A new technique for distributed fiber-optic sensing is described. It is a wavelength-scanning method that uses, as a sensing element, a polarization-maintaining fiber illuminated with a white-light source. The distribution of the mode-coupling coefficient is determined by a new digital procedure with a fast-Fourier-transform algorithm. Experimental results demonstrate that, when birefringence dispersion is taken into account, more than 300 elements can be resolved along the fiber.