Efficient direct magneto-optical phase modulation of light waves in spun microstructured fibres

We have proposed a phase modulator of optical radiation for an interferometric electric-current sensor. The modulator takes advantage of the Faraday effect in spun microstructured optical fibres. Such fibres enable small-diameter multiturn fibre coils to be produced, which is necessary for achieving a preset phase modulation amplitude at a moderate drive current. The principal characteristics of the modulator have been studied experimentally: frequency response, magneto-optical sensitivity and output signal contrast. The results demonstrate that the modulator ensures high efficiency, approaching the theoretical one, provided the modulation period exceeds the time it takes light to pass through the fibre. We have examined the influence of spun fibre parameters on the performance of the modulator.