【作者】 李密；

【导师】 马晶；

【作者基本信息】 哈尔滨工业大学 ， 物理电子学， 2010， 博士

【摘要】 近年来随着信息流量需求的迅速增长,以微波为信息载体的卫星通信技术在通信数据率的提高上逐渐显现出局限性。而卫星光通信技术相对卫星微波通信技术而言,具有设备体积小、抗干扰强和保密性高等诸多优点,同时在通信数据率方面更是有着极大的提升空间。自上世纪六十年代以来,美国、欧洲以及日本等研究机构都相继对卫星光通信技术的研究投入了巨大的人力和物力,而目前我国对该领域的关注也在不断的提高。目前国际上卫星光通信系统基本都是采用基于半导体激光器的直接调制方式。在保证大输出光功率的前提下,由于卫星光通信链路中无法实现中继放大,在直接调制方式下进一步提高通信系统调制速率的难度越来越大。而采用由半导体激光器和掺铒光纤放大器(EDFA)构成的过渡性调制子系统结构或由半导体激光器、LiNbO3波导调制器以及EDFA组成的下一代主流调制子系统结构可以解决这一难题。在上述两种解决方案中都需采用EDFA技术。然而EDFA受到空间辐射后,其光学性能指标会有所下降,这会影响到整个卫星光通信系统的通信质量。因此,本文对EDFA在空间辐射环境下的性能变化进行了理论和实验研究,主要内容包括以下几个方面:为解决EDFA辐射影响研究中原有EDFA无法直接测试的难题,在基于掺铒光纤背景损耗的速率方程与传输方程的基础上,通过在无源测试模型中引入有源测试方法给出了一个新的EDFA辐射增益特性测试模型。采用该有源测试模型,只需通过测试EDFA信号光的输出功率随辐射剂量的变化就可以直接得到单波长EDFA的辐射增益特性,这使得在EDFA整机的测试过程中不再像无源测试模型中那样必须测试掺铒光纤辐射背景损耗,从而为卫星光通信系统设计人员提供一个更为便捷的分析方法。针对光纤恢复效应所引起的测试时间受限问题,首先对能够描述常规环境下多波长EDFA增益特性的黑匣子模型的本质进行了分析。然后在此基础上将黑匣子模型引入到辐射环境中来描述多波长EDFA辐射增益特性,从而提出一种采用黑匣子模型的多波长EDFA辐射增益特性的测试方法。为了对卫星光通信系统优化选择EDFA提供更加全面的参考依据,进一步对EDFA的抗空间辐射性能进行了实验研究。主要通过掺铒光纤的铒离子浓度与辐射剂量的关系、掺铒光纤放大器与铒镱共掺光纤放大器的抗辐射性能对比以及采用电子作为辐射源这三方面对EDFA的抗空间辐射性能进行了研究分析。最后,为了研究EDFA在卫星光通信系统中的应用情况,进一步从信噪比以及误码率的角度分析了由辐射引起的EDFA性能变化对通信系统的影响。仿真结果表明受EDFA性能变化的影响,通信系统信噪比都是随辐射剂量的增加而减小,而误码率是随辐射剂量的增加而增大。但是在相同通信系统参数的情况下,采用EDFA作为前置放大器的通信系统的抗辐射性能要优于采用EDFA作为功率放大器的通信系统。上述这些研究工作将为采用EDFA技术的卫星光通信系统的设计提供参考依据,并对解决高功率与调制速率这一技术矛盾从而实现卫星光通信系统的高数据率通信传输具有重要意义。更多还原

【Abstract】 With the rapid growth of information, the limitations of inter-satellite microwave communication technique are gradually exposed in the improvement of the communication data rate in recent years. However, comparing to the technique, the inter-satellite optical communication technique has more advantages, such as smaller volume of equipment, higher anti-interference, better confidentiality, and so on. Especially, considering the potentiality of the communication date rate further, the inter-satellite optical communication technique has become one of the hottest research fields. Enormous human and material resources have been invested in this technique by the United States, Europe, Japan and other major countries since 1960s. For the same reason, our country has also given more concern to this technique.At present, the direct modulation technique, which is based on the semiconductor lasers, has been used in the most of the inter-satellite optical communication systems in overseas. However, there is no relay to amplify the signal in inter-satellite optical communication links. Therefore, with the growth of transmission data rate, it is more difficult to meet the requirements of high modulation rate under the condition of high output optical power. Usually, there are two good methods to solve the problem. One is the transitional modulation subsystem composed of semiconductor laser and eribium-doped fiber amplifier (EDFA). And the other is the next modulation subsystem composed of semiconductor lasers, LiNbO3 waveguide modulator and EDFA.It is clear that both methods indicate the EDFA has to be used as the key component in next inter-satellite optical communication systems. However, since the optical characteristics of EDFA will deteriorate after the radiation, the radiation effect on the EDFA will affect the communications quality of the inter-satellite optical communication systems. Therefore, in this dissertation, the space radiation effect on the EDFA has been investigated both in theory and experiment. The main contents of the dissertation include the following aspects:Since it is impossiable to measure the radiation characteristic of EDFA directly, an active measured method has been introduced to the passive measured model based on the rate equation and the transfer equation of radiation environment. The new active measured model can describe the gain characteristics of EDFA in the radiation environment, only by measuring the variation of optical signal output power with the dose. In this way, it can avoid measuring the deterioration of eribium-doped fiber (EDF) to get the gain characteristics of EDFA like the passive measured model. Therefore, it provides a more convinent method to the designers of the inter-satellite optical communication systems.In order to overcome the restriction of the measured time which caused by the recovery characterstics of EDF, a black box model (BBM) is introduced to describe the multi-wavelength gain characteristics of EDFA in the radiation environment successfully based on the analysis on the nature of the black box model. Then a method based on the BBM has been proposed to measure multi-wavelength gain characteristics of EDFA in radiation environment.In order to introduce the EDFA to the actual inter-satellite optical communication system better, the anti-radiation characteristics of EDFA has been further analyzed in three viewpoints. These are the relationship between the concentration of Er3+ in erbium-doped fiber and the radiation dose, the comparison of anti-radiation performance between the EDFA and the erbium-ytterbium co-doped fiber amplifier (EYDFA), and the the electron radiation effect on the EDFA.Finally, in order to understand the application of EDFA in satellite optical communication systems better, the radiation effect on the EDFA has been investigated in the communication viewpoints of signal to noise ratio and bit error rate. The calculation results indicate that the signal to noise ratio decreases with the increasement of radiation dose. And the bit error rate increases with the increasement of radiation doise. Especially, the anti-radiation performance of communication systems, in which the EDFA is used as the preamplifier, is better than the case in which the EDFA is used as the power amplifier.The research work mentioned above will be a good reference for the design of inter-satellite optical communication systems which contain the EDFAs. Especially, it is also really significant to solve the contradiction between the high output power and high modulation rate radically, and achieve the high transmission data rate for the inter-satellite optical communication eventually.更多还原