不均匀偏置磁场中磁光Bragg器件的衍射特性研究

【作者】 孙开良；

【导师】 邱昆；

【作者基本信息】 电子科技大学 ， 光学工程， 2006， 硕士

【摘要】 静磁波(MSW)是一种在磁性介质中传播的慢色散波,也是一种微波电磁波,可通过磁控方法改变静磁波的传播特性,并与具有电磁性的物质发生作用。在磁光波导中,静磁波与导波光相互作用可导致导波光的Bragg衍射,利用这一原理,可做成磁光调制器、光开关、扫描仪、频谱分析仪等新型磁光Bragg器件,并在光通信和光信息处理等领域有着十分广阔的应用前景,引起人们越来越多的关注。然而,这类新型的磁光Bragg器件至今尚未实用化、商用化,其中微波静磁波对导波光的衍射效率相对较低是主要瓶颈因素之一。本论文主要从理论上研究不均匀场中静磁正向体波(MSFVW)的激发与传播特性,以及不均匀偏置磁场在提高静磁波对导波光的Bragg衍射效率方面所起的作用。1.采用变分方法计算了横向不均匀偏置磁场作用下掺Bi的YIG薄膜中微波静磁正向体波的色散关系和交变磁化强度,分析了静磁波的激发带宽对衍射效率的影响。对于抛物型分布(开口向上)的偏置磁场,当激发静磁波的RF频率小于边缘截止频率时,磁光作用的有效长度减小(与静磁波频率有关);边缘截止频率由不均匀磁场的最大值决定,静磁波的下限截止频率由不均匀场的最小值确定。2.考虑到边缘截止效应,论文中计算了静磁正向体波对导波光的衍射效率,理论结果与实验符合;从而表明,与均匀场情形相比,适当不均匀场可以大大提高磁光Bragg器件的衍射效率。本文的分析方法可为磁光Bragg器件的优化设计提供理论指导。3.分析了不均匀场分布形式、磁场大小、磁光薄膜厚度、激发电流强度、波导材料以及磁光作用长度等因素对Bragg衍射效率和衍射光偏转角的影响。计算表明,采用适当的不均匀场对Bi:YIG薄膜进行磁化,并通过改变磁场大小,减小薄膜厚度,增加磁光作用长度或增大激发电流可提高磁光Bragg器件的衍射性能。更多还原

【Abstract】 Magnetostatic wave (MSW) is a kind of slow dispersive wave propagating in magnetic medium, which is also a microwave electromagnetic wave. So the propagation characteristics of MSW can be controlled by bias magnetic fields. In magneto-optic (MO) waveguids, the interaction between MSWs and guided optical waves (GOWs) can lead to the Bragg diffraction of the GOWs. The resulting many new devices, such as MO modulator, optical switching, scanning, frequency spectrum analyzers, can be developed with applications to optical communication and optical information processing. However, the MSW-based MO devices haven’t still been applied extensively up to now because of low Bragg diffraction efficiency.The generation and propagation characteristics of magnetostatic forward volume waves (MSFVWs) under nonuniform bias magnetic field and the Bragg diffraction efficiency of GOWs with the MSFVWs are theoretically studied in this paper.The dispersive characteristics and the dynamic magnetization of the MSFVWs in bismuth-doped YIG film under transversely nonuniform bias field are analyzed by the variational approach. The influence of MSFVW bandwidth on the diffraction efficiency is also considered. For the nonuniform bias magnetic field of U-type parabola profile, when the MSW frequency is less than the cut-off frequency at the edge of MO film, the effective MO interaction length reduces. The edge cut-off frequency is determined by the maximum of the nonuniform field.The Bragg diffraction efficiency of GOWs in bismuth-doped YIG film is caculated by considering the edge cut-off effect. The obtained theoretical curve is basically agreement with the experimental results. It is shown that the diffraction performance for MO Bragg cells can be greatly increased by using an appropriately nonuniform bias field. This theoretical method can also be applied to the optimization design of the MO Bragg devices.更多还原