Sagnac interferometric intensity-dependent refractive-index measurements of polymer optical fiber

We have applied a new modified Sagnac interferometric technique to measure the real part of the intensitydependent refractive index of a single-mode polymer optical fiber. For a 0.1% by weight squaraine dye in a poly(methyl methacrylate) core, Re([chi((3))1111]) is 12(+/-7) x 10(-13) cm(3)/erg at lambda = 1064 nm. We discuss the effect of these measurements on all-optical devices.