【作者】 李彤；

【导师】 张大明；

【作者基本信息】 吉林大学 ， 物理电子学， 2012， 博士

【摘要】 掺铒光波导放大器（Erbium Doped Waveguide Amplifier: EDWA）兼具掺铒光纤放大器（Erbium Doped Fiber Amplifier: EDFA）的偏振串扰无关性、低噪声指数等优点，及体积小型、结构紧凑的重要优势，可以与其他光波导器件集成在一起构成高效的集成光学系统。是继EDFA以后又一极具发展前途的光放大器。无机基质EDWA已经拥有了商用化的器件，但是工艺复杂周期长，设备昂贵，难以与其他光波导器件集成，EDWA的集成优势难以体现。有机基质EDWA具有价格低廉，制备工艺简单，折射率易调节，易于集成（尤其是与其他聚合物光波导器件集成）的优点，可以弥补无机EDWA的不足。但是其自身也存在着技术难题：无机稀土离子在有机体中的掺杂量和铒离子发光量子效率难以提高。本论针对两个主要技术难点，结合器件结构设计，对有机聚合物平面光波导放大器展开了一系列研究工作。主要内容与工作创新点如下：1.基于980nm泵浦下的Er-Yb共掺六能级跃迁模型，结合原子速率方程和前向泵浦下的光功率传输方程，使用重叠积分简化方法对器件进行增益特性的理论分析。采用Judd-Ofelt理论计算表征材料发光性能参数；采用基于插值的有限差分法，结合有效折射率法，用Matlab编程，更精确的分析波导模式特性，并获得模场分布。2.针对有机基质中Er荧光寿命短，发光量子效率较低这一问题，采用简单地共沉淀法合成油酸（Oleic acid:OA）修饰的LaF₃:Er, Yb纳米颗粒，采用有机改性前驱体基于sol-gel法制备有机无机杂化材料。对材料进行红外光谱分析、元素分析等一系列表征。纳米颗粒粒径约8nm，荧光寿命约100μs（La:Er:Yb=85:3:12），与有机无机杂化材料（Organic/Inorganic Hybrid Materials:OIHM）的5%失重温度都在300℃以上，OA-LaF₃:Er,Yb纳米颗粒以33wt.%比例掺杂OIHM，获得了平整的薄膜，用Judd-Ofelt理论计算其理论亚稳态能级寿命达到13.34ms。用自行搭建的近场光斑测试系统及增益测试系统，对该掺杂材料制作的嵌入式波导放大器进行测试。器件通光性良好，121mW泵浦光下，在2.9cm长的波导器件中，获得3.69dB（Ps=1mW）、3.89dB（Ps=0.5mW）和4.11dB（Ps=0.2mW）的相对增益，小信号光获得了较大增益；在一个1.9cm长的波导器件中，观察到：相对增益由抛光前的2.2dB提高到抛光后的3.2dB（Ps=1mw，Pp=188mW），抛光后泵浦效率提高。模拟计算铒镱共掺光波导放大器（Erbium-Ytterbium Co-Doped Waveguide Amplifier: EYCDWA）的增益特性。讨论了在确定的结构下Er3+离子掺杂浓度、重叠积分因子、信号光和泵浦光功率，波导长度及Er3+离子亚稳态能级寿命对增益的影响。3.为了优化器件结构，我们尝试对芯包层共同掺杂型（Core-cladding doped）波导放大器的增益特性进行分析，并将之与单芯层掺杂型（Core doped）波导放大器对比。获得结论：Core-cladding doped型波导在一定芯区厚度内，起到了提高增益的作用，但是泵浦效率较低；峰值浓度明显降低，易通过改变浓度来提升器件性能。根据材料特性和波导结构对芯包层的要求，选用具有紫外热光漂白效应的SU-8为基质材料，取高温热分解法制备的发光能力更强的OA-NaYF₄:Er,Yb纳米颗粒为掺杂剂。OA-NaYF₄:Er,Yb纳米颗粒粒径约为15nm，具有更好地无机晶格，上转换及下转换发光都更强，在SU-8中的掺杂量可以适当降低，从而确保SU-8的交联度。利用我们摸索的SU-8一般工艺条件与光漂白的工艺条件，制作了OA-NaYF₄:Er,Yb纳米颗粒掺杂SU-8的Core doped型及Core-claddingdoped型光波导，由于SU-8低损耗特性，获得良好通光效果。在1.5cm长的Coredoped型波导中获得相对增益2.08dB（Ps=1mW，Pp=170mW）。这种Core-claddingdoped型波导为提高波导放大器的增益特性提供思路。4.针对主客掺杂型材料分散能力及掺杂均匀性有限的问题，合成并表征了一种可以直接旋涂成膜的铒/镱共掺可溶性配合物Er_1.2Yb_0.8（PBa）₆（Phen）₂材料（PBa为4-戊基苯甲酸，Phen为一水合1,10-邻菲啰啉），Er含量提高到10.9wt.%（OA-LaF₃:Er, Yb掺杂OIHM中Er含量1.1wt.%）。其薄膜吸收光谱与一般主客掺杂薄膜形成鲜明对比，几乎没有基质材料的背景吸收，特征吸收峰非常清晰。粉末和薄膜的光致发光光谱的峰值都在1535nm处左右，荧光半高宽约80nm。可溶性配合物薄膜中稀土元素质量百分比高达18.4wt.%，由于存在阻碍干法气体刻蚀的问题，我们仍然采用嵌入式结构，制备嵌入式光波导放大器。在一个1.5cm长的SU-8包层波导中得到相对增益5.20dB （Ps=0.3mW，Pp=140mW）；一个2.2cm长的PMMA薄片表面的嵌入式波导中得到相对增益2.52dB （Ps=0.2mW，Pp=170mW）。针对与实验结合最紧密的四种不同上下包层组合结构及非理想刻蚀情况进行分析，结果表明：芯包折射率差大和折射率差小，可以得到大小相当的增益；折射率差大时，单模工艺难度大，但泵浦效率高；上下包层折射率差大且波导芯尺寸小时，光场向上包分散，增益下降，可考虑上包掺杂型；实验中常出现的侧向刻蚀情况会导致增益性能下降，应尽量避免。5.针对高芯区折射率波导分析中凸显出的增益与泵浦效率的竞争问题，引入低芯区折射率波导——狭缝波导。首先分析了狭缝波导的基本特性：狭缝波导的平均光强系数γ比一般的高折射率波导高出两个量级，设计中可不用考虑；狭缝波导对波长不敏感。讨论狭缝宽wS、Si侧壁宽wH及Si侧壁高h_Si对重叠积分因子Γ的影响关系，确定狭缝波导尺寸。建立1480nm泵浦下四能级跃迁模型，分析一般高折射率波导中，包括掺杂浓度、激发态吸收、合作上转换、信号光和泵浦光传输损耗、信号光和泵浦光功率、波导有效截面积以及重叠积分因子对该系统增益特性的影响，发现对于确定的材料参数，最佳泵浦强度Ip-sat近似为定值。于是可以由狭缝波导不同尺寸得到对应的最佳泵浦功率，从而计算对应最大增益；利用多层狭缝大幅度提高Γ，指出狭缝个数以3⁴层为宜。本论文分别采用具有油酸修饰的纳米颗粒（OA-LaF₃:Er,Yb和OA-NaYF₄:Er,Yb）和Er/Yb共掺可溶性配合物制作了聚合物平面光波导放大器。综合无机纳米核良好的稀土发光环境，及可溶性配合物直接旋涂成膜的思路，有望探索出更具优势的有源材料，为制作出具有高净增益的聚合物光波导放大器奠定基础。更多还原

【Abstract】 It has been widely acknowledged that all-optical communication would be theprime method in optical communication systems. The integrated optical amplificationtechnology which can amplify the optical signal without any conversion from light toelectricity is the most effective method for the loss compensation. In recent years,much attention has been devoted to the development of erbium-doped waveguideamplifiers （EDWAs）. Compared with inorganic host, polymer has excellent propertiessuch as: simple processing steps, high bandwidth, low cost, and compatibility withsilicon substrates. However, few successful EDWAs have been demonstrated usingerbium-doped polymers or organic/inorganic hybrid materials （OIHMs）. Onebottleneck is that the insolubility of Er³⁺ions in organic materials cannot meet therequirement of EDWAs’ small size and high Er³⁺-doping concentration. Anotherdifficulty is the relatively low photoluminescence quantum efficiency due to thevibration quenching caused by O-H and C-H groups and concentration quenchingcaused by the high Er³⁺-doping concentration or local non-uniform doping.In this thesis, we have made efforts to improve the polymeric planar opticalwaveguide amplifiers, particularly on the major technical difficulties mentioned aboveand the design of the device configuration. The main contents and innovations are asfollowing:1. Based on optical amplifying theory of excited emission and a six-level systemmodel for Er³⁺-Yb³⁺co-doped waveguide amplifier, the rate equations and propagationequations of optical power were established. Using the method of overlap integral, thegain characteristics of devices were numerical simulated. The luminescenceperformance parameters of materials were computed by the Judd-Ofelt theory. Toanalyze the mode characteristics and calculate the mode field distribution of an opticalwaveguide with jumps in the refractive index，the semi-vectorial finite-differencemethod （FDM） based on the Lagrange interpolation and the Effective Index Method（EIM） were implemented by programming with MATLAB. The results werecompared with the commercial software COMSOL Multiphysics and the both resultscould be confirmed.2. The Er element in the organic matrix often has lower quantum efficiency and a short fluorescence lifetime. To solve this problem, oleic acid （OA）-LaF₃:Er,Ybnanoparticles and OIHM were synthesized by chemical coprecipitation and sol-gelmethod respectively. Their properties were characterized by the method such asinfrared spectroscopic analysis, elementary analysis, etc. The diameter of the particleswas about8nm and the fluorescence lifetime was about100μs （for La:Er:Yb=85:3:12）.The5%weight-loss temperatures of nanoparticles and OIHM were both above300degree. The OA-LaF₃:Er,Yb nanoparticles were dissolved in OIHM as content of33wt.%and a film with low surface roughness was obtained. The Judd-Ofelttheoretical calculation value of the metastable level lifetime was13.34ms. TheOA-LaF₃:Er,Yb nanoparticles doped OIHM waveguides with embedded structurewere tested using the fiber-waveguide coupling test system and gain test system. Awell near-field optical spot was showed. The relative gains of3.69dB （P_s=1mW）,3.89dB （P_s=0.5mW） and4.11dB （P_s=0.2mW） were obtained in a2.9cm long devicewhen the pumping power was121mW, which showed that a smaller input signalcorresponds to a bigger gain. The relative gain of a1.9cm long device waveguideincreased from2.2dB to3.2dB corresponding before and after polishing, whichshowed that polishing was help to improve the pumping efficiency. The gaincharacteristics of the erbium-ytterbium co-doped waveguide amplifier （EYCDWA）device were simulated. The effects on the gain of the Er³⁺-doping concentration, theoverlap integral factor, the signal and pumping power, waveguide length and the Er³⁺ion metastable level lifetime were discussed.3. In order to optimize the device structure, the gain characteristics of a kind ofCore-cladding doped waveguide amplifier were analyzed and compared with the Coredoped waveguide amplifier. Within a certain thickness of the core, the Core-claddingdoped type could increase the gain, but it had a lower pumping efficiency. The peakconcentration of the Core-cladding doped type declined obviously. SU-8which hadthe UV thermo-optical bleaching effect was selected as a substrate material.OA-NaYF₄:Er,Yb nanoparticles which had a stronger luminescence property weresynthesized by high-temperature thermal decomposition method. The diameter of theparticles was about15nm. OA-NaYF₄:Er,Yb nanoparticles doped SU-8waveguidesboth of the Core doped type and the Core-cladding doped type was fabricated and hadwell optical performance. The relative gain of2.08dB （P_s=1mW, P_p=170mW） wasobtained in a1.5cm long Core doped type device waveguide.4. The dispersion ability and uniformity of the host-guest doped material werealways limited. To solve this problem, a film-formable solution-processable erbium-ytterbium co-doped complex was synthesized and characterized which had ahigh erbium concentration of10.8wt.%（In contrast,1.1wt.%corresponding that inOA-LaF₃:Er,Yb doped OIHM）. The absorption spectrum of the complex film was insharp contrast with common host-guest doped type film, which almost had nobackground absorption of matrix materials. The full width at half maximum （FWHM）was about80nm （centered around1535nm）. The relative gain of5.20dB （Ps=0.3mW,P_p=140mW） and2.52dB （P_s=0.2mW, P_p=170mW） were obtained in a1.5cm longdevice with a SU-8cladding layer and a2.2cm long device with a PMMA groove,respectively. Four different structures which were the most closely combined with theexperiment and the side-etching were analyzed to provide theoretical guidance for thedevice fabrication.5. Since there was a competition between gain and pumping efficiency in thehigh core region refractive index waveguides, a low core region refractive indexwaveguide （slot waveguide） was introduced. Firstly, the basic characteristics of slotwaveguides were analyzed. The average intensity coefficient γ in a slot waveguidewas two orders of magnitude higher than that in a high refractive index waveguide sothat it was not necessary to be considered. Slot waveguides presented low wavelengthsensitivity. The affect relationships between the overlap integral factor Γ and slotwidth, Si-sidewall width, Si-sidewall height were analyzed and the slot waveguidesize was determined. A four-level system model for Er³⁺doped waveguide amplifierwas established. The effects on the gain in a common high refractive index waveguideof the Er³⁺-doping concentration, the excitation state absorption, the cooperationup-conversion, the signal light and pump light transmission loss, signal and pumppower, the waveguide effective cross area and the overlap integral factor werediscussed. We found that there was optimal pump intensity (I_p-sat) in a certainwaveguide structure. So that for a slot waveguide, different waveguide dimensionscorresponded to different optimal pumping power and the optimal gains could becalculated using the optimal pumping powers. Multi-layer slot could greatly increasethe Γ and the most suitable slot number was3or4layers.This thesis presented two kinds of materials for fabricating polymeric planaroptical waveguide amplifiers: nanoparticles （OA-LaF₃:Er,Yb and OA-NaYF₄:Er,Yb）and film-formable solution-processable erbium-ytterbium co-doped complex. Theformer possesses a stronger luminescence property, and the latter exhibits higherbium-doping concentration and film uniformity. Taking account of these advantages,novel active materials would be prepared, which gives most promising application for enhancing the net gain of polymeric planar optical waveguide amplifiers.更多还原