Guided optical waves are very sensitive to the alteration of optical properties of dielectric media. In this report, we demonstrate the use of guided waves for studying dynamic behavior of ferroelectric liquid crystals. Propagating light in the anisotropic medium suffers a birefringent effect, which causes coupling ofp- ands-polarized light. Theoretical calculations, based on the Maxwell equations, successfully describe this phenomena, using a dielectric tensor diagonal in molecular coordinates, which is transformed to the laboratory coordinate system by three Euler angles. The waveguide measurements are able to probe the molecular orientation and movement of the liquid crystal molecules in the three dimensional coordinate system. This method has been used to examine the switching behavior in the SmC* phase. The bistable states and the path of the molecular swing under alternating external electric fields are well characterized by the reflected intensity of single and double frequency modulation.