Synthetic Aperture Digital Holography

Synthetic aperture is a well-known super-resolution technique which extends the resolution capabilities of an imaging system beyond the theoretical Rayleigh limit dictated by the system's actual aperture. Using this technique, several patterns acquired by an aperture-limited system, from various locations, are tiled together to one large pattern which could be captured only by a virtual system equipped with a much wider synthetic aperture. The use of optical holography for synthetic aperture is usually restricted to coherent imaging [1-3]. Therefore, the use of this technique is limited only to those applications in which the observed targets can be illuminated by a laser. Synthetic aperture carried out by a combination of several offaxis incoherent holograms in scanning holographic microscopy has been demonstrated by Indebetouw et al [4]. However, this method is limited to microscopy only, and although it is a technique of recording incoherent holograms, a specimen should also be illuminated by an interference pattern between two laser beams. We present a new lensless incoherent holographic system operating in a synthetic aperture mode. Spatial resolution exceeding the Rayleigh limit of the system is obtained by digital tiling several Fresnel holographic elements into a complete Fresnel hologram of the observed object. Each element is acquired by the limited-aperture system from different point of view. This method is demonstrated experimentally by combining three holographic elements recorded from white light illumination which is emitted from a binary grating. The proposed holographic method in this study is based on the recently invented system of a single-channel incoherent interferometer for generating digital Fresnel holograms [5]. In this non-scanning holographic technique, white light is reflected or emitted from a three dimensional (3-