We describe an optical fiber based interferometer
to measure velocity profiles in sheared complex fluids using dynamic light scattering (DLS).
After a review of the theoretical problem of DLS under shear,
a detailed description of the setup is given. We outline the various experimental difficulties
induced by refraction when using a Couette cell.
We also show that homodyne DLS is not well suited
to measure quantitative velocity profiles in narrow-gap Couette geometries.
On the other hand, the heterodyne technique allows us to determine the velocity field
inside the gap of a Couette cell. All the technical features of the setup,
namely its spatial resolution (≈ 50 − 100 µm) and its temporal resolution (≈ 1 s per point, ≈ 1 min per profile)
are discussed, as well as the calibration procedure with a Newtonian fluid.
As briefly shown on oil-in-water emulsions, such a setup permits one to record both velocity
profiles and rheological data simultaneously.