Several research groups throughout the world are currently working on fiber acousto-optic components, principally phase modulators, made by depositing a film of piezoelectric materials such as zinc oxide (ZnO) directly onto the optical fiber. It is well known that the quality of the resulting film is highly dependent on the temperature of the substrate (i.e., the fiber), but this has not been directly measured in situ. We present for the first time in situ measurements of the fiber temperature during the deposition process using a fiber Bragg grating temperature sensor. We show that the fiber temperature may rise substantially above that of its immediate surroundings. We also present a simple model for the heat flow for the fiber and the holder based on the heat gain from the plasma and the radiation loss between the various components in the sputtering chamber.