An optical sensing scheme for measuring the mode phase shifts and mode
amplitude modulation in a multimode fiber is proposed. The scheme use
s a double phase conjugator based on photorefractive fiberlike Bi12TiO
20 (BTO) crystal that allows to detect high speed changes of environme
ntal conditions with adaptation for slow variations. An acoustic senso
r based on the proposed scheme is used to demonstrate the scheme's fea
sibility. (C) 1995 American Institute of Physics.