Ultra-High-Capacity Optical Communications and Networking: Optical CDMA with Femtosecond Pulses for Ultra-High-Capacity Communications and Networking

在这项提案中，来自加州大学圣地亚哥分校（UCSD）的三名研究人员，专攻光学、通信和计算机网络领域，正在合作开展超高容量光通信和网络计划。许多研究人员认为，在大规模网络中利用光传输技术的最有效和最经济的方法是在电路交换模式下使用波分复用（WDM），并在电子设备上实现分组交换。虽然情况可能确实如此，但重要的是调查具有巨大潜力的替代方法。加州大学圣地亚哥分校的研究小组一直在研究通过光纤传输信息的新技术，其中使用了超短激光脉冲的码分多址（CDMA）。目前正在开发紧凑、低成本的光纤超短脉冲源，使该技术适用于未来的实际网络。当为CDMA编码超短脉冲时，该脉冲会及时扩散，类似于在光纤上传输的噪声突发。在接收节点，对来自多个用户的接收信号应用解码器，该解码器仅与期望的发送器的编码相匹配。匹配的信号成分被转换回超短脉冲形式，可以通过非线性光学技术检测到其他用户的剩余干扰。UCSD开发了一种新型的高分辨率超短脉冲合成和检测技术，可以考虑各种数据传输格式，例如带有开/关键、脉冲位置调制和幅度调制的超快数据包传输。CDMA方案可以实现对传输资源的大规模、异步、并发访问。通过适当的体系结构，可以利用这一点来简化网络控制，并提高可靠性和灵活性。本提案的目的是通过理论研究和实验验证数据调制方案，在光纤网络中结合CDMA编码超短脉冲进行有效的信息传输，从而进行基础研究。高效的调制格式将导致总传输速率超过10兆兆比特/秒，单个用户速率为1-10千兆比特/秒。本提案的具体目标包括超短高斯脉冲光CDMA的建模、传输波形的完整统计分析、以最小干扰支持数千用户的各种光CDMA码的研究、各种调制方案接收光信号的误码率分析、光纤信道引起的畸变的建模和表征。用于减少色散和其他光纤畸变的自适应均衡技术，调制方案的计算机模拟，以及通信系统的实验评估：发射器，光信道和接收器。拟议项目的各个阶段相辅相成。结合在一起，他们提供了CDMA编码超短脉冲通信的理论和实验问题的深入知识。这些发现将与科学界分享，不仅可以增强该领域其他研究人员的知识基础，还可以增强进行研究的学生的知识基础。我们将演示一个原型光网络，其中几个用户采用调制格式，当扩展到全部用户数量时，该格式将每秒携带超过10太比特的信息。这项工作的潜在影响将是证明超短脉冲光CDMA编码是可实现的，并且是WDM的理想替代品。目前，波分复用技术以其简单和低成本成为首选的复用方法。虽然WDM确实显著提高了传输带宽，但由于信道间需要保护带和信道利用率不高，仍然没有充分利用可用的光带宽。相比之下，CDMA编码的超短脉冲无需保护带即可共享整个带宽，从而有效地利用了传输资源。使用CDMA还可以提供高度灵活和健壮的基础设施，在此基础上可以覆盖分组交换。CDMA格式还提供了一定程度的安全性，因为如果不知道所使用的代码，就无法提取数据。

In this proposal, three researchers from the University of California, San Diego (UCSD), specializing in the fields of optics, communications, and computer networks, are collaborating on the Ultra-High-Capacity Optical Communications and Networking initiative. It is felt by many researchers that the most efficient and economical way to utilize optical transmission technology for large scale networking is to use wavelength division multiplexing (WDM) in a circuit switched mode, overlaid with packet switching implemented with electronics. While this may indeed be the case, it is important to investigate alternative approaches that have great potential. The UCSD team has been investigating novel techniques of information transmission via optical fiber, where code division multiple access (CDMA) using ultrashort laser pulses is employed. Compact, low cost fiber-based ultrashort pulse sources are currently being developed, making the technology suitable for future practical networks. When an ultrashort pulse is encoded for CDMA, the pulse spreads out in time and resembles a noise burst that is transmitted on the optical fiber. At the receiving node, a decoder is applied to the received signals from multiple users, which matches only the encoding of the desired transmitter. The matching signal component is transformed back to an ultrashort pulse form that can be detected over the remaining interference from other users with nonlinear optical techniques. A novel high resolution pulse synthesis and detection technique for ultrashort pulses developed at UCSD enable various data transmission formats to be considered, such as ultrafast packet transmission with on/off keying, pulse position modulation, and amplitude modulation. The CDMA scheme enables large scale, asynchronous, concurrent access to the transmission resources. With a suitable architecture, this can be exploited to simplify network control, and increase reliability and flexibility. The objective of this proposal is to conduct basic research by investigating theoretically and verifyingexperimentally data modulation schemes for efficient information transmission in conjunction with CDMA encoded ultrashort pulses in an optical fiber network. Efficient modulation formats will result in aggregate transmission rates exceeding 10's of terabits/second, with individual user rates on the order of 1-10 gigabits/second. The specific objectives of this proposal include modeling of the optical CDMA for ultrashort Gaussian pulses, complete statistical analysis of the transmitted waveforms, investigation of various optical CDMA codes that support thousands of users with minimal interference, bit error rate analysis of received optical signals for various modulation schemes, modeling and characterization of the distortions induced by the fiber channel, adaptive equalization techniques for reducing dispersion and other fiber distortions, computer simulations of the modulation schemes, and experimental evaluation of the communication system: transmitter, optical channel, and receiver. The various phases of the proposed project complement each other. Combined together, they provide for in-depth knowledge of the theoretical and experimental issues of communicating with CDMA encoded ultrashort pulses. These findings will be shared with the scientific community, enhancing not only the knowledge base of other researchers in the field, but also of the students conducting the research. We shall demonstrate a prototype optical network with several users employing the modulation format that will carry over 10 terabits per second of information, when scaled up to the full number of users. The potential impact of the work will be in the proof that optical CDMA encoding of ultrashort pulses is arealizable and desirable alternative to WDM. Currently, WDM is the preferred multiplexing method due to itssimplicity and low cost. While WDM does increase the transmitted bandwidth significantly, it still does not fully utilize the available optical bandwidth due to both the need for guard bands between channels and the under utilization of channels. In contrast, CDMA encoded ultrashort pulses share the entire bandwidth without the need for guard bands, leading to efficient utilization of transmission resources. Using CDMA can also provide a highly flexible and robust infrastructure, upon which packet switching can be overlaid. The CDMA format also provides a degree of security, as no data can be extracted without knowledge of the codes employed.