A method for measuring the delay between polarization eigenmodes in either high- or low-birefringence fibers is described. The main advantage of this interferometric method is its ability to perform the measurements without the use of any polarizing device. This results in particularly easy handling and makes this technique very suitable for systematic fiber controls. The obtained accuracy using an all-fiber setup is 0.02 ps/m for highly birefringent fibers and 0.003 ps/m when the birefringence is low.