影响光纤本征热噪声可能因素的实验研究
文献类型：学位论文
| 作者 | 黄军超 |
| 学位类别 | 硕士 |
| 答辩日期 | 2016 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 李唐 |
| 关键词 | 稳频激光，光纤本征热噪声，光纤干涉仪 |
| 其他题名 | Experimental study on possible factors to influence fundamental thermal noise in optical fiber |
| 中文摘要 | 本学位论文的内容是作者在攻读硕士学位期间的主要工作，包括影响光纤本征热噪声的可能因素的实验研究和对光纤干涉仪稳频激光器进行优化升级。 许多基于光纤应用的物理系统，如光纤干涉仪式传感器、光纤激光器以及光纤干涉仪稳频激光器，其分辨率或频率稳定度最终受限于光纤的本征热噪声，因此，对光纤本征热噪声进行理论和实验研究具有十分重要的意义。目前存在两种不同类型的光纤本征热噪声理论，一个是由K.H.Wanser和S.Foster提出的热传导噪声理论，其在高频区域与实验数据符合的非常好。另外一个Duan Lingze提出的热机械噪声理论，可以解释光纤本征热噪声的的低频区域特性，但是缺少实验数据。之前的光纤本征热噪声的初步测量实验首次实验验证了在次声波段，光纤本征热噪声仍然符合1/f的噪声谱特性；验证了光纤本征热噪声跟光纤长度的正比；发现利用聚酰亚胺涂覆层的光纤，可降低光纤低频区域的本征热噪声。同时也发现了Duan Lingze理论与实验不一致的地方,说明光纤在低频区域的本征热噪声来源依然是一个开放性的的问题。本论文在此基础上，深入实验研究了影响光纤本征热噪声的可能因素，包括光纤中杂质离子的浓度、光纤的物理状态。Foster等人提出了稀土掺杂离子的自发辐射引起的本地熵的扰动可能是有源光纤低频区域本征热噪声的来源。无源光纤内部没有稀土掺杂离子，但是有OH-离子和Ge+、P+等离子，最多的就是OH-离子，这些杂质离子也有吸收光子并自发辐射的现象。因此设计了光纤载氢实验以增加光纤中氢氧根离子的浓度，验证无源光纤中是否有同样的噪声机制。实验结果表明，光纤中氢氧根离子的浓度并不会影响光纤的本征热噪声。同时又测量了纤芯为纯石英玻璃的光纤，发现其本征热噪声并不会改变。光纤的物理状态是指光纤缠绕在支架上受到的张力和光纤弯曲半径。我们进行了光纤张力实验，实验结果表明，在低频段，自由状态下的光纤的本征热噪声比受张力为0.1N状态下的光纤的本征热噪声要高3dB，然而再继续增大光纤缠绕在支架上受到的张力，光纤本征热噪声则不再改变；光纤的弯曲半径不会影响光纤的本征热噪声。 光钟是目前精度最高的时间频率标准，而稳频激光器作为光钟的本地振荡器，其性能水平直接影响光钟的精度水平。此外稳频激光器可应用于探测引力波，验证相对论,精密光谱测量等方面。传统稳频激光器是利用PDH(Pound-Drever-Hall)方法将激光器锁定到超稳高精细度的法布里-珀罗（Fabry-Perot）腔上，该方法要求需要对光路和腔的空间模式精确匹配，具有光学结构复杂，系统昂贵，体积巨大,不容易对激光器的频率进行调节等缺点。而光纤干涉仪稳频激光器相对于超稳腔稳频激光器具有体积小、系统简单可靠、频率易调谐等诸多优势，因此具有很大的发展空间。本论文的一部分工作是对已经搭建好两套光纤干涉仪稳频激光系统进行优化升级。主要从温控和热屏蔽系统系统、可调射谐频频率综合器两个方面进行。针对温控，重新设置了加热片和热敏电阻的分布结构，并且使用温控仪对铝箱进行温控，其24小时的温度波动小于7mK。利用有限元软件Thermal desktop仿真设计光纤干涉仪多层热屏蔽装置，其热时间常数达到几十天量级。针对初步实验中可调射频频率综合器结构较为复杂的缺点，对可调谐射频频率综合器进行优化，电路拓扑结构比原系统更为简单紧凑，系统残留相位噪声小于-120dB rad2/Hz@1Hz，比原系统提高将近5dB。 |
| 英文摘要 | The content of this thesis is the author’s main works during the period of study for Master degree, including experimental study on the possible factors to influence the fundamental thermal noise in optical fiber and some works on optimizing the fiber stabilized laser. In many fiber-based systems, including interferometric fiber-optic sensors, fiber lasers, and fiber-delay-line stabilized lasers, the resolution or the frequency stability is limited by the fundamental thermal noise in optical fiber. Therefore, it is quite important to deeply research the fundamental thermal noise theoretically and experimentally. There are two theories of the fundamental thermal noise in optical fiber. The first one is Thermoconductive Noise Theory proposed by K. H. Wanser and S. Foster et al. It is proved to be consistent with the experimental data in the high frequency range. The another one is Thermomechanical Noise Theory proposed by Duan Lingze. It predicted a 1/f spectral behavior of the thermal noise at low frequencies. A measurement of the fundamental thermal noise in optical fiber down to infrasonic frequencies for the first time was performed in our group and we found that the noise spectrum roll as 1/f at low Fourier frequencies. Additionally, the experiment observed that the level of thermal noise is proportional to the fiber length and polyimide (PI) coated fiber which has thinner coatings has lower noise level than SMF-28 fiberin the low frequency range. However, the experimental data is not consistent with the Duan theory which indicate that the origin of the fundamental thermal noise in optical fiber at low frequencies is still an open question. On this basis, this thesis further experimentally studies the possible factors to influence the fundamental thermal noise in optical fiber, including the concentration of the impurity ions in optical fiber, the tensions on fiber and the bending radius of the fiber. Foster et al proposed that the spontaneous radiation disturbance of rare earth doped ions may be the origin of the fundamental thermal noise in active fiber in the low frequency range. There are no rare earth doped ions but OH-、Ge+、P+ in passive fiber. These impurity ions can absorb and emit photons like rare earth ions. Therefore, we prepared several optical fibers with different OH- concentration to verify whether there is the same physical mechanism in passive fiber. Experimental results show that the OH- concentration almost have no effect on the level of thermal noise. In addition, we repeated the measurement with the pure-silica-core fiber and found that the level of the thermal noise is same as the standard fiber. Finally, we repeated the thermal noise measurement by changing the tensions on fiber and the bending radius of the fiber. We found that the noise level of the fiber under 0.1N tension is 3dB lower than that of the free fiber while the bending radius of fiber has no effect on the thermal noise level. Currently, the most accurate frequency standards are the optical clocks. Their accuracies are dominated by the ultra-stablelasers which act as the local oscillators of the optical clocks. Besides, they play key roles in modern precision measurement, such as gravitational wave detection, precision testing of the theory of relativity. The lowest noise lasers are realized by stabilizing laser frequency onto an ultra-stable high-finesse Fabry–Perot cavity with the Pound–Drever–Hall (PDH) method. However, this approach requires stable and precise alignment of free-space optical elements. The system is bulky、fragile and expensive and they are not easy to tune frequency. Compared to the cavity stabilized laser, the fiber interferometer stabilized laser has merits such as small volume、simple and robust system and easy to tune frequency. Another work of this thesis is upgrading the fiber interferometer stabilized lasers, including active temperature control , thermal shielding system and low-phase-noise frequency synthesizer. For active temperature control, we optimized the distribution of heating films and PID parameters of control loop. reset the distribution structure of heating strips and use the temperature controller to control the sealed aluminum box.The total temperature fluctuation is less than 7mk for a period of 24 hours. Besides, by using the finite element simulation software Thermal Desktop, we design a three-layer heat shields and the thermal time constant can be dozens of days. Finally, we optimized the low-phase-noise tunable frequency synthesizer to make it more compact. The residual phase noise is less than -120dBrad2/Hz@1Hz which is approximately 5 dB lower than that of the old system. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/17003]  |
| 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 | 黄军超. 影响光纤本征热噪声可能因素的实验研究[D]. 中国科学院上海光学精密机械研究所. 2016. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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