Field Trial of Optical Fibre Cable-TV System Optical Fibre System for ...

Wavelength Division Multiplexing for
Fibre-Optic Subscriber Lines
Anna-Karin Hansson and Sten Jacobson
As a part of the field trial with cable-TV transmission over optical fibre at
Skarpnäck near Stockholm, a demonstration equipment for subscriber line using
this medium has been developed by Ericsson. The equipment demonstrates only
one of several possible solutions for subscriber connections in future interactive
networks. The subscriber lines are arranged in a star-shaped structure around a
central program exchange and the technical solution demonstrated in the trial
employs optical wavelength division multiplex, WDM, to provide a complete
multi-service subscriber connection using only one optical fibre.
The authors describe the design of the system with emphasis on the WDM
system specially developed for this field trial.
The installation handles 30 TV channels
and 20 stereo sound channels and may
be expanded to a maximum of 10 subscribers.
None of these limitations areof
a theoretical nature, however, but only a
practical limitation of the hardware used
in the field trial.
System design
The technical solution chosen for the
system is based on pulse-frequency
modulated (PFM) optical links, threechannel
two-way WDM and a data channel
for remote control of the exchange.
UDC 535.394:621.395.4.001.55
frequency division multiplexing
optical links
cable television
testing
Fig. 1
The demonstration installation for a fibre-optic
subscriber line at Skarpnäck.
The WDM system connects the two subscribers in
the living room and the TV conference room to
the sub-centre, where an exchange for TV and
stereo programs is located. The exchange is at
the centre of the star-shaped subscriber network
The purpose of the first trial at
Skarpnäck nearStockholm is notonlyto
provide practical experience, but also to
demonstrate the possibilities offered by
fibre-optics in subscriber lines for cable-
TV, and in a broader perspective, in the
interactive broadband network of the future.
In order to provide the greatest possible
technical experience the solution
should include optical single-fibre
transmission, a star-shaped network
and a central program exchange, remotely
controlled by the subscribers.
The task of the system in the field trial,
fig. 1, is to connect two subscribers in
the building of the Telecommunications
Administration to a sub-centre ca. 1 km
away.
PFM links for TV and stereo
channels
In the field trial both TV and stereo signals are
transmitted by means of a modified standard
product. ZAV 103.
ZAV 103 transmits a video signal, together with
its accompanying audio signal, via an optical
fibre. In its basic version the link uses a spectrally
filtered LED with 890 nm wavelength as
the transmitter and an APD receiver.
The transmission distance, which is limited by
material dispersion, is 6 km with a maximum
fibre attenuation of 3 dB/km and a fibre bandwidth
of 500 MHzkm.
At maximum transmission distance the link has
the following performance data:
Video
Weighted S/N ratio
Differential gain
Differential phase
IN/OUT impedance
Video signal level peak-to-peak
>48dB