## 1 Introduction  
Electronic holographic display (EHD) [1, 2, 3] is a light interference-based 3D technique that can provide non-glasses 3D scenes because it can reconstruct the natural wavefront of light emitted from objects. A hologram, including computer-generated hologram (CGHs), is an interference fringe pattern in a semi-transparent medium that is generated using the interference between the object light and the reference light [3, 4]. In contrast, a stereoscopic 3D display technique is based on multiple two-dimensional images, resulting in accommodation-convergence conflict [2, 5]. In general, the viewing angle depends on the pixel pitch of the spatial light modulator (SLM) used as a holographic 3D display [4, 5]. To reconstruct a holographic 3D (H3D) image with a moderate wide-viewing angle, current technologies of holographic 3D displays cannot satisfy demand, the state-of-the-art for SLM of which the pixel pitch goes down into about 1 \(\upmu\)m or smaller [2, 3, 4]. Alternatively, either temporally or spatially multiplexed SLMs have been applied to increase this viewing angle in utilizing these conventional displays as well as the scalability of 3D image sizes [6, 7, 8, 9], but these large-sized, complicated EHDs require further great advances in display technology towards a single integrated hardware device. In addition, a single conventional SLM cannot easily modulate both the amplitude and phase of an object's light wave [8, 9]. Recently, although a proposed, complex-modulating SLM including eye-tracking, referred to as a complex modulator, achieved conceptual improvement, it suffers from mechanically unsterilized alignment among micro-pixels between two stacked SLMs and also requires-bulky optical components [10]. In some cases, an optical filtering system must be applied to remove the unwanted diffraction orders as well as background noise, resulting in enlarged display systems [6; 9; 10; 11; 12]. Alternatively, complex-to-phase or complex-to-amplitude encoding methods can be applied to convert the complex-number hologram into a phase-only modulator or an amplitude-only modulator [10; 13; 14; 15; 16; 17]. With these existing approaches, the image quality of holographic 3D displays highly depends on the selected encoding types, and, therefore, alternative encoding methods should be further studied. Recently, the near-eye displays for extended reality (XR) including augmented reality (AR)/virtual reality (VR) and mixed reality (MR) are providing potential to bring users into new worlds where they can experience instant access to stereoscopic and multi-viewed visual information [17; 18; 19]. As for EHD devices, the key requirements, such as enlarging the viewing angle of compact holographic device and representing the complex-field's hologram in a 3D scene with high quality, can be easily overcome by merging a near-eye-typed display device and digitally encoded holographic content [17; 18; 19]. We began to pursue the very hybrid approach in the amplitude-modulating SLM to be embodied by using a novel near-eyed holographic display and an advanced encoding method that we present in the study. In this paper, we propose an advanced efficient encoding scheme, which we refer to as modified amplitude-only encoding (MAO), and from which a pair of encoded holograms per viewpoint are prepared through the image data processing for holographic 3D content, as depicted in Figure 1a. In addition, we demonstrate a prototype of the near-eye holographic 3D display (NEHD) suited for prepared 360\({}^{\circ}\) holographic content, as shown in Figure 1b. The module can split and upload a pair of MAO-encoded holograms simultaneously, and then optically reconstruct two H3D images which can be observed by the left and right eyes of an observer, respectively.