An acousto-optic fiber interferometer has been proposed and experimentally demonstrated by employing two MgF 2 sandwiches to implement concatenated flexural acoustic wave modulation onto singlemode optical fibers. The transmission spectrum of the acoustic grating pair has been experimentally investigated. Experimental results indicate that interferometric spectral fringes possess a frequency sensitivity as large as −499.0 nm∕MHz due to the Mach-Zehnder interference. Moreover, the applied radio frequency signal voltage for flexural wave generation has a great impact on the transmission spectral properties. The work presented would be of importance for the understanding of the acousto-optic interaction mechanism in concatenated acoustic fiber gratings and is helpful for the design of related acousto-optic fiber devices. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)