Efficient Faraday rotation in birefringent optical microfibre loop resonators for current sensing

The optimisation of resonantly enhanced Faraday rotation in microfibre loop resonators with linear birefringence is presented. For a sufficiently large birefringence-induced resonance separation, the evolution of differential phase between the two orthogonal polarisations can lead to efficient Faraday rotation when the loop circumference is a quarter of the polarisation beat length and the round-trip phase of the eigenmode in the fast axis is 3π/2 plus an integer multiple of 2π. This reported study provides the groundwork for fabricating microfibre loop resonator based current sensors that can operate efficiently despite the presence of birefringence.