光纤光栅的局域耦合模分析

本文运用矢量局域耦合理论分析了平均扰动折射率随Z轴变化的单模光纤光栅的纤芯模场分布、包层模场分布以及耦合系数,得到更为精确的光栅光谱特性.并分别计算了布喇格光栅和长周期光纤光栅在平均扰动折射率在Z轴有扰动时的光谱特性图.从而得出平均折射率随Z轴变化对光谱特性的危害性,并提出了解决方法.     

双模腔场中具有不同耦合常数的两原子多光子辐射谱

研究了与双模腔场具有不同耦合常数的两个二能级原子的多光子辐射谱,给出了双模多光子辐射谱的一般表达式.结果表明,当双模腔场分别处于不同数态时,虽然两原子与双模腔场之间具有不同的耦合常数,但对于任意的N₁和N₂(N_i(i＝1,2,)为模i腔场被每个原子吸收或发射的光子数),辐射谱总是关于共振频率ω₀对称分布;并且,当N₁＝N₂时,对于任意的数态光子数n₁和n₂交换,辐射谱不变.上述特点用解析方法给予了解释.计算了非简并双光子情况下的辐射谱,并得到了一些新结果.双模腔场中单原子及具有相同耦合常数的两原子辐射谱可从本文结果分别做为特例而得到.     

长周期光纤光栅中的包层模谐振

本文给出了光纤中包层模的电场形式,指出包层膜的电场形式与弱导光纤中导模的电场形式不同,对光纤中基模与包层模电场沿光纤横截面分布的重叠情况的分析表明,长周期光纤光栅除了能将HE₁₁导模耦合到HE_1p包层模外,也可以将其耦合到EH_1p包层模。基于耦合模理论的计算表明,耦合到EH_1p和EH_1,p-1包层模的耦合波长相近,对于典型的单模光纤,当p>4时耦合到这两个模式的耦合系数是可比的。     

混沌半导体激光器的弛豫振荡频率对随机序列速率的影响

利用光反馈半导体激光器产生的混沌激光作为随机数发生器的物理熵源, 分析了混沌信号自相关系数与随机序列游程数之间的联系, 在此基础上研究了激光器的弛豫振荡频率f_r与随机序列速率f_n在不同比值时, 序列游程数的变化情况. 研究发现, 当f_r/f_n=(2k+1)/4时, 随机序列的游程数容易满足NIST SP800-22随机数测试标准的要求. 当k=1时, 得到随机序列最大速率为f_n=4f_r/3.     

侧边抛磨光纤波导传输特性的理论分析

在建立侧边抛磨光纤D型光纤边界条件的基础上,用三维有限差分光束传输法计算和分析了侧边抛磨光纤器件的光功率衰减随光纤的侧边抛磨长度、光纤侧边抛磨后剩余包层的厚度、以及填充聚合物材料折射率三个参量变化的特性.结果表明,侧边抛磨光纤器件的光功率衰减随着抛磨长度的增加而增大;当抛磨长度等于9 mm时,光功率衰减随着剩余包层厚度的增大而单调递减.而当抛磨长度大于9 mm时,剩余包层厚度小于3 μm的范围内,光衰减随着剩余包层厚度的增加出现振荡;当聚合物折射率与纤芯折射率相同时,光功率衰减最大.     

两原子非简并双光子Jaynes-Cummings模型的辐射谱

本文研究了两原子非简并双光子Jaynes-Cummings模型的辐射谱,结果表明,当双模腔场处于不同数态时,辐射谱呈现如下新特性:当一腔场处于真空态,另一腔场为强场时,辐射谱为对称六峰结构,任两对称峰的间距均与√2n₂g成正比;当双模腔场均为强场时,辐射谱为对称四峰结构,两内峰的间距(4g)与数态光子数n₁及n₂无关;当一腔场处于真空态,另一腔场处于数态|n₂>时,辐射谱一般为对称六峰结构,当n₂=1时,谱变为对称四峰结构。     

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     

掺Er光纤飞秒激光器中高信噪比载波包络位相偏移频率获取的实验研究

在实验上分析了掺Er光纤光学频率梳中激光器与一级放大器之间光纤长度、 光纤扰动以及放大器抽运功率对倍频程光谱和载波包络位相偏移频率(f₀)信噪比的影响. 通过系统优化, 实现了40 dB信噪比的f₀输出, 为f₀的长期锁定和光纤光学频率梳的实现提供了技术保障.     

三明治结构Tan(B3N3H6)n+1 团簇的磁性和量子输运性质

利用密度泛函理论和非平衡格林函数方法, 本文对小尺寸团簇Ta_n(B₃N₃H₆)_n+1 (n ≤ 4)的磁性和量子输运性质进行了系统的研究. 计算结果表明, 此类体系采用三明治结构作为其基态并且具有较高的稳定性. 体系的磁矩随团簇尺寸的增大而线性增大. 当把Ta_n(B₃N₃H₆)_n+1团簇耦合到Au电极上时, 形成的Au-Ta_n(B₃N₃H₆)_n+1-Au体系在有限偏压下展示出了较强的自旋过滤能力, 因而可以被看做是一类新型的低维自旋过滤器.     

单轴晶体包层光纤Bragg光栅反射谱特性模拟研究

本文推导了包层为单轴各向异性晶体的光纤理想正规模特征方程, 应用中值定理, 结合Matlab的数值求解, 提出了这一超越方程的一种求解算法, 并在此基础上, 对包层为单轴各向异性材料的光纤Bragg光栅的反射谱与包层折射率关系进行了模拟分析. 模拟结果表明, k_cl 对反射谱有很大的影响, 不同的k_cl 可以导致不同的光栅反射率和Bragg波长.     

Uniform Core Field in Symmetrical Planar Waveguides and Circular Fibers with Nonlinear Claddings

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Uniform Core Field in Symmetrical Planar Waveguides and Circular Fibers with Nonlinear Claddings

It is known that no uniform electric field profile exists in a planar linear waveguide. The uniform core field can be shown to exist in symmetrical planar waveguides and circular fibers with nonlinear claddings. Theoretical analysis and numerical calculations are carried out to show that when the modal index equals to the core refractive-index, the core field becomes uniform at an appropriate optical power. Analysis for a step-index circular fiber with nonlinear cladding have also shown that the core field becomes uniform under similar conditions. The occurrence of a uniform field in a waveguide core may believe to have promising applications in waveguide, optoelectronic and photonic devices.     

Designing optical-fiber modulators by using magnetic fluids

To reduce interface loss between optical fibers and devices in telecommunication systems, the development of an optical-fiber-based device that can be fused directly with fibers is important. A novel optical modulator consisting of a bare fiber core surrounded by magnetic fluids instead of by a SiO2 cladding layer is proposed. Applying a magnetic field raises the refractive index of the magnetic fluid. Thus we can control the occurrence of total reflection at the interface between the fiber core and the magnetic fluid when light propagates along the fiber. As a result, the intensity of the outgoing light is modulated by variation in field strength. Details of the design, fabrication, and working properties of such a modulator are presented.     

Cladding index modulated fiber grating

A new type of fiber grating with only cladding index modulation is presented. Characteristics of both cladding index modulated short-period fiber grating (FBG) and long-period fiber grating (LPFG) are analyzed. The calculation of the modes involved in this paper is based on a model of three-layer step-index fiber geometry. Transmission of a mode guided by the core through a cladding index modulated grating when evanescent field coupling occurs is analyzed with couple-mode theory. Evanescent field coupling causes a power flowing from the core to the cladding, so the attenuation of the new grating is analyzed as well. Lower attenuation, flexible spectral characteristics are demonstrated in comparison with traditional fiber core index modulated grating.     

A rigorous analysis of the power distribution in plastic clad annular core optical fibers

Using Maxwell's field equations, an analytical investigation is presented of the relative power distributions in the different sections of a step-index plastic clad annular core optical fiber (ACF) operating in the infrared region of the electromagnetic (EM) spectrum. It is assumed that the fiber cross-section is made of two concentric circles, and the EM waves propagate through the annular region. The chosen fiber materials are widely used in low cost optical links. The wave equations are solved in the different sections of the fiber, and the general expressions for power in the core and the cladding regions are finally deduced. Plots are shown of the variation of fractional power (or the power confinement factor) in all the fiber sections against the propagation constants of sustained modes. The cases of three lowest azimuthal modal indices (i.e. meridional as well as skew modes) are described. It is observed that the confinement of power in the core section is increased for ACFs of larger cross-sectional dimensions. Also, a fairly uniform distribution of power over the sustained modes remains for large sized fibers, and this uniformity is greatly affected in ACFs of smaller dimensions. It is suggested that, because of strong evanescent fields, ACFs can be of potential use in chemical sensing. Apart from this, it is also presumed that these may be useful in the areas of communications. The improved mechanical strength adds the potentiality of ACFs.     

基于长周期光纤光栅的磁场传感方案的实现

长周期光纤光栅是近几年出现的一种新型光纤器件。其耦合机理是前向传输的纤芯基模与前向传输的各阶包层模式之间的耦合 ,这与光纤布喇格光栅明显不同。它对温度、应力、弯曲及外部折射率的变化具有相当高的灵敏度 ,是一种理想的光纤型敏感结构。提出利用长周期光纤光栅谐振波长的移动或移动变化量进行磁场强度的测量 ,并进行了理论推导、仿真实验及分析研究。得出了谐振波长变化量与外界磁场强度的关系模型。分析了设计中应该考虑的因素。     

光纤型热光可调光衰减器的设计及其衰减分析

提出了一种基于热光调节的可调光衰减器结构。该衰减器通过腐蚀光纤包层到一定厚度和长度后,在表面涂覆较大热光系数的聚合物材料得到。从模场变化角度分析了传输光束的衰减与涂覆材料折射率的关系,并从实验上测试了使用不同涂覆材料时的衰减。理论分析与实验结果均表明在涂覆材料折射率略大于原光纤包层材料折射率时,涂覆材料折射率微小的变化将引起传播光束衰减的大幅度变化,并且光纤被腐蚀的长度越长或包层材料剩余厚度越小,衰减越大。因此,由热光系数大、折射率略大于光纤包层的聚合物材料所组成的可调光纤衰减器,具有衰减调节范围大且功耗小、插入损耗小、成本低、低偏振特性、易于与其它光纤器件耦合或集成等特点。     

非线性包层多量子阱波导的TE波

给出用以分析非线性包层多量子阱波导ＴＥ模光学非线性与双稳性的理论公式与计算方法。指出用均方根等效折射率法解本征方程是有效的简化方法。用本文方法分析了模折射率对波导总功率的依赖关系,芯区功率与总功率之间的双稳性以及模场分布与模折射率的关系。讨论了波导参数对光学非线性、双稳性及模场的分布的影响。     

Bandgap guidance in hybrid chalcogenide-silica photonic crystal fibers

We report a hybrid chalcogenide-silica photonic crystal fiber made by pressure-assisted melt-filling of molten glass. Photonic bandgap guidance is obtained at a silica core placed centrally in a hexagonal array of continuous centimeters-long chalcogenide strands with diameters of 1.45 μm. In the passbands of the cladding, when the transmission through the silica core is very weak, the chalcogenide strands light up with distinct modal patterns corresponding to Mie resonances. In the spectral regions between these passbands, strong bandgap guidance is observed, where the silica core transmission loss is 60 dB/cm lower. The pressure-assisted fabrication approach opens up new ways of integrating sophisticated glass-based devices into optical fiber circuitry with potential applications in supercontinuum generation, magneto-optics, wavelength selective devices, and rare-earth-doped amplifiers with high gain per unit length.