【作者】 沈炎龙；

【导师】 许立新；

【作者基本信息】 中国科学技术大学 ， 光学， 2009， 硕士

【摘要】 原子钟频标在导弹精确制导、空间精确定位导航等方面起着至关重要的作用。自从1948年世界上第一台原子钟诞生以后,原子钟在国防军事领域,空间探索领域等具有非常重要的应用,故现在有科学家认为原子钟比原子弹更重要。原子钟频标的准确性与精确性引起广泛的关注和研究,随着空间技术的发展,各国对频标和时间基准的准确度要求是越来越高。铯(Cs)原子钟是现有的原子钟中准确度最高,稳定性最好的原子钟之一,它主要由驱动源,铯束管,探测源三个部分组成,其中驱动源采用波长为852nm的激光源,现有的852nm激光源都是半导体激光器,它们的稳定性很难得到保证,而光纤激光器具有结构紧凑、可调谐、稳定性好等优点,原子钟对此类光源有着迫切需求。从上个世纪八十年代开始,我国科学家开始进行自主时间频标铯原子钟的研制,到目前为止,国产铯(Cs)原子钟系统大部分器件都已研制成功, 852nm激光驱动源是目前唯一没有实现国产化的关键器件。本文《铯原子钟驱动源—852nm可调谐光纤激光器研究》是在国家相关项目支持下开展工作的,通过较为系统深入的研究,获得了较好的研究成果,并已通过了总装备部专家组的鉴定。本文主要的研究成果有:1.研制成功850nm波段光纤耦合器。采用光纤熔融拉锥方法,分别制作出50:50,60:40等分束比的耦合器;研制出了800nm/850nm波分复用器,其损耗低于0.5dB,隔离度高于40dB。这些器件的研制成功为后续实验搭建光路提供了必备条件。2.研制了850nm波段单模布拉格光纤光栅,中心波长在851nm附近,所刻写的光栅反射率分布在13%到95%,反射带宽<0.2nm,其为激光器提供了重要的选频元件。3.研究了光栅应力调谐原理和特性,理论计算出有机玻璃作为应力调谐材料,并制作了等强度悬臂梁应力调谐装置。研制出的应力调谐装置稳定性好,调谐范围完全满足实验要求。4.研究了基于硅基掺铒光纤上转换特性,首次提出双波长泵浦普通硅基掺铒光纤以获得852nm激光输出方案。我们采用了双向泵浦方式,双波长(800nm和792nm)泵浦方式,取得了一些初步的结论和结果,为后续的实验工作奠定了坚实的基础。5.成功研究出了利用半导体光放大器(SOA)作为增益介质、工作波长在852nm光纤激光器。激光器输出功率>20mW,光谱宽度<0.05nm,信噪比>30dB,激光器可在851nm—853nm范围内连续可调。激光器结构紧凑,稳定性好。此项成果已通过总装备部专家组验收,并获得一致好评。本文创新性研究工作主要有:1.研制了850nm波段光纤耦合器,波分复用器,研究了光纤光栅原理,并自行刻写了850nm波段单模布拉格光纤光栅。光纤光栅中心波长851nm,反射率最高95%。2.研究了硅基掺铒光纤上转换特性,首次提出用双波长泵浦普通硅基掺铒光纤方案。我们采用双向泵浦方式,双波长(800nm和792nm)泵浦等方式,取得了一些初步的结论和结果,这些结论对后续实验研究有着积极意义。3.首次研究成功了852nm光纤激光器。激光器具有性能稳定,结构紧凑,可调谐等特点。激光器功率达到20mW,信噪比>30dB,激光器可在851nm—853nm范围内连续可调。更多还原

【Abstract】 Atomic clock plays a significant role in the accurate guided missile、space positioning systems and flight navigation systems. Since the first atomic clock was developed in 1948, the atomic clock has very important applications in many areas such as national defense、military and space technology, so some scientists think that atomic clock will be more important than atomic bomb. The precision and the accurateness of the atomic clock frequency standard have attracted a lot of interests and studies, with the development of space technology, the demands for the precision of frequency and clock standard will be higher. In the present atomic clocks, Cs atomic clock has the highest precision and the best stability. The Cs atomic clock system is composed of pump source, Cs tube and light detector, where the laser source with the wavelength of 852 nm is used as pump source. Presently, almost all the 852nm lasers are semiconductor lasers, unfortunately, the stability of this kind of laser is poor, while, the fiber laser with the advantages of high stability, high plug in efficiency, high beam quality, as well as compactness, tenability, and flexibility, are the best choice for the atomic clock system. From the 80’s of last century, scientists in our country have been trying to develop the Cs atomic clock system of ourselves, up to now, all the key components of the self-determination Cs atomic clock system have been developed except the 852nm laser source.This thesis“Research On 852nm Tunable Fiber Laser for Cs atomic clock pumping source”is under the support of the corresponding national project. With the systematic researches, we gain fruitful results, and the laser system has passed through the appraisement by the experts of General Armaments Department.The major results in the dissertation are obtained as the following:1. The invention of 850nm band fiber couplers is successfully made, in which the fusing taper method is adopted, and 50:50, 60:40 fiber couplers are developed. The 800nm/850nm WDM is successfully developed of which the loss is less than 0.5dB and the isolation degree is more than 40dB. These fiber devices will meet the need of the experiment setup.2. The invention of 850nm single mode fiber Bragg grating is successfully made, of which the center wavelength is near 851nm, the reflectivities range from 30% to 95%, 3dB bandwidth of reflectivity is less than 0.2dB. The FBG provides the frequency selective part for the fiber laser.3. The principle and characteristics of the stress tuning of FBG are investigated. We calculated in theory and selected the organic material for the tuning finally. A beam of uniform strength tuning device is successfully made, of which the stability is good and the tuning range meets the need of experiment.4. The characteristics of the up-conversion of Erbium doped fiber (Si based) is investigated. We proposed that the Er doped fiber is pumped with the bi-wavelength pumping to get 852nm up-conversion laser output for the first time. With bi-direction pumping and bi-wavelength (800nm and 792nm) pumping, some results and conclusions are obtained which will instruct the next experiment.5. By using the semiconductor optical amplifier a fiber laser operating at 852nm is successfully developed. The output power of the fiber laser is higher than 20mW, 3dB bandwidth is less than 0.05nm, side mode suppression is better than 30dB. The fiber laser is compact and stable of which the working wavelength can be tuned from 851nm to 854nm continually. This achievement is passed through the identification and appreciated by the experts of General Armaments Department.The innovative results in this dissertation are as following:1. The 850nm band fiber couplers and WDM are developed. The theory of bragg fiber grating is investigated and the FBG is made by ourselves of which the center wavelength is about 851nm, the highest reflectivity is 95%.2. For the first time we proposed that the Er doped fiber is pumped with the bi-wavelength pumping to get 852nm up-conversion laser output. The characteristics of the up-conversion of Erbium doped fiber (Si based) is investigated. With bi-direction pumping and bi-wavelength (800nm and 792nm) pumping, some results and conclusions are obtained which will instruct the next experiment.3. For the first time we have successfully made out a fiber laser working at 852nm. The fiber laser is compact, stable, easily tunable, of which the output power is higher than 20mW, the side mode suppression is better than 30dB. The fiber laser can be tuned from 851nm to 854nm continually.更多还原