Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-08-19
2003-03-11
Wu, Daniel J. (Department: 2632)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06532089
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an optical cross-connect for setting and switching over a route of photo signals by use of an optical switch, and a method of switching over the optical path by use of this optical cross-connect. The present invention relates more particularly to an optical cross-connect and a using method thereof, which are capable of confirming a connectivity of the route concerned when switching over the route of the photo signals. The present invention also relates to an optical ADM (Add/Drop Multiplexer) using the optical cross-connect, and to an optical cross-connect network system.
2. Description of the Related Art
In recent years, an optical ADM (Add/Drop Multiplexer) using an optical switch and an optical cross-connect network system are combined with a wavelength division multiplexing (WDM) technology, and are thereby capable of processing a large capacity of signals. Besides, the large capacity of signals can be switched over by the optical switch, and hence setting of a signal route (path) can be facilitated. This being the case, a variety of studies and developments of the optical cross-connect network system have been made.
A technical emphasis of the optical cross-connect network system has been so far placed on a point of how much efficiently a node-to-node signal route can be set and functions such as a protection can be actualized. On the occasion of structuring the optical cross-connect network system described above, however, an operation in the case of switching over the route of the photo signals, especially the operation in case a system failure and mis-setting happen, are not necessarily objects to be examined.
A literature cited showing the construction of this type of optical cross-connect described above may be exemplified such as, e.g., Chungpeng Fan, “Examining an integrated solution to optical transport networking.”, Wavelength Division Multiplexing: (The first ever European meeting place for WDM Systems, Network, Marketing & Engineering Professionals), November 1997, London; reference pages: pp. 18-23, Satoru Okamoto et al., “Optical path cross-connect node architectures for photonic transport network.”, Journal of Lightwave Technology, Vol. 14, No. 6, June 1996, pp. 1410-1422,
FIGS. 4
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12
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In the conventional optical cross-connect, however, if the mis-setting is done in the optical switch, the mis-setting can be corrected for the time being. However, a given period of time is needed till the mis-setting is corrected since there was received an alarm that a desired service signal is cut off, resulting in such a problem that the service signal
1
is temporarily cut off. In the case of switching over the optical path for the photo signals, it is of much importance to confirm beforehand a connectivity of the optical path. Nevertheless, there has been no example in which that was recognized as a subject and specifically examined.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide an optical cross-connect capable of enhancing a reliability on an optical transmission system using an optical switch by making it feasible to confirm a connectivity before switching over an optical path.
To accomplish the above object, according to a first aspect of the present invention, an optical cross-connect comprises at least two photo signal input terminals for respectively inputting photo signals, at least two photo signal output terminals for respectively outputting the photo signals, and an optical switch for switching over an optical path between the photo signal input terminal and the photo signal output terminal. The optical switch incorporates a bridge connecting function of, if the optical path is switched over to a switchover target photo signal output terminal to which an optical path is newly connected from a pre-switchover photo signal output terminal through which the photo signal input terminal and the optical path are connected before the switchover, temporarily connecting the optical path to both of the pre-switchover photo signal output terminal and the switchover target photo signal output terminal.
The optical cross-connect of the present invention further comprises a second monitor circuit, disposed between the optical switch and the photo signal output unit, for monitoring a state of the output photo signal outputted from the optical switch. The optical cross-connect still further comprises a first monitor circuit, disposed between the optical switch and the photo signal input terminal, for monitoring a state of the input photo signal inputted to the optical switch.
A contrivance of the optical cross-connect according to the present invention is, in the case of switching over the optical path between the I/O terminals of the photo signals, not that the optical path is not switched over at one time but that there is performed a bridge connection of temporarily connecting the optical path to both of the pre-switchover photo signal output terminal and the switchover target photo signal output terminal. The monitor circuits for monitoring a state of the photo signals are disposed anterior and posterior to the input terminal and the output terminal of the optical switch, and are capable of monitoring the connectivity of the optical switch by comparing the states of the photo signals before and after the switching over the optical path with each other, especially the state of the photo signal outputted to the output terminal of the switch over target output terminal with the state of the photo signal before inputting to the optical switch.
In particular, with the connectivity monitor circuit being provided, it is feasible to monitor the connectivity of the optical switch from the connectivity information contained in the output photo signal and the input photo signal. The connectivity monitor circuit, if the connectivity information satisfies a predetermined fiducial quality of signal, outputs a control signal to a control circuit so that the optical switch executes a complete switchover from the pre-switchover photo signal output terminal to the switchover target photo signal output terminal.
Herein, the optical cross-connect of the present invention further comprises a photo signal cut-off unit, disposed between the photo signal input terminal and the optical switch, for cutting off the photo signal inputted to the optical switch from the photo signal input terminal. With this arrangement, other signals are inhibited from being inputted to the same optical path during the bridge connection. The control circuit controls the photo signal cut-off unit to cut off the photo signal inputted to the photo signal cut-off unit corresponding to the photo signal input terminal connected to the switchover target photo signal output terminal before switching over the optical path. Note that the connectivity information may be either an optical level of each of the input photo signal and the output photo signal or header information added to the input photo signal and to the output photo signal.
A wave-guide type optical switch can be applied as the optical switch incorporating the bridge connecting function used for the optical cross-connect of the present invention. A wave-guide type optical switch with a substrate composed of lithium niobate may be exemplified as the wave-guide type optical switch.
The optical cross-connect of the present invention may take such a configuration that the first monitor circuit includes a first optical splitter for splitting a part of the input photo signal and outputting the split input photo signal, and a light receiving element for monitoring the split input photo signal. The optical cross-connect may also take such a configuration that the first monitor circuit includes an optical level monitor circuit for monitoring an optical level of the input photo signal, a photoelectric converter for converting the input photo signal into an electric signal, and an electro-optic converter for converting the electric signal
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