Quad-Pass Homodyne Interferometer With Picometer Periodic Nonlinearity and No Beam Walk-Off

To accommodate the stage with large motion range and large rotating operation tolerance, a quad-pass homodyne interferometer without beam walk-off (BWO) is presented in this article. Based on the design that the measuring beam (MB) retraces the path of the incident beam, the system is immune to the inclination angle of the measured mirror (MM). The proposed optical structure eliminates BWO to improve fringe contrast, which is superior to the existing double-pass interferometers. Meanwhile, based on the characteristic of inclination immunity, the polarization leakage is isolated from the detector to effectively eliminate the periodic nonlinear error (PNL). A multichannel phase shift module (MCPSM) based on the spatial phase delay not only effectively improves the compactness of the interferometer but also can effectively suppress the PNL caused by the ghost reflection after combining with the multiple measurement signals algorithm. The interferometer is verified by simulations and experiments. In the experiments, the large rotating operation tolerance (±40 mrad) can be achieved. The residual PNL of each order is 1 pm/ $\surd $ Hz.