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Helmet mounted display system (HMD), Two optical display assemblies featuring precision-coated transparent glass panels mounted in black structural frames. The glass surfaces reflect vivid green, pink, and purple hues, indicative of specialized optical coatings. The assemblies are placed on a light background, and their reflections create colorful patterns beneath them. These components are likely used in augmented reality (AR) or head-up display (HUD) systems, where precise light manipulation is critical

Head-Up Display (HUD) Combiner Coating

A Head-up Display (HUD) provides the ability to project information onto a transparent screen in a way 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 allowing both images appear to be at the same distance.

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HUD’s were originally developed for aircraft cockpits, so that flight information can be seen by the pilot without him having to refocus his eyes and look down at flight instruments, and this principle is now being used for other applications including automotive.

For aircraft in bright cloud or sunlight conditions, the display must be sufficiently visible to contrast with the background sky. The advent of near monochromatic green phosphors led to the development of HUD’s with increased display brightness. With this comes the possibility of using narrow bandwidth reflective ‘notch’ filters, whose peak reflection is centred at the same wavelength as the phosphor.

As only a narrow portion of the visible spectrum is reflected, most of the outside world spectrum is transmitted, only losing a narrow portion of the green spectrum.

A powerful and efficient method for generating colour selective reflection coatings for HUD combiners is by rugate filter technology.

G&H has perfected techniques for the design and manufacture of rugate coatings for head-up displays which provides high visible transmission while maintaining up to 80% reflection of the display. The technology exhibits major advances over other HUD combiner technologies in terms of display brightness, photopic transmission, weight, ruggedness, insensitivity to head movement, and freedom from flare.

Rugate technology has also been applied for displays with more than one colour and G&H has pioneered the manufacture of HUD combiners for military avionics using double and triple notch rugate filters.

Manufacture is by plasma assisted deposition providing coatings that are extremely rugged and insensitive to temperature and humidity variations.

  • HUD Coating Graph

    HUD coating graph, A spectral transmission graph for a HUD (Head-Up Display) coating, showing wavelength (nm) on the x-axis (400 to 700 nm) and percentage transmission on the y-axis (0 to 100%). The curve dips sharply at three distinct wavelengths, creating deep notches around 470 nm (blue), 530 nm (green), and 640 nm (red), indicated by arrows in corresponding colors. These notches represent the wavelengths that are reflected or blocked. The rest of the spectrum remains above 90% transmission. To the right of the graph, performance metrics are noted

  • Graded Notch Combiner

    HUD combiner coating graph, A line graph titled "Graded notch combiner" displays transmittance (%) on the y-axis and wavelength (nm) on the x-axis. The graph ranges from 0% to 100% transmittance and 400 nm to 700 nm wavelength. Several colored curves (red, blue, green, purple) show a dip in transmittance centered around 545–555 nm, forming a notch-shaped pattern. Each curve has a different depth, indicating varying levels of light blocking at the center wavelength, with transmittance returning to near 100% outside the notch region.

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