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光纤参量放大器（FOPA）的低噪声相位不敏感和相位敏感放大传输系统。该项目特别关注FOPA在传输系统中的应用，通过先进的调制格式实现高频谱效率。除了数据信号放大之外，人们还开始研究基本的信号处理功能，即波长转换、相位共轭（中跨频谱反转）和再生。到目前为止，再生已在黑盒相敏FOPA中使用二进制相移键控（BPSK）实现了单波长信道。这种黑盒装置包括相位不敏感级，其中通过将信号与第一泵浦波混频来产生第二锁相泵浦波。随后，在第二相敏级中进行再生。该方案的缺点在于它不是格式透明的，因为对于不同的调制格式，需要在第一级中生成不同的谐波。作为本课题的重要延伸，本文将在课题扩展的框架下，基于16-QAM等先进调制格式的格式透明方案，研究多个波长信道的非线性相位失真的并行再生。该方案基于在发射机处生成相位共轭副本以及沿着光纤链路的并行传输。相敏FOPA用作线内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，并且-如果可能的话-尽管频谱效率由于信号的传输以及它们的相位共轭副本而降低了两倍，但是也增强了频谱效率长度乘积。该项目旨在通过优化设计具有光学相位共轭的参量放大器来最大限度地减少FOPA本身的非线性失真，并实现偏振不敏感的相位敏感FOPA。该项目工作将由柏林工业大学的两个研究小组继续进行，以进行实验工作（Grallert教授和博士）以及理论和模拟研究（Petermann教授和博士）。通过与Fraunhofer Heinrich-Hertz研究所的密切合作，我们能够在具有16-QAM等先进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.