基于新型MgO:PPLN脊波导的高效宽调谐中红外差频转换机理及器件制备研究

Trace gas detection and analysis can be achieved by using the interaction characteristics between the mid-IR light waves and the materials,since large amounts of gas molecules have intensive base absorption lines in 3-5μm waveband. Currently, mid-IR laser sources based on the DFG/QPM schemes have been the preferred choice for spectrum detection applications due to the advantages of simple structure, convenient tuning, room temperature running and no threshold limit, etc. Owing to the practical demands of high efficiency, widely tunable functions for DFG lasers, a novel annealed proton exchanged (APE) MgO:PPLN ridge waveguide is proposed for generating mid-IR emissions by using the DFG techniques in this project. Researches will be focused on the preparative techniques of large-size APE MgO:PPLN ridge waveguide, regulation and control methods of tailoring the modal distributions and the wide DFG tuning schemes, etc. Objectives in this project include, but not limited to: Study on the two-dimensional proton exchange techniques to enlarge the effective size of the ridge waveguide and establishing the physical model for the refractive index distributions in the waveguide area; Design and preparation of the broadband photonic band gap dielectric coatings for controlling the modal distributions and increasing the modal coupling coefficient; Analysis of the quasi-phase matching(QPM) characteristics in the ridge waveguide and revealing the mechanism of how the waveguide modal effects affect the DFG process and the evolution behaviors, so as to obtain wide DFG tuning schemes with a uniform grating MgO:PPLN ridge waveguide; And ultimately, widely tunable and high efficient mid-IR DFG emissions are achieved,which lay the foundation for its further practical applications.

大量气体分子的基带吸收处于3-5微米波段且谱线密集，利用中红外光波与物质之间的相互作用规律可实现气体的痕量检测与分析。基于DFG/QPM技术的中红外光源，因具有结构简单、调谐方便、室温运转和无阈值限制等优势，已成为光谱检测应用的首选光源。针对该类光源面临的高效率、宽调谐等问题，本项目提出利用一种新型APE MgO:PPLN脊波导差频产生中红外激光的新方案，重点解决大有效尺寸质子交换铌酸锂脊波导的制备、波导模场分布调控以及DFG宽带调谐等关键问题。主要研究内容包括：研究二维质子交换技术增加波导有效尺寸，进而建立波导区域折射率分布的物理模型；设计并制备近红外波段宽带光子带隙介质膜，实现对波导中导波模模场分布的有效调控,提高模场耦合系数；分析波导中的差频QPM特性，研究模式效应对差频过程的影响机理及其演变行为，获得DFG的宽带调谐方案；最终实现高效宽调谐中红外差频输出，为其进一步实用化奠定基础。

3-5μm波段的中红外光源在大气探测、工业生产、医学诊断等领域具有重要的应用价值。基于DFG/QPM 技术的中红外光源，具有结构简单、调谐方便、室温运转和无阈值限制等优势，已成为光谱检测应用的首选光源。本项目围绕如何实现中红外光源的高效差频转换，开展了APE MgO:PPLN脊波导制备、波导模场分布调控、DFG宽带调谐等方面的研究。在项目实施过程中，主要完成了：（1）APE MgO:LiNbO3 脊波导制备工艺研究，分析了脊波导制备过程中各种条件的影响，构建了波导区域的折射率分布物理模型。（2）脊波导中导波模模场分布的调控方法研究，利用有限元法分析基频光和闲频光在脊波导中导波模的模折射率与模场分布，并设计了近红外波段光子带隙介质膜，提高波导模场耦合系数。（3）基于新型二维材料和PPLN晶体，搭建了全固态绿光脉冲激光器，系统地研究了在不同泵浦功率下脉冲绿光输出功率及脉冲序列的输出特性。（4）基于块状PPLN晶体搭建了中红外DFG实验平台，测试与分析了系统的调谐特性，在此基础上构建了甲烷气体检测系统，通过扫描泵浦光波长获得了甲烷分子基频振动带2999.01cm-1处的吸收光谱。（5）基于PPLN晶体搭建的中红外DFG光源系统，实现了多波长中红外光源输出和宽调谐中红外光源输出。（6）基于脊形光波导搭建了中红外DFG实验平台，测试了脊波导传输损耗以及传输模场分布。本项目的研究结果有助于进一步优化APE MgO:PPLN的制备工艺，有效提高DFG转换效率，为痕量气体的检测奠定基础。