Grayscale Displaying Scheme Based on Petal Orbital Angular Momentum Holography

Orbital angular momentum (OAM) holography has recently been emerged and recognized as an essential technique for achieving ultrahigh capacity data transmission, data storage, encryption, and digital holographic microscopy. However, its application on grayscale image displaying is less reported. In this paper, we propose a grayscale image displaying scheme based on petal OAM holography, where the petal OAM mode is first designed by superposing the two OAM modes with an opposite topological charge $\ell$ , together with a phase $\varphi$ . The topological charge $\ell$ is utilized to selectively distinguish different images from the petal OAM-multiplexing hologram, while the $\varphi$ is exploited for dynamically adjusting the brightness of the reconstructed 'dots' in the point images to grayscale displaying. Different from the reconstructed images by the existing OAM hologram only have 'appearing' or 'disappearing' after the filtering, there is a grayscale image turned out by using the proposed scheme. The simulation and experimental results show that the proposed scheme can display an image with 11 grayscale levels by adjusting $\varphi$ to 11 values with step $\frac{\pi }{10}$ . Furthermore, the scheme can realize different displaying with different grayscales for each modules in a single picture, which makes the picture more stereoscopic. The proposed scheme may also have applications in medical diagnosis and education, advertising design and display, etc.