【作者】 张慧；

【导师】 蔡阳健；

【作者基本信息】 山东师范大学 ， 光学， 2024， 博士

【摘要】 《“十四五”国家信息化规划》指出,“十四五”时期,信息化进入加快数字化发展、建设数字中国的新阶段。近五十年以来,信息通信技术的蓬勃发展极大地促进了社会进步和经济发展。光通信是以激光作为信息载体进行信息传输的新兴通信技术,与传统的微波通信相比具有明显的优势,如极低损耗、超大带宽和高保真等。光通信在一系列技术的更新、发展推动下,步入了一个飞速发展的时期。通信容量及通信质量是实现光通信可持续发展的关键。相位调制光场在光通信中显现出独特的优势。涡旋光束携带的轨道角动量模式具有多状态性和正交性,使得轨道角动量模式成为新的自由度。通过模分复用技术可以有效缓解光通信的频谱资源紧张,提高光通信系统的频谱利用率,可用于大容量光通信。此外,在光通信系统中,随机传输介质是不可避免遇到的问题。相位调制的信号光场在随机介质（例如大气湍流,海洋湍流）的传输中会发生轨道角动量串扰、光强闪烁和光束漂移使信号中断等问题。而低相干性的光束（即部分相干光束）不仅具有相干光束的特性,而且对随机介质的扰动不敏感,在抑制随机介质引起的负面效应中具有重要的优势。因此,将部分相干相位调制光场应用到光通信领域是本论文的主要研究内容之一。本论文基于以上背景,主要围绕相干及部分相干相位调制光场,开展了其在光通信中的应用研究。本论文的主要研究内容如下:首先,研究了贝塞尔-高斯光束在水下光通信系统及自由空间光通信系统的信号轨道角动量态和串扰轨道角动量态的模式纯度。在水下光通信系统中,构建了贝塞尔-高斯光束的信号轨道角动量态和因扰动而发生串扰的轨道角动量态的接收概率的理论模型,研究发现,通过调控接收孔径的大小可以提高信号轨道角动量态的模式纯度。在自由空间光通信系统中,搭建了基于Gerchberg-Saxton相位恢复算法的自适应光通信系统。同时,在大气湍流信道中,使用涡旋达曼轴锥光栅和自适应补偿系统实现了对贝塞尔-高斯光束的轨道角动量谱的权重系数的同时测量。研究结果表明,大气湍流信道中的贝塞尔-高斯光束的由湍流引起的波前畸变可以利用自适应系统进行补偿。研究结果为提高光通信系统的质量提供了一定的理论和实验支持。其次,研究了传统关联的部分相干涡旋光束和非均匀关联的部分相干涡旋光束在自由空间光通信中的应用。从实验上测量了高斯谢尔模涡旋光束在热板模拟的大气湍流中的光束漂移。搭建了多路复用的高斯谢尔模涡旋光束的自由空间光通信系统,测量了单路/多路复用的高斯谢尔模涡旋光束在该通信系统中的误码率,所有信道的误码率曲线均低于通信系统前向纠错阈值1×10^-3。研究结果表明,随着相干性的降低,光束漂移减小,功率损失减小,误码率降低,即相干性越低的高斯谢尔模涡旋光束的抗湍流能力越强,其自由空间光通信系统更加稳健。此外,研究了非均匀部分相干涡旋光束在大气湍流信道中的通信性能。研究结果表明,通过对接收孔径的半径大小与光束束腰宽度的比值进行调控,可以提高信号轨道角动量态的探测概率,降低串扰轨道角动量态的探测概率,降低通信系统的平均误码率。上述方法和系统可以在提高光通信系统可靠性的同时为大幅度提高光通信系统的通信容量提供思路。最后,研究了携带交叉相位的高斯谢尔模光束在大气湍流信道中的闪烁指数。基于张量光学方法,构建了携带交叉相位的高斯谢尔模光束在大气湍流中的闪烁指数的理论模型。分析了湍流强弱和光束参数对闪烁指数的影响。研究发现,通过位相调控可以降低大气湍流中携带交叉相位的高斯谢尔模光束的闪烁指数,从而提高大气湍流信道中的通信质量。同时在实验上对在湍流大气传输中的携带交叉相位的高斯谢尔模型光束的闪烁指数进行了测量,实验测量的闪烁指数的变化趋势与数值结果一致。更多还原

【Abstract】 The"14th Five-Year Plan for National Informatization"points out that informatization has entered a new stage of accelerating digital development and building a digital China in five years.In the past fifty years,it has greatly promoted social progress and economic development due to the vigorous development of information and communication technology.Optical communication is a rising communication technology for information transmission using laser carrying information.Compared with traditional microwave communication,optical communication has distinct advantages,such as low loss,large bandwidth and high fidelity.Driven by a series of technological updates and developments,optical communication has moved into a period of rapid development.Communication capacity and communication quality are the key to achieve the sustainable development of optical communication.Beams modulated by phase exhibit unique advantages in the field of optical communication.The orbital angular momentum modes carried by vortex beams have multi-stage and orthogonality,and they have proved to be a new degree of freedom for the beam.The technology of mode division multiplexing is able to effectively alleviate the shortage of spectrum resources and improve the spectrum efficiency of optical communication systems,which can be used for large-capacity optical communication.In addition,random transmission media is an inevitable problem in optical communication systems.The issues of orbital angular momentum crosstalk,scintillation and beam wander that cause signal interruption occur when signal beam modulated by phase propagates in random media,such as atmospheric turbulence,ocean turbulence.Low coherent beams（i.e.partially coherent beams）not only possess the characteristics of coherent beams,but also are insensitive to the disturbance of random media.It has an important advantage in suppressing the negative effects caused by random media.Therefore,the application of partially coherent beam modulated by phase to optical communication is one of the main research contents of this thesis.Based on the above background,this thesis mainly focuses on the application of coherent and partially coherent beams modulated by phase in optical communication.The main research contents of the thesis are as follows:Firstly,the mode purity of signal orbital angular momentum states and crosstalk orbital angular momentum states of Bessel Gaussian beams in underwater communication system and free space optical communication system was studied.In underwater optical communication system,a theoretical model for the receiving probability of signal orbital angular momentum states and crosstalk orbital angular momentum states due to perturbation of Bessel Gaussian beams was constructed.It is found that the mode purity of signal orbital angular momentum states can be improved by adjusting the size of the received aperture.In free optical communication system,an adaptive optical communication system based on Gerchberg-Saxton phase recovery algorithm was built.Meanwhile,the weight coefficients of the orbital angular momentum spectrum were measured simultaneously applying a vortex Darman axis cone grating and an adaptive compensation system when Bessel-Gaussian beams propagated in atmospheric turbulence.The results indicate that the wavefront distortion caused by turbulence of Bessel Gaussian beams in atmospheric turbulent channels can be compensated by an adaptive system.it provided theoretical and experimental support for improving the quality of optical communication system.Secondly,the application of traditional correlated partially coherent vortex beams and non-uniform correlated partially coherent vortex beams in free space optical communication was studied.The beam wander of Gaussian Schell-mode vortex beams in atmospheric turbulence simulated by a hot plate was experimentally measured.A free space optical communication system with multiplexed Gaussian Schell-mode vortex beams was constructed,and the bit error rate of single/multiplexed Gaussian Schell-mode vortex beams in this communication system was measured.The bit error rate curves of all channels were lower than the forward error correction threshold of 1×10^-3 in the communication system.The research results indicate that with the decrease of coherence,beam wander,power loss and bit error rate decrease.In other world,the lower the coherence,the stronger the turbulence resistance of the Gaussian Schell-mode vortex beams,and the more robust the free space optical communication system.Furthermore,the communication performance of non-uniform partially coherent vortex beams in atmospheric turbulent channels was studied.The results indicate that the detection probability of the signal orbital angular momentum state can be increased,the detection probability of the crosstalk orbital angular momentum state can be reduced,and the average bit error rate of communication system can be reduced by adjusting the ratio of the receiving aperture radius to the beam waist width.The above methods and systems can provide a way to significantly increase communication capacity while improving the reliability of optical communication systems.Finally,the scintillation index of Gaussian Schell-mode beams with cross phase in atmospheric turbulent was studied.Based on tensor optical methods,a theoretical model of the scintillation index of Gaussian Schell-mode beams with cross phase in atmospheric turbulence was constructed.The effects of turbulence intensity and beam parameters on scintillation index were analyzed.It is found that the scintillation index of Gaussian Schell-mode beams with cross phase can be reduced by phase modulation in atmospheric turbulence,thus improving the communication quality in atmospheric turbulence.Moreover,the scintillation index of Gaussian Schell-model beams with cross phase propagated in turbulent atmospheric was measured experimentally,and the trend of the measured scintillation index was consistent with the numerical results.更多还原