Bidirectional optical space switch

DETAILED DESCRIPTION A paper to entitled "4.
times.
4 optical--Gate matrix switch" by A.
Himeno and M.
Kobayashi (Journal of lightwave Technology Vol LT-3 No.
2 April '85) discloses an optical gate matrix switch in which optical signals entering each input port I.
sub.
i of four input ports are distributed by an optical splitter S.
sub.
i to each of gate elements G.
sub.
i1 to G.
sub.
i4.
When a desired single gate G.
sub.
ij is opened a light signal which can pass through the gate to an output port O.
sub.
j via a combiner C.
sub.
j, which combines the output of all gates G.
sub.
1j to G.
sub.
4j, to an optical receiver.
This arrangement permits multiconnections between any input port I.
sub.
j and any plural output ports O.
sub.
j to be obtained.
Each optical gate G.
sub.
ij is formed by a polarisation rotator placed between its own polariser and crossed analyser to form an on-off optical gate controllable by a driving voltage applied to the polarisation rotator.
A disadvantage of this arrangement is that it is uni-directional.
According to the present invention a bi-directional optical space switch comprises: a first and a second array of inputs for emitting optical signals to be switched; a first and a second array of outputs for receiving switched optical signals from the first and second array of inputs, respectively; an active array of cells having first and second sides each cell being selectively capable of varying the polarisation state of light passing through from one side of the cell to the other in response to an applied control signal; a first optical coupling means for optically coupling the first sides of each of a plurality of groups of cells with a corresponding inputs of the first array of inputs and with a corresponding output of the second array of outputs; a second optical coupling means for optically coupling the second sides of each of a plurality of groups of cells witha corresponding input of the second array of inputs and with a corresponding output of the second array of outputs; the first and second optical coupling means including a respective first and second polarising beam splitter each arranged both to polarise light travelling from each input to the array of cells and to direct appropriately polarised light, only, passing through a cell away from the inputs and to the outputs