Add/drop multiplexer node

Details Add/drop multiplexer node Add/drop multiplexer node

1999-02-10

2000-10-17

Negash, Kinfe-Michael

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

359128, 385 17, H04J 1402

Patent

active

061340367

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/SE96/00813 filed Jun. 20, 1996.


TECHNICAL FIELD

The present invention relates to a method of adding and dropping optical channels to and from a line terminal that is connected to an optical add/drop multiplexer node, an optical add/drop multiplexer node as well as to an optical network comprising at least one such optical add/drop multiplexer node.


STATE OF THE ART

There exist within the art nodes for the selective adding and dropping of a predetermined number of multiplexed channels from and to a line terminal, which is associated with the node. However, none of the existing nodes are completely optical, but have all, in case optical signal transmission lines are used, electrical/optical and optical/electrical interfaces. The adding and dropping of channels in these nodes takes place in the electrical part of the node. This naturally imposes a restraint on the speed with which signals can be transferred in such a system and on the compatibility of different transmission devices supporting different transfer modes within the same network structure. There therefore exists a need for such a node that selectively adds and drops a predetermined number of multiplexed channels optically.
There do exist nodes that have adding and dropping devices that are completely optical. These devices do however have a few limitations. One such device, which is called a SONET ADM (Add/Drop Mulitiplexer), can only add and drop one specific channel. If several channels are to be dropped, multiplexers and demultiplexers as well as several such SONET ADMs have to be added to the node, which is a complicated way of performing selective adding and dropping of a predetermined number of channels.
Another problem with such nodes is that if several nodes are coupled together in cascade, the spontaneous emission from optical amplifiers that are required in each node tends to get high and become a serious problem. This is especially the case if the network is in the form of a ring.
In the article "Multiwavelength Survivable Ring Network Architectures" of A. F. Elrefaie in Proceedings of ICC'93, February 1993, pp 1245-1251, there is described SONET ADMs and the article further suggests that an acousto-optical tunable filter can be used for the adding and dropping of optical wavelength division multiplexed (WDM) channels. No real node structure is however described. This article also suggests the use of a grating based device for said dropping and adding of channels. In case the grating based device is used, multiplexers and demultiplexers are required to effect the dropping and adding effect. The acousto-optical filter requires an optical splitter at its input and an optical combiner at its output in order to selectively drop and add a predetermined number of channels, which two latter components are not described in the article. A node with such a structure would have a receiver connected to the splitter and a transmitter to the combiner. This combination of devices rejects the noise caused by spontaneous emission from optical amplifiers in the network. It does however have a few drawbacks. One drawback is that the filtering function is not very selective so that about half the input power is filtered away. Another problem with this arrangement is that it has a relatively high level of crosstalk. Yet another problem is the polarization mode dispersion effect, which imposes a restraint on a network using this arrangement. Because of this effect a channel that is added to the network at one node cannot be transported to node that is located more than three nodes away from said one.


SUMMARY OF THE INVENTION

The present invention solves the problem of selectively adding and dropping, in a node, a predetermined number of channels from and to a line terminal that is associated with the node without the use of multiplexers, demultiplexers or additional optical combiners and splitters.
According to the invention this problem is solved through the use of a channel-selective switch in an optical add/drop m

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patent: 5959749 (1999-09-01), Danagher et al.
Huang et al., "A WDMA Ring Network With Holographic Wavelength-Selective Partial Demultiplexes" 1993 Canadian Conference on Electrical and Computer Engineering, II(36-77):1119-1121, (1993).
Wakabayashi et al., "A synchronous DS3 Add/Drop Multiplexer with Cross-Connect" IEEE Global Telecommunications Conference, pp. 1195-1199 (1986).
Fujimoto et al., "Broadband Subscriber Loop System Using Multi-Gigabit Intelligent Optical Shuttle Nodes" IEEE Global Telecommunications Conference, 3:1449-1454 (1987).
Wehrmann et al., "Fully Packaged, Integrated Optical, Acoustically Tunable Add/Drop Multiplexers in LiNbO.sub.3 ", Proceedings 7.sup.th European Conference on Integrated Optics, pp. 487-490 (1995).
Elrefaie, "Multiwavelength Survivable Ring Network Architectures", ICC, pp. 1245-1251 (1993).

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