
perfectly or over sample the spectra from the AWGs, i.e., s 1 for all AWL ports
and all in the spectral region of interest.
A layout for a DGEF is shown in Figure 9.34. There is an MZI with thermooptic
phase shifters in each arm. Each MZI must be driven in a push–pull fashion so as
to maintain a constant phase difference between adjacent AWL arms. Using push–
pull also reduces the polarization dependence, because it reduces the maximum
required phase shift, and a typical silica thermooptic phase shifter shifts
TM-polarized light 4% more efficiently than TE-polarized light. Furthermore,
push–pull reduces the worst-case power consumption and keeps ...