基于周期性极化晶体的光纤激光倍频技术研究
文献类型:学位论文
作者 | 郝丽云 |
学位类别 | 硕士 |
答辩日期 | 2013 |
授予单位 | 中国科学院上海光学精密机械研究所 |
导师 | 周军 |
关键词 | 光纤激光 光纤放大器 受激布里渊散射 周期性极化晶体 倍频 |
其他题名 | The Second-Harmonic Generation Techniques of Fiber Laser in Periodically Poled Crystal |
中文摘要 | 基于1微米波段固体激光器倍频的小型化绿光激光器在激光显示、医疗、科研等领域有着重要应用。掺镱光纤激光器与常规的固体激光器相比,具有光束质量好、光光转换效率高、散热效果好、稳定性好、易于实现小型化和集约化等一系列优点。基于准相位匹配技术周期性极化晶体,由于不需要寻找满足相位匹配的特殊方位,可以最大限度的利用晶体的非线性系数,且大多数可以实现室温下的准相位匹配。将光纤激光器与周期性极化晶体相结合的倍频绿光激光技术,是实现高效率小型化绿光激光器的一个重要技术途径。 对周期性极化晶体而言,基频光的时、空、频域特性直接影响到晶体准相位匹配的倍频效果。通常而言,nm量级以上光谱线宽的基频光进行倍频的效率较低,谱线宽度越窄,倍频效率越高,采用单频光源进行倍频的效率是最好的。但是,单频光纤激光器却受限于受激布里渊效应(SBS)的影响难以实现高功率。如何发挥光纤激光器的优势并将其作为基频光源既能获得高功率激光输出又能获得高效率的倍频效果,是本论文研究的重点。在准相位匹配(QPM)材料中,PPMgO:LN晶体具有相对高的光折变损伤阈值和最大的非线性系数,且制造技术已比较成熟、价格低廉,是中小功率小型化绿光激光器中倍频材料的理想选择。本文建立了PPMgO:LN晶体(L=10mm)的准相位匹配理论模型,详细分析了基频光的光谱线宽对倍频效率的影响。创新性地提出采用GHz量级谱线宽度的激光作为基频光,不仅能够获得与单频光源相当的倍频效率,而且可以突破SBS的限制,获得高功率激光输出。并据此进行理论研究,设计实验方案,最终采用线偏振、窄谱宽连续波和准连续波全光纤激光振荡器对周期性极化铌酸锂(PPMgO:LN)晶体进行了单通倍频特性研究。主要研究内容包括以下几个个方面: 一、基频光特性研究 1、搭建了F-P腔(直线腔)窄谱宽光纤激光器,基于零拍测量法,测量了小功率泵浦情况下窄谱宽光纤激光器的纵模特性及以其为种子光的全光纤激光放大器SBS阈值特性。 2、建立了10W量级的单频光纤放大器,通过改变功率主放大器增益光纤与输出光隔离器之间传能光纤的长度,从理论和实验的角度分析了传能光纤长度对单频光纤放大器SBS阈值的影响。 3、仿真计算了基频光谱线宽度对周期性极化晶体倍频效率的影响,分析认为:考虑到晶体温控炉温度调节精度(0.1℃),环境因素的不稳定性及基频光谱线宽度对周期性极化晶体倍频效率的影响,用窄谱宽光纤激光器(谱线宽度为0.1nm)为基频光源不仅保持了与单频基频光源相当的倍频效率,而放大过程相对简单、且可在不受SBS阈值影响下能获得尽可能高的基频光功率。 4、采用保偏光纤光栅(PM-FBG)快慢轴交叉对准技术,自主研发了连续波和准连续波两种运转模式的线偏振窄谱宽全光纤激光振荡器作为基频光源。 二、倍频实验研究 以北京中视中科光电技术有限公司提供尺寸为1mm×2.8mm×10mm周期性极化铌酸锂(PPMgO:LN)为倍频晶体,进行了单通倍频实验特性的研究。 1、从理论和实验上研究了该种晶体的温度调谐特性、温度调谐特性随基频光波长、入射方向和功率的变化关系。 2、以连续波全光纤激光震荡器为基频光源,控制晶体温度在26.9℃,在基频光功率为8.05W时,实现了17.84%的谐波转化效率,此时绿光激光输出功率为1.437W。 3、以准连续波全光纤激光振荡器为基频光源,保持晶体在38.7℃,基频光功率为4.6W时,获得了0.563W的绿光输出,谐波转化效率为12.24%,此时基频光峰值功率57.5W,绿光峰值功率为7.04W。 在相同聚焦的情况下,相对于连续波光纤激光,以准连续波光纤激光为基频光源具有更好的二次谐波效率,但高峰值功率的绿光存在容易引起晶体损伤。 |
英文摘要 | Green laser based on frequency doubling of 1-micron band solid-state lasers was widely used in display, medical, scientific and other fields. Compared with conventional solid-state lasers, Yb-doped fiber laser has good beam quality, high conversion efficiency, good cooling effect, high reliability, easily to reach compact structure and other advantages. Based on quasi-phase-matching techniques ,the periodic crystal with no need to meet the phase matching special orientation , can use the maximize nonlinear coefficient of the crystal and most can be quasi-phase matched at room temperature. The frequency doubling technology of combining fiber laser with periodically poled crystal is a promising way to achieve high efficiency and compact green laser. As to the periodically poled crystal, the time and frequency domain characteristics of the fundamental power directly influence its SHG(Second Harmonic Generation)efficiency. Typically, the SHG efficiency of nm-order and above fundamental power is lower. The narrower the spectral line width of the fundamental power is, the higher the SHG efficiency is. The SHG efficiency of single-frequency fundamental source is the best. However, limited by stimulated Brillouin effect (SBS), it is difficult to achieve high power for single-frequency fiber laser. How to find an fundamental fiber lasers that can not only easily accessing high-power but also has high SHG efficiency, is the focus of our thesis. Among the Quasi-phase matching (QPM) materials, PPMgO:LN crystal with the advantage of relatively high photorefractive damage threshold , the most maximum nonlinear coefficient, relatively mature manufacturing technology and low cost, is the ideal crystal for low and medium power green based on frequency doubling. In this paper, theoretical model of quasi-phase matching about PPMgO:LN(1mm × 2.8mm × 10mm) is established, and the influence of the spectral line width of fundamental power on the SHG efficiency is analysised. It was put forward innovatively that the use of GHz order line-width laser, not only to obtain SHG efficiency as high as single-frequency fundamental, and can also easily reach high power output without SBS. With theoretical research done above, linearly polarized narrow spectral width continuous wave and quasi-continuous-wave fiber laser oscillator are ultimately used, and single-pass frequency doubling of periodically poled lithium niobate (PPMgO: LN) crystals is demonstrated and researched. The main contents are as follows: 1.the study of fundamental source Firstly, an FP-Cavity (linear cavity) narrow-spectral fiber laser is built. Based on homodyne measurement, longitudinal mode behavior of fiber laser and its impaction on SBS characteristics of all-fiber amplifier are studied. Secondly, the scheme of 10W level continuous single-frequency fiber laser is achieved with the use of MOPA technique in two-stage amplified modules. By changing the length of the transmitting fiber between the gain fiber and the output isolator, the power and spectral characteristics as a function pump power under different length of transmitting fiber are measured and the impaction on SBS Characteristics of all-fiber single-frequency laser are analyzed experimentally and theoretically. Thirdly, simulation about the influence of line width of fundamental power on SHG efficiency of PPMgO:LN crystal is done. Taking into account the accuracy of the oven(0.1℃), the instability of the environmental factors and the influence of spectral linewidth of basic source on SHG efficiency, fundamental source with narrow-spectral width (line width of 0.1 nm) can not only maintain a similar SHG efficiency with single-frequency one but can also reach a high power without SBS. Finally, with the technology of fast axis of HR FBG point to the slow axis of OC FBG, we developed both continuous wave and quasi-continuous-wave linearly polarized narrow spectral-width all-fiber laser oscillator as the fundamental light sources. 2. The SHG experimental 1mm × 2.8mm × 10mm 5%MgO doped periodically poled lithium niobate nonlinear crystal (PPMgOLN) provided by the company of Beijing Phoebus Vision Optoelectronic Technology is used. Single-pass, second harmonic generation(SHG) in the crystal are demonstrated and studied. Firstly, the temperature tuning characteristics as a function of pumping wavelength, incident angle and power are analyzed theoretically and experimentally. Secondly, for the continuous-wave all-fiber laser Oscillator, keeping the crystal temperature at 26.9℃, the green light output power of 1.437W is achieved at the pump fundamental power of 8.05W with the best harmonic efficiency of 17.84%. Thirdly, for the quasi-continuous wave all-fiber laser Oscillator, keeping the crystal temperature at 38.7℃, an average green light output power of 0.563W(the peak power of the green light output 7.04W) is achieved at the average pump fundamental power of 4.6W(the peak of fundamental power 57.5W) with the best SHG efficiency of 12.24%. Underling the same focus, quasi-continuous wave fiber laser have a better second harmonic efficiency than continuous-wave fiber laser, but its high peak power of green laser can easily cause damage of the crystal. |
语种 | 中文 |
源URL | [http://ir.siom.ac.cn/handle/181231/16768] ![]() |
专题 | 上海光学精密机械研究所_学位论文 |
推荐引用方式 GB/T 7714 | 郝丽云. 基于周期性极化晶体的光纤激光倍频技术研究[D]. 中国科学院上海光学精密机械研究所. 2013. |
入库方式: OAI收割
来源:上海光学精密机械研究所
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