Acoustic wave propagation along cladded fibers of trigonal crystal symmetry

An approximate method is proposed to analyze the acoustic wave propagation characteristics in nonpiezoelectric cladded LiNbO/sub 3/ fibers of trigonal crystal symmetry. The fiber axis coincides with the crystalline Z axis and the cladding thickness is infinite. This method utilizes coupled mode equations and exact solutions for corresponding cladded fibers of hexagonal crystal symmetry are used as the approximation base. The analysis concentrates on the trigonal materials of 32, 3 m, and ~3 m groups. Dispersion curves of flexural F/sub 11/, F/sub 21/ and F/sub 12/ modes in such a fiber are presented for the first time with a focus on the fundamental F/sub 11/ mode. Acoustic modal birefringence phenomenon (or polarization dispersion) has been observed, which means that the dispersion relation of a mode depends on the relative transverse polarizations of the corresponding coupled modes. It was also found that in trigonal cladded fibers there are generally no pure torsional and radial-axial modes, which agrees with results previously obtained for trigonal rods.<>