Abstract

This paper proposes incorporating multiple sensing channels in a single fiber in terms of a fiber specklegram. A fiber specklegram is a hologram formed by a speckle field from a multimode fiber and a reference beam. When the hologram is readout by the speckle field, the reconstruction of the fiber specklegram is highly sensitive to the modal phase changes of the multimode fiber. In terms of holographic multiplexing (angular or wavelength), a set of orthogonal fiber states can be recorded in the fiber specklegram and used for multiple sensing channels. The demultiplexing scheme can be either binary or harmonic, depending on the type of the signal to detect. Since the reconstruction of the fiber specklegram is essentially an output of a common path interferometer, the technique possesses both high sensitivity to the measurands and low vulnerability to the environment. A unique feature of the fiber specklegram is its multiplexing capability, which is a result of the spatial information capacity of the multimode fiber. The technique provides a simple means to construct multiple sensing channels in a single fiber with high sensitivity.

© 1991 Optical Society of America