A novel cross-phase modulation scheme that permits measurement of the optical Kerr coefficient in non-polarization-preserving fiber is presented. The scheme is based on a Michelson-type interferometer in which one mirror is replaced by an orthoconjugated mirror. The use of this device leads to an effective insensitivity with respect to the state of polarization of the probe and pump beams. (C) 1996 Optical Society of America.