| 题名 | 单频激光器噪声抑制技术研究 |
| 作者 | 秦晓琼 |
| 文献子类 | 博士 |
| 导师 | 瞿荣辉 |
| 关键词 | 单频激光器，强度噪声，线宽，相位噪声，噪声抑制 Single-frequency laser, intensity noise, linewidth, phase noise, noise reduction |
| 其他题名 | Research on Noise reduction of Single Frequency Laser |
| 英文摘要 | 单频激光器以窄线宽、低噪声、高相干性的特点，广泛应用于相干激光雷达、高分辨率激光光谱学、激光原子冷却、高精度光纤传感、引力波探测、微波光子学等前沿科学和高精度应用领域。上述的应用重点关注单频激光器的功率、噪声、线宽等关键性能指标。单频激光的功率主要与激光增益介质的浓度和激光器整体性能有关。 单频激光噪声主要包含短时间的强度噪声、 相位噪声/频率噪声以及长时间段的频率稳定性，线宽实质上也是频率噪声的一种表现形式。单频激光器的噪声性能体现了单频激光的质量， 同时也是制约单频激光发展应用的关键因素之一。单频半导体激光器（包括集成外腔半导体激光器）和短腔结构单频光纤激光器具有结构紧凑、尺寸小重量轻、能量转换效率高等优势，极具实际应用潜力。所以本论文主要以上述两类单频激光器作为研究对象，探究单频激光器噪声以及噪声抑制的技术方案， 并获得一些初步结果。 1、梳理总结了单频激光的强度噪声和相位/频率噪声的来源和表征体系，以及激光噪声测量方式。 推导了随机噪声源对载流子浓度、光子浓度和极化强度的影响。 2、搭建了主模和边模拍频强度噪声抑制实验平台，其中激光器为 Littrow 结构外腔半导体激光器，光子缓存器为参量倍频 BBO 晶体。 首先深入研究了参量倍频晶体抑制拍频强度噪声的机理。半导体激光器中激光主模和边模拍频导致的布居数振荡（CPO） 和四波混频（FWM）。 由于边模处的增益和折射率类的布居数振荡效应， 边模处的增益和折射率被布居数振荡调制了， 使得红移和蓝移的边模不对称， 我们首次在半导体激光器中观察到了强度噪声峰的双峰现象。其次在实验上， 观察到了主模和一阶 ~ 三阶非激光边模各自的拍频强度噪声峰，并且噪声峰均为双峰。实验表明，外腔半导体激光器较长的增益介质会使 CPO 和FWM 效应增强和带来更复杂的物理机制。 同时也观察到因 BBO 晶体的二次谐波效应， Littrow 结构外腔半导体激光器的拍频强度噪声被有效抑制。最后观察到越偏离 BBO 的相位匹配角，拍频强度噪声抑制的效果越差， 证明了拍频强度噪声峰因二次谐波效应抑制的。 3、设计和实现了窄线宽全光纤环滤波器， 其可用做激光腔镜，进一步压窄单频激光器的线宽。首先从理论上推导出双环光纤环滤波器的反射率表达式，并详细地数值分析和实验验证了其反射率、反射相位和群时延特性。研究结果表明： 由超低反光栅（Rg = 0.9%）和低分光比光纤耦合器（k2 = 0.15， L2 = 51cm）构成的单环滤波器具有高反射率、超窄线宽和高群时延特性， 还显示了良好的慢光效应。而双环滤波器不仅保持了以上良好特性，还因游标效应，共振幅度得到调制，具有更大的有效自由光谱范围（FSR： 28 pm）、 边模抑制比（SMSR： 3 dB） 和不易跳模等特点。有望利用全光纤环滤波器压窄线宽和抑制频率噪声等优点， 把其应用到单频激光器噪声抑制，精密光谱学等领域中。; With narrow linewidth, low noise and high coherence, single-frequency lasers have important and widespread applications in frontiers of scientific researches and high-tech fields, such as coherent laser radar, high-resolution laser spectroscopy, laser atom cooling, high-precision fiber sensor, gravitational wave detection and microwave photonics. Based on the above application requirements, the key performance indicators such as power, noise and linewidth of single-frequency lasers are focused. The power of a single-frequency laser is mainly related to the laser gain medium concentration and laser performance. Single-frequency laser noise mainly includes short-time intensity noise, phase noise/frequency noise, and frequency stability over a long period of time. Linewidth is also essentially a form of frequency noise. The noise performance of single-frequency lasers embodies the quality, and it’s also one of the key factors for further applications. Single-frequency semiconductor lasers (including integrated external cavity semiconductor lasers, ECSLs) and short-cavity single-frequency fiber lasers have the advantages of compact structure, small size, light weight, high energy conversion efficiency, and have great application potential. Therefore, this paper mainly uses these two kinds of research objects to explore the technical solutions of single-frequency laser noise suppression. The main contents are as following: 1. Combine and summarize the source, characterization system and measurement methods of a single-frequency laser noise. The influnce of random noise sources on carrier concentration, photon concentration and polarization intensity are deduced. 2. An experimental platform for noise suppression of beat intensity between main lasing mode and side non-lasing modes, in which a Littrow-type ECSLs acts as the laser and a parametric frequency-doubled BBO crystal as the photon buffer. First of all, the mechanism is deeply studied that parametric frequency-doubled crystals reduce the beat frequency noise. The coherence population oscillation (CPO) and four-wave mixing (FWM) are caused by the laser mode and side mode beat frequencies in ECSLs. The gain and the refractive index at the side mode are modulated by CPO, so that the red-shifted and blue-shifted side modes are asymmetric. Double peaks are observed for the first time in semiconductor lasers. Secondly, in the experiment, noises induced by the beating of main lasing mode and 1st ~ 3rd side non-lasing modes are observed. It is noticed that the beatings are split into two due to the asymmetric modification of the FSR by CPO and FWM, the frequency shift and the amplitudes of sub peaks are dependent on the pump current and the order of side modes. It shows that the long active medium is believed to make the effect of CPO and FWM enhanced and more complicated. The RIN is reduced sufficiently by using a BBO crystal with SHG. Finally, in order to confirm that the noise reduction is really induced by the SHG mechanism, we rotated the BBO crystal to change its SHG efficiency and proved it. 3. A narrow-linewidth all-fiber ring filters is designed and used as laser cavity mirrors to narrower linewidth. Firstly, the reflectivity expression is deduced theoretically. The characteristics, such as reflectivity, reflection phase and group delay, are numerically analyzed and experimentally verified. The results show that the single-ring filter composed of a LRFBG(Rg = 0.9%) and a low split ratio coupler(k2 = 0.15，L2 = 51cm) has characteristics of high reflectivity, ultra-narrow linewidth and large group delay, also has good slow-light effect. Double-ring filter not only maintains a good characteristic of narrow linewidth, but also due to the Vernier effect, the amplitudes of resonant peaks are modulated. And compared with the single-ring filter, it has larger effective free spectral range (FSR) and side mode suppression ratio (SMSR), then not easily mode hopping. Because of narrow linewidth, the double ring could be used in frontier fields such as precision spectroscopy. |
| 学科主题 | 光学工程 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/31088]  |
| 专题 | 中国科学院上海光学精密机械研究所 |
| 作者单位 | 中国科学院上海光学精密机械研究所 |
| 推荐引用方式 GB/T 7714 | 秦晓琼. 单频激光器噪声抑制技术研究[D]. |
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