【作者】 党玮睿；

【导师】 李儒新； 陈玉萍；

【作者基本信息】 上海交通大学 ， 光学， 2013， 博士

【摘要】 随着全光网络传输速度和容量的不断提高，以及超短脉冲光信号处理、双波长光学干涉层析、THz信号产生和检测等技术的兴起，对全光频率转换的带宽提出了新的要求。本文因此研究了基于周期性和非周期畴反转铁电晶体中的多波长全光频率转换，探索了周期性畴反转铁电晶体中二阶非线性参量过程的竞争关系，同时利用二阶非线性极化率的空间调制，优化设计了非周期畴反转铁电晶体，实现了基于级联二阶和频差频的多波长全光频率转换，并在此基础上探索了非线性拉曼纳斯衍射倍频输出的空间调制。本文从二阶非线性光学效应的理论出发，介绍了基于畴反转铁电晶体的准位相匹配技术，推导了在该非线性晶体中的二阶非线性耦合波方程，并详细分析了该方程在周期性畴反转结构和非周期畴反转结构中的不同结果，作为本课题研究的理论基础。介绍了铁电晶体的基本光学特性，回顾了基于室温电场极化法的畴反转制备方法。在此基础上制备的周期性畴反转铌酸锂晶体和非周期畴反转胆酸锂晶体，是本课题研究的实验基础。基于Type I型准位相匹配条件的多波长频率转换中，由于倍频过程与和频过程同时满足准位相匹配条件，两种参量过程将相互竞争，导致各自响应曲线畸变。本文研究了这两种参量过程同时发生时的相互竞争关系，数值模拟了其响应曲线畸变的情况，并在实验中加以验证。对二阶非线性光学参量过程竞争的研究，有助于对多波长频率转换器件进行优化设计。基于Type0型准位相匹配条件，本文利用模拟退火算法优化的非周期畴反转铁电晶体实现了在光通信波段具有平顶宽带特性的多波长频率转换，解决了周期性结构和其他非周期结构中频率转换响应曲线狭窄，带顶响应起伏大以及制备精度要求高的问题。基于设计的非周期畴反转铁电晶体，我们模拟了皮秒脉冲序列在晶体中的传输过程，证实了设计晶体在多波长频率转换性能上的提升。同时，以二阶级联倍频差频过程为基础，演示了其多波长输出的波长可调性和选择性。本文从准位相匹配技术出发理论推导并预测了畴反转铁电晶体结构对非线性拉曼纳斯衍射倍频输出分布的影响。实验上，应用设计的非周期畴反转结构，实现了对非线性拉曼纳斯衍射倍频输出的空间调制，为利用非线性拉曼纳斯衍射进一步对涡旋光轨道角动量的调制提供了理论依据和实验基础。更多还原

【Abstract】 In all-optical wavelength division multiplexing communicationnetworks, frequency conversion is the key technology to resolve thenode frequency blocking and competition. Nowadays, the frequencyconverter based on periodically domain inverted ferroelectric crys-tals have attracted much more favors and are believed to be the mostpromising one due to its pure nonlinear optical interaction, such asstrictly transparency to signal format and transmission rate, flexi-bility to realize frequency broadcasting. Nevertheless, the period-ic quasi-phase-matched structure has a negative impact by limitingthe bandwidth of the frequency conversion on the demand of multi-wavelength response for ultrafast signal processing, dual-band opti-cal coherence tomography, THz generation and so on. In this dis-sertation, we use the periodic and aperiodic domain inverted ferro-electric crystal to solve this problem, make a deep study on the op-timization process of the inverted domains’ distribution to achievetarget frequency conversion response which is then applied into spa-tial modulation of the nonlinear Raman-Nath diffraction.Quasi-phased-matching (QPM) theory is the foundation of our researches, from which we deduce the quadratic nonlinear opticalcoupling process inside of periodic domain inverted ferroelectric crys-tals, and then bring it into aperiodic crystals.After an introduction of the optical properties, especially thequadratic nonlinear optical effect, of domain inverted ferroelectriccrystals, we review the common technique to produce domain in-versions, the poling at room temperature by external electrical fieldtechnique. The samples used in the experiments of this dissertation,periodic and aperiodic, are both produced in this way.Using type I QPM in periodic domain inverted ferroelectric crys-tals, multi-wavelength second harmonic generation (SHG) at the com-munication band has been achieved. Nevertheless, sum frequen-cy generation (SFG) takes place simultaneously, and consumes thepumps’ energy together with the SHGs, which leads to the compe-tition between SHGs and SFG, resulting in a big fluctuation in thefrequency conversion response. In the dissertation, we analyze thiscompetition process, theoretically predict and experimentally veri-fy the change in the response curves of both SHGs and SFG, whichhelps to better understand the second-order nonlinear parametric pro-cesses.Type0QPM, due to its advantage of using the largest nonlinearcoefficient d33, has attract more interesting in the ferroelectric crys-tals, and various engineering has been used to offer a benefit of broadbandwidth for multi-wavelength conversion such as linearly chirpedgrating (LCG), step chirped grating (SCG) and their apodizations. However, they still bring two problems: noticeable ripples on theconversion efficiency curves lead to a bad flatness response in LCGand SCG; the small chirp step in LCG (i.e. a few hundred picome-ters), and the smallness of the initial inverted domain attributed fromapodization (i.e. one or two micrometers) lead to fabrication diffi-culties. In the dissertation, we use engineered MgO-doped lithiumniobate (MgO:APPLN) to solve these problems. Each domain ofthe crystal has an uniform width of3μm for easy fabrication, andthe arrangement of the inverted domains is optimized by the simu-lated annealing algorithm to achieve a flattop broadband for multi-wavelength conversion. Based on this engineered crystal, the multi-wavelength conversion is not only flexibly tunable through chang-ing the wavelength, wavelength spacing, and power of two employedpumps, but also selective for output by tuning the operation tempera-ture. We then numerically simulate the transmission process of seriesof picosecond pulses at1.5μm in MgO:APPLN crystal with engi-neered structure, compare its benefit with the results in other periodicor aperiodic gratings.Through a detailed analysis of the nonlinear Raman-Nath d-iffraction, we find that the frequency doubling output angles dependon the distribution of the second-order nonlinear coefficient, namelythe arrangement of inverted domains in ferroelectric crystals. Sincethe frequency doubling via the nonlinear Raman-Nath diffraction canbe used to generate and modulate the vortex beams, it is important tospatially modulate its output distribution. Therefore, we theoretical- ly deduce the connection between its output angles and the inverteddomain structure. By using the self-adjusted algorithm for optimiza-tion, we demonstrate the spatial modulation of the frequency dou-bling via the nonlinear Raman-Nath diffraction. The experimentalresults are in good accord with theoretical predicts, and parameters,such as fundamental frequency beam waist and its position of inci-dence that affect the nonlinear Raman-Nath diffraction, are discussedin detail, indicating that this type of frequency doubling is not a lo-cal reaction but should take all domains of the crystal into accounts.These analyses and discussion will help with better understanding ofthe nonlinear Raman-Nath diffraction and its further applications incontrolling orbital angular momentum (OAM) of vortex beams.更多还原