The invention concerns a protected optical switching matrix which can be used in particular as a cross connect switch for optical links.
A prior art high capacity optical switching matrix has been made from an array of lower capacity optical switches. The switches can all be of the space switching type, all of the spectral switching type or a combination of the two types.
To protect a matrix of the above kind, i.e. to keep it working without loss of capacity if any of the switches fails, duplicating each stage of the network with an identical stage that is not normally used, but which is used in place of the stage that has failed if any of the switches constituting it fails, is known per se. A protection system of the above kind is based on so-called 1 for 1 redundancy, in other words one redundant unit for each working unit. Its main drawback is that it doubles the cost of the matrix.
A protected matrix can also be modified to increase its capacity by adding matrix units without interrupting service.
In the prior art there are various architectures for an optical switching matrix:
A first prior art architecture includes a plurality of spatial switching matrix units connected in cascade, using the Clos architecture, for example. The drawbacks of this type of matrix are: PA1 A second prior architecture includes a plurality of spectral switching matrix units or a combination of spatial switching matrix units and spectral switching matrix units. This latter combination can produce a large matrix but the second architecture also has the disadvantage of necessitating 1 for 1 redundancy for the entire matrix if it is to be protected.
High insertion losses, which cannot be compensated simultaneously in both of the ranges of optical wavelengths routinely used: 1 300 nm and 1 550 nm. This limits the maximum size of the optical matrices that can be made using this architecture. PA2 Protecting the matrix necessarily entails the use of 1 for 1 redundancy for the entire matrix, which is costly. PA2 The number of matrix units that must connected in cascade is high, leading to high cost.