發(fā)布時間：2018-03-19 03:01

  本文選題：光纖耦合　切入點：自由空間光通信　出處：《中國科學院大學(中國科學院光電技術研究所)》2017年碩士論文　論文類型：學位論文

【摘要】：隨著空間通信技術在社會服務、科學應用等方面發(fā)揮著越來越重的作用,傳統(tǒng)微波通信已經難以滿足一些通信鏈路的需求,而自由空間光通信技術的通信容量大、傳輸速率快、抗干擾能力強,已經成為了通信領域的研究熱點。同時,為了提高通信鏈路的傳輸速率與探測靈敏度,基于光纖通信技術的自由空間光通信系統(tǒng)也得到了廣泛的研究與應用。對于上述空間光通信系統(tǒng)來說,首先需要將接收到的空間光束耦合進單模光纖中。然而,空間光束到單模光纖地耦合總是十分困難,其主要受到兩方面的限制:單模光纖纖芯尺寸小,對準誤差、熱效應等因素會造成聚焦光斑無法精確對準單模光纖;空間光束傳輸質量極易受到大氣湍流效應影響,光束波前相位畸變嚴重。以上因素都會導致通信系統(tǒng)的誤碼率增加,嚴重影響通信鏈路的正常工作。因此,保證空間光束高效地耦合進單模光纖是空間光通信系統(tǒng)中的關鍵技術之一。自適應光學技術能夠對大氣湍流擾動所造成的波前畸變進行實時測量和校正,有效改善光束傳輸特性。但是,平臺振動、系統(tǒng)噪聲等因素的存在,仍會導致聚焦光斑隨機偏移單模光纖,光纖耦合效率有待進一步的提高。為了充分發(fā)揮自適應光學技術的優(yōu)勢,提高空間光通信系統(tǒng)的耦合效率與穩(wěn)定性,在系統(tǒng)中引入校正機構結合自適應光學技術構成二級校正系統(tǒng)是十分必要的。本文首先以空間光束耦合單模光纖的理論模型為基礎,仿真分析了靜態(tài)對準誤差以及隨機抖動對單模光纖耦合效率的影響,結果表明:兩者的存在會引起嚴重的耦合損耗,為了獲得較高的耦合效率,必須對其進行補償。然后對不同湍流強度時耦合效率的變化情況展開了研究,根據結果可知:湍流強度越強,通信系統(tǒng)的光纖耦合效率衰減越嚴重,需要對更高階的像差進行校正才能改善耦合效率。利用AO技術對湍流效應影響進行補償實驗,實驗結果表明,AO技術能夠有效緩解湍流效應,校正波前畸變,光束傳輸質量得到改善。為了進一步改善自適應光學系統(tǒng)中的光纖耦合效率,針對單模光纖耦合方案展開了研究:將模擬退火算法與隨機并行梯度下降算法應用于光纖耦合方案,分別對兩種算法的基本原理以及在改善光纖耦合效率上的應用流程展開了討論,通過數(shù)值仿真對比分析了兩者對耦合效率的優(yōu)化情況以及收斂速度;在此基礎上,提出了一種基于光柵螺旋掃描與隨機并行梯度下降算法的單模光纖耦合方案,并針對隨機抖動情況仿真分析了耦合效率的優(yōu)化迭代過程與收斂效果。仿真結果表明:通過設定最佳掃描步長,光柵螺旋掃描算法能夠有效的校正初始對準誤差,校正成功概率高于99%,并且校正后的殘余初始偏移集中在0.5μm 6.5μm范圍內,耦合效率得到初步改善;開啟SPGD控制算法后,聚焦光斑與光纖間的隨機橫向偏移得到校正,耦合效率能夠有效提升至0.81,接近無湍流情況下的理論極限。根據上述方案搭建了相關的軟硬件實驗平臺,實驗結果表明,該單模光纖耦合方案可以有效校正橫向偏移誤差,光纖耦合功率能夠快速收斂到極值。
[Abstract]:With the development of space communication technology in the service of society, plays a more and more important role in scientific applications, traditional microwave communication has been difficult to meet the needs of some communication link, and communication capacity of free space optical communication technology, fast transmission speed, strong anti-interference ability, has become a hot research field in communication. At the same time. In order to improve the transmission rate and the detection sensitivity of the communication link, free space optical communication system of optical fiber communication technology has been widely studied and applied. Based on the space optical communication system, first of all need to be received by the space beam coupled into a single-mode fiber. However, the beam space to single mode fiber coupling is always very difficult and it is constrained by two aspects: single-mode fiber core size, alignment error, thermal effect and other factors will cause the focal spot of inexact quasi monomode fiber Space; beam quality is extremely easy to be influenced by the effects of atmospheric turbulence, the beam wavefront distortion is serious. These factors will lead to the error rate of communication system increase, seriously affect the normal work of the communication link. Therefore, to ensure the efficient coupling of spatial beam into a single-mode fiber is one of the key technologies of space optical communication system. Adaptive optics technology the atmospheric turbulence wavefront distortion caused by the real-time measurement and correction, effectively improve the beam transmission characteristics. However, the vibration, noise and other factors, will lead to the focused spot random offset single-mode optical fiber, optical fiber coupling efficiency to be further improved. In order to give full play to the advantages of adaptive optics technology, improve coupling efficiency and the stability of space optical communication system, introducing the correction mechanism combined with two order correction adaptive optical system technology in the system The system is very necessary. In this paper, a theoretical model of spatial beam coupling single-mode fiber based on the simulation analysis of static alignment error and the influence of random jitter on single-mode fiber coupling efficiency. The results showed that the presence of both will cause the coupling loss is serious, in order to obtain high coupling efficiency, the compensation is necessary. Then the change of coupling efficiency when different turbulence intensity was studied. According to the results, the turbulence intensity is stronger, the coupling efficiency of the fiber communication system's attenuation is more serious, the need for more high order aberration in correction can improve the coupling efficiency. The influences of the turbulence compensation experiment using AO technology, the experimental results show that AO technology can effectively alleviate the effect of turbulence wavefront distortion, beam quality improved. In order to further improve the fiber coupling efficiency in adaptive optical system According to the rate of single mode fiber coupling scheme is studied: simulated annealing algorithm and stochastic parallel gradient descent algorithm is applied to the optical fiber coupling scheme, respectively. The basic principle of the two kinds of algorithm and application in improving the process of fiber coupling efficiency is discussed, through numerical simulation, comparative analysis of the optimization of the coupling efficiency of both convergence and speed; on this basis, puts forward a raster spiral scanning with stochastic parallel gradient descent algorithm based on single-mode fiber coupling scheme, and analyses the iterative process of optimization and the convergence effect of the coupling efficiency for random jitter simulation. The simulation results show that by setting the optimal scanning step, raster spiral scanning algorithm can effectively correct the initial alignment error the correction of the probability of success is higher than 99%, and the initial residual offset correction after concentrated in 0.5 m 6.5 m range, coupling effect The rate of initial improvement; open SPGD control algorithm, spot and fiber between random transverse offset correction, which can effectively improve the coupling efficiency to 0.81, close to the theoretical limit of non turbulent condition. According to the hardware experimental platform has been set up. The experimental results show that the single-mode fiber coupling scheme can effectively the transverse offset error correction, fiber coupled power can quickly converge to the extreme.

【學位授予單位】：中國科學院大學(中國科學院光電技術研究所)
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TN929.1

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