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New ways to produce colors

Traditional ways to produce colors are printing technology and combining different colors in a display technology. At the InFotonics Center Joensuu and Nanocomp Ltd. researchers are developing a new technology for color production based on ideas of researcher Joni Orava. This technology is based on diffractive optics.

In this technology, light is guided to a plate, where is an optical fine structure. This structure is designed so, that only predefined wavelengths are reflected from the plate. The optical fine structure has been drawn by electron beam. In this drawing the width of a line is few tens of nanometers. The basic principle is shown in Figure 1.

Figure 1. Formation of colored light as reflection from grating structure.

In color production, the narrow wavelength peaks of a fluorescent light (a normal office light, Figure 2) have been utilized. These peaks produce pure colors and the office light looks white as combination of these colors.

Figure 2. Color spectrum of an office light. Narrow peaks of different color components are easily recognizable.

For example in television the colors are produced as combination of red, green, and blue color. In this diffractive optical technology, the colors are formed by combining four colors: blue, bluish green, green, and red (Figure 3).

Figure 3. Color spectra of four component colors produced by diffractive optical technology. Desired color is produced by combining these four colors: blue, bluish green, green, and red.

The colors, which are recognizable to humans are bordered by blue line in Figure 4. The colors are represented in xy-chromaticity coordinates. Dashed line border those colors, which can be produced by a TV-screen or by a computer display. Solid red line marks the region of colors reproducible by the diffractive optical technology. As can be recognized, diffractive optical technology can produce colors, which are not producible e.g. by standard TV-technology.

Figure 4. The regions of possible colors in the xy-chromaticity coordinates, human perceived colors (Blue line), colors reproducible e.g. on a standard TV-screen (dashed red line), and the colors reproducible by diffractive optical technology (solid red line).

The basic colors produced by diffractive optical technology, are shown in Figure 5 and the reproducible colors in xy-chromaticity coordinates are shown in Figure 6. Both images are photographed directly from the metal plate, on which the colors are produced. In order to produce colors, a grating structure with a line width of some tens of nanometers have been drawn by an electron beam on the metal (1 nanometer is 1 millionth of millimeter).

Figure 5. Basic colors of diffractive optical color technology.

Figure 6. xy-chromaticity color coordinates on a metal plate produced by diffractive optical technology.