  The enhanced-NA Fresnel hologram reconstructs a holographic image at a
viewing angle larger than the diffraction angle of a hologram pixel. The image
space is limited by the bandwidth of a digital hologram. In this study, we
investigate the property of image formation in the extended image space beyond
a diffraction zone. A numerical simulation using the phase Fresnel hologram is
carried out to observe an extension of image space and the effect of this on
the changes in the angular field of view. The phase Fresnel hologram,
synthesized by restricting the angular view range to a diffraction angle, can
reconstruct a uniform image without high-order noises within the primary
viewing zone, which is well confirmed by optical experiments. On the other
hand, the overlapping of high-order images is inevitable when the viewing angle
depends on the hologram numerical aperture. The high-order images are
distributed in the direction cosine space, which could be effectively removed
through an angular low-pass filter. We discuss the development of method for
expanding the image space while maintaining the viewing angle of a holographic
image.
