perturbation in the sediment layer is attributable to the sound-speed variations, resulting in volume scattering due to medium inhomogeneities. An approach based upon perturbation theory, combining with a derived Green's function for a slab bounded above and below, respectively, by a fluid and an elastic half-space, is employed to obtain an analytic solution for the coherent field in the sediment layer. A linear system is then constructed to facilitate the computation of the coherent reflection field. The results of the coherent reflection coefficient for various sediment randomness, frequency, sediment thickness, and sea floor elasticity have been numerically generated and analyzed. It is found that the higher/larger the randomness, frequency, thickness, and shear-wave speed, the lower is the coherent reflection. Physical interpretations for the characteristics of the various results are provided.     

碳纤维层合板有限元分析

碳纤维材料作为一种优良的复合材料,越来越广泛地应用于水下攻防领域。 主要研究了有限元法对碳纤维层合板的分析。 首先介绍层合板理论,基于该理论对碳纤维层合板模型进行理论分析,然后利用大型有限元软件 ANSYS 对同一模型进行有限元仿真计算。 最后,对二者计算结果进行比较,讨论有限元法对碳纤维层合板的强度计算的可行性,为工程设计运用提供参考。