Abstract

When an optical fibre crosses a magnetic field, a Faraday effect is generated, which perturbs the optical propagation, causing a modulation of the state of polarization (SOP) of the optical signal along the fibre [1]. This well known effect is often used to develop optical fibre current sensors. Yet, in optical communications systems relying on polarization sensitive elements (e.g. coherent detectors, modulators and integrated-optic components) the SOP Faraday-induced perturbation represents a source of noise. Strong unwanted Faraday effects have been detected in aerial optical cables in presence of lightning events [2]. Moreover, Faraday effects could impair system performances in access and datacom networks with electrical cables and optical fibres in close proximity. Recently, it has been reported that the combination of a quarter-wave plate (QWP) followed by a mirror, named mirrored quarter-wave plate (MQW), can compensate for polarization effects induced by any non-reciprocal circular birefringence, as in the case of Faraday-induced polarization rotation [3,4]. This property has also been experimentally proved in a free-space optical retracing circuit with a MQW at the reflective end, cancelling the effect of a variable Faraday rotator inserted in the circuit [3].

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