Polarization and longitudinal modes of Mobius fiber ring lasers

Mobius optical cavities have attracted great interest for their unique topological properties. Here, the polarization and longitudinal modes of two types of Mobius fiber ring lasers are investigated. Atheoretical model is established with Jones matrix to solve the polarization eigenmodes and longitudinal modes of a twisted polarization-maintaining fiber ring cavity. It is found that twisting the fiber axis causes polarization hybridization and a geometry-dependent phase, which induces a frequency shift to the longitudinal modes. The Mobius cases (180 degrees and 90 degrees splicing) are analyzed in detail, in which the 90 degrees case leads to peculiar polarization and longitudinal mode properties. We believe the presented fiber ring laser provides a convenient platform to study lasers with a Mobius structure, and could enable further fiber laser applications.