【作者】 王海滨；

【导师】 杨德兴；

【作者基本信息】 西北工业大学 ， 光学工程， 2006， 硕士

【摘要】 DWDM（密集波分复用）技术是未来光网络的关键,也是大容量光通信及对现有网络扩容的最佳方案,其技术重点是在现有通信波长范围内,尽可能增加复用的波长通道数量。近年来,体全息Bragg光栅以其良好的角度及波长选择性和制作上的各种优势,为光波分复用器件的发展提供了一种新的思路和方法。本文在研究体全息光栅的光写入过程中,提出了基于层状多重Bragg光栅的解复用方法,并在此基础上探讨其特有的记录方式以及其红外通信波段的解复用衍射特性。其主要内容包括: （1）阐述了光折变效应的产生机制和光折变Bragg光栅的形成机理:以体全息光栅的耦合波理论为基础,讨论了光折变晶体中体全息光栅的衍射效率,角度及波长选择性:从Bragg衍射公式出发探讨了体全息Bragg光栅用于波分复用时的波长关系及宽光谱应用时光栅的Bragg失配量。 （2）测量了三种LiNbO₃晶体的光谱透过率,并通过透过率及晶体参数计算了晶体的光谱吸收系数,从中选耿最适合于本文光栅写入实验的晶体;对晶体中体全息Bragg光栅的写入和擦除时间常数进行了测量,在此基础上对多重光栅的时间递减曝光序列进行了讨论。从实验中探讨折射率调制度、写入角对记录光栅衍射效率的影响;对于平面光及球面光写入的体全息光栅作了光波衍射分离实验,研究其分光特点。 （3）讨论了层状多重体全息Bragg光栅的光写入方法,并在实验基础上,对层状多重体全息Bragg光栅用于波分复用器的可行性进行了实验论证。利用空间复用和角度复用技术,在片状LiNbO₃:Fe晶体中写入了3层×8重Bragg光栅,并成功得到了它们在红外通信波段分离的衍射谱,对于其解复用滤波特性进行了测量和分析。 （4）提出了一种全新的制作特殊体全息光栅的光擦除法。利用该方法可以在LiNbO₃:Fe晶体c轴方向上写入周期性结构的体全息光栅,而这种光栅结构是普通的光栅记录方法所不能完成的。阐述光擦除法写入此类光栅的两步制作方法,并在实验中利用光擦除法在片状晶体里制作得到了体全息光栅。实验结果表明:该方法完全可行。更多还原

【Abstract】 Dense wavelength division multiplexing（DWDM） is an important technology of choice for expanding capacity in optical fiber communication, and wavelength division multi/demultiplexers is one of the key elements in the fiber-optical networks. The volume Bragg grating is promising greatly to be applied to DWDM system and the demultiplexer based on the VBGs （volume Bragg gratings） shows that it can be used as one of advantageous multi-channel components because of its excellent angle and wavelength selectivities. A kind of multiple VBGs with layered structure and its fabrication method are presented here. According to the method, the layered multiple VBGs （volume Bragg gratings） were recorded in LiNbO₃:Fe crystals, and the infrared demultiplexing characteristics of the formed VBGs were measured and analyzed. The main contents are as follows:（1） The mechanisms of the photorefractive effect and the creation of photorefractive grating are explained. Based on the Kogelnik’s coupled wave theory, the Bragg diffraction efficiency, the angle selectivity and wavelength selectivity of VBGs formed in photorefractive crystals are analyzed. According to the Bragg’s diffraction formula, the relation of the demultiplexing angle on communication wavelengths to the writing angle of VBG, and the Bragg mismatching value during wavelength demultiplexing with wide spectra by employing VBG are discussed.（2） The spectral transmissivity and absorptivity for three slices of LiNbO₃ crystal were measured, and the optimal one among them was chosen for the writing experiment of VBGs. The holographic time constants were gained by recording and erasing a single grating in a slice of LiNbO₃:Fe crystal. According to the recording and erasing time constants, the exposure time schedule of superimposed gratings was achieved. It was experimentally investigated that the dependence of the diffraction efficiency of VBG on the refractive index modulation and the recording angle. The VBGs were recorded in the crystal by a parallel beam and a spherical beam, and the diffraction experiments were performed subsequently.（3） The recording approach of the layered multiple VBGs in LiNbO₃: Fe crystal was investigated in detail. Eight superimposed VBGs in three layers respectively were recorded alternately in a slice crystal, and the infrared filtering characteristics of 24 formed gratings were measured and analyzed. The experimental results show that the layered VBGs are promising to be employed for a multi-channel demultiplexer in the range of infrared communication.（4） According to the photorefractive properties of LiNbO₃:Fe crystal, the volume holographic grating with the grating vector normal to c-axis of the crystal are obtained hardly.A new method—light erasing method presented in this paper can be applied to fabricate this kind of grating. According to the method, the theoretical analysis as well as experimental investigation was accomplished orderly. The experiment results demonstrate that the light erasing method for fabricating volume holographic grating with grating vectors normal to c-axis in LiNbC>3 crystal is feasible.更多还原