A coating capable of expanding the diameter of a laser beam by a factor of one hundred has been developed by a Fraunhofer institute in collaboration with SeeReal Technologies. The technology could enable backlighting for holographic displays, which would allow 3D films to be watched without the need for 3D glasses.
In order for holographic displays to present complete three-dimensional display of images, the laser beam needs to be expanded in accordance to the size of the display. However, creating a laser beam with a diameter of a cinema screen, for example, is difficult to realise. Conventional methods involve the use of large lens systems, which are clunky as well as expensive to manufacture.
The coatings developed by the Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology, in collaboration with SeeReal Technologies, a company involved in the research and development of holographic display technology, enable the use of low power lasers for illumination.
The laser is directed at a very flat angle onto a glass plate (here 5 degrees, respectively 85 degrees against the vertical). In a similar way to how a person’s shadow extends as the sun sets, the diameter of the laser beam increases; a small spot becomes an elongated ellipse.
In a second step, the elongated ellipse impinges again on a second glass plate at 5 degrees, whereby the second direction of the ellipse, the ‘short axis’, is elongated. Therefore, the laser spot is expanded to a circle large enough to illuminate the entire display.
If the same laser was fired onto an uncoated glass plate at such a flat angle, approximately 73 per cent of the beam would be reflected. And, in the case of two ‘expansion steps’, more than 90 per cent of the original intensity would be lost.
The anti-reflective coatings, which were manufactured at Fraunhofer FEP, were installed into a demonstrator of SeeReal Technologies. For this demonstrator, 24 layers of the anti-reflective coating were required. The layer thickness of all 24 layers had to be deposited consistently, with precision of within a few nanometres. Even slight deviations would have led to loss of the desired anti-reflective properties, which would impact picture and colour quality.