Multiplex communications – Wide area network – Packet switching
Patent
1986-08-25
1990-01-30
Griffin, Robert L.
Multiplex communications
Wide area network
Packet switching
455606, 455617, 370 3, H04B 900
Patent
active
048978302
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to optical networks comprising a plurality of transmitting and receiving terminals; cross-coupling means, the transmitting and receiving terminals being optically coupled with the cross-coupling means whereby modulated carrier signals transmitted from the transmitting terminals are fed to the receiving terminals via the cross-coupling means; selection means associated with each receiving terminal to select the modulated carrier signal to be received; and a plurality of first sources of optical signals optically coupled with the transmitting terminals to supply carrier signals to the transmitting terminals. Such optical networks are hereinafter referred to as of the kind described.
BACKGROUND AND SUMMARY OF THE INVENTION
A simple form of optical network of the kind described includes an optical source (typically a laser) and a modulator at each transmitting terminal and a second optical source together with homodyne or heterodyne detecting apparatus at each receiving terminal. The optical sources associated with the transmitting terminals each provide carrier signals with different wavelengths which are modulated by an information signal and then transmitted to the cross-coupling means. This distributes the received modulated carrier signals equally between all receiving terminals. In order to receive a transmitted signal, the optical source associated with a receiving terminal is tuned appropriately.
A practical difficulty of building a network of the kind described above is that each laser associated with a transmitter must be referenced to the other to prevent cross-talk interference. Thus, if one carrier signal laser were to drift not only would the receiving terminal have to follow it, but beyond certain limits it would cause interference with other channels. Clearly it is very difficult to reference this large number of optical sources.
In accordance with the present invention, in an optical network of the kind described, the plurality of first souces of optical signals optically coupled with the transmitting terminals are grouped together.
In this arrangement the referencing of the first optical sources is much less difficult since the sources are grouped together, preferably at a central location. Also, the terminal equipment is simplified so that only a modulator is required in the transmitting terminal. A further advantage is that the grouped components can be put on an optical integrated circuit.
Where the network is to be used solely in a broadcast configuration, the transmitting terminals may be grouped together with the first sources of optical signals. In other arrangements, however, the first sources are grouped together remotely from the transmitting and receiving terminals.
In some cases, the selection means may comprise a wavelength selector such as a grating demultiplexer thus allowing direct detection to be achieved. Conveniently, this selection means is located adjacent the grouped first sources.
In another example, the selection means comprises a plurality of second sources of optical signals grouped together remotely from and optically coupled with the receiving terminals to supply tuning signals to the receiving terminals.
In one example, respective first and second sources of optical signals are coupled with each of the receiving and transmitting terminals. In this example, each of the optical sources coupled with the receiving terminals is preferably tunable in order to select the channel which is received by the corresponding receiving terminal. This is particularly useful in the case of for example a cable TV network where a particular receiving terminal may only receive certain channels.
In another example, the network further comprises switch means for optically coupling selected ones of the first optical sources with selected transmitting terminals.
In this example, where second optical sources are provided, the switch means is conveniently adapted to optically couple selected ones of the second optical sources with selected re
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Rocks-"Optische multiplex-Systeme"-Frequenz-vol. 36, #12, Dec. 1982, Berlin (DE) pp. 319-327.
Cheng et al. "Subscriber Loop Architecture", AT&T Disclosure #75 Sep. 1984, pp. 9-10.
Brosio et al., CSELT Rapporti Tecnici-vol. VIII #4, Dec., pp. 259-261, "A low Consumption Light Powered Telephone on Optical Fiber".
Hill Godfrey R.
Smith David W.
Stanley Ian W.
Beek L. Van
British Telecommunications Public Limited Company
Griffin Robert L.
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