The non-resonant third order nonlinearity of conjugated polymers appears to
be potentially useful for all-optical devices in waveguide formats.[l,2]
This nonlinearity manifests itself as an intensity-dependent refractive
index which leads to a nonlinear phase shift over some propagation distance.
Device research over the last few years has shown that there are certain
minimum requirements for the nonlinear phase shift that need to be achieved
over one absorption length of the material.[l,3] There are two principal
sources of absorption, the usual linear absorption which is independent of
fluence, and two photon absorption for which the absorption scales linearly
with intensity. Thus the usefulness of a nonlinear material for all-optical
switching devices can be evaluated from a limited number of material
parameters, namely n2 (in n = n0 + n2I
where I is the local intensity), α0 which is the low power
absorption coefficient and β which is the two photon
coefficient (in α = α0 + βI). The problem for a
given material is to identify spectral regions over which the minimum
required phase shift can be achieved.
Direct interferometric test of the nonlinear phase-shift gate
