Design and performances of logarithmic wavelength demultiplexers

We investigate the performance and furnish design guideline for a 1×N router realized as a tree of Mach-Zehnder interferometers, with free-spectral ranges that follow a logarithmic progression. We show that the crosstalk can be reduced and the channel passband flattened by inserting all-pass (AP) filters in the interferometers arms, with a suitable choice of the coupling ratios. The proposed device is inherently low loss and the chromatic dispersion introduced by the AP filters can be easily compensated. Two different realizations are investigated, and the power penalties induced by losses and dispersion are evaluated numerically.