利用二阶非线性参量下转换过程可以实现高频率激光向低频率激光扩展，也可以实现单光子、量子纠缠光、量子压缩光等非经典光源，特别是利用参量振荡器（OPO）实现中波脉冲激光和利用自发参量下转换（SPDC）实现通讯波段偏振纠缠光源（PEPPs），成为了当前各自领域的研究热点。本论文工作中，将强非线性耦合作用的OPO与弱非线性耦合作用的SPDC进行初步研究对比。理论研究中，一方面基于耦合波理论对时空高斯分布的双共振近简并平平腔OPO建立了光强迭代模型，详细考察了单程泵浦下的OPO阈值特性、脉冲形成过程与转换效率，另一方面在海森堡互作用绘景中对共线简并双光子纠缠源亮度评价建立了定量计算模型。理论研究结果对于实验研究中波OPO和C波段PEPPs具有重要指导意义。实验研究中，首先基于弱耦合SPDC过程研究了如何获得高亮度通信C波段PEPPs，深入分析高纠缠亮度、高纠缠品质、小型化等问题。采用外腔反馈、饱和吸收谱稳频和锥形放大技术，研制出瓦级、线偏振、单频、稳频780 nm半导体激光器。利用该激光器双向激励置于Sagnac干涉环中的II类PPKTP晶体，结合多模光纤与大尺寸有源面积的单光子探测器，实现了高谱线亮度、高保真度的高品质PEPPs。其次基于强耦合OPO过程研究了中波波段脉冲激光输出，利用铥光纤-钬固体级联激光泵浦I类临界相位匹配ZGP-OPO方案，深入分析高重复频率、高能量、高转换效率等问题。利用国产掺铥光纤激光器（TDFL）带内泵浦Ho: YAG晶体，获得了连续功率16.7 W和脉冲能量13.5 mJ（重复频率1 kHz）的2.09 μm线偏振激光输出。基于该脉冲光源，在双共振平平腔ZGP-OPO中，实现了1.25 mJ（1 kHz重复频率）、峰值功率72 kW、转换效率42%、斜效率53%的4 μm激光输出。最后针对中波ZGP-OPO及其泵浦激光器，提出了3个优化方向：第1个优化方向是利用光纤耦合1.94 μm LD替代TDFL，在Ho: YLF晶体低掺杂的情况下，获得了接近量子极限的2.06 μm激光输出，最大连续功率超过1.8 W、脉冲能量超过1 mJ（重复频率100 Hz）。第2个优化方向是利用II-VI族新型Cr2+: CdSe动调Q替代声光调Q，腔型紧凑且Q开关免温控，在TDFL泵浦的Ho:YAG系统中，获得了1.77 mJ（重复频率685 Hz）的2.09 μm激光输出，对应峰值功率约115 kW。第3个优化方向是利用889 nm Cr: LiSAF激光器直接泵浦重掺杂Ho: BYF晶体替代ZGP-OPO，在晶体30 at.%掺杂时，获得了5.6 mJ（重复频率1 Hz）的3.9 μm激光

With the second-order nonlinear frequency down conversion (SNFDC) technique, on one hand, the short-wavelength fundamental light can be freely converted to the mid-infrared band even to the far-infrared band when the incident light is strong enough, on the other hand, the non-classical light source is available when the incident light is very weak, such as the single photon source, the quantum entanglement photon pairs, and the quantum squeezed light source. The former high-intensity light source has much more advantages on the thermal management, the wavelength tuning range, and the long-wavelength scalability than the traditional radiated lasers. Meanwhile, the latter ultra-low-intensity light source has the extra advantages on the controllability, the free transmission range, and the brightness scalability if compared with the quantum dot technique, the ion trap technique, etc. Thus SNFDC has become an important tool for researchers, no matter to develop the macroscopic laser system or study the microscopic quantum mechanics. Therein, two typical applications, the mid-infrared optical parametric oscillator (OPO) and the telecom-band polarized entanglement photon pairs (PEPPs), have moved into the main stream of each research field. In this work, a comparative study is demonstrated for them.In the theoretical study, an iterative model of parametric intensity based on the coupling wave model was firstly developed for the double-resonant degenerate plane-cavity OPO with a spatial and temporal Gaussian input. Several important parameters, parametric threshold, pulse building process and conversion efficiency, were simulated and analyzed. The numerical results indicated that the small-signal parametric gain was applicable for OPO, but unable to estimate the brightness of PEPPs. Then a quantitative calculation model of entanglement brightness was developed for the collinear degenerate entanglement source with the quantum mechanics theory, which can be used to precisely evaluate the brightness of PEPPs. The above theoretical research is beneficial for the guidance of the following experimental study of mid-infrared ZGP-OPO and C-band PEPPs.In the experimental study, C-band PEPPs were firstly prepared with SPDC, and the key problems about entanglement brightness, entanglement quality, and miniaturization were studied in detail. We adopted synthetically the techniques of external cavity feedback, semiconductor amplifier, and saturated absorption spectrum (SAS) frequency-stabilization to get high power, linearly polarized, frequency stabilized 780 nm laser. Then a high-brightness quality 1.56 μm PEPPs was accomplished with a PPKTP down-converter inside a Sagnac-type interferometer and multi-mode fiber collection way. The maximum spectral brightness is about 1.33×105 pairs(s?mW•nm)?1 with a pump power of 200 mW and a spectral bandwidth of 1.34 nm. Under the condition of maximum entanglement brightness, a high fidelity of 97.27 %±0.23% for the ideal Bell state was obtained, and the CHSH-type Bell inequality was violated with a value of 2.8196±0.0098 (96 σ).Next, the mid-infrared pulsed laser were obtained with a fiber-bulk tandem Ho3+ laser-pumped type-I phase-matched ZGP approach, and the key problems about high pulse energy at high repetition rate, and high conversion efficiency were studied in detail. By employing the homemade high-power thulium-doped fiber lasers and the in-band pumped Ho: YAG scheme, maximum output power of 16.7 W and maximum output energy of 13.5 mJ at repetition rate of 1 kHz were obtained. With this 2.09 μm Ho: YAG laser, 4 μm ZGP-OPO was achieved with the maximum pulse energy of 1.25 mJ, peak power of 72 kW, conversion efficiency of 42% and slope efficiency of 53%.Finally, three possible improvement directions were introduced to further simplify the ZGP-OPO system. The 1st direction was to simplify the pump source structure with 1.9 μm diode lasers. A fiber-coupled diode-pumped low-dopant Ho: YLF laser was presented with an extremely high slope efficiency of > 80%. The maximum output power can be >1.8 W, and the pulse energy can be >1 mJ at 100 Hz. The 2nd direction was adopting a saturable absorber (SA) to passively Q-switching the Ho: YAG laser. Cr2+: CdSe crystal was firstly applied as an SA, and the pump bleaching curve was measured and analyzed in detail. Pulse energy of almost 1.8 mJ at average repetition rate of 685 Hz was obtained. The maximum pulse peak power reached 115 kW. The 3rd direction was using the 889 nm directly pumped heavily dopant Ho: BYF laser to obtain 4 μm pulsed light. A preliminary experiment was finished with output pulse energy of >5.6 mJ at 1 Hz. The spectroscopic properties of 30 at.%-doped Ho: BYF crystal were studied with the Judd-Ofelt theory.