The interaction frequencies between longitudinal acoustic waves and fiber Bragg grating are numerically and experimentally assessed. Since the grating modulation depends on the acoustic drive, the combined analysis provides a more efficient operation. In this paper, 3-D finite element and transfer matrix methods allow investigating the electrical, mechanical and optical resonances of an acousto-optical device. The frequency response allows locating the resonances and characterizing their mechanical displacements. Measurements of the grating response under resonant excitation are compared to simulated results. A smaller than <1.5% average difference between simulated-measured resonances indicates that the method is useful for the design and characterization of optical modulators.

The interaction of a fiber Bragg grating and longitudinal acoustic waves in a three-airholes suspended core fiber is experimentally investigated and employed to mode-lock an ytterbium-doped fiber laser. An optimized design of an acousto-optic modulator based on two piezoelectric transducers and 1 cm grating length is also proposed. For an electrical signal strength of 10 V applied to the modulator, the results indicate output pulses with a width of less than 550 ps at a repetition rate of 10 MHz. The reduction of the grating length and the power consumed by the transducer, when compared to previous studies, points out to more efficient, compact and fast acousto-optic modulators for mode-locked all-fiber lasers.

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