The human eye has tremendous capabilities, but it is limited in its ability to focus on objects placed very near the eye. This inability to focus on near objects has lead traditional near-eye display developers to come up with complex optical solutions that make the near-to-eye image source appear to be located further away than it actually is. Innovega is developing an alternative display architecture that is based on enhancing the human eye’s normal vision capabilities so that it can focus on objects placed very near to it. This approach eliminates the need for any imaging optics in the near-eye display since the eye is now free to focus on this display just as it can focus on a traditional desk top display.
The ability to focus on near objects is achieved by embedding special optical components inside a contact lens called iOptikTM by Innovega. These components are small enough that they do not interfere with the wearer’s normal vision.
The picture below illustrates the key components of this special contact lens. The center path contains a small focusing lens that collects the un-collimated light radiating from the display and collimates it prior to its entry into the pupil. This collimated light can then be focused onto the retina normally by the eye’s biological optics. A narrow band RGB band-pass filter behind the small focusing lens prevents light from the surrounding environment from passing through the center region.
The outer region contains a three-band RGB notch filter that blocks the light radiating from the display panel. This is necessary in order to preserve image quality since display light bypassing the center lenslet would not be focused properly onto the retina. The notch filter ensures that the light from the display is only allowed into the pupil through the center focusing lens. A band-pass filter is also placed in front of the image source to ensure that only narrow bands of red, green, and blue are emitted from the eyewear.
Light from the viewer’s environment consists of broad band light so almost all of it is able to pass through the outer notch filter enabling the viewer to see the environment with normal vision.
The net affect of this light processing is to enhance normal human vision without detracting from the normal operation of the eye. Wearing these contact lenses is transparent to the user, except now they have the enhanced visual ability to see microscopic detail of anything with the proper spectral bandwidth. By making the red, green, and blue light coming from the micro-display panel match the spectral bands of the iOptikTM contact lens, every detail of the micro-display's image can be clearly seen by the user.
The separation of the display light processing from the surrounding environment light processing can also be done using polarization instead of spectral filtering. Innovega has used this polarization approach as a means to demonstrate its technology. The photograph on the right shows the polarization version of the iOptikTM contact lens. The central region contains the micro-display imaging optic. Surrounding that and completely covering the user's pupil is a polarization filter (light gray in the photo).
Placed on the eye, this contact lens is not visible to an observer. In addition, the wearer is not able to see any change to their vision other than the newly enhanced vision ability to see micro-displays located very close in to their eye. The components in the contact lens are not visible because they are located in the eye's "aperture plane" which is too close to the eye to be imaged onto the retina.
The iOptikTM contact lens allows light from the display to pass through the center of the pupil, and light from the surrounding environment to pass through the outer portion of the pupil. Each of these sets of light rays produces an image on the retina simultaneously with the other set. The brain then superimposes these two images to form a single image.
The picture below illustrates how the special contact lens works in conjunction with a micro-display to produce a virtual image. The outer filter within the outer region of the contact lens prevents the display light from entering the pupil except through the center aperture opening. The display light passing through the center opening first passes through the small focusing lens where it is collimated. It then passes through the center filter modified. From that point it enters the pupil where it is focused onto the retina by the eye’s biological optics.
Ambient light from the environment is able to pass through the outer filter. This light enters the pupil and is processed by the eye’s biological optics normally which focuses it onto the retina. The surrounding environment light that passes through the center focusing lens is actually defocused by this lens, but it is then blocked by the center filter preventing this defocused light from interfering with normal vision. The shadow cast by this blocked light does not affect the image other than to slightly lower the image intensity on the retina by about 5%.
There are two different types of filters that can be used for the center and outer filters. These filters can either be polarizing filters, or they can be spectral filters. In the case of polarizing filters, the outer filter would be oriented to block light from the micro-display (which also has a polarizer filter in front of it). The unpolarized light from the surrounding ambient would be free to pass through this filter. The center polarization filter would be oriented to pass the polarized light from the micro-display. In the case of spectral filters, the outer filter would be a three-band RGB notch filter. This notch filter would block the light from the micro-display because the micro-display would be designed to only emit narrow bands of red, green, and blue light. The broadband light from the ambient would be free to pass through this outer filter. The center filter would be an RGB band-pass filter. This would block all light except for the narrow bands of red, green, and blue. Since the micro-display is emitting narrow bands of red, green, and blue, its light would pass through the center band-pass filter.
This optical system allows for very wide field of view display images with high visual acuity without interfering with the wearer’s normal vision. The display image surface can either be an occluded display or a transparent display. For an occluded display, existing OLED and LCD micro-displays make excellent images. Transparent OLED or LCD display technologies are well suited for a transparent display which allows viewing digital images superimposed on the real world.