An absolute surface encoder for measurement of absolute in-plane position with a mode-locked femtosecond laser and a planar scale grating having variable periods along the two orthogonal directions is proposed. In the proposed method, the absolute in-plane position is measured through observing the spectra of the coupled groups of the positive and negative first-order diffracted mode-locked femtosecond laser emanated from a single point on the planar scale grating. Due to the dispersive effect of the planar scale grating having variable periods, each of the diffracted modes has a unique angle of diffraction associated with the absolute position information. Therefore, the absolute in-plane position can be detected by obtaining the peak frequencies in the optical spectra of the coupled positive and negative first-order diffracted beams received by dual detector units. The dual-detector configuration of the optical head also contributes to improving the robustness of the absolute position measurement against the angular error motion of the planar scale grating. Furthermore, interference signals capable of being used for the improvement of the absolute position measurement can be generated under the dual detector configuration. Results of the numerical calculations for the theoretical verification of the proposed method, fabrication of a scale grating having a variable period (VLS grating) with interference lithography, design and development of the optical head, as well as the results of basic experiments by using the developed optical head and the VLS grating, are reported.

提出了一种绝对表面编码器，其用于利用锁模飞秒激光器和沿两个正交方向具有可变周期的平面光栅来测量平面内的绝对位置。在所提出的方法中，通过观察从平面刻度光栅上的单个点发出的正，负一阶衍射锁模飞秒激光的耦合组的光谱来测量平面内的绝对位置。由于具有可变周期的平面刻度光栅的色散效应，每个衍射模式具有与绝对位置信息相关的唯一衍射角。因此，通过获得由双探测器单元接收到的正负负一阶衍射光束的光谱中的峰值频率，可以探测出绝对平面内位置。光学头的双检测器配置还有助于提高绝对位置测量抵抗平面光栅尺的角误差运动的鲁棒性。此外，在双检测器配置下可以产生能够用于改善绝对位置测量的干扰信号。数值计算的结果，用于理论验证该方法，用干涉光刻技术制造具有可变周期的光栅尺（VLS光栅），光学头的设计和开发，