Head up combiner

 Triple Notch Rugate Combiner Spectrum

Thin Film coatings for Head-up Displays

A head-up display (HUD) provides the ability to project information onto a transparent screen so that it appears to be floating in space as a virtual image. With suitable optics, the virtual image is combined with the view of the real world seen through the screen so that both images appear to be at the same distance. In this case, the screen is known as a combiner. When used in aircraft, the combiner enables the pilot to see flight information without having to refocus on flight instruments.

Because of advances in light engines using LED’s and lasers, these sources can generate very bright images in several colors, spurring the transition from monochromatic to multiple-color displays. With rugate technology, it is now possible to design and fabricate coatings with multiple reflective-notch coatings for the HUD combiner screen but providing high reflection efficiency of individual colors while maintaining clarity of view to the outside scene.  A typical example is shown on the home page.

John Allen of AJ Thin Films has a wealth of experience in the design of rugate coatings for single and multiple notch combiner coatings. In addition, designs and processes have been configured for dual graded rugate combiners for a number of military aircraft programmes. The rugate designs allow much greater display brightness simultaneously with high visibility through the combiners compared to conventional graded combiners. The powerful flexibility of the rugate approach allows the ability to vary the notch depth independently of the wavelength, a vital requirement in graded combiners.

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