We show that lambda/4-shifted distributed-feedback nonlinear devices c
an be used as an all-optical switch at relatively low input intensitie
s. The lambda/4 shift opens a narrow transmission window whose peak po
sition within the stop band depends on the input intensity, a feature
that can be used for low-power optical switching. The nonlinear couple
d-mode approach is used to analyze the stationary operating regime of
such a device and determine the transmittivity as a function of the in
put intensity. A closed-form solution, rather than a numerical one, is
found for what we believe is the first time.