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Principle of operation is easily described by the following figure.
A flexural acoustic wave is launched onto an optical (two mode) fiber by a cone shaped aluminium "horn". If the acoustic wavelength matches the beat length between two modes of the optical fiber, the acoustic wave will couple light between these two modes. When this coupling happens the frequency of the light is changed by an amount equal to the acoustic frequency.
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This effect may be used for several purposes such as:
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Optical filtering.
The mode coupling condition (acoustic wavelength=beat length of modes) is satisfied only at a small wavelength band. Both optical pass band and stop band filters have been demonstrated. These filters are tunable.
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Acoustic scanned compensating interferometer for white light interferometry.
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Optical frequency shifters.
Here are three online papers describing the work of Bjørnar Langli and Dan Østling (both have now finished their Ph.D.) in the field of acoustooptic interactions in optical fibers:
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B. Langli, P. G. Sinha and K. Bløtekjær, "Pulse Shapes In Acousto-Optically Scanned White-Light Interferometers" , Proc. Eleventh International Conference on Optical Fiber Sensors , May 21-24, 1996, Sapporo, Japan.
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D. Östling, B. Langli and H. E. Engan, "Intermodal Beat Lengths In Birefringent Two-Mode Fibers", Optics Letters, Vol.21, No.19, pp.1553-1555, October 1996.
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B. Langli, P. G. Sinha and K. Bløtekjær, "Acousto-Optic Mode Coupling of Partially Coherent Light in Two-Mode Fibers" , Optical Review, Vol.4, No.1A, pp.121-129, Jan./Feb. 1997. Abstract.
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