Klaus Oestreich

Detection and Decoding for Optical Communication Systems

Today the core networks for the internet mainly consist of fiber optical cables as they enable large information throughputs. To cope with the ever increasing data traffic in the internet optical communication systems with high bit rates are required. These high bit-rate transmission systems are affected by signal distortions like chromatic dispersion (CD), polarisation mode dispersion (PMD) and noise. In order to detect the transmitted information correctly, powerful receivers are necessary.

A promising solution is a combined approach of equalization and decoding, known as Turbo equalization. Presently installed optical systems are almost exclusively based on intensity modulation on the transmitter side and direct detection at the receiver. For such an optical link operating at a bit rate of 10 Gbit/s, the performance of turbo equalization have been investigated at our institute. A Turbo equalizer with a low-density parity-check (LDPC) code for forward error correction with high performance was found.

In order to further increase the performance of optical communication systems multilevel modulation formats with coherent detection appears as a key enabler. For today's envisaged 100-Gbit/s transmission systems coherent detection with polarization division multiplexing combined with a higher-order modulation appears as a promising solution. Polarization division multiplex doubles the data rate without need for additional optical bandwidth as two orthogonally polarized signals are transmitted. In order to cope with CD, PMD, noise and other distortions, powerful detection and decoding schemes for such a system has to be found.