绝对式光栅尺母尺刻划曝光系统

Exposure optical system in lithographic main scale of absolute optical encoder

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14mm×10mm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0.403～0.407μm和调焦光源0.525～0.535μm)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 2Dmicro-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 14mm×10mm.A confocal projective system at two wavebands（exposure source at 0.403-0.407μm and focusing source at 0.525-0.535μm）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 reachesdiffraction 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.