A Diffraction Grating Scale for Long Range and Nanometer Resolution Kuang-Chao Fan*, Bai-Kun Li and Chi-Hui Liu Dept. of Mechanical Engineering, National Taiwan Univ., 1, Sec.4, Roosevelt Rd., Taipei 106, Taiwan ABSTRACT This paper presents a novel design of a laser linear encoder based on the principle of diffractive interferometry. It adopts a special design in optical path that can increase the alignment tolerance between the optical head and the grating. Because of the simple optical configuration and the merit of compact size, it can effectively reduce the environmental disturbance and allow higher stability. In addition, the signal process circuit can effectively decrease three major errors: the DC shift difference, the electronic gain difference and the phase orthogonal error of two sinusoid al output signals. The resolution can reach to 1nm. Experiment results showed the standard deviation was below 17nm for 15mm travel in normal laboratory environment. Keywords: Linear encoder, diffraction gratings, interferometer, nanometer resolution 1. INTRODUCTION In the development for micro/nano technology, many nano-scaled manufacturing and measuring systems adopt capacitance sensor to measure nanometer displacement, but the measuring range is limited. However, sensors with long measuring distance and high resolution, such as laser interferometer, are expensive and subjected to be affected by unstable environment. Thus the need of compact, high resolution, high stability and easy-to-use displacement sensor or is becoming more indispensable. The displacement measurement of interference technique of grating has been widely used. Ishii and Nishimura proposed a radial grating which can detect diffraction light and modulate intensity of light source 1 . Sawada used lithography method to develop an extremely small integrated microencoder whose size is less than 1mm long 2 . Lee used aberration compensation method to correct the wavefront of diffraction light in laser encoder 3 . *fan@ntu.edu.tw; phone 886 2 2362-0032; fax 886 2 2364-1186 Fifth International Symposium on Instrumentation Science and Technology, edited by Jiubin Tan, Xianfang Wen, Proc. of SPIE Vol. 7133, 71334J © 2009 SPIE CCC code: 0277-786X/09/$18 · doi: 10.1117/12.815188 Proc. of SPIE Vol. 7133 71334J-1