  We investigate the angular field of view (AFOV) of a holographic image
reconstructed from the digital Fresnel hologram in holographic display. The
theoretical analysis reveals that the AFOV of a holographic image is
fundamentally determined by the hologram numerical aperture (HNA) other than a
diffraction angle of pixel pitch of a pixelated modulator. This property is
proved for various types of the digital holograms by using a numerical
simulation and optical experiments. The high-HNA hologram reconstructs the
image with a high viewing-angle, although the image contraction is inevitable
due to the Nyquist sampling criterion. We propose the method for extending the
viewing-angle of a holographic image in the manner of increasing the object
size during the high-HNA hologram synthesis and removing the high-order
aliasing images.
