This work presents a new technique to study polymers under strong geometrical confinement in nano porous films. The procedure is based on sensing the changes of the optical properties of the porous matrix due to polymer imbibition into the pores by using optical interferometry. A simple theoretical model is used to correlate the time dependent optical thickness of the film with the polymer dynamics as a function of temperature. To test the method applicability, the imbibition of ethyl vinyl acetate in porous silicon membranes was studied. A large variation of the polymer viscosity was measured by varying the temperature from 20 to 110 degrees C. In addition, the confinement degree was varied in about 2 orders of magnitude by using matrices with different pore radius. A remarkable decrease in the viscosity was observed when the mean pore radius was reduced. Moreover, the interferometric technique enables the study of very low molecular weight polymers as well as measuring along a wide range of temperatures in a single nondestructive experiment.