The optical cross-connect is a very important device of a modern optical switching system. A 2x2 optical cross-connect or switch forms the basic module of a switching system.

Up till now we had only one input. Let now have 2 inputs connected to the two waveguides of the directional coupler. Signal 1 is connected to waveguide A and signal 2 is connected to waveguide B as shown in Fig.

If signals and 1 and 2 are incoherent, their flow on the directional coupler will not be affected by each other.

When signal 1 is connected B2, but at the same time signal 2 will be connected to A2 as shown by dotted lines and arrows. This state is called the cross-state ( state) of the switch.

Using the basic 2X2 switch a complex multiple input multiple output switch architecture can be built. For example a 3X3 non-blocking switch using basic 2X2 modules is shown in Fig. A non-blocking switch is the one where connection between any input-output pair is possible irrespective of the other connections as long as the given input-output pair is free for connection.