Types of pattern coatings

OE® supplies both laser-engraved and photolithography technique patterns for projection or distortion calibration.

Laser engravings

Several layers of dielectric material are deposited over the glass substrate. The result is a "dichroic" mirror which is very similar to Aluminium coating. A laser source is then used to remove parts of the substrate and let light pass through the engraved surface areas.
This technique is fast, inexpensive, but not very accurate as the laser spot side is 30-40 micron and real geometrical resolution can't be precisely stated.

Photolithography

A chrome layer is present on the glass substrate. With a similar technique to that used for electronics boards manufacturing, a photoresistor is placed on the chrome layer and then gets UV developed. Acid is then used to remove the undeveloped photoresistor areas so that the desired chrome pattern is left on the glass surface. With the UV development being carried out by means of a high precision plotter, a geometrical accuracy in the range of few a microns over a surface of some tens of millimeters can be easily achieved.

The roughness of the pattern edges is also very limited, in the range of 1.5 micron roughness or less.