提出了基于数字微镜器件(DMD)的双曝光头总体结构, 该结构可同时刻划母尺的周期和非周期两个光栅码道。单曝光头包含曝光光源、调焦光源、DMD和投影镜头四部分, 曝光光源由激光器、准直镜组、二维微透镜阵列和场镜组成。本文利用光学软件TracePro设计该光源, 实现了能量的平顶分布, 在14 mm×10 mm的照明面上均匀性达到95%以上。利用光学软件Zemax设计了工作在双波段(曝光光源0.403~0.407 μm和调焦光源0.525~0.535 μm)的共焦投影镜头, 采用了二向色镜和分光棱镜使其能在曝光的同时进行实时调焦, 优化后的系统在曝光波段和调焦波段均达到衍射极限, 最大畸变为0.009%。与传统的光栅尺刻划技术对比, 设计的曝光系统具有工艺简单、制作速度快、精度高等优势, 可用于长、超长计量光栅的制作。

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 mm×10 mm. A confocal projective system at two wavebands (exposure source at 0.403-0.407μm and focusing source at 0.525-0.535 μm) 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.