Introduction

Based on information gathered at SID Display Week and AWE, I have many articles to write based on the thousands of pictures I took and things I learned. I have been organizing and editing the pictures.

As its name implies, Display Week is primarily about display devices. My major takeaway from that conference is that many companies work on full-color MicroLEDs with different approaches, including quantum dot color conversion, stack layers, and single emitter with color shifting based on current or voltage.

AWE moved venues from the Santa Clara Convention Center in Silicon Valley to the larger Long Beach Convention Center south of LA. More than just a venue shift, I sensed a shift in direction. Historically, at AWE, I have seen many optical see-through AR/MR headsets, but there seem to be fewer optical headsets this year. Instead, I saw many companies with software running on VR/Passthrough AR headsets, primarily on the Meta Quest 3 (MQ3)and Apple Vision Pro (AVP).

This article was partly inspired by Hypervision’s white paper discussing whether micro-OLEDs or small LCDs were the best path to 60 pixels per degree (PPD) with a wide FOV combined with the pictures I captured through Hypervision’s HO140 (140° diagonal FOV per eye) optics at AWE 2024. I have taken thousands of pictures through various headsets, and the Hypervision picture stood out in terms of FOV and sharpness. I have followed Hypervision since 2021 (see Appendix: More on Hypervision).

I took my first pictures at AWE through the Sony XR (SXR) Headset optics. At least subjectively, in a short demo, the SXR’s image quality (sharpness and contrast) seemed higher than that of the AVP, but the FOV was smaller. I had on hand (thousands) of pictures I had taken through the Big Screen Beyond (BSB), AVP, Meta Quest Pro (MQP), and Meta Quest 3 (MQ3) optics with the same camera and lens, plus a few of the Hypervision HO140 prototype. So, I decided to make some comparisons between various headsets.

I also want to mention LightPolymers’ new Quarter Waveplate (QWP) and Polarization technologies, which I first learned about from a poster in the Hypervision AWE booth. In April 2024, the two companies announced a joint development grant. They offer an alternative to the plastic film QWP and Polarizers, where 3M dominates today.

Hypervision’s HO140 Display

Based on my history of seeing Hypervision’s 240° prototypes for the last three years, I had, until AWE 2024, largely overlooked their single display 140° models. I had my Canon R5 (45Mp with 405mp ” 3×3 sensor pixel shift mode”) and tripod with me at AWE this year, so I took a few high-resolution pictures through the optics of the HO140. Below are pictures of the 240° (left) and 140° (right) prototypes in the Hypervsion Booth. Hypervision is an optics company and not a headset maker and the demos are meant to show off their optics.

When I got home and looked at the pictures through the HO140, I was impressed by the overall image quality of the HO140, after having taken thousands of pictures through the Apple Vision Pro (with Micro-OLED displays) and Meta’s Quest Pro, Quest 3 (both with mini-LCD displays), the Big Screen Beyond. It usually takes me considerable time and effort, as well as multiple reshoots, to find the “sweet spot” for the other devices, but I got good pictures through the HO140 with minimal effort and only a few pictures, which suggests a very large sweet spot in Hypervision’s optical design. The HO140 is a prototype of unknown cost that I am comparing to production products. I only have this one image to go by and not a test pattern.

The picture below is from my Canon R5, with a 16mm lens netting a FOV of 97.6° horizontal by 73.7° vertical. It was shot at 405mp and then reduced to 45mp to avoid moiré effects due to the “beat frequencies” between the camera sensor and the display devices with their color subpixels. All VR optics pincushion, which causes the pixel sizes to vary across the display and increases the chance of getting moiré in some regions.

The level of sharpness throughout the HO140’s image relative to other VR headsets suggests that it could support a higher-resolution LCD panel with a smaller pixel size if it existed. Some significant chroma aberrations are visible in the outer parts of the image, but these could be largely corrected in software.

Compared to other VR-type headsets I have photographed, I was impressed by how far out into the periphery of the FOV the image maintains sharpness while supporting a significantly larger FOV than any other device I have photographed. What I can’t tell without being able to run other content, such as test patterns, is the contrast of the display and optics combination.

I suggest also reading Hypervision’s other white papers on their Technology & Research page. Also, if you want an excellent explanation of pancake optics, I recommend Arthur Rabner’s, CTO of Hypervision, one-hour and 25-minute presentation on YouTube.

Sony XR (SXR)

Mechanical Ergonomics

AWE was my first time trying the new Sony XR (SXR) headset. In my CES 2024 coverage, I wrote about the ergonomic features I liked in Sony XR (and others compared to Apple Vision Pro). In particular, I liked the headband approach with the flip-up display, and my brief try with the Sony headset at AWE seemed to confirm the benefits of this design choice (which is very similar to the Lynx R1 headset), at least from the ergonomics perspective relative to the Apple Vision Pro.

Still, the SXR is still pretty big and bulky, much more so than the AVP or Lynx. Having only had a short demo, I can’t say how comfortable it will be in extended use. As was the case for the HO140, I couldn’t control the content.

“Enterprise” Product

Sony has been saying that this headset primarily aims at “enterprise” (= expensive high-end) applications, and they partner with Siemens. It is much more practical than the Apple Vision Pro (AVP). The support on the head is better; it supports users wearing their glasses, and the display/visor flips up so you can see the real world directly. There is air circulation to the face and eyes. The headset also supports adjustment of the distance from the headset to the eyes. The headset allows peripheral vision but does have a light shield for full VR operation. The headset is also supposed to support video passthrough, but that capability was not demonstrated. As noted in my CES article, the SXR headset put the pass-through cameras in a much better position than the AVP.

Display Devices and Image Quality

Both the AVP and SXR use ~4K micro-OLED display devices. While Sony does the OLED Assembly (applying the OLED and packaging) for its headset and the AVP’s display devices, the AVP reportedly uses a custom silicon backplane designed by Apple. The SXR’s display has ~20% smaller 6.3-micron pixels than the AVP’s 7.5-micron. The device size is also smaller. The size factors of the SXR favor higher angular resolution and a smaller FOV, as is seen with the SXR.

The picture below was taken (handheld) with my 45MP Canon R5 camera with a 16mm lens like the HO140, but because I couldn’t use a tripod, I couldn’t get a 405MP picture with the camera’s sensor shifting. I was impressed that I got relatively good images handheld, which suggests the optics have a much larger sweet spot than the AVP, for example. To get good images with the AVP requires my camera lens to be precisely aligned into the relatively small sweep spot of the AVP’s optics (using a 6-degree-of-freedom camera rig on a tripod). I believe the Apple Vision Pro’s small sweet spot and the need for eye-tracking-based lens correction, and not just for foveated rendering, are part of why the AVP has to be uncomfortably clamped against the user’s face.

Given that I was hand-holding both the headset and camera, I was rather surprised that the pictures came out so well (click on the image to see it in higher, 45mp resolution).

At least in my brief demo, the SXR’s optics image quality seems better than the AVP’s. The images seem sharper with lesser chroma (color) aberrations. The AVP seems heavily dependent on eye tracking to correct optics problems with the optics, but it does not always succeed.

Much more Eye Refief (enabling eye glasses) but lower FOV

I was surprised by how much eye relief the SXR optics afforded compared to the AVP and BSB, which also use Micro-OLED microdisplays. Typically, the requirement for high magnification of the micro-OLED pixels compared to LCD pixels inherently makes eye relief more difficult. The SXR magnifies less, resulting in a smaller FOV, but also makes it easier optically for them to support more eye relief. But note, taking advantage of the greater eye relief will further reduce the FOV. The SXR headset has a smaller FOV than any other VR-type headset I have tried recently.

Novel Sony controllers were not a hit

While I will credit Sony for trying something new with the controllers, I didn’t like finger trackpad and ring color are great solutions. I talked with several people who tried them, and no one seemed to like either controller. It is hard to judge control devices in a short demo; you must work with them for a while. Still, they didn’t make a good first impression.

VR Headset “Shootout” between AVP, MQP, Big Screen Beyond, Hypervision, and Sony XR

I have been shooting VR headsets with the Canon R5 with a 16mm lens for some time and built up a large library of pictures. For the AVP, Big Screen Beyond (BSB), and Meta Quest Pro (MQP), I had both the the headset and the camera locked down on tripods so I could center the lens in the sweet spot of the optics. For the Hypervision, while the camera and headset were on tripods, my camera was only on a travel tripod without my 6-degree-of-freedom rig and the time to precisely locate the headset’s optical sweet spot. The SXR picture was taken with my hand holding the headset and the camera.

Below are through-the-optics pictures of the AVP, BSB, MQP, Hypervision HO140, and SXR headsets, all taken with the same camera and lens combination and scaled identically. This is not a perfect comparison as the camera lens does not work identically to the eye (which also rotates), but it is reasonably close. The physically shorter and simpler 16mm prime (non-zoom) lens lets it get inside the eye box of the various headsets for the FOV it can capture.

FOV Comparison (AVP, SXR, BSB, HO140, MQ3/MQP)

While companies will talk about the number of horizontal and vertical pixels of the display device, the periphery of the display’s pixels are cut off by the optics, which tend to be circular. All the VR headset optics have a pincushion distortion, which results in higher resolution in the sweet spot (optical center), which is always toward the nose side and usually above the center for VR headsets.

In the figure below, I have overlaid the FOV of the left eye for the headsets on top of the picture HO140 image. I had to extrapolate somewhat on the image circles on the top and bottom as the headset FOVs exceeded the extent of the camera’s FOV. The HO140 supports up to a 2.9″ diagonal LCD (that does not exist yet), but they currently use a 2.56″ 2160×2160 Octagonal BOE LCD and are so far beyond the FOV of my camera lens that I used their information.

As can be seen, the LCD-based headsets of Hypervision and Meta typically have larger FOV than the micro-OLED-based headsets of AVP, Meta, and Sony. However, as will be discussed, the micro-OLED-based headsets have smaller pixels (angularly and on the physical display device).

Center Pixels (Angular Size in PPD)

Due to handholding the SXR and having pixels smaller than the AVP, I couldn’t get a super-high-resolution (405 mp) image from the center of the FOV and didn’t have the time to use a longer focal length lens to show the pixel boundaries. The SXR has roughly the same number of pixels as the AVP but a smaller FOV, so its pixels are angularly smaller than the AVP’s. I would expect the SXR to be near 60 pixels per degree (PPD) in the center of the FOV. The BSB has about the same FOV as the AVP but has a ~2.5K micro-OLED compared to the AVP’s ~4K; thus, the BSB pixels in the center are about 1.5x bigger (linearly). The Hypervision’s display has a slightly smaller center pixel pitch than the MQP (and MQ3) but with a massively bigger FOV.

The MQP (and the very similar MQ3) rotate the display device. To make it easier to compare the pixel pitches, I included a rotated inset of the MQP pixels to match the alignment of the other devices. Note that the pictures below are all “through the optics” and thus include the headset’s optical magnification. I have given the angular resolution in PPD for each headset. I have indicated the angular resolution (in pixels-per-degree, PPD) for each of the headset’s center pixels. For the center pixels pictures below, I used a 28mm lens to get more magnification to see sub-pixel detail for the AVP, BSB, and MQP. I only took 16mm lens pictures of the HO140 and, therefore, rescaled the image based on the different focal lengths of the lens.

The Micro-OLED base headsets require significantly more optical magnification than the LCD models. For example, the AVP has 3.2x (linearly) smaller display device pixels than the MQP, but after optics, the pixels are ~1.82x smaller. As a specific example, the AVP magnifies the display by ~1.76 more than the MQP.

Outer Pixels

I capture pixels from a similar (very approximately) distance from the optical center of the lens. The AVP’s “foveated rendering” makes it look worse than it is, but you can still see the pixel grid with the others. Of the micro-OLED headsets, the BSB and SXR seem to do the best regarding sharpness in the periphery. The Hypervision HO140 pixels seem much less distorted and blurry than any of the headsets, including the MQP and MP3, which have much smaller FOVs.

Micro-OLED vs. Mini-LCD Challenges

Micro-OLEDs are made by applying OLEDs on top of a CMOS substrate. CMOS transistors provide a high current per unit area, and all the transistors and circuitry are underneath the OLED pixels, so it doesn’t block light. These factors enable relatively small pixels of 6.3 to 10 microns. However, CMOS substrates are much more expensive per unit area, and modern semiconductor FABs limit of CMOS devices is about 1.4-inch diagonal (ignoring expensive and low-yielding “reticle stitched” devices).

A basic issue with OLEDs is that the display device must provide the power/current to drive each OLED. In the case of LCDs, only a small amount of capacitance has to be driven to change the pixel, after which there is virtually no current. The table on the right (which I discussed in 2017) shows the transistor mobility and the process requirements for the transistors for various display backplanes. The current need for an emitting display device like OLEDs and LEDs requires crystalline silicon (e.g., CMOS) or much larger thin-film transistors on glass. There are also issues of the size and resistivity of the wires used to provide the current and heat issues.

The OLED’s requirement for significant current/power limits how small the pixels can get on a given substrate/technology. Thin-film transistors have to be physically big to supply the current. For example, the Apple Watch Ultra Thin Film transistor OLED display has 326 PPI (~78 microns), which is more than 10x larger linearly (100x the area) than the Apple Vision Pro’s pixel, even though both are “OLEDs.”

Another issue caused by trying to support large FOVs with small devices is that the higher magnification reduces eye relief. Most of the “magnification” comes from moving the device closer to the eye. Thus, LCD headsets tend to have more eye relief. Sony’s XR headset is an exception because it has enough eye relief for glasses but does so with a smaller FOV than the other headsets.

Small LCDs used in VR displays have different challenges. They are made on glass substrates, and the transistors and circuitry must be larger. Because they are transmissive, this circuitry in the periphery of each pixel blocks light and causes more of a screen door effect. The cost per unit area is much lower than that of CMOS, and LCD devices can be much larger. Thus, less aggressive optical magnification is required for the same FOV with LCDs.

LCDs face a major challenge in making the pixels smaller to support higher resolution. As the pixels get smaller, the size of the circuitry relative to the pixel size becomes bigger, blocking more light and causing a worse screen door effect. To make the pixels smaller, they must develop higher-performance thin-film transistors and lower resistance interconnection to keep blocking too much light. This subject is discussed in an Innolux Research Paper published by SPIE in October 2023 (free to download). Innolux discusses how to go from today’s typical “small” LCD pixel of 1200 ppi (=~21 microns) to their research device with 2117 ppi (=~12 microns) to achieve a 3840 x 3840 (4K by 4k) display in a 2.56″ diagonal device. Hypervision’s HO140 white paper discusses Innolux’s 2022 research prototype with the same pixel size but with 3240×3240 pixels and a 2.27-inch panel, as well as the current prototype. The current HO140 uses a BOE 2.56″ 2160×2160 panel with 21-micron pixels, as the Innolux panel is not commercially available.

Some micro-OLED and small LCD displays for VR

YouTuber Brad Lynch of SadlyItsBradley, in an X post, listed the PPI of some common VR headset display devices. I have added more entries and the pixel pitch in microns. Many VR panels are not rectangular and may have cut corners on the bottom (and top). The size of the panels given in inches is for the longest diagonal. As you can see, Innolux’s prototypes have significantly smaller pixels, but almost 2x linearly, than the VR LCDs in volume production today:

• Vive: 3.6″, 1080p, ~360 PPI (70 microns)
• Rift S*: 5.5″, 1280P, ~530 PPI (48 microns)
• Valve Index: 3.5″, 1440p, ~600 PPI (42 microns)
• Quest 2*: 5.5″, 1900p, ~750 PPI (34 microns)
• Quest 3: ~2.55″ 2064 × 2208, 1050 PPI (24 microns) – Pancake Optics
• Quest Pro: 2.5″, 1832×1920, ~1050 PPI (24 microns) – Might be BOE 2.48″ miniLED LCD
• Varjo Aero: 3.2″, 2880p, ~1200 PPI (21 microns)
• Pico 4: 2.5″, 2160p, 1192 PPI (21 microns)
• BOE 2.56″ LCD, 2160×2160, 1192 PPI (21 microns) – Used in Hypervision HO140 at AWE 2024
• Innolux 2023 Prototype 2.56″, 3840×3840, 2117 ppi (12 microns) -Research prototype
• Apple Vision Pro 1.4″ Micro-OLED, 3,660×3,200, 3386 PPI (7.5 microns)
• SeeYa 1.03″ Micro-OLED, 2560×2560, 3528 PPI (7.2 microns) – Used in Big Screen Beyond
• Sony ~1.3″ Micro-OLED, 3552 x 3840, 4032 PPI (6.3 microns) – Sony XR
• BOE 1.35″ Micro-OLED 3552×3840, 4032 PPI (6.3 microns) – Demoed at Display Week 2024

In 2017, I wrote Near Eye Displays (NEDs): Gaps In Pixel Sizes (table from that article on the right) talks about what I call the pixel size gap between microdisplays (on Silicon) and small LCDs (on glass). While the pixel sizes have gotten smaller for both micro-OLED and LCDs for VR in the last ~7 years, there remains a sizable gap.

Contrast – Factoring the Display and Pancake Optics

Micro-OLEDs at the display level certainly have a better inherent black level and can turn pixels completely off. LCDs work by blocking light using cross-polarization, which results in imperfect blacks. Thus, with micro-OLEDs, a large area of black will look black, whereas with LCDs, it will be dark gray.

However, we are not looking at the displays directly but through optics, specifically pancake optics, which dominate new VR designs today. Pancake optics, which use polarized light and QWP to recirculate the image twice through parts of the optics, are prone to internal reflections that cause “ghosts” (somewhat out-of-focus reflections) and contrast loss.

Using smaller micro-OLEDs requires more “aggressive” optical designs that support higher magnification to support a wide FOV. These more aggressive optical designs can be more prone to being more expensive, less sharp, and loss of polarization. Any loss of polarization in pancake optics will cause a loss of contrast and ghosting. There seems to be a tendency with pancake optics for the stray light to bounce around and end up in the periphery of the image, causing a glow if the periphery of the image is supposed to be black.

For example, the AVP is known to have an outer “glow” when watching movie content on a black background. Most VR headsets default to a “movie or home theater” rather than a background. While it may be for aesthetics, the engineer in me thinks it might help hide the glow. People online suggest turning on some background with the AVP for people bothered by the glow on a black background.

The complaints of outer glow when watching movies seem more prevalent when using headsets micro-OLEDs, but this is hardly scientific. It could be just that the micro-OLEDs have a better black level and make the glow more noticeable, but it might also be caused by their more aggressive optical magnification (something that might be or has been (?) studied). My key point is that it is not as simple as considering the display’s inherent contrast, you have to consider the whole optical system.

LightPolymers’ Alternative to Plastic Films for QWP & Polarizers

LightPolymers has a Lyotropic (water-based) Liquid Crystal (LC) material that can make optical surfaces like QWP and polarizers. Silicon Optix, which the blog broke the news of Meta buying them in December 2021 (Exclusive: Imagine Optix Bought By Meta), was also developing LC-based polarized light control films.

Like Silicon Optix, Light Polymers has been coating plastic films with LCs, but LightPolymers is developing the ability to directly apply their films to flat and curved lenses, which is a potential game changer. In April 2024, LightPolymers and Hypervision announced the joint development of this lens-coating technology and had a poster in their Hypervision’s booth showing it (right)

3M Dominates Polarized Light Plastic Films for Pancake Optics

3M is today the dominant player in polarized light-control plastic films and is even more dominant in these films for pancake optics. At 3M’s SID Display Week booth in June 2024, they showed the ByteDance PICO4, MQP, and MQ3 pancake optics using 3M polarization films. Their films are also used in the Fresnel lens-based Quest 2. It is an open secret (but 3M would not confirm or deny) that the Apple Vision Pro also uses 3M polarization films.

According to 3M:

“3M did not invent the optical architecture of pancake lenses. However, 3M was the first company to successfully demonstrate the viability of pancake lenses in VR headsets by combining it with its patented reflective polarizer technology.“

That same article supports Kopin’s (now spun out to Lightning Silicon) claims to have been the first to develop pancake optics. Kopin has been demonstrating pancake optics combined with their Micro-OLEDs for years, which are used in Panasonic-ShiftAll headsets.

3M’s 2017 SPIE Paper Folded Optics with Birefringent Reflective Polarizers discusses the use of their films (and also mentions Kopin developments) in cemented (e.g., AVP) and air gap (e.g., MQP and MP3) pancake optics. The paper also discusses how their polarization films can be made (with heat softening) to conform to curved optics such as the AVP.

LightPolymers’ Potential Advantage over Plastic Films

The most obvious drawbacks of plastic films are that they are relatively thick (on the order of 70+ microns per film, and there are typically multiple films per lens) and are usually attached using adhesive coatings. The thickness, particularly when trying to conform to a curved surface, can cause issues with polarized light. The adhesives introduce some scatter, resulting in some loss of polarization.

By applying their LCs directly to the lens, LightPolymer claims they could reduce the thickness of the polarization control (QWP and Polarizers) by as much as 10x and would eliminate the use of adhesives.

In the photos below (taken with a 5x macro lens), I used a knife to slightly separate the edges of the films from the Meta Quest 3’s eye-side and display-side lenses to show them. On the eye-side lens, there are three films, which are thought to be a QWP, absorptive polarizer, and reflective polarizer. On the display-side lens, there are two films, one of which is a QWP, and the other may be just a protective film. In the eye-side lens photo, you can see where the adhesive has bubbled up after separation. The diagram on the right shows the films and paths for light with the MQ3/MQP pancake optics.

Because LighPolymers’ LC coating is applied to each lens, it could also be applied/patterned to improve or compensate for other issues in the optics.

Current State of LightPolymer’s Technology

LightPolymers is already applying its LC to plastic films and flat glass. Their joint agreement with Hypervision involves developing manufacturable methods for directly applying the LC coatings to curved lens surfaces. This technology will take time to develop. LightPolymer business of making the LC materials and then works with partners such as Hypervision to apply the LC to their lenses. They say the equipment necessary to apply the LCs is readily available and low-cost (for manufacturing equipment).

Conclusion

Hypervision has demonstrated the ability to design very wide FOV pancake optics with a large optical sweet spot and maintains a larger area of sharpness than any other design I have seen.

Based on my experience in both Semiconductors and Optics, I think Hypervision makes a good case in their white paper 60PPD: by fast LCD but not by micro OLED, getting to a wide FOV while approaching “retinal” 60PPD is more likely to happen using LCD technology than micro-OLEDs.

Fundamentally, micro-OLEDs are unlikely to get much bigger than 1.4″ diagonally, at least commercially, for many years, if not more than a decade. While they could make the pixels smaller, today’s pancake optics struggle to resolve ~7.5-micron pixels, no less small ones.

On the other hand, several companies, including Innoulux and BOE, have shown research prototypes of 12-micron LCD pixels, or half the (linear) size of today’s LCDs used in VR headsets in high volume. If BOE or Innolux went into production with these displays, it would enable Hypervision’s HO140 to reach about 48 PPD in the center with a roughly 140-degree FOV, and only small incremental changes would get them to 60 PPD with the same FOV.

Appendix: More on Hypervision

I first encountered Hypervision at AWE 2021 with their blended Fresnel lens 240-degree design, but as this blog primarily covered optical AR, it slipped under my radar. Since then, I have been covering Optical and Pass-Through mixed reality, particularly pass-through MR using Pancake Optics. By AR/VR/MR 2023, Hypervsion demonstrated a single lens (per eye) 140-degree and a blended dual lens and display 240-degree FOV (diagonal) Pancake Optics designs.

These were vastly better than their older Fresnel designs and demonstrated Hypervision’s optical design capability. In May 2023, passthrough MR startup Lynx and Hypervision announced they were collaborating. For some more background on my encounters with Hypervision, see Hypervision Background.

Hypervision has been using its knowledge of pancake optics to analyze the Apple Vision Pro’s optical design, which I have reported on in Hypervision: Micro-OLED vs. LCD – And Why the Apple Vision Pro is “Blurry,” Apple Vision Pro Discussion Video by Karl Guttag and Jason McDowall, Apple Vision Pro – Influencing the Influencers & “Information Density,” and Apple Vision Pro (Part 4)—Hypervision Pancake Optics Analysis.