In this letter, we analyze the integrated optical N x N generalized Mach-Ze
hnder interferometer (GMZI) employing multimode interference (MMI) couplers
. A transfer matrix is used to derive analytic expressions for the intensit
y distribution at the output ports of the GMZI as a function of the phase s
hifts applied to the arms. These expressions form a system of nonlinear equ
ations which are numerically solved for the phase shifts, enabling a new in
terpretation of the GMZI as a variable-ratio power splitter. The performanc
e of the GMZI has been simulated, and it is found that the power splitting
ratio is tolerant to both the accuracy of the applied phase shifts and to f
luctuations in wavelength.