A simple technique for eliminating the nonlinearity of a heterodyne interferometer

A simple technique has been found to eliminate the nonlinearity of a heterodyne interferometer by using a simple phase compensation system with a rotated polarizer set up before the detector. This technique is generally valid for the nonlinearity caused by possible optical sources, such as ellipticity, and nonorthogonality of incident laser polarization states, imperfections of the beam splitter and retardation plates, as well as the variation of polarizing states caused by glass and mirror transmission, losses of optical power and misalignment of the interferometer. With this method, the elimination of the nonlinearity error is dependent on the rotation angle measurement and phase comparison which can easily achieve a high resolution better than 0.1°. Thus, the nonlinearity error can be easily reduced under a sub-nanometer resolution.