Acousto-optic filters for fiber systems

Basic principles and several key applications of wavelength tunable acousto-optic filters are described. The devices utilize periodic coupling of guided and/or dissipating modes in optical fibers provided by traveling acoustic wave in the same fibers. The wavelength tuning is realized by tuning the applied acoustic frequency, and proper phase matching condition selects filtered optical wavelength. Application of the acousto-optic filters to gain flattening of fiber amplifiers, wavelength selection, optical switching, and non-reciprocal filtering will be discussed.