基于拉锥光纤分布瑞利散射的窄线宽光纤激光器实验研究

发布时间：2018-02-09 02:23

本文关键词： 窄线宽单纵模瑞利散射布里渊散射拉锥光纤　出处：《哈尔滨工业大学》2015年硕士论文　论文类型：学位论文

【摘要】：窄线宽(kHz量级)激光器由于其超长的相干长度和极低的相位噪声,在密集波分复用DWDM、光学传感、光学探测和微波光子学等领域具有很大的前景。单纵模窄线宽光纤激光器其输出激光中只包含一个纵模形式,因此激光输出线宽即为单纵模线宽。利用光纤中的瑞利散射效应实现的单纵模窄线宽激光线宽可窄至-810 nm,比窄线宽DFB激光器的线宽甚至可以窄两个数量级,比目前光通信中应用的信号光源线宽甚至窄5个数量级。该论文的研究内容即为基于高受激布里渊阈值拉锥光纤中瑞利散射的单纵模窄线宽光纤激光器。主要工作如下:从理论出发,调研了光纤中布里渊散射和瑞利散射的理论基础,重点描述了光纤瑞利散射线宽压窄的机理。实验测量了一定长度单模光纤的受激布里渊阈值,来验证理论计算值。介绍了几种行之有效的抑制光纤中受激布里渊的方法,并根据布里渊散射产生的机理及影响布里渊散射的因素,确定出本论文将要采用的抑制光纤中受激布里渊散射的方法:拉制纤芯直径周期分布变化的拉锥光纤以改变声模场从而抑制受激布里渊的产生。介绍了几种常用的窄线宽激光的线宽测量方法,着重介绍本论文将要采用的延时频移自外差法,并进行了公式推导,计算出测量指定量级激光线宽所需的延时光纤的最短理论长度。最后对特定激光线宽采用不同长度延时光纤进行自外差法测量,对比不同长度延时光纤对测量结果的影响,当延时光纤的长度小于激光的相干长度时,由延时自外差法测得的功率谱存在边带波纹,测量误差较大。随着延时光纤长度增长,测得的功率谱向洛伦兹线型收敛,测得的激光线宽也逐渐收敛于激光实际线宽。利用拉制的高受激布里渊阈值的拉锥光纤作为分布反馈介质,进行了环形腔光纤激光器的实验。文中详细介绍了拉锥光纤的拉制过程,最终拉制出长150 m,每隔5 m一段锥区共30段锥区,每个锥区长度约2 cm,束腰直径约80m的高受激布里渊阈值光纤,经测量该拉锥光纤的损耗仅1 dB,受激布里渊阈值提高了近10 dB。经微调腔内损耗和泵浦功率,该激光器稳定输出了3 dB线宽25 kHz的单纵模激光。后又对环形腔进行改进,引入自注入反馈机制来进一步压缩线宽并稳定纵模输出,经调节自注入反馈的功率,输出最窄3 dB线宽至13.5 kHz的单纵模激光,且纵模十分稳定,边模抑制比达52 dB,输出功率在6 mW以上。
[Abstract]:Because of its ultra-long coherent length and extremely low phase noise, the laser is used in dense wavelength division multiplexing (DWDMs) for optical sensing. Optical detection and microwave photonics have great prospects. Single longitudinal mode narrow linewidth fiber laser has only one longitudinal mode in its output laser. Therefore, the laser output linewidth is the single longitudinal mode linewidth, which can be reduced to -810 nm by the Rayleigh scattering effect in the fiber, and even two orders of magnitude smaller than that of the narrower linewidth DFB laser. The linewidth of signal source is even 5 orders of magnitude narrower than that used in optical communication at present. The research content of this paper is the Rayleigh scattering single longitudinal mode narrow linewidth fiber laser based on high stimulated Brillouin threshold in tapered fiber. Do the following: starting from the theory, The theoretical basis of Brillouin scattering and Rayleigh scattering in optical fiber is investigated, and the mechanism of narrow linewidth of Rayleigh scattering is described. The stimulated Brillouin threshold of a certain length single-mode fiber is experimentally measured. Several effective methods for suppressing stimulated Brillouin scattering in optical fiber are introduced. According to the mechanism of Brillouin scattering and the factors affecting Brillouin scattering, The method of restraining stimulated Brillouin scattering in fiber is determined in this paper. The tapered fiber with periodic distribution of core diameter is drawn to change the sound mode field and restrain the generation of stimulated Brillouin. Several kinds of commonly used methods are introduced. A method for measuring the linewidth of a narrow linewidth laser based on, This paper mainly introduces the method of time-delay frequency shift self-heterodyne which will be used in this paper, and deduces the formula. The shortest theoretical length of the delay fiber needed to measure the laser linewidth of a given order of magnitude is calculated. Finally, the self-heterodyne method is used to measure the length of the specific laser line width by using the different length delay fiber, and the effect of the different length of the delay fiber on the measurement results is compared. When the length of the delayed fiber is smaller than the coherent length of the laser, the power spectrum measured by the time-delay self-heterodyne method has sideband ripple and the measurement error is large. With the increase of the length of the delayed fiber, the measured power spectrum converges to the Lorentz line. The measured laser linewidth gradually converges to the actual laser linewidth. The tapered fiber with high stimulated Brillouin threshold is used as the distributed feedback medium. The experiment of ring cavity fiber laser is carried out. The drawing process of tapered fiber is introduced in detail. Finally, 150 m long conical region with 30 cones every 5 m interval is produced. The length of each cone is about 2 cm and the beam waist diameter is about 80 m. The loss of the tapered fiber is only 1 dB, and the stimulated Brillouin threshold is increased by nearly 10 dB. The single longitudinal mode laser with 3 dB linewidth of 25 kHz is output stably, and then the ring cavity is improved. The self-injection feedback mechanism is introduced to further compress the linewidth and stabilize the longitudinal mode output, and the power of self-injection feedback is adjusted. The single longitudinal mode laser with the narrowest linewidth of 3 dB up to 13.5 kHz is output, and the longitudinal mode is very stable. The edge mode suppresses Prida 52 dB and the output power is above 6 MW.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN248

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