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

Directional couplers are electrooptical 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 the rate of terabits 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 crosstalk inside a switching system. In this paper, we explore the wavelength approach to achieve the same goal. We show that if two wavelengths are available for sending data, the number of couplers suffering the first-order crosstalk can be reduced to zero while the total number of couplers remains the same as in a network without any crosstalk constraint.