  Addition of random phase to the object light is required in
computer-generated holograms (CGHs) to widely diffuse the object light and to
avoid its concentration on the CGH; however, this addition causes considerable
speckle noise in the reconstructed image. For improving the speckle noise
problem, techniques such as iterative phase retrieval algorithms and
multi-random phase method are used; however, they are time consuming and are of
limited effectiveness. Herein, we present a simple and computationally
inexpensive method that drastically improves the image quality and reduces the
speckle noise by multiplying the object light with the virtual convergence
light. Feasibility of the proposed method is shown using simulations and
optical reconstructions; moreover, we apply it to lens-less zoom-able
holographic projection. The proposed method is useful for the speckle problems
in holographic applications.
