【作者】 吕丁成；

【导师】 张晓萍；

【作者基本信息】 兰州大学 ， 无线电物理， 2009， 博士

【摘要】 本文提出了一类由单轴晶体材料作为光纤光栅包层或者芯层、其光轴平行于光栅主轴（z轴）的新型光纤光栅模型，这些模型包括：单轴晶体为包层的短周期和长周期光纤光栅、单轴晶体为芯层的短周期和长周期环形光纤光栅。从经典电磁理论出发分析了各个模型的场分布，应用线性和非线性耦合模理论研究了该类新型光纤光栅的线性和非线性特性。研究结果表明单轴晶体材料对该类光纤光栅的线性与非线性特性均有显著影响，其影响的大小与单轴晶体的主轴折射率比参量K_cl的取值密切相关。其中单轴晶体芯层长周期环形光纤光栅线性特性受主轴折射率比参量K_cl的影响最大，当K_cl从0．9变化到1．1时，该类光纤光栅的谐振波长变化达到65nm，这种对应关系可以用于单轴晶体材料折射率特性测量。对于单轴晶体为包层的布拉格光纤光栅非线性特性研究表明：当折射率比参量从0．6变化到1．6，输入脉冲峰值功率为160kW时，布拉格波长的红移从0．22nm增加到0．34nm；当折射率比参量K_cl从0．6变化到1．6，输入脉冲峰值功率为1．5kW时，透射率从0．25增加到0．95。研究结果表明，采用正单轴晶体制作光栅包层，可以更有利于实现光栅在非线性领域的应用，K_cl越大，非线性特性越明显。同时在理论上分析了电光效应对这类新型光栅线性特性的影响，研究发现，对作为光纤芯层或者包层材料的单轴晶体上施加沿光栅轴向分布的外加电场可以改变光栅的谐振波长或者布拉格波长以及透射谱或者反射谱。本文设计了3种不同单轴晶体材料（分别为LiTaO₃、LiNbO₃、KDP）为包层或者芯层的光纤光栅，并分别计算得到短周期光纤光栅中布拉格波长和反射光谱随外加电场变化关系以及长周期光纤光栅中谐振波长随外加电场的变化关系。研究表明单轴晶体芯层长周期环形光纤光栅线性特性受外加电场的影响最大，当轴向外加电场从1×10⁶V／m变化到8×10⁶V／m时谐振波长变化达到3．5nm。在不改变光栅结构参量的情形下，通过改变单轴晶体材料的折射率比参量或者施加外加电场可以明显改变光纤光栅的线性与非线性特性，这一与普通光纤光栅显著不同的特性预示了这种新型光栅有良好的应用前景。本文研究为制作新型场强传感器、电调谐光滤波器以及新型光开关奠定了理论基础。更多还原

【Abstract】 A series of fiber gratings with cladding or core made of uniaxial crystal materials whoseoptical axis is parallel to the axis of grating,i.e.,z-axis are proposed.These fiber gratings modelsinclude short period fiber grating with cladding made of uniaxial crystal,long period fibergrating with cladding made of uniaxial crystal,coaxial short period fiber grating with core madeof uniaxial crystal and coaxial long period fiber grating with core made of uniaxial crystal.Thelinear and nonlinear characteristics have been theoretically analyzed using linear and nonlinearcoupled-mode theory respectively.The calculated results indicated that unxiaxial crystalmaterials have strong impact on the characteristics of these gratings.The degree of the impact isclosely related to the value of the ratio of the extraordinary to the ordinary ray refractive indexK_clof uniaxial crystal.The influence of K_clto the characteristics of fiber grating is mostremarkable in the coaxial long period grating with core made of uniaxial crystal.When K_clvariesfrom 0.9 to 1.1,the resonant wavelength has the increases of 65nm.The relationships betweenK_cland grating characteristics,especially the resonance wavelength,can be utilized to measuresome characteristics of the uniaxial material.Numerical results showed that K_clhas also strongimpact on the fiber grating’s nonlinear characteristics.When the ratio of index has changed from0.6 to 1.6 the red shift of Bragg wavelength due to 160kW input pulse peak power has increasedfrom 0.22nm to 0.34nm.Meanwhile the transmissivity has increased from 0.25 to 0.95 whenpeak power of input pulse is 1.5kW.It is indicated that it is propitious to develop nonlinearapplication of FBG using uniaxial positive crystal as a grating cladding.Electro-optic effect inthese kinds of fiber gratings are theoretically analyzed for the first time.The influences of theelectric field applied to the uniaxial crystal materials along z-axis on Bragg wavelengthλ_B orresonance wavelength and the reflectivity spectra of this series gratings are examined.Thecurves of Bragg wavelength or resonance wavelength as a function of an external electric fieldare obtained respectively for three kinds of uniaxial crystal materials as the grating cladding orcore.The calculated results indicate that the coaxial long period fiber grating with core made ofuniaxial crystal has been affected most remarkably by electric field.When the axial electric fieldapplied to the grating cladding varies from 1×10⁶ V/m to 8×10⁶ V/m,resonant wavelength hasthe decreases of 3.5nm.This promises the good application foreground of this new kind ofgrating.New-style electric field senor and tunable optical fiber grating filter can be manufacturedbased on the property that resonance wavelength can be changed by electric field.更多还原