No abstract

Diffraction is the main physical effect involved in the imaging process of holographic displays. In the application of near-eye displays, it generates physical limits that constrain the field of view of the devices. In this contribution, we evaluate experimentally an alternative approach for a holographic display based mainly on refraction. This unconventional imaging process, based on sparse aperture imaging, could lead to integrated near-eye displays through retinal projection, with a larger field of view. We introduce for this evaluation an in-house holographic printer that allows the recording of holographic pixel distributions at a microscopic scale. We show how these microholograms can encode angular information that overcomes the diffraction limit and could alleviate the space bandwidth constraint usually associated with conventional display design.

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.