<title>Micro-optical elements in holography</title>

Abstract

Modern optical instrumentation increasingly requires miniaturization of the devices used, as is the case, e.g., in the field of endoscopy. The combination of such technology with holography offers advantages such as 3-D documentation and display with the possibility of large magnification a posteriori as well as metrology in form of holographic interferometry of objects with difficult optical access. Miniaturized holographic instrumentation requires small illumination and imaging systems, as well as minute recoding devices. As could be demonstrated, these requirements can be met by introduction of micro-optical elements. The use of (single-mode) optical fibers offers easy handling and flexibility. In particular, new single-mode imaging fiber bundles show improved performance data (high lateral resolution, low speckle noise, and low mode interaction) at submillimeter diameters. Assembled gradient- index rod lenses commonly are used for submillimeter imaging systems. In holographic endoscopy, speckle noise caused by these small limiting apertures can be reduced by using such a gradient-index imaging system simultaneously for both imaging and illumination. The use of electro-optical crystals opens the possibility of developing a minute holographic storage device for in-site recording, reconstruction, and erasure with fast repetition rate.