RESEARCH Optical Communication Theory & Techniques

Area Leader Prof. Enrico Forestieri

The research in the area of Optical Communication Theory and Tech¬niques is mainly focused on the analysis of optical systems from a communication theory point of view, devising novel solutions and investigating their performance.

Whenever possible, we seek to analytically establish the system performance and the impact of the various impairments. As this is not always possible, advanced simulation techniques are used as a complementary tool and also for validating analytical findings and approximations. We look for novel modulation/transport formats and equalization techniques for increasing the bit-rate, achievable distance and robustness to impairments.

Current research activities include devising countermeasures for nonlinear effects in fiber optic systems, transmission over multimode fiber links, and analysis of system solutions for upgrading existing long-haul links to 100 Gb/s. In order to account for the impact of nonlinear effects, some effective analytical techniques, allowing for fast performance evaluation, have been proposed, and a nonlinear equalizer for coherent optical systems has been devised.

The upgrade to 10 Gb/s of installed multimode fiber links in local area networks is hampered by the impact of the modal dispersion, so electronic equalization and coding techniques for mitigating the arising intersymbol interference are currently under investigation. New challenges are also posed by the upgrade to 100 Gb/s of long-haul links based on singlemode fibers. In this case, conventional direct detection systems are not suitable and new solutions have to be pursued. Next generation systems will be either multiple or single channel based, but, most probably, coherent detection and electronic equalization will be adopted in either case. Multiple channel systems based on subcarrier modulation have the disadvantage of requiring more bandwidth with respect to single channel ones, unless orthogonal frequency division multiplexing is used. On the other hand, multiple channel systems require less stringent requirements on the electronics speed, unless some parallelization techniques are also used in the single channel case. Currently, we are performing feasibility studies aimed at determining the most suitable transport format under the constraints imposed by current technology.