全光通信作业1

1、 ROF通信技术以及基于RF调制的光标记交换技术中若干关键问题的研究专业：通信工程 班级：通信081班学号：200809448 姓名： 徐 娅 论文题目：ROF通信技术以及基于RF调制的光标记交换技术中若干关键问题的研究中 文 摘 要近年来的全球信息化浪潮使人们对通信系统的容量和质量的需求迅速提高，以光纤接入为代表的有线接入虽然能够提供很大的带宽，但是终端的移动性受到限制，而无线通信由于其接入的灵活性和移动性更受用户的欢迎。但目前低频无线通信系统的带宽较窄并且频谱资源已经相当拥挤，无法满足未来的移动多媒体、流媒体等宽带业务需求，提高无线接入系统传输容量的有效途径是利用带宽资源丰富的高频无线电波

2、。灵活方便的宽带无线接入正在成为未来通信的主要发展方向，特别是像北京这样高度信息化的大都市更是倍加关注。40-70GHz的毫米波可以承载速率达Gbit/s数据信号，而且频谱资源丰富。该频段的无线信号适于组建具有较高频谱空间复用率的微小蜂窝无线通信系统，因此它将是未来Gbit/s的宽带无线接入首选的频段。然而，高频无线信号的传输问题和高频设备的高昂价格严重制约着这类无线系统的应用。融合光纤通信和移动通信技术优点的光载射频（ROF）通信技术是实现宽带无线信号传输的有效手段，该技术利用光纤的几乎无限的带宽资源和低损耗优势，使多路宽带无线信号的传输距离达数十公里，并可以将原来放置在基站的高频设备转移到

3、中心站实现资源共享，进而可对数量庞大的基站的结构和功能（光电、电光转换和天线收发是必备功能）进行简化，降低系统成本。同时在ROF系统中采用光学方法产生毫米波信号，可以简化基站和中心站的结构。因此，基于ROF技术的无线通信系统能够使宽带无线接入的实现更加容易。基于ROF技术的无线通信系统具有明显优势，它不仅可用于宽带无线接入，而且在车载移动通信、热点地区和室内覆盖、雷达信号传输等方面有广阔的应用前景。构建城域宽带网、建设覆盖城乡的信息服务体系已列为北京市信息化发展规划以满足未来对宽带接入需求，以ROF技术为基础的无线宽带接入能够提供更大的接入带宽和灵活性，可以为北京市城域宽带网的无线接入部分提供

4、技术支撑。最近，ROF通信技术已经成为光通信领域的研究热点，国内外很多科研机构和高校都展开了ROF技术的研究工作，很多研究组已经在实验室搭建了试验平台，这些研究工作将推着ROF技术逐渐走向商用应用。另外，在光标记交换领域，利用高频的无线信号调制光波实现的副载波（SCM）光标记和光载波抑制（OCSS）光标记现已有一些研究，这两种标记实现方案有很好的应用前景，但还有一些问题需要深入研究，本论文对SCM光标记信号的传输距离受限问题和OCSS光标记分组的全光波长变换问题进行了深入研究，并得到了一些有价值的结论。本论文对ROF技术和基于射频调制的光标记交换技术进行了深入研究，主要研究内容和成果（黑体部分

5、）如下：1分析比较了直接调制、外调制、光外差和频率上转换等多种光载射频信号产生技术。首先介绍了直接调制技术产生的光载毫米波信号的基本原理及其性能。然后重点研究了基于铌酸锂外调制器的光载毫米波信号的产生问题，分析了基于M-Z结构的铌酸锂外调制器的光外调制技术产生的三种频谱结构（DSB、SSB和OCS）的光载毫米波信号的机理和所需要的偏置电压、射频信号的幅度和相位等参数，并对所产生的光载毫米波信号的光谱结构和光电流等进行了详尽的理论和实验研究。分析表明：DSB光载毫米波信号的频谱效率只有SSB和OCS光载毫米波信号的频谱效率的一半；产生相同频率的光载毫米波信号，OCS调制方案所需要的射频信号频率只

6、有DSB和SSB调制方案的一半；在光纤传输之前，这三种光载毫米波各光波成分的初始相位虽然不同，但由光电探测器解调得到的毫米波信号性能并无明显差别。在分析铌酸锂调制器的调制特性的基础上，得到了光载毫米波载波各光频成分的初始相位与调制深度之间的关系，为后面推导DSB光载毫米波幅度衰落的节点和腹点位置奠定了基础。在分析光外差技术原理的基础上，深入讨论了注入锁定、反馈锁相环、注入锁定和前馈锁相等技术对降低光载毫米波信号的相位噪声、提高毫米波信号的频谱性能方面的作用；通过对基于双模激光器的光载毫米波信号的频谱特性的分析，发现所产生的毫米波相位噪声明显较低。最后阐述了频率上/下转换技术产生光载毫米波信号的

7、原理和基于WDM技术的ROF系统的光载射频信号源的实现方案。2 从理论上深入研究了三种典型频谱结构的光载毫米波在光纤中传输时受色散的影响，并通过仿真和实验对理论结果进行了验证。重点分析了DSB光载毫米波载波沿光纤传输时光电流的射频成分的幅度衰落的原因，并从理论上阐述了射频幅度衰落节点和腹点位置与三个光频成分的初始相位之间的关系，并推导了衰落周期公式。通过光纤色散对OCS光载毫米波信号在光纤传输中性能影响的理论分析和实验研究，发现：当OCS光载毫米波被数据信号调制时，信号光电流的射频成分没有幅度衰落和由光纤色散引起的射频信号脉冲变窄，而光电流中的基带信号的脉冲宽度逐渐变宽。对这一现象原因进行理论

8、分析后，得到了脉冲变窄与信号传输距离、光纤色散和光载毫米波信号频率之间的关系，并给出了OCS光载毫米波信号最大传输距离公式。通过光纤色散对OCS光载毫米波信号在光纤传输中性能影响的理论分析和实验研究，得到了毫米波信号的光电流射频成分幅度衰落与光载毫米波频谱结构之间的关系，分析了由光纤色散引起的基带信号脉冲和射频信号脉冲码形畸变的原因，从理论上得到了脉冲变窄与信号传输距离之间光纤色散和光载毫米波信号频率之间的关系，并推导了SSB光载毫米波信号最大传输距离公式。在此基础上提出了克服脉冲变窄的方案（即将信号脉冲调制在单个载波上，而另一个光载波没有信号），仿真结果表明该方案能够大大延长SSB光载毫米信

9、号的传输距离。对DSB光载毫米波信号在光纤中传输时色散引起的两种效应（幅度衰落和边带脉冲走离）进行了深入研究，发现：调制到边带上的信号脉冲的走离不仅造成了信号幅度的衰落，还引起信号码形的畸变，幅度衰落造成衰落节点的信号幅度非常小。在这两种效应的共同作用下，较远距离传输的信号码形严重畸变，只有接收机处于有限的几个衰落腹点附近时，信号的性能才有保证。最后，讨论了光纤的偏振模色散对光载射频信号传输性能的影响。3 研究了ROF双工链路和网络结构。首先探讨了ROF系统中全双工链路的实现方案，从ROF系统的要求出发分析了基站的简化思路，研究了将射频信号源转移到中心站、利用双工的光/电和电/光转换器等方法简

10、化基站功能及结构的实现方案；根据光载射频信号的光谱特点，讨论了WDM在ROF系统中的应用，利用波长间插方法实现多路光载射频信号的波分复用，能够进一步提高光纤带宽的利用率；接着从理论上分析了WDM-ROF系统存在的三种信道间窜扰；最后分析了ROF系统中的星型、环型和总线型三种基本的网路结构及其特点。4对基于射频调制的两种光标记技术（SCM和OCSS）中的关键问题进行了研究。在讨论光标记交换技术原理的基础上，分析了基于射频调制的副载波复用(SCM)光标记实现方案，深入研究了光纤色散对SCM光标记信号传输性能的影响以及载荷与标记信号之间的窜扰问题。理论分析和仿真结果表明：由光纤色散引起的SCM光标记

11、信号脉冲展宽对信号传输距离、眼图张开度等链路性能有明显影响，造成标记信号的传输距离受限。在此基础上提出了利用改进的射频调制方式增加SCM光标记信号的传输距离、减小窜扰的措施；分析表明通过提高中间节点光栅的载波抑制比可以减小来自载荷的窜扰。在分析OCSS光标记分组波长变换特点的基础上，对基于HNL-DSF的FWM效应的单泵浦和双泵浦全光波长变换的频谱结构、偏振敏感性等特性进行了理论和实验研究，发现：在单泵浦情况下光标记分组的频谱发生翻转，且对偏振很敏感；而在共极双泵浦情况下波长变换所产生的新OCSS光标记分组的频谱发生平移且偏振不敏感；最后通过对双泵浦情况下两个泵浦光的偏振方向对波长变换的偏振敏

12、感性和转换效率影响的究，发现在正交双泵浦情况下，波长变换的转换效率很低，且对信号光偏振很敏感。根据波动方程和光纤的三阶非线性特性从理论上解释了这些现象产生的原因。关键词：光载射频（ROF），铌酸锂调制器，双边带调制，单边带调制，光载波抑制调制，光纤色散，衰落效应，走离效应，光标记交换，脉冲展宽，副载波光标记，OCSS光标记，全光波长变换，偏振敏感性。Research on some key issues of radio-over-fiber technology and optical labeling based on RF modulationMa JianxinABSTRACTRece

13、ntly, the global informization trend makes our demand of the capacity and quality of the communication system increase rapidly and wideband wireless communication is becoming a major direction of the future communication, especially for the metropolitans like Beijing. Though the wire access, represe

14、nted by fiber to home, can provide huge bandwidth, the mobility of the terminals is limited severely. Wireless access are more popular because of its easily access and mobility, but the current mobile telecommunication has a much narrow bandwidth and suffers from the shortage of the spectrum, so it

15、will never meet the future service requirements of the broadband wireless access, such as mobile multimedia serves and stream media serves. The only way to improve the wireless access capacity is by using the radio with higher frequency and plentiful bandwidth source. 40-70GHz radio can carry the Gb

16、it/s data signal with plenty of spectrum source, and the wireless telecommunication system with this band has much smaller cells, which means a higher spatial multiplexing of the radio source. Therefore, such frequency band is the first option for the Gbit/s wireless access in the future. However, t

17、he transmission of the higher frequency signals and the higher price of the electrical equipments in the higher frequency systems limit their application. This issues need to be overcome.The radio-over-fiber (ROF) technology, combining merits of the fiber communication and the wireless communication

18、 technologies, is a good means to implement the wideband wireless access scheme. The broadband and low loss fiber can transmit the higher frequency radio signals over tens of kilometers, which can transfer the expensive higher frequency equipment from the base station to the center station to co-sha

19、re and so simplifies the configuration and function of a great number of the base stations, whose obligatory devices includes antenna, O/E and E/O converters. Moreover, the generation of the millimeter-wave by optical technique can also simplify the system and reduce its cost. So high frequency radi

20、o communication based on ROF technology makes the implement of the wireless access easily.There are many advantages for the ROF communication system. The ROF technology not only can be used in wideband wireless access system, but also in many other fields. As an informizated metropolitan with a larg

21、e number of talents, Beijing will require to construct the broadband Metropolitan Area Network (MAN) to meet the rapid increase of the wireless access in the future. In such MAN, the Gbit/s broadband wireless access based ROF technology is a good optional scheme because of its advantages mentioned a

22、bove. Recently, ROF technology has become the hot topic in the optical communication field and many research groups are focusing their interesting on it. Some ROF testbeds are setup in the laboratories and all the research work are driving the ROF technology to the commercial application. Moreover,

23、the high frequency radio can also be used in the optical label switching. The subcarrier multiplexing (SCM) optical label and optical carrier suppression and separation (OCSS) optical label are based on modulating lightwave by radio, which were studied much and maybe have a good future.The main rese

24、arch works and the contributions (blacked) of this dissertation are presented as below:1. The generation techniques of the optical millimeter-wave, such as the direction modulation, external modulation, optical heterodyning technique and frequency up-conversion, are analyzed and compared Firstly, th

25、e principle of the optical millimeter-wave signal based on direction modulation of the laser diode is described and its characteristics are summarized. Secondly, the generation scheme of the optical millimeter-wave based on LiNbO3 Mach-Zehnder Modulator (MZM) is investigated in detail. The generatio

26、n mechanism of the optical millimeter-wave with three different spectra (DSB, SSB and OCS) is analyzed and the parameters, such as the bias voltage, the voltage and phase of the local oscillator signal, etc. are evaluated. The spectrum configurations and the photocurrents are studied theoretically a

27、nd experimentally. The results show that the spectral efficiency of the DSB optical millimeter-wave is only the half of the SSB and OCS ones; to generate the optical millimeter-wave with the same frequency, the local oscillator frequency required by the OCS modulation is only the half of the DSB and

28、 SSB. The photocurrents detected by PIN photodiode show no obvious difference for the three kinds of optical millimeter-wave signal before they are transmitted along the fiber, though they have different initial phases. On the basis of the known modulation characteristic of the MZM, the relationship

29、 between the modulation depth and the initial phases of the three tunes of the DSB optical millimeter-wave which sets up the base of deducing position of the fading node of the DSB optical millimeter-wave. Based on the principle of the optical heterodyning technique, the capacity of the phase lockin

30、g techniques, are discussed and analyzed, such as, the injection lock, phase lock loop and its combing, as well as the feed-forward phase locking, for reducing the phase noise and improve the spectral performance of the generated optical millimeter-waves, and the spectrum of the optical millimeter-w

31、ave signal based on the dual-mode laser is also characterized. At last, the principle of generating optical millimeter-wave signal based on frequency up/down-conversion is described and the optical millimeter-wave sources used in the WDM-ROF system is also discussed. 2. The influences of the fiber d

32、ispersion on the three typical kinds of the optical millimeter-wave signal are investigated theoretically as they are transmitted along the standard single mode fiber, and the theoretical results are confirmed by the simulation and experimental results.After analyzing the fading effect of the DSB op

33、tical millimeter-wave, the relationship between the positions of the fading nodes and loops of the DSB optical millimeter-wave and the relative initial phases of the three tones of the DSB optical millimeter-waves is deduced, and the period format of fading is obtained.The influence of the fiber dis

34、persion on the OCS optical millimeter-wave signals as transmitting along the fiber is investigated. It is found that there is no fading but the code pulse-width becomes narrow for the RF photocurrent, while the baseband signal pulse-width of the photocurrent becomes narrow. The reason is discovered

35、theoretically and experimentally, and the maximum transmission distance is formulated according to relationship between the time shift of sidebands and the transmission distance.The performance degradation of the SSB optical millimeter-wave signals as it transmitting along the fiber is checked and i

36、t is found that the fading effect is related with its spectrum configuration. It is the fiber chromatic dispersion that causes the code pulse-width to become narrow and code outline to be distorted. The maximum transmission distance is also formulated theoretically. Basis on this, a scheme to extend

37、 the transmission is proposed, in which the signal is modulated only on one optical carrier while the other one is blank. The simulation results show that the scheme extends the transmission distance of the optical millimeter-wave greatly.The influence of the two effects (fading effect & sideban

38、d pulses walk-off) caused by fiber dispersion on the DSB optical millimeter-wave is investigated. The walk-off of the pulses on the optical sideband causes the distortion of pulse outline, and then limits the maximum transmission distance, while the fading effect suppresses the signals at the fading

39、 nodes greatly. Because of the two effects, the DSB optical millimeter-wave signals rapidly degraded periodically, and only the signals received around some fading loops within a limited transmission distance can be kept a good performance.At last, the influence of the fiber polarization-mode disper

40、sion on the transmission performance of the optical millimeter-wave signal is also discussed.3. The implement of the duplex link in the ROF system and the simplification of base station are discussed. After the analysis of the application of WDM technology in the ROF system, three kind of ROF networ

41、ks are checked. According to the technical requirement of the ROF system, I have discussed the simplification of the base station, the transferring the RF source from the base station to the central station and the simplified base station with the duplex E/O and O/E converters. Then the spectral cha

42、racteristic and the fiber bandwidth efficiency of the WDM-ROF system are analyzed. According to the spectral configuration obtained above, it can be seen that the spectral scheme with wavelength interleave can improve the fiber bandwidth efficiency. Then the three kinds of crosstalk between the chan

43、nels in the WDM-ROF system are analyzed. At last, the network configuration and its performance of the three typical topologies are discussed.4. Some key issues in the two kinds of the optical label switching (SCM and OCSS) based on RF modulation are investigated. After discussing the principle of t

44、he optical label switching technique, the implement of the subcarrier modulation (SCM) optical label switching is analyzed and the influence of fiber dispersion on the SCM label signals is deduced. The theoretical and simulation results show that it is the code expansion caused by the fiber dispersi

45、on that causes eye the diagram closure and the transmission distance limitation. On this basis, an improved scheme is proposed to overcome the code expansion, by which, the transmission distance is extended and the crosstalk is reduced. Although there is the crosstalk from the payload carried by the carrier, it can be reduced by improving the e