基于结构性改变的光子晶体光纤光栅研究

利用多极法结合耦合模理论对一种基于结构性改变的光子晶体光纤光栅进行了研究,建立了其结构模型,理论分析了此种成栅工艺原理.计算了七层三角形对称排布空气孔包层有效折射率随波长变化情况,比较了不同光子晶体光纤结构成栅效果的差异.研究结果表明,光子晶体光纤包层中空气孔周期性塌缩可以形成光栅,空气孔排布层数,空气孔占空比、空气孔塌缩层数和塌缩程度等参数对光子晶体光纤光栅的传输特性有重要影响,得出了谐振波长和谐振带宽与上述参数之间的变化关系,并给出这种变化关系的解释.     

基于二次曝光法的切趾2mm短栅距光纤布拉格光栅制作研究

研究了基于二次曝光法的2 mm短栅距型光纤布拉格光栅(FBG)的制作及切趾函数参数控制.针对所选取的3种切趾函数,在耦合模理论基础上,利用传输矩阵法进行了FBG光学特性仿真分析,给出了最佳切趾参数下的光栅反射谱.FBG制作实验结果表明,所选取的不同切趾型短栅距FBG性能较好满足传感用性能要求,为高反射率、较窄带宽、高边模抑制比的短栅距型FBG的制作研究提供了有益的参考.     

啁啾光子晶体光纤光栅反射谱和时延特性研究

用有限元法和传输矩阵法,对基于包层空气孔为柚子型结构的光子晶体光纤啁啾光栅的反射谱进行了理论分析。通过对均匀光栅仿真结果与实验结果的对比,可知此方法是可行的。研究表明光子晶体光纤的啁啾光栅有多个明显的反射峰,并且分析了啁啾系数、折变量对各谐振峰带宽和反射率等的影响。计算结果显示,随着啁啾系数和折变量的增大,光栅反射谱呈规律变化,当啁啾系数增大到一定程度时几个反射峰会连到一起,形成一个大的反射带宽。同时对光栅基模反射谱对应的时延特性进行了研究,可知其同样具有比较平滑的时延曲线,可以用于色散补偿。     

倾斜切趾光纤光栅的理论与实验研究

针对飞秒激光刻写均匀光纤布拉格光栅的反射主峰存在较高旁瓣,容易对主峰形成串扰的问题,开展基于倾斜切趾光纤光栅的理论与实验研究。根据飞秒激光诱导产生的折射率特点,修正耦合模模型中的交流耦合系数,并利用有限元仿真的形式,验证了倾斜切趾法的切趾类型为高斯型。之后对影响切趾效果的关键参数进行实验研究,结果表明：实验结果与仿真计算基本一致;初始横向位移为5~10 μm,且不对称偏移量小于±2 μm时,边模抑制比可提高到15 dB。研究成果为提高光纤光栅边模抑制比提供了重要理论支撑与实践指导,对于推动光纤光栅制备工艺技术发展具有重要意义。     

保偏微结构光纤光栅 F-P腔折射率传感特性分析

针对提高光纤光栅折射率传感器抗干扰能力以及增加反射率的需求,本文提出了一种基于Fabry-Perot腔的保偏微结构光纤(PM-MOF)布拉格光栅折射率传感器.根据传榆矩阵法和有限元方法,分析了微结构光纤光栅F-P腔中被测物折射率与F-P腔反射谱中两个偏振模谐振波长差的关系,在此基础上讨论了中心孔直径、F-P腔长度等参数对传输特性的影响.研究结果表明,随着空气孔中填充物折射率的增加,保偏微结构光纤光栅F-P腔的两个偏振态的谐振波长差将逐渐减小;F-P腔的干涉作用使反射率较单个光栅有很大提高,便于长距离传输和实时解调;两个偏振模对外界干扰具有相似的响应,因此该传感器具有更强的抗干扰能力.本文研究结果为保偏微结构光纤光栅在折射率传感器及其生物传感器方面的应用提供了理论依据.     

太赫兹波段塑料光子晶体光纤的特性分析

本文利用有限元法对太赫兹波在塑料光子晶体光纤中的传输特性进行了模拟,分析了光纤结构与基模有效折射率、波导色散、基模有效面积的关系,给出了本文设计结构下,塑料光子晶体光纤的传输特性随空气孔径、孔间距等参数变化的规律。     

高双折射光纤光栅扭转特性分析与应用

通过对高双折射光纤光栅的特性进行分析,提出了一种新型的可埋入工程材料的扭转传感器结构。基于光纤光栅的模耦合理论和高双折射光纤的扭转特性,建立了扭转高双折射光纤光栅传输光波的数学模型,并分析其光谱特性,仿真结果表明扭转高双折射光纤光栅的反射谱不具备方向性,只与扭转角度大小有关。当扭转角度从0变化到360°时,高双折射光纤光栅的2个主峰波长都随之产生漂移,x方向的光向短波长方向移动,y方向的光向长波长方向移动,并且反射谱峰值逐渐减小,通过前向耦合模理论与反向耦合模理论结合分析并仿真,得出x和y方向上波峰值变化量,以及相应的中心波长的变化量,最后通过实验数据对高双折射光纤光栅的变化参数与扭转角度的关系作出验证。     

微纳Taper光纤干涉传感器的折射率测量理论研究

利用微纳taper光纤干涉方程和微纳光纤传输模式函数关系,建立了微纳taper光纤干涉波长随环境折射率变化的数学模型,指出微纳taper光纤干涉波长的响应规律由基模高阶模有效折射率差、色散因子和环境折射率3个因素所决定.详细研究了微纳taper光纤传感器的灵敏度变化规律,结果表明,传感器的灵敏度随光纤半径变小而急速增大,并随环境折射率的增大而非线性增加,而且探测波长越长,其灵敏度越大.     

保偏光子晶体光纤模间干涉的研究

针对椭圆芯保偏光纤模间干涉灵敏度和温度稳定性相对较低的缺点,本文提出了采用保偏光子晶体光纤(PM-PCF)来设计模间干涉光纤传感器的方案.对一种保偏光子晶体光纤的模间干涉特性进行了仿真研究,分析了PM-PCF的两个低阶模式LP01模和LP11偶模的传输特性,得到了相对有效折射率与波长的关系以及模间相位差同干涉输出光强分...     

基于1550nm的全固态PBG—PCF的设计

设计了一种三角晶格结构的全内反射型光子晶体光纤,并在其包层孔内分别填充折射率为n=1．55～3．35（△n=0．3）的介电材料,使其等效为全固态光子带隙型光子晶体光纤,利用全矢量平面波展开法对其带隙特性进行分析,发现随着折射率的增加,光子带隙的位置逐渐向长波方向移动,导模也越来越少。设计一种工作波长为1550nm的全固态光子带隙型光子晶体光纤,计算得到其对应的归一化传播常数β=8．2时,导模的宽度大约为100nm。该光纤在光电转换或者电光转换等方面具有潜在的应用价值。     

Effective way of reducing coupling loss between rectangular microwaveguide and fiber

We introduce an anamorphic photonic crystal fiber (PCF) produced by postprocessing techniques to improve the coupling loss between a conventional single-mode fiber and rectangular microwaveguide. One end of the round core is connected with the conventional fiber, and the other end of the rectangular core is connected with the rectangular microwaveguide, then the PCF is tapered pro rata. In this way, the loss of mode mismatch between the output of the conventional fiber and the input of the waveguide would be reduced, which results in enhanced coupling efficiency. The conclusion was confirmed by numerical simulation: the new method is better than straight coupling between the optical fiber and the rectangular microwaveguide, and more than 2.8 dB improvement of coupling efficiency is achieved.     

Improved single mode property in elliptical air hole photonic crystal fiber

The single mode property of a holey, index-guided two-dimensional photonic crystal fiber (PCF) is investigated using the alternate direction implicit method. The modal analysis of a three-ring elliptical air hole photonic crystal fiber is performed and compared with the equivalent three-ring circular air hole photonic crystal fiber keeping the air-fill fraction the same for both cases. The fiber is investigated for single mode operation. The effect of the rotation of the ellipse axes on these characteristics is also considered. It is observed that a PCF with elliptical air holes exhibits a better single mode property over a wider wavelength range in the optical domain. Also when the diameter of the air hole is properly catered for, they can show an endlessly single mode property.     

Efficient Bragg gratings in phosphosilicate and germanosilicate photonic crystal fiber

We present ArF laser-induced dynamics of Bragg grating (BG) growths in phosphosilicate-doped or germanosilicate-doped core photonic crystal fibers (PCFs). To this end, we have adapted the technique of H2 loading, usually used in conventional fiber, to the case of microstructured fiber, allowing both the concentration of hydrogen in the PCFs to be kept nearly constant for the time of the exposure and the BG spectra to be easily recorded. We compared the characteristics of BG growths in the two types of PCF to those in conventional step-index fibers. We then conducted a study of the thermal stability of the BGs in PCFs through 30 min of isochronal annealing. At the same time we discuss the role played by the microstructuration and the doping with regard to the grating contrast and the Bragg wavelength stability.     

Linear and nonlinear optical properties of hollow core photonic crystal fiber

We review the optical guidance properties of hollow-core photonic crystal fibers. We follow a historical perspective to introduce the two major optical guidance mechanisms that were identified as operating in these fibers: photonic bandgap guidance and inhibited coupling guidance. We then review the modal properties of these fibers and assess the transmission loss mechanisms in photonic bandgap guiding hollow-core photonic crystal fiber. We dedicate a section to a review of the technical basics of hollow-core photonic crystal fiber fabrication and photonic microcell assembly. We review some of the early results on the use of hollow-core photonic crystal fiber for laser guiding micro-sized particles, as well as the generation of stimulated Raman scattering, electromagnetically induced transparency and laser frequency stabilization when the fiber core is filled with a gas-phase material. We conclude this review with a non-exhaustive list of prospects where hollow-core photonic crystal fiber could play a central role.     

Design of a single-polarization single-mode photonic crystal fiber with a near-Gaussian mode field and wide bandwidth

Single-polarization single-mode (SPSM) fiber can efficiently eliminate polarization mode coupling, polarization mode dispersion, and polarization-dependent loss. Up to now, most single-polarization fibers have been designed based on form birefringence, which would result in a non-Gaussian field distribution and a small effective mode field area. In this paper, a novel structure of SPSM photonic crystal fibers based on the resonant coupling phenomena is proposed and analyzed by using a full-vector finite-element method with a second-order transparent boundary condition. From the numerical results it is confirmed that this fiber has a near-Gaussian mode field within the wavelength range from 1.46 to 2.2 μm, where only one polarized mode exists effectively, and the mode field area is about 79 μm(2) at the wavelength of 1.55 μm, matching that of the conventional single-mode fiber.     

Design of a broadband highly dispersive pure silica photonic crystal fiber

A highly dispersive dual-concentric-core pure silica photonic crystal fiber is designed with a maximum chromatic dispersion value of about -9500 ps/(nm km) around the 1.56 microm wavelength region and a full width at half-maximum (FWHM) of 55 nm. The change in the dispersion-bandwidth product as a function of period is carefully studied by using the plane wave expansion method. The coupled mode theory matches well with the plane wave expansion method that was used to simulate the chromatic dispersion. This kind of a photonic crystal fiber structure is suitable for high-dispersion application in phased array antenna systems based on photonic crystal fiber arrays.     

Analysis of photonic crystal waveguide gratings with coupled-mode theory and a finite-element method

Both rod and air-hole types of photonic crystal waveguide gratings are proposed and their coupling coefficients and transmission characteristics are effectively investigated by using a simple coupled-mode theory combined with a finite-element method. The results obtained are compared with the results obtained by using a full numerical simulation method. A new definition for unperturbed waveguides is introduced to obtain accurate coupling coefficients. It is shown that, by using a pi-phase-shifted waveguide structure in the case of an air-hole type of photonic crystal waveguide grating, the coupling coefficient is strongly enhanced. The accuracy of the method is discussed through numerical examples of high-index-contrast waveguide gratings.