Wide-frequency fiber-optic phase modulator using piezoelectric polymer coating

The highly sensitive response of a fiber-optic phase modulator that is coated with 80-90- mu m-thick vinylidene fluoride/trifluoroethylene copolymer on an 80- mu m-diameter single-mode fiber and made piezoactive by radial poling is demonstrated over a wide frequency range, from 500 Hz to 50 MHz. In the range of 10 kHz up to 2 MHz, a relatively flat response is measured, whereas at high frequencies between 6 and 50 MHz, the phase modulation exhibits multiple peaks dominated by radial resonances of the fiber-jacket composite. Theoretical considerations on the phase shift and experimental results are given.<>