Strictly and wide-sense nonblocking photonic switching systems under crosstalk constraint

Photonic switching systems based on directional coupler switching elements can switch multiple-wavelength signals at the speed of tera-bits per second. Crosstalk is an intrinsic shortcoming of the directional couplers which must be overcome in the construction of an efficient switching system. Therefore, it adds a new dimension to the design of the networks based on directional couplers. We explore the principles of constructing strictly nonblocking directional coupler-based photonic switching systems under various crosstalk constraints. We show that a lower level of crosstalk can be achieved at a cost of additional hardware. We also introduce a rule that limits the routing of the new connections based on the state of the switching network. Such a rule can significantly reduce the undesired crosstalk and the hardware complexity of the strictly nonblocking network at the same time. The resulting network is therefore categorized as a wide-sense nonblocking network.