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From Microscopic Holograms to New Optical Concepts and Design, the Institute Unveils Key Results Towards Integrated Retinal-Projection Displays
Silicon photonics is to optics what microelectronics is to electronics: a solution for integration that underlies the development of smaller and more energy-efficient devices, said Christophe Martinez, CEA-Leti's retinal projection team that proposes the four papers. The tremendous growth of mobile phone use would not have been possible without the achievements in microelectronics. We expect silicon photonics to bring comparable advances in optical systems.
We demonstrated for the first time at CEA-Leti our capability to record a series of microscopic holograms with good uniformity, said Martinez, the lead author of the paper. "This approach gives us early insights into the photo material behavior, and will help us increase the complexity of our next holograms.
Standard optical designs for AR glasses are based on planar waveguides, which transfer an image from a micro-display to the eye as a whole, like a letter in an envelope. This technique produces design complexities that push some AR researchers to look for disruptive solutions, in particular for device integration, a concept that underlies all development of silicon photonics. However, applying silicon photonics to AR design is challenging because new optical concepts have to be developed with the adapted technologies.
The use of integrated photonics required adjusting locally the properties of out-coupling holographic elements with specific angular distribution. As a first step towards this, the team used a simple Lippmann recording configuration that focused on the material behavior of the pixelated process, and demonstrated the ability to record distribution of holographic elements of only a few micrometers in size, and compare the experimental results to the first elements of simulation.
This is the sense of our investigation: a new optical concept based on self-focusing and an adapted technology based on a holographic printer," Martinez said. To follow the letter analogy, the image is transferred as the data of an email: sequentially and in a digital format. The content of the image appears in the system only when the eye of the viewer plays the role of a detector
The way we form the image on the retina is different from the conventional approach. We need to understand all the physical phenomenon that could allow a better device design, Martinez said.
Another paper, "Improved Mathematical Model for a Dense Network of Waveguide and Electrode Design", introduces a mathematical model used to design a network of waveguides and electrodes with random behavior. This model is required to address the light in the display in an efficient way.
CEA-Leti will unveil its retinal-projection display concept with a static demonstrator later this year. The project team also will begin working on a demonstration of dynamic retinal projection.
CEA is a French government-funded technological research organisation in four main areas: low-carbon energies, defense and security, information technologies and health technologies. A prominent player in the European Research Area, it is involved in setting up collaborative projects with many partners around the world.