# The Zerotrope, a Dynamic Holographic Display: Design and Implementation
## 1 Introduction  
Three-dimensional (3D) displays constitute an important research topic [1; 2; 3]. Most current approaches use the stereoscopic principle [4], which can cause visual discomfort and visual fatigue for the viewer [5]. Inspired by the pre-movie mechanical devices history, the authors designed the Fantatrope(tm) in 2018. It is a holographic zoetrope composed of a series of twelve ultra-realistic full-color holograms arranged in a chronological sequence and mounted on a cylindrical rotating base [6]. A strobe light synchronized with the rotation speed successively illuminated the different frames and the recorded character was animated. The operation was successful and generated the effect of a real 3D display without the need for special glasses or other viewing aids. The purpose of this research was to build a second dynamic holographic display that was lighter and used a single hologram. The main inspiration for building this novel display was the phenakistiscope, the first device that created a fluid illusion of motion and was invented in 1833 by [PERSON]. The phenakistiscope comprises a spinning disc mounted vertically on a handle. A series of equidistant radial slots and pictures representing the phases of movement of a character are arranged around the circumference of the disk. The viewer rotates the disk by hand and views the sequence reflected in a mirror through the moving slots. Then, this rapid succession of pictures creates an illusion of a moving image for the viewer. However, this device demonstrates some limitations. As it is turned by hand, the rotation speed and the animation are not constant. Furthermore, the animation can be viewed by only one person at a time. Moreover, the user cannot observe the animation directly but only through a slot and a mirror. The earliest improvement of the phenakistiscope was the zoetrope, which was designed by [PERSON] [7] and gained popularity after 1867. The zoetrope is a cylinder with slots cut vertically on its sides and a band of paper consisting of a set of sequenced drawings or photographs on the inner surface. The illusion of motion is produced through a rapid succession of these static images observed through the slits. Modern 3D zoetropes exploit a principle similar to that of the traditional zoetrope, with three-dimensional (3D) solid models on a rotating turntable synchronized with a strobe light. These devices have attracted considerable interest in recent times due to the development of 3D printers. The 3D zoetrope demonstrates several improvements over the classical zoetrope. The speed rotation is constant and the animation is directly observable by several individuals. Moreover, the flashing strobe light produces clearer, sharper, and distortion-free results. However, this device also demonstrates some limitations. The animation needs to be observed in darkness to experience the strobe light effect. The 3D models need to be secured precisely on the turning table, and they can be fragile, heavy, and difficult to transport. This paper presents the ZerotropeTM, which is an improved version of the classic phenakistiscope and 3D zoetrope, devices owing to the inclusion of a single ultra-realistic full-color hologram. The name Zerotrope includes \"zero\" (for zero-degree hologram) and the Greek-root word \"tropos\" (turning). This new 3D display retains the advantages of the previously described devices while addressing their limitations and improving the results. To build the Zerotrope, a zero-degree transplane hologram is recorded with a series of 3D characters arranged radially and horizontally around the center of the disk, as in a phenakistiscope. This hologram is then mounted on a rotating disk and illuminated with a synchronized strobe light as in a 3D zoetrope. All the principal functions of this new device can be regulated. This paper explains its construction and evaluates its performances.