Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Patent
1989-07-05
1992-09-01
Coles, Sr., Edward L.
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
359128, H04J 1400
Patent
active
051444658
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a switched optical network for connecting signals from any one of a plurality of transmitter stations with any one of a plurality of receiver stations. It is of particular, but not exclusive, application to telecommunications networks.
BACKGROUND AND SUMMARY OF THE INVENTION
It is generally desirable to have a switched network which is non-blocking for connecting transmitter stations with receiver stations, that is, one in which any transmitter station can be connected to any free receiver station at any time.
A space switching circuit employing a single stage of crosspoints requires a number of switches equal to the product of the number of transmitter stations, T, and receiver stations, R. This arrangement becomes increasingly impracticable as the number of stations increases because of the need to incorporate a rapidly increasing number of switches. One approach to solving this problem is to use a multistage switching network which can be made non-blocking for a given number of stations by means of specific interconnections. Although this approach reduces the number of switches needed from the T and R product, disadvantages of this approach are that it is not easily expandable and the control system needed to control the switches is increasingly complex. As a second approach, if only a few extra stations are to be added to such a network, a number of additional switches can be added and kept to a minimum only at the expense of redesigning and reconfiguring the interconnections between switches. If this latter approach is to be avoided the existing stages of the multistage circuit must essentially be duplicated, thus requiring some design for add-on stages, which while reducing the redesign necessary, has more switching capacity than may be required.
Another method of providing a non-blocking switched network is to multiplex the signals from the transmitter stations and broadcast the multiplexed signals to the receiver stations and demultiplex the required channel. Various multiplexing schemes have been employed, for example pulse position coding, time domain multiplexing and frequency or wavelength multiplexing. Wavelength multiplexing in optical networks has been recognized as providing, in principle, the means of multiplexing many thousands of optical signals but in practice there are severe obstacles to be overcome in providing an optical network employing a multiplexing of such a large number of frequencies. In an optical fibre network the wavelengths need to be closely spaced to fall within the useable wavelength window of the fibre and the optical sources of the many wavelengths have to be extremely accurately tuned. Similarly the optical detectors of the receivers need to be very accurately tunable to receive only one wavelength with minimum crosstalk from adjacent wavelengths.
It is an object of the present invention to provide a switched optical network which can handle large numbers of signal channels more readily than hitherto possible. It is a further object of the present invention to provide a switched optical network that can be readily expanded to accomodate a relative few extra stations. Accordingly there is provided a switched optical network for connecting signals from any one of a plurality of transmitter stations with any one of a plurality of receiver stations comprising:
at least two optical multiplexing means each responsive to signals from two or more transmitter stations to provide optical multiplexing corresponding to the transmitter station signals;
a plurality of demultiplexing means each responsive to optical multiplexing and a selection signal to output one transmitter station signal to the corresponding receiver station; and
an optical switch means responsive to switch signals to optically couple any one of the optical multiplexers to any one of the demultiplexing means.
The signal from each transmitter station is converted into an optical signal forming part of one of the optical multiplexers coupled to the optical swi
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British Telecommunications public limited company
Coles Sr. Edward L.
Negash Kinfe-Michael
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