  The expansion of viewing angle is a crucial factor in holographic displays
implemented with a spatial light modulator having a finite space-bandwidth. The
enhanced-NA Fresnel hologram reconstructs a holographic image at an angle
larger than the diffraction angle by a hologram pixel, where it has a
difficulty in achieving this without an interference of high-order noises. This
study presents the theoretical foundation for optimizing the enhanced-NA
Fresnel hologram to recover the low space-bandwidth. The higher spectrum
components of the digital hologram beyond the bandwidth exists in the form of
their replications. The expansion of angular spectrum by its repetition during
optimization procedure increases the image resolution, resulting in a viewing
angle that is dependent on the hologram numerical aperture. We numerically and
experimentally verify our strategy to expand a viewing angle of holographic
image.
