Acoustic wave propagation along cladded fibers of trigonal crystalsymmetry

摘要

An approximate method is proposed to analyze the acoustic wavenpropagation characteristics in nonpiezoelectric claddednLiNbO3 fibers of trigonal crystal symmetry. The fiber axisncoincides with the crystalline Z axis and the cladding thickness isninfinite. This method utilizes coupled mode equations and exactnsolutions for corresponding cladded fibers of hexagonal crystal symmetrynare used as the approximation base. The analysis concentrates on thentrigonal materials of 32, 3 m, and ¯3 m groups. Dispersion curvesnof flexural F11, F21 and F12 modes innsuch a fiber are presented for the first time with a focus on thenfundamental F11 mode. Acoustic modal birefringence phenomenonn(or polarization dispersion) has been observed, which means that thendispersion relation of a mode depends on the relative transversenpolarizations of the corresponding coupled modes. It was also found thatnin trigonal cladded fibers there are generally no pure torsional andnradial-axial modes, which agrees with results previously obtained forntrigonal rods