Optical response of an all-fibre acoustooptic phase modulator using aluminium nitride coating

For the first time we present results on an all-fibre acoustooptic phase modulator using aluminium nitride (AlN) thin film as the piezoelectric coating. Two-dimensional axisymmetric finite element analysis was employed to determine the response of the modulator over a wide frequency range from 10 kHz to 700 MHz. Phase shifts of 0.823 rad/V/m in the low frequency region and 0.374 rad/V/m in the high frequency region were observed. At frequencies higher than 28 MHz the response is dominated by radial resonances of the fibre-coating composite. A theoretical investigation of the acoustic impedance showed that there is good impedance matching between the AlN piezoelectric coating and the glass fibre resulting in a high acoustic energy transfer of similar to 82% at the coating-fibre interface. (C) 2000 Elsevier Science B.V. All rights reserved.