Ivan-Christophe Robin | Aledia: Why do AR glasses waste over 90% of the light from their microdisplays?
00:03:48 - 00:05:52
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Summary of the clip:
Why do AR glasses waste over 90% of the light from their microdisplays?
The fundamental challenge for AR microdisplays is the extreme inefficiency of coupling light into a waveguide. Waveguides, the transparent optics that deliver the image to the user's eye, have a very narrow acceptance angle, typically only Ā±10 to Ā±20 degrees. However, standard microLEDs are Lambertian emitters, meaning they radiate light in a very wide pattern, with most of the energy emitted at high angles that completely miss the waveguide's input cone. This results in more than 90% of the generated light being wasted before it even enters the optical system.
A conventional approach to solve this is to use a microlens array to collimate the light from each pixel. While effective in principle, this imposes a severe constraint: for efficient collection, the lens must be significantly larger than the light source. For the ultra-small pixel pitches required for AR (e.g., 2-micron subpixels), this would force the microLED's active area to be less than one micron. This is a major problem for traditional planar microLEDs.
As the size of a planar microLED shrinks, its efficiency drops dramatically due to a well-known issue where non-radiative recombination at the etched sidewalls of the pixel begins to dominate. This "size-efficiency trade-off" makes the microlens approach impractical for high-resolution AR displays, as the required emitter size would be too inefficient. This creates a critical need for a new type of microLED that is natively directional, eliminating the need for external collimating optics and bypassing the efficiency-size bottleneck.
In this short video, you can learn:
* The fundamental mismatch between microLED emission patterns and AR waveguide acceptance cones.
* Why using microlenses forces a trade-off that drastically reduces conventional microLED efficiency.
* The critical need for a microLED technology that is inherently directional without sacrificing performance.
š **Clip Abstract** AR systems lose most of their light due to the mismatch between the display's wide emission and the waveguide's narrow input angle. Conventional solutions like microlenses are impractical at the small pixel sizes required, creating a major efficiency bottleneck.
š Link in comments š
#ARMicrodisplays, #OpticalWaveguides, #MicrolensArrays, #MicroLEDEfficiencyLoss, #AugmentedReality, #MicroLEDTechnology
This is a highlight of the presentation:
MicroLEDs with built-in directive emission and RGB capability for power efficient AR microdisplays
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00:05:53 - 00:08:22
Can you engineer a microLED to emit light only in the direction you want?
Can you engineer a microLED to emit light only in the direction you want?
Aledia's core innovation is the use of Gallium Nitride (GaN) nanowire arrays that function as a built-in photonic crystal. Instead of a flat, planar emitting surface, each pixel is composed of a dense, highly-ordered lattice of sub-micron GaN wires grown directly on a silicon wafer. This periodic arrangement of materials with different refractive indices is the key to controlling the direction of light.
This photonic crystal structure fundamentally alters how light is emitted from the device. Unlike a randomized array of nanowires which would emit light diffusely, the regular lattice creates photonic bands. By carefully designing the diameter, pitch, and arrangement of the nanowires, these bands can be engineered to suppress light emission at high angles and strongly enhance it in the forward direction, creating a highly directional beam of light within a narrow cone (e.g., 0 to 20 degrees). This allows for direct and efficient coupling into an AR waveguide without external optics.
This nanowire platform provides a second crucial advantage: monolithic, full-color integration. The emission wavelength of a GaN nanowire is highly dependent on its physical diameter. By using lithography to define different diameter nanowires for red, green, and blue subpixels, all three primary colors can be grown simultaneously on the same silicon wafer in a single epitaxial run. This combines the benefit of engineered directionality with a streamlined, scalable manufacturing process for full-color microdisplays.
In this short video, you can learn:
* How a regular array of GaN nanowires creates a photonic crystal effect.
* The use of photonic bands to engineer a highly directional light emission profile.
* How nanowire diameter can be tuned to achieve monolithic RGB emission on a single wafer.
š **Clip Abstract** Aledia's GaN-on-Silicon nanowires are arranged in a periodic lattice, creating a photonic crystal that funnels light into a narrow, forward-facing cone. This technology not only solves the waveguide coupling problem but also enables monolithic RGB integration by tuning the nanowire diameter for each color.
š Link in comments š
#GaNNanowires, #PhotonicCrystal, #DirectionalLightEmission, #MonolithicRGB, #MicroLEDDisplays, #ARWaveguides
00:09:23 - 00:11:22
How can you lock an LED's color so it never shifts, no matter the brightness?
How can you lock an LED's color so it never shifts, no matter the brightness?
A common issue in conventional LEDs is wavelength instability, where the emitted color shifts as the drive current (and thus brightness) changes. This is caused by physical effects like band-filling and the quantum-confined Stark effect. For a high-fidelity display, this color shift is highly undesirable, as it compromises color purity and makes it difficult to maintain a consistent white point across different brightness levels.
Aledia's nanowire technology solves this problem through the same photonic crystal effect that provides directionality. The highly ordered nanowire lattice creates a high-quality optical cavity with a very sharp, well-defined resonant wavelength determined by its physical geometry. The quantum wells within the nanowires are strongly coupled to this cavity, which forces them to emit light predominantly at the cavity's fixed resonant frequency, a phenomenon related to the Purcell effect.
This "locking" mechanism makes the emission wavelength remarkably stable. Even if the natural emission peak of the quantum wells tries to shift with increasing current, the powerful influence of the photonic crystal cavity pulls the emission back to its fixed wavelength. The speaker presents data for a red device showing zero wavelength shift over three decades of current density. This provides a massive advantage for display applications, enabling brightness control via current modulation without any degradation in color purity.
In this short video, you can learn:
* The common issue of color shifting with brightness in conventional LEDs.
* How a photonic crystal cavity creates a fixed resonant wavelength for light emission.
* The resulting stabilization of the emission wavelength, independent of current density.
š **Clip Abstract** The photonic crystal structure in Aledia's nanowire LEDs creates a powerful optical cavity that locks the emission wavelength. This prevents the color shift typically seen in LEDs as brightness changes, ensuring perfect color stability across the entire dynamic range.
š Link in comments š
#NanowireLEDs, #PhotonicCrystal, #OpticalCavity, #WavelengthStability, #MicroLEDDisplays, #ARDisplays