Improvements to holographic screens designed to enhance virtual and augmented reality

The researchers developed a new approach that improves image quality and contrast for holographic displays. The new technology can help improve the close-up screens used for virtual and augmented reality applications.

“Virtual and augmented reality systems are poised to have a transformative impact on our society, providing a seamless interface between the user and the digital world,” said Jonghyun Kim, member of the research team, technology company NVIDIA and the University Stanford. “Holographic monitors can overcome some of the biggest remaining challenges for these systems, improving the user experience and enabling more compact devices.”

Inside Optica, Journal of The Optical Society (OSA), researchers describe their new holography display technology called Michelson holography. The approach combines a new optical configuration inspired by Michelson interferometry with recent software development. The configuration generates the interference patterns needed to make digital holograms.

“While we have recently seen tremendous progress in computer-generated holography driven by machine learning, these algorithms are basically limited by the underlying hardware,” said Kim. “We co-designed a new hardware configuration and algorithm to overcome some of these limitations and demonstrate state-of-the-art results.”

Increasing quality Holographic monitors have the potential to outperform other 3-D screen technologies used for virtual and augmented reality, allowing for more compact screens, improving the user’s ability to focus their eyes at different distances and offering the ability to adjust for users who wear corrective lenses. However, the technology has not yet achieved the image quality of more conventional technologies.

For holographic displays, image quality is limited by an optical component known as a phase space light modulator (SLM). SLMs create diffracted light that creates the interference pattern needed to form visible 3-D images. However, the phase-only SLMs normally used for holography exhibit low diffraction efficiency which significantly degrades the quality of the observed image, especially the image contrast.

Since it is difficult to dramatically increase the diffraction efficiency of SLMs, the researchers designed a completely new optical architecture to create holographic images. Instead of using a single-phase SLM like most configurations, his Michelson holography approach uses only two-phase SLMs.

“The central idea of ​​Michelson’s holography is to destructively interfere with the diffracted light from one SLM using the non-diffracted light from the other,” said Kim. “This allows non-diffracted light to contribute to the formation of the image, instead of creating spots and other artifacts.”

Optimizing the image The researchers combined this new hardware arrangement with a camera-in-the-loop (CITL) optimization procedure that they modified for their optical configuration. CITL optimization is a computational approach that can be used to directly optimize a hologram or to train a computer model based on a neural network.

CITL allowed researchers to use a camera to capture a series of images displayed. This meant that they could correct minor misalignments of the optical system without using accurate measuring devices.

“Once the computer model is trained, it can be used to discover precisely what a captured image would look like, without physically capturing it,” said Kim. “This means that the entire optical configuration can be simulated in the cloud to perform real-time inference of computationally heavy problems with parallel computing. This can be useful for calculating a computer-generated hologram for a complicated 3-D scene, for example . “

The researchers tested their new Michelson holography architecture using an optical bench setup in their laboratory. They used it to display several holographic 2-D and 3-D images, which were recorded with a conventional camera. The demonstration showed that the holographic dual-SLM display with CITL calibration provides significantly better image quality than existing computer-generated hologram approaches.

Making the new system practical would require translating the bench configuration into a system that would be small enough to be incorporated into a usable or augmented reality system. The researchers point out that their hardware and software co-design approach can be useful for improving other applications of computer screens and computational images in general.