Simulation of speckle in pixelated hologram image recovery: application for AR retinal projection device

Abstract

Our team works on a disruptive concept of Near Eye Display for Augmented Reality (AR) applications. This device requires distributions of holographic elements described as Emissive Points Distributions (EPDs) to create a composite planar wavefront emitted towards the eye. The crystalline lens focuses this signal onto the retina in a mix of diffraction and refraction processes, to form the pixels of an image. We experimentally recorded an image of the letter “R” with pixelated holograms. At the reading of this image, we observe speckle that partially alters the image. Using image processing on the experimental results, we can suppress this speckle and recover the initial “R”, which validates our concept. We develop a simulation tool based on Fourier optics to better understand the emergence of this speckle noise. With the knowledge of the recording process and the form of the hologram given by microscopy, we simulate the electric field 𝐸𝑛 reflected by the different holographic elements from a unique collimated laser. Each field 𝐸𝑛 encodes an angular pixel of the recorded image. The sum of these optical beams in field and/or in intensity allows us to analyze the role of the different optical elements in the generation of a speckle. In particular, the role of the cross interferences between different EPDs is questioned. The experimental analysis is brought for periodic EPDs but can be extended to the case of random EPDs. It gives some insights into some possible evolutions of our concept in terms of optical implementation.

Evaluation of a pixelated holographic display concept for a near-eye display: recent results and technological developments

“…We observe that a strong speckle noise disturbs the image quality. The analysis of this speckle is part of our investigation and simulations of this phenomenon are presented in PW23 17 . If we use the various orders of diffraction to average the noise, we observe that the signal progressively converges toward the expected result.…”