Abstract
A general structure for two photolithographic heads based on Digital Micro-mirror Devices (DMDs) is proposed for simultaneously lithography of the double-track codes of an absolute optical encoder. The total optical system includes an exposure light source, an focusing light source, a DMD and a projective lens. The exposure light source mainly consists of a laser, a collimation lens, a 2D-micro-mirror array and a field lens. The exposure light source is designed by TracePro software, and the uniformity of the energy distribution is above 95% in the area of 14 mm10 mm. A confocal projective system at two wavebands (exposure source at 0.403-0.407 m and focusing source at 0.525-0.535 m) is designed by Zemax software, in which the exposure and focusing can be realized in real time with a dichroscope and a prism. The imaging quality of the projective lens reaches diffraction limit at exposure waveband and focusing waveband, and the maximum distortion is 0.009%. Compared with traditional grating lithography methods, the exposure optical system has advantages on simpler process, fast manufacturing and high precision. It can be used in manufacturing long and ultra-long metrological gratings.
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