Anisotropic polarization maintaining optical fiber ring resonators

Suppression of the polarization drift of optical fiber ring resonators is investigated both theoretically and experimentally by employing anisotropy in a polarization maintaining fiber ring. A general analytic expression for the transmission of the device is derived allowing the fiber modes to exhibit any combination of polarization crosstalk, differential loss or differential coupling. The analysis shows that a moderate level of ring anisotropy, such as that of 10 dB in line polarizer or polarization selective coupler, is sufficient to greatly suppress the drift of the eigenstates of polarization (ESOPs), finesse and resonant point, restoring the device's suitability for most practical applications. An inevitable consequence of introducing ring anisotropy is the loss of orthogonality of the ESOPs. This effect limits the anticipated benefit in high sensitivity applications. A practical anisotropic PMRR is demonstrated by inserting a thin film of nematic liquid crystal between the two halves of the polished coupler of the ring. This resonator demonstrates a polarization response immune to environmental perturbations.