Polarization analysis of LP01 and LP11 intermodal interference in highly birefringent bow-tie optical fibers

A polarization analysis of bimodal highly birefringent fibers in which LP₀₁, LP₁₁, interference takes place is performed. The polarization state of the interference pattern is theoretically described in terms of recently proposed spatial Stokes parameters on the basis of coupled-mode equations and Jones matrix formalism. The general quasimonochromatic case is considered and depolarization as well as interference fading are accounted for. Special attention is paid to application of the results to fiber-optic sensors, and the basic schemes for the detection of the interference beat signal are discussed. The theoretical conclusions are supported by experiments in which the modal polarization and intermodal interferometric response to elongation of a bow-tie bimodal fiber is investigated. Measurements are carried out on both a separate fiber and on a multifiber assembly at various input conditions