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。

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.