Frequency response and phase-shift nonlinearity of a cylindricalPVF2-film-based fiber-optic phase modulator

A cylindrical coil configuration for a polyvinylidene-fluoride (PVF₂)-film-based fiber-optic phase modulator is studied, focusing on the frequency response and the nonlinearity of the phase shift at the resonant frequency. This configuration, hitherto used for PVF₂ film modulators, offers resonance at well-defined, controllable, and higher frequencies than possible for the flat-strip configuration. Two versions of this configuration that achieve selective mode suppression or enhancement and hence provide a choice of the resonance frequency at which a large phase shift occurs are presented. It is shown that a coil version in which the fiber loops are bonded strongly to each other leads to large reduction in the phase shift. A comparative study of the existing piezoelectric fiber-optic phase modulator designs is also presented