本文選題：自由空間光通信 + 自適應(yīng)光學(xué)��； 參考：《吉林大學(xué)》2017年碩士論文

【摘要】：隨著全球通信業(yè)務(wù)的增長(zhǎng),通信容量不斷增加,無線信道頻譜資源日益緊張,人們將通信頻段不斷向高頻頻段擴(kuò)展,因此光通信以通信頻率高、頻帶寬、傳輸速率高、保密性好的特點(diǎn),成為重要的通信手段。其中自由空間光通信(Free Space Optical Communication,簡(jiǎn)稱FSOC)因其頻譜資源豐富、組網(wǎng)靈活的特點(diǎn),在衛(wèi)星通信、應(yīng)急通信和接入網(wǎng)等方面發(fā)揮著重要作用。但在FSOC中,光信號(hào)在大氣中傳播,受到大氣湍流的干擾,相位發(fā)生擾動(dòng),產(chǎn)生像差,導(dǎo)致波前畸變,從而增大誤碼率,降低通信質(zhì)量。因此,大氣湍流導(dǎo)致的波前畸變問題始終是一個(gè)重要課題。作為補(bǔ)償大氣湍流導(dǎo)致的波前畸變的一種實(shí)用有效方法,自適應(yīng)光學(xué)技術(shù)利用波前傳感器或相機(jī)探測(cè)光束波前的信息,然后將這些數(shù)據(jù)傳給波前控制器,利用一定的算法計(jì)算出控制波前校正器的電壓,使其產(chǎn)生與畸變波前相共軛的波前,抵消原來的畸變。本文的研究重點(diǎn)是控制波前校正器的算法。在總結(jié)現(xiàn)有利用自適應(yīng)光學(xué)進(jìn)行波前畸變校正算法的基礎(chǔ)上,確定了一種組合補(bǔ)償算法,用于控制波前校正器產(chǎn)生與畸變波前共軛的波前,抵消原來的畸變。組合補(bǔ)償算法將直接斜率法和隨機(jī)并行梯度下降算法相結(jié)合。由于直接斜率法無需波前重構(gòu)、計(jì)算量小但是對(duì)高階像差的校正能力較差,隨機(jī)并行梯度下降算法無需波前探測(cè)、機(jī)制簡(jiǎn)單但是對(duì)畸變嚴(yán)重的像差校正的收斂速度慢,所以直接斜率法校正較低階像差,隨機(jī)并行梯度下降算法校正較高階像差,從而提高整體校正效果,減少迭代次數(shù),加快收斂速度。為了驗(yàn)證組合補(bǔ)償算法的校正效果,本文利用Zernike多項(xiàng)式分別模擬了不同精度的多組畸變波前和不同湍流強(qiáng)度下的多組畸變波前,以斯特列爾比(Strehl Ratio,簡(jiǎn)稱SR)作為系統(tǒng)性能指標(biāo),對(duì)組合補(bǔ)償算法進(jìn)行仿真。仿真結(jié)果表明,組合補(bǔ)償算法能夠使這兩種算法互相取長(zhǎng)補(bǔ)短,得到明顯優(yōu)于直接斜率法和隨機(jī)并行梯度算法的校正效果,即更高的SR,達(dá)到相同的SR需要的迭代次數(shù)明顯減少,尤其是對(duì)波前畸變更嚴(yán)重的波前的校正效果更明顯,校正速度的改善也更加明顯。組合補(bǔ)償算法能夠有效提高SR,使更多的光能量耦合到接收光纖中,從而降低誤碼率,提高通信質(zhì)量,符合FSOC系統(tǒng)對(duì)實(shí)時(shí)性的要求。在進(jìn)行理論研究的同時(shí),本文還進(jìn)行了自適應(yīng)光學(xué)系統(tǒng)實(shí)驗(yàn),包括平臺(tái)的搭建、校準(zhǔn)和波前畸變校正的實(shí)驗(yàn)驗(yàn)證。該自適應(yīng)光學(xué)平臺(tái)經(jīng)校準(zhǔn)后原始波前峰谷值小于1μm,引入波前畸變后,能夠校正畸變,使波前峰谷值下降到1μm,具有較好的校正效果,因此為FSOC系統(tǒng)的實(shí)現(xiàn)打下了堅(jiān)實(shí)的基礎(chǔ)。
[Abstract]:With the growth of global communication services, the communication capacity is increasing, and the spectrum resources of wireless channels are increasingly tight. People expand the communication frequency band to the high frequency band, so the optical communication has high communication frequency, high frequency bandwidth and high transmission rate. Confidentiality of good characteristics, become an important means of communication. Free Space Optical Communication, plays an important role in satellite communication, emergency communication and access network because of its rich spectrum resources and flexible networking. However, in FSOC, the optical signal propagates in the atmosphere, which is disturbed by atmospheric turbulence, and the phase is disturbed, resulting in aberration, which leads to the distortion of the wavefront, which increases the bit error rate and reduces the communication quality. Therefore, the wavefront distortion caused by atmospheric turbulence is always an important subject. As a practical and effective method for compensating wavefront distortion caused by atmospheric turbulence, adaptive optics uses wavefront sensors or cameras to detect beam wavefront information, which is then transmitted to the wavefront controller. The voltage of the control wavefront corrector is calculated by using a certain algorithm to produce the wavefront conjugated with the distorted wavefront to cancel the original distortion. The emphasis of this paper is on the algorithm of controlling wavefront corrector. On the basis of summarizing the existing wavefront distortion correction algorithms using adaptive optics, a combined compensation algorithm is proposed, which is used to control the wavefront corrector to produce wavefront conjugated with the distorted wavefront and cancel out the original distortion. The combined compensation algorithm combines the direct slope method and the stochastic parallel gradient descent algorithm. Because the direct slope method does not require wavefront reconstruction, the computation is small but the correction ability for high order aberrations is poor, the random parallel gradient descent algorithm does not need wavefront detection, the mechanism is simple but the convergence rate for aberration correction with serious distortion is slow. So the direct slope method corrects the lower order aberrations, and the random parallel gradient descent algorithm corrects the higher order aberrations, which improves the overall correction effect, reduces the number of iterations, and accelerates the convergence speed. In order to verify the correction effect of the combined compensation algorithm, the Zernike polynomial is used to simulate the multi-group distortion wavefront with different accuracy and the multi-group distortion wave front under different turbulence intensity respectively. The Strehl Ratio (short for short) is taken as the system performance index. The combined compensation algorithm is simulated. The simulation results show that the combined compensation algorithm can make the two algorithms learn from each other's weaknesses, and get a better correction effect than the direct slope method and the stochastic parallel gradient algorithm, that is, higher SRs, and the number of iterations needed to achieve the same SR are obviously reduced. Especially, the correction effect of the wavefront with more serious wavefront distortion is more obvious, and the improvement of correction velocity is more obvious. The combined compensation algorithm can effectively improve the SRS and make more optical energy coupled to the receiving fiber, thus reducing the bit error rate, improving the communication quality and meeting the real-time requirements of the FSOC system. At the same time, the experiments of adaptive optics system are carried out, including platform construction, calibration and wavefront distortion correction. After calibration, the peak and valley value of the original wave front is less than 1 渭 m. After introducing the wavefront distortion, the distortion can be corrected, and the peak and valley value of the wave front can be reduced to 1 渭 m, which has a good correction effect, so it lays a solid foundation for the realization of FSOC system.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TN929.1

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