Comparison of TMI thresholds in non-PM and PM Fibers

This study experimentally compares the TMI thresholds of two few-mode large mode area fibers, one PM and one non-PM, drawn from the same preform. Both fibers are tested in the same setup under the same conditions. The results indicate that the TMI threshold of the PM fiber (operated along the slow axis) is approximately 300 W, while the non-PM fiber shows a threshold of about 330 W. This 10% difference in threshold is attributed to an increase in the refractive index and V-number resulting from the mechanical stresses in the PM fiber. However, rotating the polarization in the PM fiber can lead to higher TMI thresholds, demonstrating its potential advantages in terms of TMI suppression. Overall, while the PM fiber exhibits a slightly lower TMI threshold when aligned with the slow axis, it offers significant performance benefits when polarization is adjusted parallel to the fast axis or at an intermediate angle around 45° between the slow and fast axis.