Analysis of cladded fibers of trigonal crystal symmetry

An approximate method is proposed to analyze acoustic wave propagation characteristics in nonpiezoelectric cladded fibers of trigonal crystal symmetry. This method utilizes mode coupling equations, and exact solutions for corresponding cladded fibers of hexagonal crystal symmetry are used as the approximation base. Dispersion curves of flexural F₁₁, F₂₁, and F₁₂ modes in such a fiber with infinite cladding are presented for the first time. Acoustic modal birefringence phenomenon has been observed, which means the dispersion relation of a mode depends on its transverse polarization. It is found that in trigonal cladded fibers there is generally no pure torsional and radial-axial modes. Furthermore, the acoustic characterization results obtained from experimental investigations indicate that MgO doped cladded LiNbO₃ fibers may be appropriate for ultrasonic use