## 1 Introduction  
Recently, display technologies [1; 2] have grown dramatically, and flat-panel displays based on LCDs or organic LEDs dominate the market. Especially in the last decade, three-dimensional (3D) display systems [3; 4; 5] have greatly advanced. Compared with a flat panel display, 3D technologies can not only provide images, but also deliver depth information to create a more immersive vision experience. According to whether the observer needs to wear 3D glasses or not, 3D displays can be classified as stereoscopic and autostereoscopic systems, which have different applications in human life. Traditional 3D displays are based on the principle of binocular parallax [6; 7], in order to give the observer two different images for both eyes to merge as one 3D image. According to the human visual experiment [8; 9], the accommodation of the eye lens is focused on the display plane, which is different from the varc, which is directed towards the reconstructed object. This mismatch is called varc. It induces dizziness and makes the observer feel uncomfortable. Therefore, floating image display systems, which can reconstruct images in space with real depth cues in order to solve the VAC issue, are one of the prime goals of 3D display technology. One way to implement a floating image display is to synthesize a wave field, so that it appears to be scattered by a natural scene or object. Currently, two different approaches are reported, which can be classified under this category: holographic displays and light field (LF) displays. Holographic displays are often considered as the gold standard of 3D display systems. They can, in principle, create any arbitrary wave field and therefore provide the most comfortable experience to the observer. Because the shape of the wavefield can be fully controlled, a well-made hologram can appear indistinguishable from a real object. However, while holography works great for static scenesusing holographic film material, up to now there exists no practical solution for dynamic displays. The reason for this is that holography relies on forming wavefields based on the physical principle of diffraction. This calls for a huge space bandwidth product (i.e., number of pixels on the order of \(10^{11}\)) which is required to generate the fine diffractive structures across the area of a macroscopic display screen [10; 11; 12]. On the other hand, the structure of LF display technologies [13; 14; 15; 16; 17; 18; 19; 20] is simple. It just consists of a micro-lens array (MLA) and a display panel. The aim of an LF system is to approximate the light field of a natural scene. From a wave field perspective, the light field can be described by a set of plane waves. However, the number of plane waves in an LF system is limited by the number of display pixels, and the diameter of the plane waves typically equals the diameter of the involved micro-lenses, i.e., is comparably small. This leads to a strongly fragmented representation of the ideal wave field. As a consequence, light field systems usually have to find a trade-off between spatial and angular resolution and can only display very limited scenes. In addition, the depth range around the central depth plane (CDP) [21], which is the plane of the highest spatial resolution, is usually narrow. In this publication, we present a new approach to a floating image display system, which is based on synthesizing spherical waves instead of plane waves in order to overcome these drawbacks. Similar to an LF system, the corresponding setup consists of a display panel and a lens array (LA). Yet, compared with the LF system, the aperture size of the individual lenses is much larger. Additionally, in order to control the curvature of the spherical waves, the distance between the display and the LA is dynamically changed. The benefit of this approach can be understood in the wave field picture, since using spherical waves instead of plane waves adds more degrees of freedom to the base functions of the synthesis.