We propose what we believe is the first all-optical fiber sensing system without any electronic processing. A multiple-mode fiber detects external perturbations and serves as a random phase generator. A crystal serves as the volume hologram recorder and database and provides the interconnections between a specific incoming random phase and the corresponding output pattern indicating the external perturbation on the fiber. All aspects of the sensing system, including detection of the external perturbation, interconnection, and display of the result, are performed by optical means. © 2001 Society of Photo-Optical Instrumentation Engineers.