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Computer-generated holography (CGH) has demonstrated significant promise as a display technique, with benefits including the ability to display images supporting true refocus at diffraction-limited resolution at the eye, and brightness levels meeting the most demanding requirements for outdoor augmented-reality applications. Whereas historically the computational load required for CGH has been a barrier to wider adoption, this has been demonstrated to be within reach of modern mobile devices for many real-world use cases. However, one area which remains a concern for CGH, as with other laser-based display technologies, is the reduction of noise arising from coherent illumination, loosely known as laser speckle. In this work we identify and model the modes in which Speckle affects the apparent visual quality of images generated using 2D and 3D holography and compare the effectiveness of known and theoretical optical and algorithmic techniques for speckle reduction. Reduction of speckle noise is of particular interest to CGH, but there is significant extant literature on speckle-reduction techniques from other disciplines, such as microscopy using coherent illumination, and laser metrology. These techniques are examined and their applicability to CGH considered. Approaches including a diffusing element are typically limited to 2D CGH, as they destroy the coherence required to support multiple depth planes. For techniques that in a broad sense act on the spatial/temporal coherence of the system to reduce speckle, such as use of a superluminescent light emitting diode (SLED), or a moving optical element, a trade-off between speckle reduction and reduced resolution must be found. In addition, we review the impact of algorithmic techniques used in CGH to reduce speckle-like noise during the generation of holograms, and compare the effectiveness of these techniques to hardware-based solutions.

Augmented and Mixed Reality promises another leap forward in productivity and lifestyle, offering benefits with a magnitude and impact matching that of the introduction of smartphones. However, to enable this, many significant technical challenges must be overcome. Here we review the state of the art, identifying key challenges established in the literature to consumer-wearable devices. In particular, we discuss: vergence-accommodation conflict (the detrimental effect of overlays that are optically inconsistent with the real-world objects they augment), the need to present overlays visible against the vast dynamic range that the human eye can process, and constraints surrounding the scalability and cost of manufacture of optics. We demonstrate that digital holography as a display mechanism not only provides an effective solution to the aforementioned challenges, but also that various hardware requirements become far less stringent. By operating in the Fourier Domain, holographic displays are freed of design compromises driven by the constraints of a pixelated screen. However, the computational cost of CGH has previously been considered prohibitive. We demonstrate that for real-world applications the latest advancements made by VividQ deliver sufficient focal accuracy at a computational cost within reach of personal mobile devices. We prove that it is now possible to clear the barriers preventing mass adoption of Augmented and Mixed Reality products with Computer-Generated Holography.