Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Patent
1997-05-07
1999-11-09
Chan, Jason
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
359128, 359139, 359165, H04B 1020, H04J 1408
Patent
active
059825162
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to optical networks, and especially, although not exclusively, to telecommunications, data communication, networks and optical computing systems.
BACKGROUND OF THE INVENTION
In certain optical networks, such as passive optical networks, signals are sent along optical fibres which may, for example, include a 3 dB coupler at a node in the network so that the signals are transmitted over the entire network. In many cases, however, it would be desirable for optical signals to be routed along the network, for example in order to improve security of the system to unauthorised access to data. In electric networks, data routing typically involves reading the address of the data into a computer at a node of the network and determining the path of the data in accordance with the data address. Such a system has the disadvantage that the rate at which data can be sent along the network is limited by the speed at which the computer can perform the necessary reading and comparison operations. Even in optical networks that involve routing, the switching operates in the same manner as in electrical networks, with the result that the data rate is still limited by the computer speed. For example an optical switching matrix is described in EP-A-0 497 667 and by Jacob & Gabriagues, Communication et Transmission, Vol. 16, No. 2, 1994 pp. 5-14, in which incoming optical signals contain routing tags that are read and processed by a computer in order to assign carrier wavelengths to the signals that correspond to the signal destinations. The signals, modulated to different wavelengths corresponding to their destinations, are then sent to a space switching stage, and the signals leaving the space switching stage are filtered by optical bandpass filters in each output line to allow only those signals with the appropriate carrier wavelengths to pass.
BRIEF SUMMARY OF THE INVENTION
According to the present invention, there is provided an optical network in which data signals are transmitted along an optical line and are encoded with a wavelength corresponding to the address of the signals, and which includes, at at least one point on the optical line, a data routing switch, characterised in that the data routing switch comprises: associated therewith a characteristic wavelength so that it will send the data signal along the gate enabling line or not in accordance with the relationship between the data signal encoding wavelength and the characteristic wavelength of the comparator; and passage of the data signal along the optical line in response to the presence or absence of the data signal in the gate enabling line.
Preferably, the network includes a plurality of data routing switches, each of which may have a different characteristic wavelength from the or each other data routing switch. Thus, for example, a data routing switch may be incorporated in each arm of a branch in the network downstream of the branch so that passage of data through the branch is determined by which switch characteristic wavelength matches the data encoding wavelength.
The network according to the invention has the advantage that the comparison of the data address at the nodes in the network is a passive process and occurs effectively instantaneously, with the result that the comparison can be performed significantly faster than routing techniques employing computer data processing techniques. Thus, for example, data may pass through a data routing switch with a speed that is limited only by the speed of the gate (typically about 1 ps), whereas a period of about 10 ps would be required in a conventional routing arrangement.
The term "address" as used herein is not, in its broadest sense, limited to a single user terminal of the system, but may include a significant region of the network. Thus, it would be possible for the network to contain only two addresses, one for high security data which could only be received at one part of the network, and another for low security data which could be received at ot
REFERENCES:
patent: 4894818 (1990-01-01), Fujioka et al.
patent: 5541756 (1996-07-01), Chang-Hasnain et al.
patent: 5608825 (1997-03-01), Ip
Haigh Neil Richard
Murphy Michael Matthew
BICC Public Limited Company
Chan Jason
Nath Gary M.
Sedighian Mohammad
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