Propagation of ultrashort pulses in multimode fiber in space and time.

We perform 3D cross-correlation measurements of the optical field distribution resulting from an ultrashort pulse propagating in 6 meters of multimode fiber. Spatial amplitude and phase distributions of the optical field at the output of the fiber are measured using a time-gated spatial heterodyne interferometer as a function of time delay between the signal and the reference optical fields. We show that the measured signal represents an approximation to the optical impulse response of the multimode fiber.