Study on acoustic modes via stimulated Brillouin scattering in photonic crystal fibers

The wave equation of the acoustic wave in photonic crystal fibers is derived. The characteristics of acoustic modes and the dependency of the acoustic modes coupling on optical fiber parameters, pump wavelength and the fiber core refractive index in small-core photonic crystal fibers are investigated by effective index method. The results indicate that both the mixed longitudinal acoustic modes and transverse acoustic modes resonance together produce the acoustic fields, and their coupling forms the hybrid acoustic modes; the propagation constant of acoustic modes can be changed with the pump wavelength.