OTDM/WDM systems

The goal of this project is to investigate the possibility of merging two existing techniques, Optical Time Division Multiplexing (OTDM) and Wavelength Division Multiplexing (WDM), into one network, hereby increasing the transmission capacity.
In the European ACTS-project HIGHWAY techniques for Time Division Multiplexing were demonstrated for a single channel. The base rate was 10 Gbit/s and the aggregated bit-rate was 40 Gbit/s. The final demonstrator at COM demonstrated that the techniques developed in HIGHWAY could be applied to four wavelength channels, hereby increasing the capacity from 40 Gbit/s to 160 Gbit/s. Furthermore, it has been demonstrated that some of the components developed within the project could be operated at 80 Gbit/s. Consequently, the project has provided techniques that are well suited for upgrading to an OTDM/WDM system.
Merging of the two techniques is an on-going discussion, however, a very likely scenario is WDM-islands connected with high-speed OTDM-trunk lines. An important issue for this topology is the development of interfaces between a single OTDM high-speed channel and several WDM channels at lower bit rates. This has been achieved at COM using novel technique based on bi-directional Four Wave Mixing in a Semiconductor Optical Amplifier (SOA).
A recent activity is also the use NOLMs (Non-linear Optical Loop Mirrors) for high-speed optical communication. We have demonstrated 8x40 Gbit/s transmission over 55 km standard single mode fiber using a new RZ source based on a NOLM.