Keywords optical communication networks, LANs
Start Date: 01-MAR-89 / Duration: 33 months
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This project has proposed coherent multichannel (CMC) techniques for the realisation of ultra-wideband optical local area networks with multigigabit-per-second overall capacity. The UCOL workplan has addressed comprehensively optical component technologies as well as networking aspects of coherent multichannel concepts (eg topologies, access protocols, network management methods).
The well known advantages of frequency division multiplexing systems and the very efficient exploitation of the huge bandwidth offered by a single mode fibre are only accessible if the formidable technical problems (eg tuneable narrow-band lasers, carrier modulation/demodulation, polarisation diversity receiver) are solved in a cost effective way and the network management tasks can be handled.
At the physical layer the UCOL system approach is based on coherent multichannel transmission over a passive star network where all signal carriers are locked to a distributed optical reference comb. This very original approach together with the proposed access protocols and network management offer :
Since the UCOL system demonstrator could not be finalised as originally planned a simplified coherent transmission link demonstrator consisting of hardware components developed by three partners has been built up. The demonstrator system includes the integration and test of very original conceptual approaches (eg a mode-locked semi-conductor laser used as optical comb generator for frequency stabilisation) and high performance subsystems (eg coherent DPSK receiver including fibre polarisation diversity hybrid). In the system the feasibility of the following have been tested:
The results of the transmission link are promising. Firstly, long term stabilisation with respect to the comb lines has been demonstrated. Secondly, the DPSK receiver has been tested by using a LiNbO phase modulator. This receiver consists of a fibre based hybrid, two low noise preamplifiers, and a DPSK demodulator. The receiver sensitivity has been determined to -57.5 dBm. The third aspect concerns active phase modulation, of which the feasibility has also been demonstrated. Active phase modulation introduces a penalty of 2.9 dB compared to passive modulation. This penalty must be ascribed to spurious intensity modulation, and possible to non-perfect modulation response. The optical amplification process provides however a possible system expansion increase of 12 dB. This improved power budget can be increased even further, if better amplifiers are used. It is expected that by tuning the laser wavelength relative to the gain ripple, the penalty of intensity modulation can be decreased. Moreover, the intensity modulation penalty can almost completely be avoided, if two-section amplifiers are being used. In such a system, an increase of more than 15 dB in power budget is feasible.
The UCOL project was stopped before the essential phase of system demonstrator integration and multichannel network management tests was reached. However, the spin-off of some component work (eg fibre laser, fibre amplifier, optical filter, mode-locked laser) reaches far beyond the UCOL project and can certainly be used as promising basis for future R&D projects.
Furthermore, within this project essential parts of basic investigations on Erbium-Doped Fibre Amplifiers (EDFAs) have been supported as necessary precondition for a product development. UCOL was one of the first CEC projects to support the important and rapidly evolving EDFA technology, promoting the position of European industry versus strong Japanese and US competitors. The rapid realisation of an early EDFA product version for analogue CATV distribution and the ambitious plan of the German DBP-Telekom to deploy extensively Fibre-in-the-loop (FITL) systems in the new Bundesländer starting in 1993, form an excellent precondition and unique chance for a successful market exploitation of this advanced EDFA product version.
Mrs Daniela De Angeli
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ALCATEL FACE RESEARCH CENTRE - I - C
DAIMLER-BENZ RESEARCH - D - P
UNIVERSITY OF SOUTHAMPTON - UK - P
INESC - P - P
IDATE - F - P
ALCATEL ALSTHOM RECHERCHE - F - P
SEL ALCATEL RESEARCH CENTRE - D - P
TELETTRA ESPAÑA - E - P
PTT RESEARCH - NL - P
COSI - I - P
STC PLC - UK - A
UCOL-2 - 2054, December 1993
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html version of synopsis by Nick Cook