In a polyconjugated main chain polymer strip waveguide the nonlinear, nonresonant refractive indexn2was measured by monitoring the signal spectrum broadening due to self-phase modulation. The two photon absorption coefficient&agr;2was obtained by calibrating the inverse transmission measurement. The nonlinear coefficients were determined to ben2=0.85×10−14 cm−2/W and&agr;2=0.08 cm/GW at a wavelength &lgr;=885.6 nm. The used polymer was poly[1,4-phenylene1,2-di(phenoxyphenyl)vinylene]. The result is in good agreement with interferometer measurements. The material is suitable for all-optical switching. ©1997 American Institute of Physics.