Achieving stability in remote holography using flexible multimode image bundles.

Commercial flexible image bundles (boroscopes, endoscopes, etc.) are made up of tens of thousands of coherently arrayed multimode optical fibers whose modal propagation characteristics are unavoidably affected by bending losses. Consequently, light wave fronts transmitted through such bundles are subject to significant changes whenever the bundle is flexed anywhere along its length. For this reason images transmitted through such multimode image bundles cannot normally be used to generate holograms unless the bundle is rigidly fixed at every point. This requirement represents a substantial limitation on the use of fiber optics to generate and record holograms of remote subjects. However, this study demonstrates an original technique using ultralow frequency in situ holograms that can be transmitted through a multimode image bundle and recorded remotely even while the bundle is being moved.