Reflecting CEA-Leti’s steady pursuit of developing silicon photonics and integrated optics for augmented reality (AR) glasses, the institute will update its progress on a variety of key technological building blocks such as retinal projection and holography via 15 papers and poster presentations at Photonics West 2023 in San Francisco, Jan. 28-Feb. 2.
Over the past 10 years, the unique immersive experience that near-eye displays (NEDs) offer users has fueled intense interest in augmented reality, virtual reality and mixed reality for smart glasses or head-mounted displays (HMD) for medical surgery, education and military applications. These technologies even may in time change how humans work and interact socially.
The global market for AR glasses is expected to grow from nearly $12 billionin 2022 to more than $74 billion by 2032, a CAGR of 20.3 percent, according to Future Market Insights.
Silicon photonics allows scientists to precisely manage the positioning of light on the surface of a device. It offers the ability to densify these light positions with extreme rates, allowing the concentration of complex optical functions on small surfaces. Its application on glass substrates, with silicon nitride as a guiding material, opens the way to applications related to the visual field and augmented reality.
CEA-Leti’s research on retinal projection has been structured around a breakthrough in adapting silicon photonics technologies in the visible spectral range, instead of the infrared spectral range where they historically have been implemented.
“Implementation of photonic integrated circuits in the visible spectral range is a breakthrough because of the very strong dimensioning constraints associated with short wavelengths,” said Christophe Martinez, a lead-and-contributing author on several papers. “Our challenges are both technical, to establish the right manufacturing processes, and theoretical, e.g. to know the physical effects related to these technology evolutions,” he explained.
The Eye Forms the Image
While all vision-related applications use optical systems to project images on the retina, retinal projection uses only the eye to form the image provided by a device. Instead of transporting an image towards the eye, the device provides the information that allows the eye itself to generate the image.
Following its 2018 introduction of a disruptive concept for an integrated smart-glass display for augmented reality glasses based on hologram pixelization for image formation, CEA-Leti will validate this holographic technology in the paper, “Evaluation of a Pixelated Holographic Display Concept for a Near Eye Display, Recent Results and Technological Developments”. The paper presents first convincing results on this imaging part by pixelated holograms and evaluates the transparency of these holographic components that must be integrated on glasses. In a near-eye display configuration, the paper also will show how a periodic distribution of holographic pixels of about 25µm allows the projection of an angularly coded image without an optical system between the eye and the display.
Summaries of other papers:
“Multilayer Photonic Integrated Circuit Design for Dense Random Waveguide Distribution Addressing, Application to Near-Eye Display”
Also following up on an earlier potential AR proposal, this work presents the design and optimization of a dense photonic routing architecture for a disruptive concept for an AR near-eye display. Thousands of randomly distributed emissive points at a 532nm wavelength are used to form an image on the retina with the self-focusing effect and this work presents a single-mode photonic IC routing architecture to address the emissive points. The retinal projection is based on the use of complex integrated photonic circuits. The paper also reports the work of a student researcher on a novel routing architecture that allows light distribution that is both random and precisely controlled spatially. This paradox is made possible by the use of two levels of interconnected waveguides that can cross each other without disturbing each other.
“Simulation of Speckle in Pixelated Hologram Image Recovery, Application for AR Retinal Projection Device”
Speckle is a visual disturbance effect linked to the presence of random structure in a beam of light and whose amplitude depends on the coherence of the light. Like retinal projection, it exists only in the eye because the eye forms it on the retina through interference effects. This paper explains efforts to simulate it in the framework of project measurements. These simulations, conducted by a student researcher at CEA-Leti, helped explain the physical phenomena of self-focusing involved in the process of retinal projection.
“Study and Validation of Switchable Grating Using Liquid Crystal for Active Waveguide Addressing”
This work investigates the use of a retinal projection display based on the association of pixelated holograms and a dense distribution of waveguides. It studies the use of gratings impregnated with liquid crystal to actively extract light from waveguides using two extraction strategies: tuning the refractive index contrast between the grating teeth and grooves to erase the grating diffraction effect and changing the index of the waveguide cladding to tune the evanescence of the guided mode. The retinal projection is based on the interaction between holography and photonics on silicon. A window in the middle of this interaction allows the passage from one technology to the other. This window consists of a diffraction element, controlled by a liquid crystal. The paper describes the latest results on research aiming at the development of this switching window, and describes the results of two student researchers of the laboratory.
“Convergence of Mathematical and Physical Optical Designs for the Development of Random Photonic Integrated Circuits for an Unconventional AR Display Concept”
This presentation is in response to conference organizers’ request that student researchers present their work as an optical design challenge. Their project develops mathematical and physical models necessary for the design of a random addressing circuit in silicon photonics. The team investigates a disruptive near-eye display concept that combines integrated photonics and holography. One Ph.D. student in physics developed a dense SiN photonic architecture operating at a wavelength of 532nm that includes a projector and a routing architecture to address the emissive points. The projector is made of a dense grid of waveguides and electrodes, where emissive points are generated at waveguide-electrode crossings. In order to obtain a random distribution of emissive points, another Ph.D. student in mathematics proposes to shape the waveguides and the electrodes as a random succession of sloping segments, mathematically approximated using B-splines.
Invited Oral Presentation
“From Research to Industry, CEA-Leti Offers Innovative Solutions for AR/VR/MR Applications”
Active in the display domain for more than 20 years, CEA-Leti is focused on providing innovative and disruptive solutions for industry in augmented reality, virtual reality and mixed reality applications. This presentation will highlight the institute’s activities in the field of microLED displays, as well as innovative retinal projection concepts and, beyond optical considerations, the development of new functionalities taking into account human cognition through eXtended reality.
“Optimized Design and Manufacturing Process of Diffuse Micro Corner Cubes for Head-Up Projection Display Applications”
In parallel with its research on near-eye devices, CEA-Leti also is investigating innovative designs of head-up displays. Pointing the way to possible industrial implementation, this paper demonstrates how realization of a transparent, diffusing and retro-reflecting projection surface could allow development of head-up display solutions with enlarged visual fields for AR applications. Institute scientists and their partners evaluated the feasibility of such a surface structure using microelectronic manufacturing technologies, and demonstrated first results validating the project concepts.
CEA-Leti scientists will discuss components and systems for applications such as retinal projection, multi-gas sensors, imaging and quantum technologies at booth 959A in the Moscone Center’s French Pavilion during the conference. Retinal projection also will be discussed at the institute’s photonics workshop, starting at 5:30 p.m. on Feb. 1 in the San Francisco Museum of Modern Art.