Introduction to MicroLED Displays
MicroLED displays are considered the longer term of display technology, with the flexibility to output tens of millions of nits of brightness. However, this may occasionally seem excessive for outdoor use, because the physics of waveguides end in only a fraction of the sunshine reaching the attention. To address this issue, micro-optics like micro-lens arrays (MLA) are used to semi-collimate the sunshine and increase nits, but the quantity of help this provides is proscribed by the pixel pitch and size of the LED light emitting area.
The Efficiency of Waveguides
Though diffractive waveguides are popular in MicroLED prototypes, reflective waveguides are more efficient, leading to brighter and more power-efficient displays. Companies like Lumus claim that their 2D reflective waveguides typically have a 9 times larger entrance area, with their semi-reflective facets losing less light in comparison with diffraction gratings. PlayNitride also showcased their MicroLEDs using Lumus 2D and older 1D reflective waveguides.
Investment in MicroLED Technology
Major AR corporations, comparable to Apple, Meta (formerly Facebook), Google, Snap, and Vuzix, have invested in or secured exclusive deals with at the very least one MicroLED startup. However, Microsoft has yet to buy a MicroLED company. On the opposite hand, Microsoft’s patent application US 2020/0271932 A1, titled "Eyewear With Spectrally Selective Waveguide," shows a way of mixing separate monochrome red, green, and blue MicroLEDs spatially with three inputs.
The Challenge of Waveguide Efficiency
When first hearing of MicroLEDs outputting tens of millions of nits, you may think it should be overkill to deliver hundreds of nits to the attention for outdoor use with a waveguide. But because of pupil expansion and lightweight losses, only a tiny fraction of the light-in makes it to the attention. This figure diagrams the efficiency issues with waveguides using a diffractive waveguide.
The Pros and Cons of MicroLED Technology
The query stays whether the thrill and investment surrounding MicroLED technology are justified or just a results of the "grass being greener" with this relatively recent display technology. While the "tens of millions of nits" output has generated headlines, concerns persist regarding manufacturability, full-color production, and, most significantly, power efficiency. Although MicroLEDs show promise, there are pros and cons to using them in AR.
Current Developments in MicroLED Technology
Jade Bird Display (JBD) is currently the one company known to be shipping MicroLEDs in production, and their 640×480 green-only MicroLEDs are utilized in all working headsets announced up to now, including those from Vuzix, Oppo, and WaveOptics (prior to being acquired by Snap). JBD is reportedly developing devices with higher pixel depth and determination and has sampled some devices. Presently, JBD’s green MicroLEDs support only 4 bits per pixel or 16 (24) brightness levels, which might result in contour lines in smooth shaded areas. JDB has announced a brand new ASIC controller that can support more levels.
Challenges in Achieving Full-Color MicroLEDs
While there have been continuous improvements in pixel-to-pixel brightness differences and variance in brightness across a tool, there remains to be a visual "grain" stays in what needs to be a solid area and variances in uniformity. These uniformity issues will grow to be much more apparent with full-color implementation as brightness variations in a single color will turn into color shifting.
The Roadmap to Full-Color Devices
Perhaps the largest issue for prime volume applications is the roadmap to having full color devices. Using three monochrome MicroLEDs combined with a color X-Cube or combined spatially with waveguides is seen as a stopgap approach. Spatially putting red, green, and blue emitters side by side, as is completed with larger displays, will end in a pixel size that is just too big to support high resolution in an AR headset form factor. Companies comparable to Porotech, Ostendo, and Innovation Semiconductor are developing single MicroLED emitters that may produce the total color gamut, but these are still a few years away from being commercially available with the uniformity and image quality people have come to expect from display devices.
Alternative Optical Designs
Other optical designs, comparable to Bird Bath, Freeform, and VR-pancake optics, are more likely to proceed using Micro-OLEDs or LCDs for the foreseeable future. This is because, despite being much brighter than Micro-OLEDs, MicroLEDs are still years away from having comparable color control and uniformity. In contrast, Micro-OLEDs are anticipated to proceed getting brighter, with some experts claiming roadmaps reaching as much as about 30K nits.
Conclusion
In conclusion, while MicroLED technology shows promise, there are still significant challenges to beat before it could actually be widely adopted. The efficiency of waveguides, the problem of achieving full-color devices, and the restrictions of current production methods are only a number of of the hurdles that have to be addressed. Despite these challenges, major corporations are investing heavily in MicroLED technology, and it is probably going that we are going to see significant advancements in the approaching years. As the technology continues to evolve, it would be exciting to see how MicroLEDs are utilized in various applications, including augmented reality headsets.
