基于PPLN晶体和双波长光纤激光器的可调谐THz辐射
发布时间：2019-02-24 20:15
【摘要】：太赫兹波具有很多独特性质,如宽带性、互补性、瞬态性、相干性等。在成像与感测等应用领域和医药、化学与生命科学等基础研究领,以及国防技术领域都带来了比较深远的影响。因此,THz科学与技术成为最近几年比较热门的研究课题。目前,THz有众多热门且有实际应用价值的研究方向,包括THz辐射源、THz隐身以及THz波导等研究。其中,怎样才能获得可调谐的THz辐射源是THz科学与技术研究的关键性问题。经过许多人的实验研究验证,非线性光学差频获得THz波辐射的方法是一种比较理想的方法,其优点是能够在常温下稳定运转且输出可调谐和相干的THz波。非线性光学差频方法产生THz辐射的原理是由两束波长接近、相干性好的激光通过非线性晶体在满足相位匹配的条件下差频获得THz波。大多数选用的激光器是固体以及气体激光器,采用光纤激光器的方法还比较少,尤其是采用1550nm附近的双波长单纵模掺铒光纤激光器。 本文重点研究了基于PPLN晶体和双波长光纤激光器的可调谐THz辐射源,探讨了PPLN晶体的相关特性如何影响THz辐射,并对基于PPLN晶体实现THz波的调谐进行分析。通过分析非线性差频对双波长源的要求以及双波长光纤激光器,得出双波长单纵模掺铒光纤激光器是差频生成系统(DFG)较为理想的双波长源。最终,本文设计出一种基于非线性放大环镜(NALM)的双波长单纵模掺铒光纤激光器。由此,为将来可调谐THz辐射源的光纤化工作打下基础。 论文的主要工作有： (1)对非线性差频理论进行研究,建立满足相位匹配时的非线性三波互作用的稳态耦合波方程,从而得出生成THz波辐射的条件,并介绍了相位匹配的方法。在准相位匹配理论分析的基础上,讨论了PPLN晶体的相关特性对准相位匹配的影响,如折射率和相干长度等,从而得到如何优化PPLN晶体结构的方法。 (2)对THz波调谐方式进行分析,重点分析了温度调谐,极化周期调谐以及二者结合方式的调谐。并分析THz波谱宽,得到基于PPLN晶体差频生成THz辐射源的THz波普图。以及得到PPLN晶体相位失配时的极化周期允许带宽,最后对THz输出功率进行了分析。 (3)对用于差频生成THz辐射的双波长源进行分析,得出双波长掺铒光纤激光器是一种比较理想的双波长源。设计了一种基于非线性放大环镜的双波长单纵模掺铒光纤激光器,从而得到1550nm附近的双波长光纤激光器,经过测量仪的测量分析得到的双波长是否满足DFG系统中双波长源的要求,为以后THz辐射源的光纤化工作打下基础。
[Abstract]:Terahertz wave has many unique properties, such as wideband, complementarity, transient, coherence and so on. In the field of imaging and sensing applications, medicine, chemistry and life sciences, and national defense technology have brought more far-reaching impact. Therefore, THz science and technology has become a hot research topic in recent years. At present, THz has many hot and practical applications, including THz radiation sources, THz stealth and THz waveguides. Among them, how to obtain tunable THz radiation source is a key problem in THz science and technology research. It has been proved by many experiments that the method of obtaining THz wave radiation by nonlinear optical differential frequency is an ideal method. The advantage of this method is that it can operate stably at room temperature and output tunable and coherent THz waves. The principle of generating THz radiation by nonlinear optical differential frequency method is that the THz wave is obtained by using a laser with good coherence and two wavelengths close to each other. Most of the lasers used are solid and gas lasers, and the methods of using fiber lasers are relatively few, especially the dual-wavelength single-longitudinal-mode erbium-doped fiber lasers near 1550nm. In this paper, the tunable THz radiation source based on PPLN crystal and dual-wavelength fiber laser is studied, and how the related characteristics of PPLN crystal affect the THz radiation is discussed, and the tuning of THz wave based on PPLN crystal is analyzed. By analyzing the requirement of nonlinear differential frequency for dual wavelength source and dual wavelength fiber laser, it is concluded that dual wavelength single longitudinal mode erbium doped fiber laser is an ideal dual wavelength source for (DFG). Finally, a dual wavelength single longitudinal mode erbium doped fiber laser based on nonlinear amplifying loop mirror (NALM) is designed. Therefore, it will lay a foundation for the fiber conversion of tunable THz radiation sources in the future. The main work of this paper is as follows: (1) the nonlinear differential frequency theory is studied, and the steady-state coupling wave equation satisfying the nonlinear three-wave interaction in phase matching is established, and the conditions for generating THz wave radiation are obtained. The method of phase matching is also introduced. Based on the theoretical analysis of quasi-phase matching, the effects of correlation characteristics of PPLN crystal on phase matching, such as refractive index and coherent length, are discussed, and the method of optimizing the structure of PPLN crystal is obtained. (2) the tunable mode of THz wave is analyzed, especially the temperature tuning, the polarization period tuning and the combination tuning. The spectrum width of THz is analyzed, and the THz wave diagram of THz radiation source is obtained based on the difference frequency of PPLN crystal. The allowable bandwidth of polarization period for phase mismatch of PPLN crystal is obtained. Finally, the output power of THz is analyzed. (3) the dual-wavelength source used to generate THz radiation from the differential frequency is analyzed, and it is concluded that the dual-wavelength erbium-doped fiber laser is an ideal dual-wavelength source. A dual-wavelength single-longitudinal-mode erbium-doped fiber laser based on nonlinear amplifying loop mirror is designed, and a dual-wavelength fiber laser near 1550nm is obtained. Whether the dual-wavelength can meet the requirements of the dual-wavelength source in DFG system can be obtained by the measurement and analysis of the instrument, which will lay a foundation for the future work of the THz radiation source.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN248
本文编号：2429893
[Abstract]:Terahertz wave has many unique properties, such as wideband, complementarity, transient, coherence and so on. In the field of imaging and sensing applications, medicine, chemistry and life sciences, and national defense technology have brought more far-reaching impact. Therefore, THz science and technology has become a hot research topic in recent years. At present, THz has many hot and practical applications, including THz radiation sources, THz stealth and THz waveguides. Among them, how to obtain tunable THz radiation source is a key problem in THz science and technology research. It has been proved by many experiments that the method of obtaining THz wave radiation by nonlinear optical differential frequency is an ideal method. The advantage of this method is that it can operate stably at room temperature and output tunable and coherent THz waves. The principle of generating THz radiation by nonlinear optical differential frequency method is that the THz wave is obtained by using a laser with good coherence and two wavelengths close to each other. Most of the lasers used are solid and gas lasers, and the methods of using fiber lasers are relatively few, especially the dual-wavelength single-longitudinal-mode erbium-doped fiber lasers near 1550nm. In this paper, the tunable THz radiation source based on PPLN crystal and dual-wavelength fiber laser is studied, and how the related characteristics of PPLN crystal affect the THz radiation is discussed, and the tuning of THz wave based on PPLN crystal is analyzed. By analyzing the requirement of nonlinear differential frequency for dual wavelength source and dual wavelength fiber laser, it is concluded that dual wavelength single longitudinal mode erbium doped fiber laser is an ideal dual wavelength source for (DFG). Finally, a dual wavelength single longitudinal mode erbium doped fiber laser based on nonlinear amplifying loop mirror (NALM) is designed. Therefore, it will lay a foundation for the fiber conversion of tunable THz radiation sources in the future. The main work of this paper is as follows: (1) the nonlinear differential frequency theory is studied, and the steady-state coupling wave equation satisfying the nonlinear three-wave interaction in phase matching is established, and the conditions for generating THz wave radiation are obtained. The method of phase matching is also introduced. Based on the theoretical analysis of quasi-phase matching, the effects of correlation characteristics of PPLN crystal on phase matching, such as refractive index and coherent length, are discussed, and the method of optimizing the structure of PPLN crystal is obtained. (2) the tunable mode of THz wave is analyzed, especially the temperature tuning, the polarization period tuning and the combination tuning. The spectrum width of THz is analyzed, and the THz wave diagram of THz radiation source is obtained based on the difference frequency of PPLN crystal. The allowable bandwidth of polarization period for phase mismatch of PPLN crystal is obtained. Finally, the output power of THz is analyzed. (3) the dual-wavelength source used to generate THz radiation from the differential frequency is analyzed, and it is concluded that the dual-wavelength erbium-doped fiber laser is an ideal dual-wavelength source. A dual-wavelength single-longitudinal-mode erbium-doped fiber laser based on nonlinear amplifying loop mirror is designed, and a dual-wavelength fiber laser near 1550nm is obtained. Whether the dual-wavelength can meet the requirements of the dual-wavelength source in DFG system can be obtained by the measurement and analysis of the instrument, which will lay a foundation for the future work of the THz radiation source.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN248
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