Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-02-10
2001-03-20
Chan, Jason (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C370S222000
Reexamination Certificate
active
06204943
ABSTRACT:
DESCRIPTION
1. Technical Field
This invention relates to a reconfigurable transmission network for semi-permanent or, more generally, temporary links.
It is particularly applicable to optical telecommunications.
2. State of Prior Art
Known networks that make temporary links between two users are based on a star architecture and multiplexing in wave length.
The resources of a network of this type are pooled by an optical coupler.
Each station in the network is equipped with a matchable optical filter that selects the wave length used as a support to transmit the information.
With commercially available components, the filter has to be locked onto the working wave length in order to provide stable operation.
In this respect, refer to document (1) which is mentioned in the references at the end of this description, like the other documents mentioned later.
A data network superposed on the star network manages the network and initiates communication.
The disadvantage of this type of star network is due to the lack of security means if there is a simple failure of an optical fiber.
Two optical fibers transmit information between the optical coupler which can be single or multiple, and a station.
If a fiber is interrupted, the station will then be isolated from the rest of the network.
Document (2) also describes a passive star architecture.
Known rings designed for transmission called Synchronous Digital Hierarchy or SDH comprise two optical fibers which go in opposite propagation directions and are capable of transmitting information even if the cable is broken.
Document (3) provides further information on this subject.
Known reconfigurable architectures are based on spectral routing and the use of matchable optical filters.
Document (4) provides further information on this subject.
Two filter categories are currently available.
The first category comprises Fabry-Perot fiber filters made using micro-optic techniques.
Several products of this type are commercially available.
The corresponding insertion losses are about 2 dB and the fineness is between 100 and 200.
However, these fiber Fabry-Perot filters are components with two channels that are only capable of selecting one out of several wave lengths.
The add-drop function is obtain using an optical coupler.
The second category consists of the acousto-optical modulator made in integrated optics on LiNbO
3
.
This modulator performs the add-drop function directly and its matchability range is about 100 nm.
It also has the advantage that it enables multiple channel selection.
It has been designed for transmission with a distance between channels of 4 nm.
Document (5) provides further information on this subject.
Modulators of this type are still at the laboratory stage and they have the disadvantage of a high level of cross talk (from 15 to 18 dB) which limits their application to long distances between channels (greater than 4 nm) and makes reuse of wave lengths critical.
These modulators have a high temperature coefficient (of the order of 0.1 nm/° C.) and consequently a stable temperature is necessary for stable operation.
Finally with the two filter categories considered, a servocontrol has to be used to lock a station onto the chosen wave length, in addition to the control which selects this wave length.
DISCLOSURE OF THE INVENTION
The purpose of this invention is to overcome the previous disadvantages related to the use of matchable filters.
In order to do this, the invention uses spectral routing on a ring network with fixed optical filters and optical switches designed to set up links between network stations or users.
Specifically, the purpose of the invention is a reconfigurable transmission network for connection of users, this network comprising at least one information transmission ring in optical form and network management means, each ring comprising:
several nodes, each node being associated with a site on which there is at least one user, and
at least one optical fiber in the form of a ring that passes through each node in turn and which is designed to carry information in a given direction,
this network being characterized in that it also comprises:
on each site, transmission-reception means for one or more particular wave lengths, and
at each node, optical add-drop means for the particular wave length and optical switching means that are capable of being in first and second states, are controlled by the network management means and are capable of optically connecting the transmission-reception means included on the corresponding site, to the add-drop means when they are in the first state, and optically isolating the transmission-reception means from the add-drop means when they are in the second state, these add-drop means being designed to extract information at the particular wave length from each optical fiber in the ring, to send them to the transmission-reception means on the corresponding site and to insert information at the particular wave length from these transmission-reception means in each optical fiber in the ring,
in order to create temporary optical links for the particular wave length under the control of the management means, between users on distinct sites, for two users at a time.
According to a preferred embodiment of the network according to the invention, each node comprises an electronic add-drop multiplexer that is designed to exchange information in optical form with the corresponding site and which is used by management means to control optical switching means at this node.
According to a first specific embodiment of the network according to the invention, the ring is connected to a main information transmission network, at least one electronic add-drop multiplexer being installed on this main information transmission network, fitted with transmission-reception means for a particular wave length and connected to the ring by add-drop means for the particular wave length.
According to a second particular embodiment, the network comprises several rings connected to a main information transmission network, several electronic add-drop multiplexers being installed on this main information transmission network each associated with rings, each electronic add-drop multiplexer being equipped with transmission-reception means for the particular wave length and connected to the corresponding ring by add-drop means for the particular wave length.
At least one site may comprise N users associated with N transmission-reception means on this site, where N is an integer number equal to at least 2, the node corresponding to this site also comprising N optical switches of the 1 to N type which are controlled by network management means so as to create an optical link for the particular wave length between any of the users on this site and a user on another site.
Preferably, the network comprises two optical fibers in the form of a ring, designed to carry information in opposite directions.
The optical switching means that may be in the first or second state may be cross-bar type switches.
For example, the information in the optical form has a wave length equal to 1.3 &mgr;m and the particular wave length is equal to 1.5 &mgr;m.
Each site may comprise transmission-reception means for several particular wave lengths, associated respectively with several optical add-drop means for these particular wave lengths, in order to simultaneously set up several temporary optical links.
Each ring is preferably designed to use the Synchronous Digital Hierarchy standard.
REFERENCES:
patent: 5550818 (1996-08-01), Brackett et al.
patent: 5576875 (1996-11-01), Chawki et al.
patent: 5930016 (1999-07-01), Brorson et al.
patent: 0 743 772 A1 (1996-11-01), None
U.S. application No. 08/643,459, filed May 8, 1996.
U.S. application No. 08/802,483, filed Feb. 20, 1997.
Wagner S S Et Al: “Multiwavelength Ring Newworks for Switch Consolidation and Interconnection”, Discovering a New World of Communications, Chicago, Jun. 14-18, 1992 Bound Together With B0190710, vol. 4, vol. 3 of 4, Jun. 14, 1992, Institute of Electrical and Elect
Hamel Andre
Laville Daniel
Stoschek Jean
Chan Jason
France Telecom
Pearne & Gordon LLP
Sedighian M. R.
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