Fiber-optic parametric amplifiers for signal regeneration in transmission systems with advanced modulation formats

目前正在进行的项目致力于研究用于传输系统中低噪声相敏和相敏放大的光纤参数放大器(FOPA)。该项目特别关注FOPA在传输系统中的应用，该系统通过先进的调制格式实现了高频谱效率。除了数据信号放大外，它还开始研究基本的信号处理功能，即波长转换、相位共轭(中跨谱反转)和再生。到目前为止，在黑盒相敏FOPA中显示了采用二进制相移键控(BPSK)的单波长通道的再生。这样的黑盒设置包括一个不敏感的阶段，在该阶段中，通过将信号与第一泵浦波混合来产生第二锁相泵浦波。随后，再生发生在第二阶段敏感阶段。该方案的缺点在于它不是格式透明的，因为第一级需要为不同的调制格式产生不同的谐波。作为当前项目任务的重大扩展，基于16-QAM等高级调制格式的格式透明方案，将在项目扩展框架内研究多个波长通道非线性相位失真的并行再生。该方案基于在发射机产生相位共轭副本，并沿光纤链路并行传输。相敏光纤放大器被用作在线放大器，并提供相位再生。其目标是提高光纤链路的非线性阈值，如果可能的话，还可以提高频谱效率长度乘积，尽管由于信号和它们的相位共轭拷贝的传输，频谱效率降低了两倍。进一步的任务是由目前正在进行的项目的结果推动的，该项目利用光学相位共轭的参数放大器的优化设计来最小化光纤放大器本身的非线性失真，以及实现偏振不敏感的相敏光纤放大器。该项目的工作将继续进行柏林工业大学的两个研究小组都进行了实验工作(Grallert教授)以及理论和模拟调查(Petermann教授)。结合与夫琅和费海因里希-赫兹研究所的密切合作，能够在16-QAM等高级调制格式的光传输系统中实现FOPA的独特研究。

The presently running project is devoted to the investigation of fiber-optic parametric amplifiers (FOPA) for low-noise phase-insensitive and phase-sensitive amplification in transmission systems. The project particularly focuses on the application of FOPAs in transmission system with high spectral efficiency which is achieved by means of advanced modulation formats. In addition to data signal amplification, it was begun to investigate basic signal processing functionalities, i.e. wavelength conversion, phase conjugation (mid-span spectral inversion) and regeneration.Up to now, regeneration was shown for a single wavelength channel with binary phase-shift keying (BPSK) in a black-box phase-sensitive FOPA. Such a black box setup consists of a phase-insensitive stage, in which a second phase locked pump wave is generated by mixing the signal with a first pump wave. Subsequently, regeneration takes place in the second phase sensitive stage. The drawback of this scheme is given by the fact that it is not format transparent, since different harmonics need to be generated in the first stage for different modulation formats. Moreover, it is difficult to implement multi-wavelength regeneration with this scheme.As significant extension of the tasks of the presently running project, parallel regeneration of nonlinear phase distortions of several wavelength channels will be investigated based on a format transparent scheme for advanced modulation formats such as 16-QAM in the framework of the project extension. This scheme is based on generation of phase conjugated copies at the transmitter and parallel transmission along the fiber link. Phase-sensitive FOPAs are used as inline amplifiers and provide phase regeneration.It is targeted to increase the nonlinear threshold of the fiber link and -if possible- also an enhanced spectral efficiency length product despite the fact that the spectral efficiency is reduced by a factor of two due to the transmission of the signals and their phase conjugated copies as well.Further tasks are motivated by the results of the presently running project to minimize the nonlinear distortions of the FOPA itself using an optimized design of the parametric amplifier with optical phase conjugation as well as to realize a polarization insensitive phase-sensitive FOPA.The project work will be continued by both research groups at TU Berlin to carry out the experimental work (Prof. Dr. Grallert) as well as the theoretical and simulative investigation (Prof. Dr. Petermann). In combination with the close collaboration with the Fraunhofer Heinrich-Hertz Institute unique studies on the implementation of FOPAs in optical transmission systems with advanced modulation formats such as 16-QAM are enabled.