How Display Technologies work in AR/VR

When you put on a virtual reality (VR) headset, you are connecting virtually to another place whether that be real or imagined. Using AR you are able to overlay and view things on top of your real life. As these technologies become more and more engaging, people will start to connect VR and AR with not only gaming, but also other increasingly growing industries like healthcare, military, retail and the government which are finding new applications for the evolving technology already.

Today, the smartphone is a big deal when it comes to using a VR headset. But as this technology grows, there are still several more technical display requirements that must be met in order to fully achieve the affect and improve the user experience. It is important to understand how these work, and what Imaging Technologies already exist so that we can better understand how far we really can go with the technology.

Head-Mounted Devices

However, before going deeper into the fundamentals of Optics, we must properly understand how the human eye works, and the properties our eyes have.

Basics of the Human Eye

The Field of View is basically the total angular size of the image that would be visible to both the eyes. Binocular vision is a type of vision which basically explains how humans with two eyes are able to perceive three-dimensional images of its surroundings. Generally, the horizontal binocular FOV is 200 degrees in total and 120 degrees of that is a binocular overlap. The vertical FOV is around 130 degrees.

Inter-pupillary distance (IPD)

As the name suggests, it is the distance between the pupils of the eyes and is an extremely important consideration for binocular viewing systems. However, this can be a bit difficult to identify because this distance can vary depending on the gender and ethnicity of a person. Average IPD for adults is around 63 mm and the minimum IPD for children is around 40 mm.

It is very important to be accurate with the IPD or else there can be poor eye-lens alignment, image distortion, strain on the eyes or can cause a headache.

Eye relief
This is the distance from the cornea of the eye to the surface of the first optical element. It defines the distance at which the user can obtain full viewing angles. This is an important consideration especially for people who wear corrective lenses or glasses. Eye relief for spectacles is approximately 12 mm. Of course we want the customer to feel comfortable which is why enabling users to adjust the eye relief is extremely important for head mounted displays.

Augmented Reality (AR) displays

Optical see through

Binocular
In a Bi-nocular view each eye gets a different view which creates a stereoscopic view. Binocular display types provide a lot of depth cues and a sense of immersion. On the other hand, they can be very heavy and also very complex.

Some examples of this kind of display includes: Microsoft’s Hololens, and Epson’s Moverio.

Monocular
You probably guessed it, yes, this display provides a single channel for viewing. Generally, this channel is in front of one eye so that the user is able to view the real world completely through another eye. Monocular displays are often are good for information displays, mobile computing or video viewing with connectivity to mobile devices. However, these type of displays provide less stereo depth cues than binocular cues.

Google Glass and Vuzix Smart Glasses are both good examples of monocular display.

Video see through

Immersive Displays

Cave automatic virtual environment

Hemispheres and Domes

Example of a Cave automatic virtual environment in real life

Optical Design System

Non-pupil forming
Non-pupil forming is made up of a single lens. This type of architecture uses a single magnifier to directly align the rays of light from the display panel.

Pupil forming
The non-pupil using an effect known as pincushion distortion. In pupil forming architectures, another lens that produces a barrel distortion is used to nullify the effect. These are usually commonly seen in more non-immersive type displays.

Imaging Technologies

  1. Liquid Crystal Displays (LCD): A flat-panel display that uses the light-modulating properties of liquid crystals which do not emit light directly, instead using a back light or reflector to produce images in colour. This can be commonly seen in HD TV's.
  2. Organic Light Emitting Diode (OLED): A light-emitting diode (LED) which works without a back light because it emits visible light.
  3. Liquid Crystal on Silicon (LCoS) Microdisplay: This is a smaller reflective “micro display” which uses a liquid crystal layer on top of a silicon back plane. This is how LCD projectors use transmissible, allowing light to pass through the liquid crystal.

Major Takeaway

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