Acoustic torsional waves used for coupling between optical polarization modes in optical fibers

In an optical fiber the fundamental LP₀₁ spatial mode occurs in two polarization modes. Coupling between these polarization modes can be provided by acoustic torsional waves propagating along the fiber. This coupling is analyzed in detail. Analytic results of the coupling coefficients based on the combined effect of birefringence and photoelastic contributions are obtained. The results show that for regular fibers the birefringence component is the larger of the two. It has also been found that by using higher radial orders of the acoustic torsional modes the coupling efficiency can be increased