Fiber-optic phase modulator using piezoelectric copolymer coating

An optical fiber was coated with vinylidene fluoride/trifluoroethylene piezoelectric copolymer (P(VDFx/TRFE100-x), x = 73 mole%) to a thickness of 85-100 μm via extrusion method. To create peizoelectricity, this fiber was processed to have polarization in the radial direction by corona discharge poling and was used to construct a fiber phase modulator; ac/dc voltages were applied to concentric cylindrical electrodes attached to the optical fiber and phase shifts were investigated in relation to the applied electric field. The wavelength characteristics of phase modulation sensitivity were measured in a wide range of 20 Hz to 50 MHz. The phase modulation sensitivities were 2.1 × 10−5 rad/(V/m)/fiber length (m) in the low-frequency range and 3.5 × 10−6 rad/(V/m)/m in the high-frequency range. At frequencies higher than 1 MHz, resonances in the fiber-jacket composite were observed clearly. Next, to explain the phase modulation characteristics, the theoretical investigation of a two-layer model from silica glass and piezoelectric copolymer coating was carried out.