Optical waveguides – With optical coupler – Plural
Reexamination Certificate
2001-11-27
2004-08-24
Sanghavi, Hemang (Department: 2874)
Optical waveguides
With optical coupler
Plural
C385S037000, C398S082000, C398S083000, C398S084000, C398S085000, C398S087000
Reexamination Certificate
active
06782156
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based on French Patent Application No. 00 15 887 filed Dec. 7, 2000, the disclosure of which is hereby incorporated by reference thereto in its entirety, and the priority of which is hereby claimed under 35 U.S.C. §119.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to wavelength division multiplex fiber optic transmission systems and more precisely to cross-connecting or switching wavelengths in them.
2. Description of the Prior Art
The context of the present invention is that of optical switches, or cross-connect units, having a multigranularity architecture. The granularity concept reflects the data transmission capacity of the optical network. To switch the total traffic at the level of a switch, this type of architecture therefore takes account of different data transmission capacity levels. For example, one portion of the total traffic may be switched at the fiber level, which corresponds to a high level of granularity, another portion may be switched at the band of wavelengths level, which corresponds to an intermediate level of granularity, and a final portion may be switched at the wavelength level, which corresponds to a low level of granularity. Supplementary levels of granularity can also be taken into account.
Transmission capacity in fiber optic systems is increasing all the time, because the number of channels transmitted by wavelength division multiplexing in each fiber is increasing and the number of fibers per cable is increasing. This gives rise to the problem of routing and cross-connecting channels in switching devices and, to be more specific, the problem of the complexity of switching devices liable to be required to route an increasing number of channels.
K. Harada et al, “Hierarchical optical path cross-connect systems for large scale WDM networks”, proposes an optical cross-connection architecture corresponding to a hierarchical optical path structure with two layers. The paper proposes grouping adjacent wavelengths to form bands and switching the bands. This solution limits the number of wavelength converters used in each optical cross-connect unit.
FIG. 1
shows the principle of demultiplexing adjacent bands.
In the
FIG. 1
example, the fiber consists of 12 channels or wavelengths &lgr;
1
to &lgr;
12
. Each band consists of four adjacent channels. The fiber is therefore demultiplexed into three bands each of four adjacent channels by means of a fiber to band demultiplexer Demux F→B. Each band is then demultiplexed into wavelengths by means of a band to wavelength demultiplexer Demux′ B→W. A band switch BXC is disposed between the band stage and the wavelength stage, immediately ahead of the band to wavelength demultiplexers Demux′ B→W.
In the
FIG. 1
example, the signal from the fiber is therefore filtered to separate the adjacent bands.
Accordingly, the demultiplexer Demux F→B used for fiber to band demultiplexing is an adjacent band demultiplexer. This kind of multiplexer uses filtering with a wide pass band and the transfer function FTb shown diagrammatically in FIG.
1
. The filtering applied by the adjacent band demultiplexer Demux F→B isolates all of the channels of the same band. A first band therefore consists of four adjacent wavelengths &lgr;
1
to &lgr;
4
, a second band consists of adjacent wavelengths &lgr;
5
to &lgr;
8
, and a third band consists of adjacent wavelengths &lgr;
9
to &lgr;
12
.
For band to wavelength demultiplexing, each band, after routing in the band switch BXC, is demultiplexed into four channels via the band to wavelength demultiplexer Demux′ B→W. Each demultiplexer Demux′ B→W used is a 1-to-4 deinterleaving demultiplexer. This kind of deinterleaving demultiplexer uses periodic filtering whose transfer function FTc′ is shown diagrammatically in
FIG. 1
, based on Mach-Zehnder filters or on array waveguide gratings (AWG). The channel filtering applied by the deinterleaving demultiplexer Demux′ B→W is therefore periodic filtering to isolate one channel in the band.
Accordingly, to obtain the wavelengths, it is necessary to use deinterleaving demultiplexers, i.e. demultiplexers in which filtering is effected by periodic filters of the type described above.
In the case of multigranularity optical cross-connection architectures, because of the presence of switching stages such as the band switch BXC, it is not possible to know a priori the adjacent band that will be demultiplexed at the input of each band to wavelength demultiplexer. A deinterleaving demultiplexer, in which the filtering is periodic, takes account of all the adjacent bands. This kind of demultiplexer does not depend on the band at the input. Thus all wavelengths can be demultiplexed.
Another way to cross-connect wavelengths in wavelength division multiplex fiber optic transmission systems is to define interleaved bands rather than adjacent bands. The French patent document whose title in translation is “AN INTERLEAVED BAND OPTICAL CROSS-CONNECTION SYSTEM” therefore proposes, for cross-connecting optical transmission channels, grouping the various channels or the various wavelengths into interleaved bands. In this case, the bands are formed of wavelengths or channels that are not adjacent.
FIG. 2
shows the principle of demultiplexing when interleaved bands are used. The fiber consists of 12 wavelengths &lgr;
1
to &lgr;
12
. Three bands each of four channels are obtained by means of a fiber to band demultiplexer Demux′ F→B.
Thus the fiber is demultiplexed into three bands which are interleaved, i.e. one channel of one band is adjacent channels of other bands. Accordingly, a first band consists of the wavelengths &lgr;
1
, &lgr;
4
, &lgr;
7
and &lgr;
10
, a second band consists of the wavelengths &lgr;
2
, &lgr;
5
, &lgr;
8
and &lgr;
11
, and, finally, a third band consists of the wavelengths &lgr;
3
, &lgr;
6
, &lgr;
9
and &lgr;
12
. The channels of the same band are separated by a constant spectral gap.
Each band is then demultiplexed into wavelengths by means of a band to wavelength demultiplexer Demux BOW. Before being demultiplexed, the bands are switched in a band switch BXC.
For the fiber to band demultiplexing, the fiber is demultiplexed into three interleaved bands by the fiber to band demultiplexer Demux′ F→B. The demultiplexer Demux′ F→B used is a 1-to-3 deinterleaving demultiplexer. This kind of demultiplexer uses periodic filtering, based on Mach-Zehnder filters or array waveguide gratings, whose transfer function FTb′ is shown diagrammatically in FIG.
2
and which isolates all the channels of the same band.
For band to wavelength demultiplexing, each band of wavelengths is demultiplexed into four channels by the band to wavelength demultiplexer Demux B→W. Each demultiplexer Demux B→W used is an adjacent band demultiplexer, i.e. a demultiplexer that uses filtering with a wide pass band. The transfer function FTc of this kind of channel filter is shown diagrammatically in FIG.
2
.
To obtain the wavelengths, it is necessary to use adjacent band demultiplexers Demux B→W because, as explained above, due to the presence of the band switch stage BXC, it is not possible to know a priori the interleaved band that will be demultiplexed. This is why all the wavelengths are demultiplexed using adjacent band demultiplexers with a wide pass band, regardless of the interleaved band at the input.
However, the teaching of each of the above prior art documents is unsatisfactory. The two prior art systems, one with adjacent bands and the other with interleaved bands, in fact require the same demultiplexing devices.
In particular, where the system with adjacent bands is concerned, to go from fibers to wavelengths it is first necessary to use an adjacent band demultiplexer Demux F→B to obtain the adjacent bands and then deinterleaving demultiplexers Demux′ B→W to obtain the wavelengths. Where the system with interleaved ba
Faure Jean-Paul
Noirie Ludovic
Alcatel
Rojas Omar
Sanghavi Hemang
LandOfFree
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