Optical heterodyne laser encoder with sub-nanometer resolution

This paper presents a novel laser encoder for sub-nanometer displacement measurement. It is based on optical heterodyne interferometry and two sets of conjugate optics with a symmetric and quasi-common-path optical configuration. It offers displacement measurements of high stability, high resolution. The theoretical analysis shows that our method can effectively compensate misalignments resulting from the dynamic runout in laser encoders. Experimental results reveal that the laser encoder can detect a displacement variation down to sub-nanometer range