Use of Multimode Interference Couplers to Broaden the Passband of Dispersive Integrated WDM Filters

One of the problems encountered with conventional waveguide-based WDM filters now being developed for use in WDM telecommunications and computer fiber networks is that their spectral passbands are “peaked”. Deviation of a signal wavelength from the center of a filter passband thus introduces excess loss. All signal wavelengths and filters have therefore to be very precisely aligned if a high-performance system is to be obtained, which places very tight constraints on both device and system design and operation.