【作者】 刘涛；

【导师】 顾畹仪；

【作者基本信息】 北京邮电大学 ， 电磁场与微波技术， 2009， 博士

【摘要】 准相位匹配(QPM)技术是一种通过对光学晶体非线性极化率进行周期性调制来补偿由于折射率色散所造成的光波之间相位失配的技术,它以其独特的优点在诸多领域都有着重要的应用价值。本文利用理论和数值的分析方法,对基于QPM技术的周期极化铌酸锂(PPLN)晶体在光参量放大和光波长转换方面中的应用进行了研究。论文的主要内容和创新点如下:一、阐述了QPM技术的基本原理和国内外研究发展现状;总结了形成周期反转结构的各种方案;介绍周期极化晶体的类型和特性;对基于周期极化晶体的光参量放大和光波长转换的原理和发展历程作了介绍。二、理论和数值研究了宽带可调谐非共线光参量放大过程,首次提出了两种不同的非共线结构用以实现基于PPLN晶体的光学参量放大。针对超短脉冲光波,提出了最大极化周期的概念用以描述非共线相位匹配和群速度匹配同时满足时晶体的极化周期所能达到的最大值,并给出了用于计算不同温度下PPLN晶体的最大极化周期的数学公式,进而确定了宽带可调谐超短脉冲光参量放大过程应使用的最佳极化周期和最佳非共线结构。在上述基础上提出了一个用于最大化光参量放大过程的信号光调谐带宽、确定工作温度等最佳工作参数以及简化实验操作方法的优化方案,并证实了此方案可以被进一步扩展到其它周期极化晶体和使用不同泵浦光波长的情况中。针对纳秒脉冲光波,同样给出了在获得相对最大的信号光调谐带宽时应使用的最佳极化周期和最佳非共线结构。三、利用泰勒级数展开法和直接计算法对参量带宽进行了分析,分析过程中综合考虑到了非共线结构和极化周期所带来的影响。与原有的单一结构光参量放大相比,通过改变非共线结构可以获得更大的参量带宽。对超短脉冲而言,使用合适的非共线结构对参量带宽的增强效果比调整极化周期更好;对于纳秒脉冲而言,合理的选择极化周期和非共线角更为重要。此外,还对泰勒级数展开法和直接计算法取得的结果进行了对比,指出了这两种分析方法各自的优越性。四、深入研究了非共线光参量放大过程的增益带宽和参量增益。利用泰勒级数展开法得到了群速度匹配条件和相位匹配条件同时满足时增益带宽的解析表达式,并分析了非共线结构和极化周期对增益带宽的影响,同时讨论了增益带宽与参量带宽的差异。系统考虑晶体的极化周期、非共线结构、泵浦光强度和晶体长度对参量增益所带来的影响,给出了获取高增益的合理方案。五、提出了不完全非共线光参量放大的概念,并阐明了其与完全非共线光参量放大的区别,同时给出了基于PPLN晶体的三种不完全非共线光参量放大形式,随后对实际中较常用的两种不完全非共线光参量放大的信号光调谐带宽和参量带宽进行了研究。在对参量带宽和信号光的调谐范围要求不是很高的情况下,采用其中的一种不完全非共线光参量放大形式可以简化实验操作,而另一种不完全非共线光参量放大形式在中红外波段有很好的结果。六、研究了分段光栅结构对五种不同波长转换方案:直接差频效应、单通SHG+DFG、单通SFG+DFG、双通SHG+DFG和双通SFG+DFG的转换效率和转换带宽的影响,其中对后面四种的研究工作尚属首次,随后分别给出了每种方案相应的结构优化参数。在保证可以获得几乎相同的转换效率前提下,分段光栅结构的使用能够很好的扩展信号光的转换带宽,增强泵浦光的稳定性。综合考虑到晶体制备的复杂性、转换效率和转换带宽等因素,推荐实际的波长转换器中使用两段光栅结构的PPLN晶体。更多还原

【Abstract】 The phase-dismatching among interacting light waves can be efficiently compensated by use of the quasi-phase matching（QPM） technology,thus it is used in many areas.In this dissertation,the optical parametric amplification （OPA） and optical wavelength conversion（OWC） based on QPM technology is investigated theoretically and numerically.The main contents are as follows:1.The principle and development of the QPM technology,especially its use in the area of optical parametric amplification and optical wavelength conversion are summarized.The characteristics and types of the periodically poled crystals are discussed.The schemes applied to convert the pole of the domain are summarized.2.The effects of grating period and noncollinear geometry on the broadly tunable bandwidth of optical parametric amplification are investigated theoretically and numerically for quasi-phase-matched crystal. For ultra-short pulse OPA,the concept of maximum grating period is proposed to achieve the phase matching and group-velocity matching simultaneously in a wide range.By employing the maximum grating period, geometryⅠis recommended due to the much wider signal tunable range compared with geometryⅡ.An expression is proposed to calculate the maximum grating period for congruent periodically poled LiNbO₃（PPLN） with 800nm pump wave.A feasible scheme is presented to determine the working temperature and noncollinear angleα,maximize the tunable range and simplify the tuning by rotating angleθonly.This scheme can also be used for other QPM crystals and other pump waves.For nanosecond pulse OPA,the optimal grating period and noncollinear geometry are presented to obtain the maximum tunable bandwidth.3.The parametric bandwidth of PPLN based optical parametric amplification with different noncollinear geometries is investigated by expanding the wave-vector mismatch in a Taylor series and retaining terms through second order and by use of the definition directly.The parametric bandwidth can be enhanced in different signal wavelength range by employing suitable geometry or by tuning the grating period.For ultra-short pulses,the enhancement of parametric bandwidth by utilizing suitable geometry is better than that of tuning grating period.But for nanosecond pulses,suitable grating period and noncollinear angleθare more important. The methods of achiving parametric bandwidth by expanding the wave-vector mismatch in a Taylor series or by use of the definition directly are compared.4.The gain bandwidth and gain of PPLN based OPA are studied.On the conditions of phase matching and group velocity matching satisfied simultaneously,an expression is obtained by expanding the wave-vector mismatch in a Taylor series.The effect of grating period and noncollinear geometry on the gain bandwidth is analysised,the difference between parametric bandwidth and gain bandwidth is discussed too.Compared with increasing pump intensity,the gain can be effectively improved by increasing crystal’s length,while the grating period and the noncollinear amplification geometry almost have no effect on the gain.5.Three types of non-absolute noncollinear OPA based on PPLN are proposed.The difference between absolute noncollinear OPA and non-absolute noncollinear OPA is discussed.The parametric bandwidth and the signal tunable bandwidth are studied for two types of non-absolute noncollinear OPA which are used often.6.The conversion bandwidth and conversion efficiency of difference frequency generation（DFG）-based,single-pass/double-pass cascaded second-harmonic generation（SHG）+DFG interactions-based and single-pass/double-pass cascaded sum frequency generation（SFG）+DFG interactions-based wavelength conversion in an aperiodic optical superlattice lithium niobate crystal are studied theoretically and numerically.Compared with uniform grating,the conversion bandwidth and stability of the signal and pump wave can be enhanced by optimizing the aperiodic grating,on the presupposition of achiving the same conversion efficiency.Systemcally considered the conversion efficiency,conversion bandwidth and the manufacture of PPLN,two-segment PPLN is recommended to be used in wavelength converter.更多还原