Multiplex communications – Wide area network – Packet switching
Patent
1989-02-28
1990-03-20
Griffin, Robert L.
Multiplex communications
Wide area network
Packet switching
370 1, 455607, 455612, 455605, H04B 900
Patent
active
049107267
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to optical fibre networks having at least one transmitting station and a plurality of receiving terminals connected to the transmitting station.
BACKGROUND AND SUMMARY OF THE INVENTION
In these networks it is necessary to provide additional optical power for the oscillator associated with each receiving terminal which provides the power for the mixing action in the photodiode of the receiving terminal, and which acts as the primary means of channel selection by frequency tuning in a multi-channel network. Optical power is also required for the modulator. The efficient provision of optical power is therefore a key requirement, particularly for wideband systems to which many terminals are connected. The requirements are particularly demanding in a coherent system where local oscillator power is needed and many more terminals are possible.
The most widely used method of providing optical power is to associate an individual laser with each terminal. Although technically simple, the expense of providing a laser for each terminal and the potential maintenance costs make this solution unattractive. An alternative is to site a single more powerful laser, or a bank of lasers, at a central point in the network and to distribute the optical power along the same optical fibres as the information carrying signals. Such an arrangement shares the laser power and simplifies maintenance but necessitates routing the optical power through many isolators, polarization controllers, combiners and other optical components. Together with the fibre, these introduce considerable optical loss and can absorb a significant part of the optical power.
In accordance with the present invention, an optical fibre network has at least one transmitting station and a plurality of receiving terminals connected to the transmitting station by monomode optical fibres; and one or more sources of temporally coherent optical power connected to the network to feed optical power locally to the receiving terminals, wherein the number of sources is less than the number of terminals.
This invention makes use of the important properties of monomode optical fibres which is that the losses associated with such fibres are much lower than with multimode fibres. This enables optical power to be fed locally to a number of terminals so that the optical losses involved are only those associated with the local optical fibres and not the main network. Furthermore, the number of sources is reduced from one per terminal.
In some cases, each source may comprise a plurality of subsidiary sources for supplying optical power of respectively different wavelengths; and selection means for selecting one of the subsidiary sources to be connected to the network.
This is particularly useful in wideband networks where signals with different wavelengths are passed along the network and enables the correct channel to be received by a receiving terminal.
In general, each source or subsidiary source will comprise a laser transmitter. The selection means may comprise an optical space switch.
In many networks the receiving terminals are arranged in one or more limbs of series connected groups of terminals and in this case each source of optical power may be connected to a respective one or more of the groups.
The networks may take the form of a star or tree distribution structure or a combination of both.
When the receiving terminals are connected in this way, there are a variety of methods by which the sources may be connected to the network. For example, at least one source may be associated with a respective terminal, whereby the source delivers optical power to the associated terminal and to other receiving terminals in the same group downstream of the associated terminal. Conveniently, the associated terminal is positioned at an upstream end of the limb so that all receiving terminals in the same limb are supplied with optical power from the same single source.
Preferably, a multi-port beam splitter (for example with four, six or ei
REFERENCES:
patent: 4434510 (1984-02-01), Lemelson
patent: 4530084 (1985-07-01), Strebel et al.
patent: 4601027 (1986-07-01), Scarr et al.
patent: 4635246 (1987-01-01), Taylor et al.
patent: 4686667 (1987-09-01), Ohnsorge
Brosio et al., CSELT Rapporti Technici-vol. VIII, #4, Dec. 1980, pp. 259-261, "A Low Consumption Light Powered Telephone on Optical Fiber".
A new copy of the Australian has been ordered.
Cheng et al., "Subscriber Loop Architecture", AT&T Disclosure #75, Sep. 1984, pp. 9-10.
Beek L. Van
British Telecommunications public limited company
Griffin Robert L.
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