Space-wavelength trade-off in the design of nonblocking directional-coupler-based networks under crosstalk constraint

Directional couplers are electro-optical switching devices that are capable of switching multiple wavelength signals. Once the state of a coupler is set up, optical signals can pass through the coupler with a rate of tera bits per second. A directional coupler-based photonic switching system however, suffers from the intrinsic crosstalk problem. This shortcoming has been the most limiting factor in building a large switching network of this kind. It has been shown that by using more hardware (couplers) we can reduce the number of crosstalk-generating couplers along the path of a connection in a Banyan-type switching system. We explore the wavelength approach to achieve this task. We show that if there are two wavelengths available, the number of couplers suffering the first-order crosstalk can be reduced to zero while the total number of couplers will remain the same as a network without any crosstalk constraint.