Apple has unveiled its long-awaited MR device, “Vision Pro,” which provides a clearer perspective on the potential and applications of AR devices. Despite not being as bulky as VR devices, Vision Pro still has a way to go before reaching the ideal form of AR glasses.

Apple’s Vision Pro utilizes Micro OLED technology and can display facial expressions on the outer screen. The industry anticipates that as AR technology evolves, a transition from Micro OLED to the equally next-gen Micro LED could make AR devices lightweight and more like glasses.

However, the question remains: what advantages does Micro LED bring to AR technology? Why did Apple opt for Micro OLED initially? And are there other display technologies suitable for AR applications?

AR devices: Striking a Balance between Ideal and Reality

In reality, achieving the truly ideal AR product might be premature given current technology. Most AR functional products strictly employ video see-through (VST) technology, where cameras capture real-world scenes, and computational and computer graphic techniques combine to display them on opaque screens.

The ideal is optical see-through (OST) technology, where users perceive the real world through a semi-transparent optical combiner in front of their eyes, coupled with projections onto the user’s eyes, merging the real and virtual worlds.

TrendForce discloses that ideal see-through smart glasses must meet three criteria: firstly, the display light engine must be compact, around 1 inch or smaller, to minimize the glasses’ wearing burden. Secondly, in terms of content recognition requirements, the display brightness specifications should reach at least 4,000 nits to ensure resistance to external factors like weather and environment. Lastly, the resolution must be at least 3,000 PPI for clear projected images.

Industry experts note that see-through AR glasses’ main scenarios are outdoors and on the move. These scenarios require consideration of outdoor weather and brightness, particularly as current waveguide lens efficiency is low, around 0.1-1%, causing substantial light loss. Generally, AR display brightness must exceed 1 million, even 10 million nits.

AR Glasses Development: Which Display Technology Holds the Edge?

Mainstream display technologies for AR glasses include PM(Passive Matrix) micro-display technology, AM(Active Matrix) micro-display technology, and scanning display technology.

PM micro-display technology encompasses LCD, LCOS (Liquid Crystal on Silicon), and DLP (Digital Light Processing) technologies, requiring RGB LED or RGB laser light sources. While mature, they tend to have larger light engines compared to other technologies.

AM micro-display technology includes Micro OLED and Micro LED. Micro OLED features self-emission properties but struggles with brightness. Micro LED outperforms Micro OLED in contrast, lifespan, and power efficiency, but integrating RGB remains challenging.

Scanning display technology (LBS) employs RGB lasers and MEMS for scanning imaging but might lead to speckle.

Analysis of Micro OLED, Micro LED, LCOS, and LBS Technologies

• Micro OLED: Suited for VR/MR devices, but brightness is a limitation

Apple’s Vision Pro uses Micro OLED technology, but its organic light-emitting characteristics result in lower brightness compared to Micro LED, LBS, LCOS, and DLP.

Despite efforts to enhance brightness through different layers, pattern adjustments, and phosphorescent materials, increasing brightness shortens organic material lifespan. Sony remains a key Micro OLED provider, but but recent reports indicate that LGD (LG Display) has joined Apple’s Vision Pro Micro OLED supply chain, potentially boosting production and reducing costs.

• Micro LED: Strongest contender for AR applications but faces technological challenges

Micro LED excels in PPI, brightness, contrast, and light engine size. However, its technological maturity is a major concern. Micro LED AR glasses predominantly display monochrome images due to colorization barriers. Achieving high resolution requires chip scaling, with Micro LED sizes shrinking to 5um. Challenges include uniform wavelength distribution and external quantum efficiency for red LEDs.

• LCOS: Mature but high power consumption and low contrast limit development

LCOS is a common AR device display technology with low cost and broad color gamut. Its reflective nature achieves high brightness, up to 40% light utilization, and increased resolution as semiconductor processes refine. However, it suffers from low contrast and requires a polarizing beam splitter (PBS), hindering downsizing.

• LBS: Small light engine rivaling Micro LED, but technology remains nascent

LBS employs RGB lasers as light sources, via optical element calibration and MEMS image scanning. Light then couples into waveguides. LBS offers high brightness, low power consumption, pure color, and high contrast. However, laser-induced speckle is possible. Ams OSRAM developed an RGB integrated laser with MEMS, shrinking the light engine to under 1cc.

Key Hurdle in AR Glasses Technology: Light Engine Size

Light engine size is pivotal for lightweight AR glasses. To achieve a near-normal glasses form factor, the light engine must be around 1cc or smaller, becoming an industry consensus.

For full-color light engines to reach this target, only LBS, Micro OLED, and Micro LED have opportunities. Micro LED’s pixel size, light efficiency, and brightness outperform Micro OLED, making it the preferred choice for light engines.

However, TrendForce states that while Micro LED’s technology maturity is evolving, challenges remain with red LED external quantum efficiency, micro display size, and FOV issues. Additionally, long-term wear and sensor integration for data transmission and processing pose further challenges.

(Photo credit: Apple)