【作者】 沈剑威；

【导师】 沈永行；

【作者基本信息】 浙江大学 ， 物理， 2009， 博士

【摘要】 单晶光导纤维是一种具有光纤形式的特殊单晶体。它不但具有光纤的诸多优点,如导光性好、重量轻、体积小、抗电磁干扰,而且由于其本身材料是单晶,所以又具有单晶体固有的特性。近年来,随着光纤传感技术、光纤激光技术的发展,特别是单晶光纤在制备工艺上的不断成熟,不同基质的单晶光纤无论在生长还是应用方面都得到了普遍关注。本论文所涉及的研究工作的主要目标是研究单晶光纤在高温传感和激光领域的应用潜力。首先,采用激光加热基座(LHPG)法生长一系列蓝宝石单晶光纤和掺钕钇铝石榴石(Nd：YAG)单晶光纤。在制备过程中,深入分析了单晶光纤生长的机理,研究了熔区界面对于单晶光纤生长稳定性以及光纤中气泡包裹的影响。通过不断优化生长参数,生长出了高性能的优质单晶光纤。本文研究了基于蓝宝石光纤的FBG堆传感头的制备及相关特性。与传统的方法不同,本文采用真空镀膜技术制备光纤高温传感器。通过反复的实验研究,在蓝宝石基底上研制出了具有复合相纳米晶结构的薄膜,解决了光学膜在高温下由于结晶而产生失透的问题。在此基础上,通过选用合适的材料,以及设计-合理的膜层结构,成功制备出了基于蓝宝石单晶光纤的FBG堆高温传感器,最高的测量温度可达1050℃。此外,为了分析反射峰在超过1100℃时消失的原因,设计并进行了对照实验,通过比较,得出在1100℃以上反射峰的消失是由于膜层间不同组分相互扩散的结论。在激光应用领域,对选用高品质的Nd：YAG单晶光纤作为增益介质的光纤激光器进行了深入研究。由于影响单晶光纤激光器性能的因素十分复杂,所以本文通过大量的实验,对这些因素进行分别研究,例如光纤的冷却问题、泵浦光中心波长与Nd：YAG光纤吸收谱的匹配问题、腔镜的优化问题等,最后对这些因素进行综合考虑,得出了系统优化后的最佳参数,并且在输入60W泵浦功率时,得到了13W的连续光输出。此外,本论文还采用该Nd：YAG单晶光纤进行了小信号激光放大的尝试。通过对种子激光、单晶光纤、泵浦光源三者独立水冷的方式,经过反复的实验比较,深入分析了影响信号激光放大的因素,得出了如何进行系统优化的参考意见。本论文的实验结果表明,采用激光加热基座法生长的蓝宝石单晶光纤和Nd：YAG单晶光纤品质优良,通过进一步的深入研究,可望在高温传感和光纤激光放大领域发挥更大的作用。更多还原

【Abstract】 Single crystal fibers (SCFs) are special crystals with fiber appearances. They have many advantages of the general optical fibers, such as good light guiding, light weight, small size and strong ability of anti-electromagnetic interference. Meanwhile, they have the inherent characteristics of the single crystal. In recent years, along with the development of optical fiber sensing and laser technology, especially with the maturity of the fabrication technique of SCFs, much attention has been paid to the growth and utilization of the SCFs with different medium.The aim of the work in this thesis is to develop high temperature sensors and high power lasers by adopting the SCFs. A series of sapphire fibers and Nd:YAG fibers have been grown by the laser heated pedestal growth (LHPG) method. The mechanism of growth was deeply analyzed. The effects of growing interface on stability of growth and involvement of bubbles have been further discussed. High quality SCFs were grown by optimization of growing parameters.Different from the general FBG fabrication methods, the vacuum coating technology was used for fabricating high temperature FBG stack sensors. Through repeated experimental investigation, a composite nano-crystalline structured thin film was realized on the sapphire substrate, and the devitrification effect at high temperature has been eliminated. Based on this, fiber Bragg grating (FBG) stacks were successfully fabricated at the end surface of sapphire fibers by adopting appropriate materials and thin film structures. The device thus fabricated can be used as a high temperature sensor, with a maximum working temperature of 1050℃. To explain the phenomenon of reflection peak disappearance after annealing at high temperature of 1100℃, a control experiment was carried out. A conclusion of inter-diffusion between layers of stack, which resulted in reflection disappearance, was obtained.In the aspect of laser, the single crystal fiber laser was investigated by adopting a high quality Nd:YAG single crystal fiber as the gain medium. Because the factors that affect laser performance were very complicated. a large number of experiments were carried out to study these factors respectively. e.g. cooling for the single crystal fiber, spectral matching of the pumping laser and crystal absorption spectrum, selection of the cavity mirrors, etc. After a general consideration for those parameters, a maximum output power of 13W was obtained at a pump power of 60W. Besides, an attempt was made to study the laser amplification by using the same Nd:YAG single crystal fiber as the gain medium. In particular, the water cooling systems were separately used for seed laser. single crystal fiber and pumping source. By comparing the results of repeated experiments, the factors which affect the signal amplification were studied, and a conclusion was made to optimize the performance of the system.Results thus obtained show the great prospect of using those sapphire fibers and Nd:YAG fibers in high temperature sensing and fiber laser applications.更多还原