The interaction of light waves and acoustic vibrations of the lattice manifests in a variety of phenomena. The non-equilibrium phonons in solids are created in two ways: using ultrasonic techniques, the coherent waves of relatively low frequencies as compared to kT/h are generated, and using thermal pulse techniques, the waves with random phases in a wide frequency range with the central frequency of order kT/h are injected. The interaction of waves of the latter type with a light propagating in the surface optical waveguides is the subject of the present lecture. Depending on the lifetime of the phonons, the ballistic and diffusive propagation cases should be distinguishable. Here we consider the diffusive propagation case only, describing the phenomena in terms of the lattice temperature.