Optical Communication based on Nonlinear Fouriertransformation

• Applicant: Professor Dr.-Ing. Christian Schäffer
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 432471840

The ever growing capacity demand is a major challenge for the realization of optical trans-mission systems. The compensation of nonlinear impairments limiting the spectral efficiency and reach of the systems is a key topic of research. The application of coherent transmission technology enables the usage of signals optimized for the nonlinear channel using a new powerful mathematical tool, the Nonlinear Fourier Transform (NFT). The propagation in an optical fiber is described by the nonlinear Schrödinger equation (NLSE). This is integrable for noise- and lossless systems. The complex eigenvalues and their spectra can carry infor-mation while the channel acts as linear phase rotation and scaling of magnitude. Since the theoretical assumption of a lossless transmission is violated the impacts of realistic conditions like limited bandwidth, loss and amplification as well as noise on the NFT solutions have to be investigated. Due to the novelty and mathematical complexity several proposals for realiza-tions exist while a holistic, feasible approach to implement an NFT based system is still miss-ing. The quality of signalgeneration, -propagation and –detection is limited by the technical realization. Aim is to investigate their influence on the propagation of the eigenvalues and to get an estimate about the robustness of the generated signals. In the nonlinear frequency regime the superposition principle is no longer valid. This encourages the development of a new spatial frequency analysis method to depict the contributions of individual eigenvalues along the fiber. These insights on the propagation of such complex, nonlinear signals together with an investigation of the impact of a variation of the nonlinear phase induced by the signal on the eigenvalues shall be used to generate optimized launch signals.The benefits of a NFT approach are obtained using a large bandwidth. Thus the impairments of the linear and nonlinear characteristics, the converter resolution and the phase noise of the optical transceivers are investigated in order to be modeled and compensated since the theoretical time functions are sensitive due to their varying bandwidth and partly high peak powers. Previous experimental implementations rely on the usage of a single laser for transmitter and receiver. Our receiver will be realized with a free running local oscillator laser for the first time. Methods of machine learning will be used in the novel receiver for phase estimation and decision Since the conventional link level control might be inappropriate for NFT transmission, a new level control approach shall be designed by extending the NLSE with respect to attenuation and enhance the perturbation analysis with an additional term. This will be verified experimentally.An increase of the spectral efficiency of NFT based systems can be realized by using a po-larization multiplex approach and an increase of the number of eigenvalues used in the ex-periments.

• DFG Programme: Research Grants