【作者】 林航友；

【导师】 宁继平；

【作者基本信息】 天津大学 ， 物理电子学， 2004， 博士

【摘要】 集成光学声光可调谐滤波器具有可调谐范围大、带宽窄、同时多波长选择和可作为增益平衡器等特点,该器件在光通信和光网络方面将得到广泛的应用,并具有巨大的经济价值。本文围绕集成声光可调谐波长滤波器中的关键技术,对光波导设计、偏振无关、侧瓣抑制、拓宽调谐范围等技术进行理论与试验研究,完成了一套集成光学声光可调谐滤波器,其性能处于国际领先水平,为了进一步提高该器件性能,在宽带声光耦合叉指换能器、集成光学反射镜、Si包层偏振模转换器等分立器件做了相关研究。论文的主要创新点为以下几个方面:一、 光波导设计 1.首次采用调和 Airy 函数的 WKB 法对 Ti:LiNbO3 平板波导进行了理论研究。并首次证明了波导的截止相移为一常数,即π /6,这一理论结果可为单模光波导的设计提供准确的归一化频率范围和准确的工艺参数。 2.理论上,首次提出了一组具有新特性的矢量有限元基函数。该函数在单元边界权重为零,同时旋度不为常数,弥补了以往矢量有限元线性基函数的两点缺失特性。同时,在单元中心点仍然保持了散度为零的特性,由于该基函数具有相互正交特性,使运算效率明显提高。二、侧瓣抑制方法与消除多普勒频移 1. 为了克服采用声定向耦合器的 IAOTF 的几个缺点:驱动功率高、实际的侧瓣抑制水平差、结构复杂等,首次提出了准共线声波导(模转换器)的基本思想,由于声波的强度分布呈类似 Hamming 函数的分布,使得模转换特性曲线的侧瓣大大降低、结构和制作工艺简单、滤出带宽更窄,因而该结构比其它类型的声光滤波器更具优势。从理论上导出了光波导与薄膜声波导之间的优化夹角,并首次从理论上研究了薄膜波导对光波导有效折射率的影响。实验上,制作了该结构的模转换器,将侧瓣抑制到-13.2dB,带宽 1.46 nm,接近理论值-13.4dB 和1.44 nm,目前在国际同类器件的性能上处于领先水平。 2.为了进一步压低侧瓣和消除多普勒频移,首次提出了采用集成光学反射镜来实现 IAOTF 的级联概念,并制作了集成光学反射镜。三、拓宽调谐范围和提高滤出光波偏振态的纯度 1. 首次提出了一种新型的宽带声光表面波叉指换能器 (SAW-IDT), 该换能器应用双梯形倾斜电极,可对单梯形倾斜电极 IDT 通带的高频成分进行补偿,使通带更宽更平直,并无需外补偿网络,该器件可望作为 1.15～1.65 红外频谱分析仪的分光器件。 2. 由于定向模分离器具有频率特性,模分离比在整个调谐频谱范围内不为常数,为了克服这个缺点,首次采用了 Si 薄膜包层的偏振模分离器设计思想,并实际制作了该器件,其模分离比为 34dB,由于该器件结构简单,只需在原模分离器的输出端口镀上一层 Si 膜,没有特殊的附加工艺过程,就可进一步改善IAOTF 的性能。更多还原

【Abstract】 The integrated acoustooptic tunable filters (IAOTFs) have demonstratedpotential applications and exhibit their enormous potential in economy inwavelength-division multiplexed (WDM) optical fiber communication systems fortheir large tunability, narrow bandwidth, low drive power requirement, uniqueproperties of simultaneous multiwavelength filtering and as gain equalizers. In thispaper, the crucial technologies of IAOTFs such as optical waveguide design,polarization-independent, sidelobe suppression as well as wide tunability have beenstudied experimentally and theoretically. A IAOTF has been fabricated with itsperformance at the top place in the world. To enhance its performance, somecomponents of IAOTF such as wideband acoustooptic interdigital transducer,integrated optical reflection mirror and Si-coated polarizer have been investigated.Some innovations in the paper are as follows: 1. Waveguide design 1) The theory of Ti:LiNbO3 waveguide is studied by using modified Airyfunction in WKB method for the first time. The cutoff phase shift is testified as aconstant number, i.e., π / 6, which can provide an exact normalization frequencyand processing parameters for designing the single-mode waveguides. 2) A novel set of vector basis functions is presented for the first time. The weightof such basis functions is vanished at the edge of finite elements, and also its curlvaries with the position within finite element. These two properties make up theabsent characteristics of the primary tangential vector basis functions. At the sametime, the zero-divergence property of the primary tangential vector basis function iskept in the center of elements. The compute efficiency is improved obviously sincethese basis functions are orthogonal each other. 2. Sidelobe suppression & Dopple shift eliminating 1) To overcome the drawbacks of high power requirement, inefficient sidelobesuppression and complex configuration, the concept of quasi-collinear acoustoopticalcouple is presented for the first time. The acoustooptical couple is closed to Hammingfunction, which leads to high efficiency of sidelobe suppression, simple configurationand fabrication process and narrow bandwidth. The influence of SiO2/In2O3 film SAWguide on the mode index of optical waveguide has been investigated for the first time.The prototype has been fabricated, the measured FWHM is 1.46 nm and the measured ii<WP=5>ABSTRACTsidelobes level is -13.2 dB, as compared to theoretical values of 1.44nm and -13.4 dB,respectively. Nowadays, it is the best performance in such kind of IAOTFsinternationally. 2) To overcome the drawbacks of frequency shift imposed in single-stage devicesand to achieve a higher sidelobe suppression, the concept of cascading of two stagesby an integrated reflection mirror is put forward and this mirror has been fabricated aswell. 3.Widening tunability & Enhancing the purity of polarization 1) A novel bouble-tapezia-electrode interdigital transducer (IDT) to compensatehigh-frequency component of the slanted single-electrode IDT is presented for thefirst time. It makes flatter amplitude response and wider bandwidth than those of thelatter. At the same time, the external compensating network is eliminated. The deviceis expected to be a integrated optics acoustooptical spectroscope in spectrometer for1.15~1.65 μm..2) To overcome the drawbacks of the frequency characteristic of the polarizationsplitter in IAOTFs, a novel design of a TE-pass waveguide polarizer based on Si on aTi:LiNbO3 waveguide is presented. This polarizer is fabricated and itspolarization-dependent measurements lead to the best polarization extinction ratio~34dB and the insertion loss< 0.4 dB. By splashing a Si film on mode splitter at theoutput of IAOTFs with simple processing steps, the performance of IAOTF will befurther improved.更多还原