Calculation method for reconstruction at arbitrary depth in CGH with Fourier transform optical system

A computer-generated hologram (CGH) is generated by simulating light waves propagated from virtual objects, and we are able to observe natural 3-D images without feeling tired. However, the resolution of current output devices, liquid crystal displays, is not high enough to display CGH data, so the size of reconstructed images are restricted. To increase image size, a method by using the Fourier transform optical system has been proposed. The Fourier transform optical system converges reconstructed light by arranging a lens between an observer and hologram and reconstructs floating images near the observer. In the system, a reconstruction position is confined around a focal point of the lens because a CGH calculation method had not yet been developed . To solve this problem, this describes a CGH calculation method using a unified formula to reconstruct images at arbitrary depth. This formula is derived by considering image formation of a lens and hologram. Moreover, process for eliminating unnecessary light elimination processing is described in this paper. By changing the elimination process according to the reconstruction position, images are reconstructed without overlapping unnecessary light at arbitrary depth. To confirm the effectiveness of the proposed method, we conducted optical reconstruction experiments. The results show that correctly sized images are reconstructed at correct depth, and unnecessary light is eliminated. It is possible to observe large and free-depth 3-D images with the proposed method.