  Using the Jones formalism, it is shown that electro-optic modulators used for
phase modulation generate a modulation of the output polarization induced by
the difference of phase modulation depth along the crystallographic axes of the
modulator. We study two consequences of this polarization modulation in the
fiber setups, limiting the performance of high sensitivity measurement devices.
The first one is its partial conversion into a residual amplitude modulation
(RAM) within any component presenting polarization dependent losses (PDL). The
second one is a new effect that consists of the distortion of the signal
detected at the output of a fiber cavity. The theoretical expressions of the
detected signals are computed in each case.
