WDM routers based on hierarchic optical discrete Fourier transform matrices

We have introduced the possibility of synthesizing WDM routers based on N X N hierarchic star couplers. We have examined how the required phase shifts can be introduced by means of path length differences, and studied in detail the crosstalk introduced by the frequency dependence of these phases. We have found that crosstalk levels are moderate, even in units designed for a wavelength range as large as 64 nm. Additional opportunities exist for improving performance further, by implementing the phases by different path differences. The many degrees of freedom of hierarchic star couplers could also be used for making versatile reconfigurable routers.