A kind of optical interference measuring system with 8 times optical path difference

A kind of 2-D measuring system with nanometer accuracy is proposed. Based on a new method called coupled differential interferometry, an optical system with 8 times optical path difference is adopted, with characters of simple, stable and compact optical layout, coupled differential interferometry. Symmetrical optical paths, multiplication optical path difference, Abble principle are utilized. Large-scale micromotion constant controllable piezoelectric motor is used for the driving equipment, with the controlling system which moves much more reasonable and steady. The high accuracy interferometric signal processing system, with Heydemann model, the three errors (quadrature phase error, unequal, amplitude of two signals and zero offsets) are compensated. Then the displacement is obtained. Finally the accuracy of the total measuring system is analyzed. The calculated accuracy of the total system is about ±2.5nm. On the base of accuracy analysis, the test was given by comparing with the capacitive micrometer and obtained the measuring accuracy of 10-12nm.