混合导引型光子晶体光纤中纤芯折射率相关的导光特性研究

利用全矢量有限元法研究了一种混合导引型光子晶体光纤在纤芯折射率改变时,光纤导光机理和模式的演变特性.当纤芯折射率小于混合包层中空气孔包层的有效折射率时,芯模的导光机理为"双带隙导引型";当纤芯折射率位于空气孔和高折射率两套包层的有效折射率之间时,芯模的导光机理为"单带隙+全内反射导引型";当纤芯折射率大于高折射率棒包层的有效折射率时,芯模的导光机理为"全内反射导引型".并对该光纤在上述三种条件下的导光特性进行了比较和讨论.这些结果对设计特殊用途的光子晶体光纤具有指导意义. 关键词： 混合导引型光子晶体光纤 带隙 模式     

GaAs多结电池宽光谱ZnS/Al2O3/MgF2减反射膜的设计与分析

 为了提高砷化镓(GaAs)多结太阳电池的光电转换效率,设计了宽光谱(300 nm～1 800 nm)ZnS/Al2O3/MgF2三层减反射膜,分析了各层的厚度及折射率对三层膜系有效反射率的影响。结果表明： 对于整个波长,ZnS厚度对有效反射率的影响要大于Al2O3和MgF2,MgF2厚度对有效反射率的影响最小;适当减小MgF2的折射率或增加ZnS的折射率可得到更低的有效反射率。同时,当 ZnS,Al2O3和MgF2的最优物理厚度分别为52.77 nm,82.61 nm,125.17 nm时,此时最小有效反射率为2.31％。     

内壁涂覆石墨烯的双椭圆中空表面等离子波导

本文设计了一种内壁涂覆单层石墨烯的双椭圆形中空表面等离子波导,采用有限元的方法对其传输特性进行了研究。结果表明,椭圆之间的距离和半短轴的长度增大时,有效折射率的实部减小,传输距离增大,模式面积减小;圆化半径增大时,有效折射率的实部增大,传输距离减小,模式面积增大;工作频率增大时,有效折射率的实部减小,传输距离减小,模式面积减小;温度升高时,有效折射率先增大后减小,传输距离减小,模式面积减小。本文的工作为研究基于石墨烯的波导器件提供了理论依据。     

长周期光纤光栅折射率特性仿真的新方法

基于长周期光纤光栅的模式耦合机理,提出一种快速模拟长周期光纤光栅折射率特性的方法。该方法在计算包层模式的有效折射率时分开计算,在环境折射率小于包层折射率时采用二分法和分步搜索法结合计算包层模式的有效折射率,在环境折射率大于包层折射率时采用Nelder-Mead加分步搜索法求解包层模式的有效折射率。在应用谐振波长的决定式求解与环境折射率的匹配的谐振波长时,采用变区间应用二分法求解而不是传统的逐步搜索法求解谐振波长。数值结果与实验结果做了对比,两者基本一致。实践证明,该方法方便快捷,比一般的方法速度提高7倍以上。     

用于倾斜入射的波分复用薄膜滤光片的特性及改进

对倾斜入射时窄带薄膜滤光片的特性作了描述 ,由于低折射率间隔层的滤光片 ,倾斜入射时 p偏振分量的通带比s分量更移向短波 ,而高折射率间隔层的滤光片则反之 ,因此可把间隔层同时设计成高、低折射率两种材料 ,或选用适当的中间折射率材料 ,使p分量和s分量两个通带的中心波长重合。设计了用于 2 0°入射角的密集波分复用 (DWDM )滤光片 ,并给出了实验结果。     

影响玻璃微珠回向反射性能的主要因素分析

从理论和实验两方面分析了玻璃微珠的回向反射特性,主要讨论了玻璃微珠的折射率和其反射层面积这两个因素对回向反射性能的影响. 研究结果表明,折射率增大, 折射率小于2时,回向反射性能逐渐增强, 相反, 在折射率大于2时, 回向反射性能减弱; 反射层面积的大小会影响入射光线的完整回向反射过程; 最后定义了有效回向反射角度, 并给出了玻璃微珠在激光照射下的二维回向反射光照度分布.     

基于1stOpt求解光学玻璃折射率温度系数经验公式常量的方法

为了解决ZEMAX软件拟合计算折射率温度系数经验公式常量时,参量回归计算的折射率和折射率温度系数与实验值存在较大偏差的问题,用1stOpt差分进化法求解折射率温度系数经验公式常量.以氟冕D-FK61和特种火石H-TF3A光学玻璃为例,用该方法求解的λtk常量与其通用数值范围0.08~0.33相吻合,参量回归计算的折射率和折射率温度系数与实测值的偏差分别小于1×10~(-5)、2×10~(-7)/℃.该方法作为ZEMAX软件计算光学玻璃折射率温度系数的有效补充,计算的准确性高,可为热补偿光学系统设计提供准确的光学参量保障.     

电光有机聚合物多模干涉分束器

分束器是光纤通信系统中光无源网络和光子集成回路的重要器件.1×2 MMI(multimode interferences)电光有机聚合物分束器是利用自成像效应设计的.分析了1×2 MMI 的工作原理.利用有效折射率方法(effective index method,EIM)计算出1×2 MMI 三维多模脊形波导的有效折射率分布.利用自成像效应的成像规律计算出成像位置并用导模传输分析法(guided-mode propagation analysis,MPA)对输出波导的光强进行模拟.分析表明:在波长为 1.55μm 的情况下,1×2 MMI 的输出波导的光强在未加电极时可以实现预定分束比输出;加上电极之后,由于电光效应可调控有机聚合物波导折射率的改变,利用有限差分光束传播法模拟输出波导的分束比可在7.6 dB 范围内可调.     

光波导材料与制备

通过数值计算模拟了K 一Na 二次扩散玻璃波导的折射率轮廓,阐述了利用K 一Na十二次离子交换的方法在BK7玻璃上制作波导的过程,分析了极化率不同的扩散离子对的选择对波导有效折射率变化的影响,以及扩散平衡时体积变化对表面折射率的影响,描述了扩散引起的波导内部诱导应力变化。设计了测试波导损耗以及波导     

一种新型的多包层光子晶体光纤的分析方法

传统有效折射率方法只能模拟具有相同空气孔大小的单包层光子晶体光纤.针对这一问题,提出了一种改进的有效折射率法,能够计算具有不同孔径的多包层光子晶体光纤的传输特性.并用此方法对三包层光子晶体光纤的基模有效折射率和色散等特性进行了数值模拟,结果与多极法模拟出的结果符合得很好.这种改进的有效折射率法拓展了传统有效折射率法的适用范围,对快速准确地分析和设计具有不同传输特性的多包层光子晶体光纤提供了理论依据. 关键词： 光子晶体光纤 多包层 有效折射率方法 色散     

光纤纤芯及包层模有效折射率计算及仿真

光纤结构设计、模间色散求解、光纤光栅模式耦合等问题的研究, 都需要对光纤纤芯及包层模的有效折射率进行精确计算. 本文以光纤三层结构模型为基础, 结合该模型下的模式本征方程, 使用截弦法求解了纤芯模有效折射率, 并将计算结果与COMSOL软件模拟的对应纤芯模的传输光场进行对比, 验证了计算结果正确.使用区间遍历算法对包层模有效折射率进行了求解, 与已有的传统方法相比, 该方法可以有效防止求解过程中根的遗漏、避免特征方程产生的奇点, 并能保证模式的正规性.本文采用Mathematica软件对求解过程进行仿真, 获得了纤芯模和包层模有效折射率与波长关系曲线. 关键词： 光纤传输模式 有效折射率 截弦法 区间遍历算法     

Terahertz multi-metal-wire hybrid-cladding hollow waveguide for refractive index sensing

We propose a design of terahertz refractive index sensing based on the multi-metal-wire(MMW) hybrid-cladding hollow waveguide. The proposed terahertz hybrid-cladding hollow waveguide comprises one air core in the center surrounding MMW surrounded dielectric. The central air core is used for filling lossless measurands and transmitting terahertz light. In particular, the refractive index sensing is realized by measuring the mode field area(MFA) variation of radially polarized mode. The modal effective refractive index, mode field intensity distribution, and mode field area properties responding to the measurand refractive indexes for different operating frequencies and structure dimensions are investigated, respectively.Simulations show that the proposed terahertz refractive index sensor can realize easily the measurement of the measurand refractive index. Meanwhile, the effects of operating frequency and structure parameters on sensitivity and measurement accuracy are also studied. In view of the trade-off between sensitivity and measurement accuracy, the reasonable choice of the operating frequency and structure parameters can optimize appropriately the sensitivity and measurement accuracy, and the sensitivity can reach approximately 0.585 mm~2/RIU(RIU is short for refraction index units) with the proper frequency and structure parameter.     

Effective index method for planar lightwave circuits containing directional couplers

A simple and intuitive effective index method for planar lightwave circuits containing directional couplers is proposed. The optimal cladding refractive index of the effective two-dimensional planar waveguide is found according to the coupling length of the directional coupler involved. Numerical examples indicate that this proposed effective index method gives accurate results while saving significant computation time in simulation and design of planar lightwave circuits containing directional couplers.     

OMNIDIRECTIONAL HIGH REFLECTOR FOR INFRARED WAVELENGTH

We have purposed the design of omnidirectional high reflectors with wide bandwidth (nearly 6300A⁰) for the infrared wavelength. Using translational matrix method for numerical calculation, it is found that a complete photonic band gap high reflector covering the wavelength region 11500A⁰ to 17800A⁰ is obtained for the quarter wave stack air / (n_L n_H)⁷ / air by using the tellurium (n=4.60) and TiO₂ (n=2.35) as material of high reflective index and SiO₂(n=1.45) low refractive index. Due to high refractive index of contrast of the structure i.e. SiO₂/tellurium, a large complete photonic band gap, omnidirectional high reflector, has been observed for the infrared wavelengths. This type of omnidirectional high reflector can be used in telecommunication. Besides this, we have studied the effective refractive indices (phase and group) of the proposed structures. It is observed that the effective refractive indices (phase and group) of the high omnidirectional reflector band are largely changed near the band edges due to the high refractive index of contrast, and the reflections from the internal interfaces of the structure.     

Optical humidity-sensitive mechanism based on refractive index variation

A novel composite model is put forward for humidity-sensitive material based on Maxwell-Garnett and effective medium theory. The analytical expression of the relation between effective refractive index and relative humidity is shown with different absorption factors and porosities. The larger the absorption factor is, the higher the refractive index is. The refractive index of humidity-sensitive SiO2 film decreases with the increase of ceramic material porosity. The sensitivity of optical humidity sensor can reach the magnitude of 10-3. In comparison with the experimental humidity-sensing curve by the method of p-polarized reflectance and the analysis of mechanism, theoretical simulation is in agreement with experimental results. Therefore, this composite model is proved to be reasonable which lays new theoretical foundation in further research on optical humidity sensor.     

Structure design of refractive index sensor based on LPFG with double-layer coatings

Based on the coupled-mode theory, the mode transition and transmittance of LP modes in an LPFG with double-layer coatings are studied theoretically. As a refractive index sensor, this LPFG structure is designed for high sensitivity by selecting a suitable thickness and refractive index of the double-layer coatings. Date simulation indicates that the effective index of the LP cladding mode increases in steps with the first coating thickness, thus LP mode is guided to the overlay and the mode transition takes place, where the LP modes can be easily affected by the ambient. Thereby, the coated LPFG sensor should be designed to operate at the transition region. In addition, the effective refractive index of LP cladding modes also increases in steps with the refractive index of the second overlay. For the higher order LP modes, the transition regions are broaden and the dynamic responses are greater than the lower LP modes, which means the higher order LP modes can be used for lower index overlay sensing. Further, the transmittance spectrum, sensitivity and measurable dynamic range of this LPFG are analyzed. The sensitivity of the LPFG sensor is available to $10^{3}$ with suitable overlay thickness and measurable dynamic range of the sensitive film refractive index is available to $10^{-2}$ . So the presented LPFG sensor enhances the design flexibility and enlarges the scope of application, which will likely be developed for high sensitivity LPFG sensors.     

Design Method for Optical Waveguide Filters Having Corrugation Structures by Corrugation Width Modulation

A method to design a corrugated optical waveguide filter by modulating the corrugation width profile is proposed. This method is based on combined applications of the Fourier transformation and the F-matrix formalism. The method achieves the spatial profile of the corrugation width required to design a filter with any specified spectral profile of the reflection coefficient. The idea of the technique is that the spatial variation of the effective refractive index can be transformed, with the help of the F-matrix formalism, to variation of the corrugation width while maintaining a constant amplitude of the refractive index variation. Two examples are given applying the technique to the design of optical waveguide filters with reflectivity profiles of two- and four-rejection bands.     

掺半导体玻璃(SDG)波导非线性饱和的导波测量方法

掺半导体玻璃波导的折射率分布是通过多模波导有效折射率测量得到的.当耦合进入波导的激光功率密度变化时,可在不同模深度处,测量到波导的非线性折射率系数,并获得波导非线性折射率系数与功率密度的关系.从而得到波导的非线性饱和值为1.54×10-4.     

气溶胶粒子散射和吸收特性对复折射率依赖性的数值研究

利用米散射理论数值计算分析了尺度参数为0.1~100时球形典型气溶胶粒子的散射和吸收特性对复折射率的依赖性关系。气溶胶粒子复折射率的实部和虚部是一个有机的整体,粒子复折射率的实部和虚部可以分别影响其散射和吸收特性。若实际大气气溶胶粒子大多是成核模态和积聚模态的小粒子,基于气溶胶的散射和吸收特性可以获得其复折射率的唯一解。但是,如果大气中存在大量的粗模态粒子时,气溶胶散射和吸收特性对其复折射率的依赖性较为复杂,只有选择有限的合适复折射率库区间,才有可能获得更合适的有效复折射率。