Cascaded coupler Mach-Zehnder channel dropping filters for wavelength-division-multiplexed optical systems

We describe the design and characteristics of cascaded coupler Mach-Zehnder (CMZ) channel adding/dropping filters that select every nth channel (n=2,3,4,...) from the wavelength-division-multiplexed (WDM) optical signal. Using the truncated binomial coupling weight distribution, which appears to be optimal, such filters achieve low (<-30 dB) sidelobe levels and good finesse with just a modest number of stages. We also show that the number of filter stages grows only linearly with the required filter finesse and thus the number of selectable channels. Such WDM filters can be conveniently implemented using the silicon or InP integrated optical technology