Display technology is essential for human beings to obtain information. In display technology, holographic display is considered the most influential display technology, as it can reconstruct all the information of real or virtual scenes without visual fatigue. Color holographic display is a significant technology that can record and reconstruct the color and three-dimensional (3D) information of the original object. Compared with monochrome holograms, color holograms can reflect the real information of objects, having a more wide application. In this paper, we propose an iterative method for generating multiplane color phase-only holograms based on time-division multiplexing. This method is based on the Gerchberg-Saxon (GS) algorithm. When holograms are recorded, amplitude constraints are imposed on each channel plane, which is repeated. The red (R), green (G), and blue (B) channel information of color images is recorded in three phase-only holograms respectively. During reconstruction, RGB channels overlap at the same distances, and the target color images are reconstructed. The reconstruction results of one, three, and five color images are displayed. Compared with the deep-division multiplexing (DDM) method, the quality of reconstructed color images by the proposed method is improved, and the crosstalk between different channel planes is effectively avoided. Numerical simulation and optical reconstruction results prove the effectiveness of the proposed method.

The red, green, and blue channels of color images are set to the same distances when encoding in this study. When recording, we set the amplitude of the initial holograms of three-color channels as a constant of 1 and the phase as a random. When the wavefront propagates to the object plane through angular spectrum diffraction, its amplitude information is replaced by the amplitude of the object plane. The amplitude constraint is relaxed by applying a small nonzero value to the zero-intensity region of the object plane, and the phase is preserved. The wavefront continues to propagate backward, and the amplitude in the hologram plane is replaced by a constant of 1. The phase is preserved, and the process is repeated. Eventually, their three-color channel information is recorded in three holograms respectively. When reconstructing, the three-color channels of the color images are reconstructed at the same distances, and then the color images are reconstructed. When the wavefront propagates to the object plane through angular spectrum diffraction in holographic recording, a small nonzero value is applied to it to relax the amplitude constraint of the object plane. In holographic reconstruction, the original color images are reconstructed at a set distance. It can effectively reduce the speckle noise of the target color images by padding with zeros to the original images. As laser speckle often reduces the quality of the reconstructed images in optical experiments, we adopt the time averaging method. Through the time integration effect, the intensity information of reconstructed images of multiple holograms is superimposed to suppress speckle noise. For the optical reconstruction system, the chromatic aberration caused by the objective lens may lead to different image sizes in red, green, and blue channels. In this study, we construct an optical system with achromatic optical elements to avoid the problem of inconsistent size and distance of reconstructed images.

Our proposed method shows excellent performance in both numerical simulation and optical experiment (Fig. 6). The proposed method and DDM method can reconstruct the single-color image well. However, the original color image reconstructed by the DDM method has color deviation, which may be caused by the hologram recording images of different color channels during recording. The original color image can be reconstructed well by our method. We introduce the correlation coefficient as an index to measure the quality of color image reconstruction. The correlation coefficient values of our proposed method in reconstructing single and multiple color images are higher than those of the DDM method (Fig. 7). The DDM method reconstructing multiplane color images is very limited. When recording holograms, we need to keep multiple color channels at different distances, whereas this work will be very hard within a limited calculation distance. Eventually, crosstalk will inevitably occur between different channels, leading to color deviation. Because reconstructing n color images will eventually reconstruct n×3 channels, the possibility of crosstalk between different channels greatly increases. However, when we reconstruct n color images, only n channels will be reconstructed. Our method can reconstruct more color images, but we need to pay attention to the distance setting between different images to avoid crosstalk.

In this paper, we propose a phase-only hologram generation method for reconstructing multiplane color images. In holographic recording, the red, green, and blue color channels of color images are recorded in three holograms respectively, and finally, the original color images are reconstructed at the set distances. The traditional DDM method needs to record multiple information of different color channels when encoding. Therefore, the quality of the reconstructed images is poor and crosstalk occurs. Our method effectively avoids crosstalk between different planes by setting the distance between different planes reasonably during recording. When reconstructing multiplane color images, it can still maintain high quality. The correlation coefficients of our proposed method are significantly higher than that of the DDM method when reconstructing single and three images. Both numerical simulation and optical experiment results show the novelty and effectiveness of our proposed method.