fig5 d shows two tunable optical filters f5 and f6 of the layer ch2 which are respectively associated with two tunable shifters t5 and t6 of this layer fig5 a to 5e do not show the management means of the optical crossconnect in question moreover for greater clarity of fig5 a to 5e the unused elements of these figures inputs and or outputs of certain couplers filters and shifters have not been shown for example one of the two inputs and one of the two outputs of the coupler 12 of the layer ch2 have been shown the third output channel of the demultiplexer d2 associated with the loop b2 is no longer shown let us assume that the node a 3 1 sends a message to the node a 2 2 this message is transmitted to the wavelength u03bb3 circulates in the loop b1 and arrives at the optical crossconnect in the layer ch3 in this layer it is selected by the filter f9 of the output s3 and then transposed to the wavelength u03bb2 by the shifter t9 the signal thus leaves on the output s3 at the wavelength u03bb2 which corresponds to the node a 2 2 the second node of the loop b2 so as to send a message from the node a 1 1 to the node a 2 1 the filter f3 is tuned on u03bb1 and the shifter t3 on u03bb2 so as to send a message from the node a 2 1 to the node a 1 1 the filter f1 is tuned on u03bb2 and the shifter t1 on u03bb1 so as to send a message from the node a 1 2 to the node a 3 1 the filter f7 is tuned.