Fiber sensing with photorefractive fiber

Optical fibers have been widely used for transmitting temporal signal. However, the transmission of spatial signal has not been fully exploited. Although multimode fiber has a large space-bandwidth product (roughly equal to the number of modes), transmitting spatial signals by using a fiber is rather difficult When a laser beam is launched into a multimode fiber, the exit light field produces a complicated speckle pattern caused by the modal phasing of the fiber. It is difficult to recover the transmitted information from the speckle field. However, the fiber speckle field can be used for fiber sensing with a holographic method. In other words, if a hologram is made with the speckle fiber field, the information of the fiber status can be recovered. Thus by reading the hologram by the same speckle field, the reference beam can be reconstructed, which represents the detection of the speckle field. In other words, instead of exploiting the temporal content, the spatial content from a multimode fiber can be exploited for sensing. Our analyses and experimentations have shown that the fiber specklegram sensor (FSS) is highly sensitive to perturbation, and it is less vulnerable to the environment factors. Applications of the FSS to temperature, transversal displacement, and dynamic sensing are also included.