  We report the observation of modulation instability in the mid-infrared
spectral region by pumping a hybrid polymer-chalcogenide optical microwire with
a femtosecond optical parametric oscillator operating at 2.6 {\mu}m. It is
further shown that this modulation instability occurs in the normal dispersion
regime through negative fourth-order dispersion and leads to far detuned
parametric frequency conversion at 2 {\mu}m and 3.5 {\mu}m, despite the
presence of a strong absorption band around 2.8 {\mu}m. Stochastic nonlinear
Schr\"odinger equation simulations of mid-infrared modulation instability are
in excellent agreement with experiments.
