The optical properties of sputtered fluorinated ethylene propylene (FEP) thin films (100-400 nm) were analyzed using spectroscopic ellipsometry. Glass (similar to BK7) and silicon substrates were used, and deposition rates on glass were found to be on average 37% higher than on silicon. Refractive indices of the deposited films at 630 nm ranged from 1.379 to 1.392 on glass and from 1.381 to 1.417 on Si, which roughly corresponds to a 4.3% increase when compared to the bulk material value of 1.335. By using the optical properties of the deposited FEP films, it was shown through modeling that they present a possible alternative when fabricating dual-mode surface-plasmon resonance sensors that can differentiate bulk and surface refractive index changes.