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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.In this paper, we explore the principles of constructing strictly nonblocking directional coupler-based photonic switching systems under various crosstalk constraints. We will 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 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.