Optical fibre electrets and electro-acousto-optic transduction

Abstract

Optical fibres have been used to sense many different physical quantities (magnetic fields, vibrations, temperature, rotation etc.). There is however, one important exception; optical fibres are insensitive to electrical fields due to the inversion symmetry of the glass matrix, which ensures that the Pockels coefficients are zero. Most of the electric field sensors reported so far are hybrid devices, employing an extrinsic active component constructed from a piezoelectric or electrooptic crystal. Only one report exists of the observation of a Pockels effect in optical fibre poled with high electric fields, but the value of the induced electrooptic coefficient was very small (of the order of 10 pm/V) and unstable. A recent break-through is the recent observation of high second-order nonlinearities of the order of 1 pm/V in glasses and 0.2 pm/V in optical fibres using a variety of different techniques: thermal poling, corona poling, and electron implantation. Based on these results it is possible to expect a value of electrooptic coefficient in poled fibre of the same order as in crystalline quartz (1 pm/V). This value is high enough to construct an all fibre-optic electrooptic field sensor. In this paper we report the observation of a strong response of thermally poled fibre to an electric field. Phase shifts as high as 1 rad have been obtained at applied voltages of 50 V.

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