Pancake lenses bring compact VR HMD
Why are Today’s VR HMD So Big?
It’s natural to wonder why even the latest VR headsets are essentially just as bulky as the first generation launched back in 2016. The answer is simple: optics. Unfortunately the solution is not so simple.
Every consumer VR headset on the market uses effectively the same optical pipeline: a micro display behind a simple lens. The lens is there to focus the light from the display into your eye. But in order for that to happen the lens needs to be a few inches from the display, otherwise it doesn’t have enough focusing power to focus the light into your eye.
That necessary distance between the display and the lens is the reason why every headset out there looks like a box on your face. The approach is still used today because the lenses and the displays are known quantities; they’re cheap & simple, and although bulky, they achieve a wide field-of-view and high resolution.
Why the pancake optics are emerging as a leading candidate for VR HMD?
Rcently in the effort to make VR headsets more compact,the pancake optics are emerging as a leading candidate. Using polarization, the pancake technology is possible to bounce light back and forth multiple times along an optical path before eventually letting it out and into the wearer's eye to allow the lens and the display to move much closer together, resulting in a more compact headset. But if it's perfect one?
Probably not. Pancake lenses have very low optical efficiency – they block most light, making typical displays look dim and washed out. This can be worked around with very bright displays, but that increases the power requirement, which could be a barrier to battery-powered devices. Smaller, closeup displays also make it challenging to deliver a wide field of view.
The differences between Pancake and Fresnel lenses?
When comparing Fresnel and Pancake, there are a few factors to consider. Where the screen light is originating from and the shape of the lens. The time it takes entering the lens versus exiting. As well as the wavelength (color) of the light itself.
The Fresnel optics features a wide field of view compared to Pancake but is prone to chromatic aberrations (ghosting/overlapping colors). Furthermore, software calibration taking up processing power must account for the Fresnel lens known as ‘pincushion distortion’. This distortion is similar to an image being stretched out in all four corners. The software then must artificially stretch the image further to normalize what is viewed by the wearer, all in real-time.
Pancake, on the other hand, works by folding many lenses together in a curve, bouncing light within the glass or plastic. In effect, slimming the distance needed between the wearer’s eyes and the display. This opens VR HMDs to be thinner and lighter, while it also frees up processing power, as the distortion problem for the Pancake is not present. Lastly, the Pancake design does not have the chromatic aberration present like the Fresnel.
The downside to the Pancake optics, compared to Fresnel, stems from Pancake’s bouncing of light within the lens itself, resulting in low light efficiency. In short, it dims the perceived image for the wearer and that is why John C.C. Fan, the founder of Kopin, pointed out that the P95 Pancake lens works well with ‘high-brightness micro displays’. Furthermore, the problem of ghosting is also a scourge for the Pancake lens.
In summary, Pancake features more benefits than disadvantages compared to Fresnel, both in perceived image quality and the significantly slimmer and lighter form factor that Pancake enables.
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Conclusion
Like augmented reality, VR is on a path to a slimmer and lighter future. A design philosophy, expanding the VR market, as casual consumers will see interest in adopting a VR HMD. Effectively, this will mature the virtual reality market and expand ancillary services propelling the technology further.
The best indicator of this trend was the released?HTC Vive Flow focusing on a stylish design, a broader customer segment, and differentiation on non-tech elements such as meditation.
The enabling technology behind this trend is the Pancake lens design, by itself nothing new but revolutionary within VR HMDs. It will bring on stylish designs that attract a wider audience and will be able to detach itself from external devices such as a capable laptop or smartphone.
2022 and beyond will be the time when virtual reality matures in both hardware and use cases, and the not-talked-about-enough technology, the Pancake optics design, is the enabler of this.
The Role of us in Pancake optic for VR HMD?
We, as an electronics manufacturer best known for its microdisplays. In recent years has been eyeing the emerging XR industry as a viable market for their wares. To that end, we has been steady at work creating VR displays and optics that it hopes headset makers will want to snatch up. We have developed a pancake lens for 1.03" micro oled and has been for mass production.
This Optical assembly module is a see-close type applied in near eye display application. It consists of a 1.03inch OLEDoS module, several lenses and optical films, inner and outer tubes and other mechanical parts. It has following main features： ?
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