Introduction to Near-Eye Displays
The world of computing and artificial intelligence is rapidly advancing, and technologies like augmented reality (AR) and virtual reality (VR) have gotten more practical. A vital component of AR and VR systems is the necessity for near-eye displays. However, traditional near-eye displays will be uncomfortable for prolonged use resulting from their close proximity to the attention. To address this issue, optical elements are obligatory to regulate the sunshine path and reduce eye strain.
The Challenge of Traditional Near-Eye Displays
Conventional refractive optical components are sometimes large and hulking, which generally is a problem for head-mounted devices that require more compact optics. Various compact solutions, resembling pancake optics, holography, and leaky waveguides, have been proposed, but they often encounter issues like low efficiency. Achieving a balance between portability and high performance stays a big challenge.
The Potential of Metalenses
Metalenses, made from nano-structures arranged in two dimensions, offer an modern approach for compact near-eye display systems. Their ultra-thin and light-weight characteristics make them well-suited for head-mounted devices. With advancements in nano-fabrication technology, significant developments have been reported regarding metalenses operating within the near-infrared and visual spectrum, enabling various applications, including holography, beam shaping, and microscopy.
Overcoming the Limitations of Metalenses
One of the challenges of metalenses is achieving a large field of view (FOV) that mirrors human vision. To address this, researchers have stacked multiple metalenses into doublet or triplet configurations, allowing for greater design flexibility and enhanced performance. Other strategies involve combining single-layer metalenses with apertures, which may produce nearly diffraction-limited imaging across a large FOV. However, these designs often feature entrance apertures of lower than 1 mm in diameter, restricting their applicability in practical near-eye display scenarios.
Recent Advancements in Metalenses
Recent advancements in machine learning and algorithm optimization have led to the event of multi-layer metalenses, which may achieve each a large FOV and a big aperture in light field modulations. A team of researchers has introduced a metalens doublet system with a big aperture, specifically designed for near-eye displays. This modern configuration incorporates two-layer metalenses and a pupil, achieving a broad FOV of as much as 60° and even 80°.
The Working Principle of the Metalens Doublet
The metalens doublet system works by utilizing the human pupil as an aperture, simulating a distant scene that appears to be at infinity, despite the display being situated near the eyes. This approach enhances direct and natural vision, relatively than merely projecting a picture onto a sensor. The researchers developed and optimized two metalens doublets with diameters within the centimeter range, paired with apertures measuring several millimeters, effectively mimicking the size of the human eye and pupil.
Conclusion
The development of metalenses has the potential to revolutionize near-eye display applications. By optimizing the compact design, aperture size, and FOV, the performance of a metalens doublet can rival that of conventional refractive eyepieces, meeting common benchmarks for near-eye display. While there remains to be room for improvement, this advancement highlights the numerous role that meta-optics can play in advancing high-performance near-eye displays and night vision systems. As technology continues to evolve, we are able to expect to see much more modern applications of metalenses in the sphere of AR and VR.
