Abstract of IMPRS project(s)

All-optical signal processing for advanced communication systems

Optical transmission systems are the basis for the world-wide communication network of our modern information society. During decades a steadily growing demand for transmission capacity internet based services are still the driving force of their further development. The ever increasing requirements in transmission speed and reach, flexibility and robustness require a fast transition of results from research to market and motivate research activities also in the field of optical signal processing for communication systems.

Future system generations are supposed to use advanced multilevel modulation formats in combination with polarisation- and wavelength-division multiplexing to achieve very high spectral efficiency, as well as multi-core fibres and space-division multiplexing for further increase of transmission capacity. Optical signal handling, conditioning and regeneration will come more and more into the focus. Common opto-electro-optical signal processing will be very complex because of the limited speed of the electronic components and is accordingly, bulky and highly power consuming. In contrast to that, all-optical signal processing has the potential to process ultra high bitrate signals due to its extremely large bandwidth, to manipulate many channels simultaneously, and to be much more power efficient.

While the high bandwidth has already been demonstrated many times, simultaneous channel processing and low power consumption are still under investigation. Processing of signals with advanced modulation formats is also rather new. While functions such as switching and routing, wavelength conversion, time-domain multiplexing and demultiplexing are often modulation format transparent, signal regeneration is much more involved and has so far been extensively studied mainly for binary modulation formats only.

Regeneration of advanced signals with simultaneous multilevel modulation of lightwave amplitude and phase is a completely new field with only a few pioneering publications. Completely new principles are to be developed for this application. Most perspective designs are based on interferometer schemes and optical parametric processes. The first ones have intrinsic periodicity because of the periodicity of the interference conditions. The second type of design uses phase-sensitive amplifiers necessary for signal phase regeneration. In order to be compact and power efficient, photonic integrated circuits with highly nonlinear elements are to be used, whereas basic principles, new designs and proof-of-concept experiments are possible with already available components.

Another very important, fundamental physical problem is the simultaneous regeneration of multiwavelength signals. Just a few all-optical realisations have already been proposed. Most of them are processing only a limited number of channels and are not suitable for advanced multilevel modulation formats. There is no ready-for-use solution yet but attention has to be paid to the suppression of the nonlinear channel cross-talk using either materials with inhomogeneous broadening of nonlinearity, such as quantum dots, microspheres and microrings or space-division demultiplexing in cavities and waveguide lattices.

The OCOM group has expertise in the field of phase-preserving amplitude regeneration using fiber nonlinearity and parametric amplification. Recent results on regeneration of multilevel signals are very promising. Future research will focus on specific all-optical signal processing topics for next generation optical communication systems.

Publications J. Wen, P. Banzer, A. Kriesch, D. Ploss, B. Schmauss, U. Peschel, Experimental cross-polarization detection of coupling far-field light to highly confined plasmonic gap modes via nanoantennas, Appl. Phys. Lett., 98, 101109, (2011)

J. Wen, A. Kriesch, D. Ploss, P. Banzer, B. Schmauss, U. Peschel, Investigating plasmonic gap modes coupled to nanoantennas, European Quantum Electronics and Laser Science Conference, (Optical Society of America), , , (2011)

J. Wen, P. Banzer, D. Ploss, A. Kriesch, B. Schmauss, U. Peschel, Excitation of gap plasmonic waveguides by nano antennas, Quantum Electronics and Laser Science Conference, OSA Technical Digest (CD) (Optical Society of America), paper QMF1, , , (2010)