[OPTICAL REVIEW Vol. 4, No. 1A (1997) 121-129]

Acousto-Optic Mode Coupling of Partially Coherent Light in Two-Mode Optical Fibers

Bjørnar LANGLI, Pranay G. SINHA* and Kjell BLØTEKJÆR

Department of Physical Electronics, Norwegian University of Science and Technology, Trondheim, Norway

(Received July 4, 1996; Accepted September 13, 1996)

An acoustic pulse propagating on a two-mode fiber can act as a beam splitter in a scanning interferometer. When this device is employed in white-light interferometry, the effects of distributed coupling and dispersive interferometer arms need to be considered. A theory suitable for treating acousto-optic interaction of partially coherent light in a moving interaction region was developed. It was found that differential optical dispersion should be negligible and the acoustic pulse length short. Also the coherence time should be short but long compared to the intermodal group delay difference over a pulse length. Experiments with long acoustic pulses were performed, and fairly good agreement with theory was obtained.

Key words : fiber optics, white-light interferometry, acousto-optic interaction, scanning interferometer