Sinusoidal phase-modulation interferometer capable of measuring 1D displacement and 2D in-plane displacement

Interferometers for displacement measurement with picometer resolution are required. The main cause of degradation of interferometer resolution is air fluctuation. To investigate the effect of air fluctuation on displacement resolution, we have developed a sinusoidal phase modulation interferometer capable of measuring 1D displacement with 10 picometer resolution and 2D in-plane displacement (air fluctuation). The interferometer is of Michelson type with different polarizations in the reference and measurement arms. By exchanging the phase-modulated electro-optical modulator and photodetector of this interferometer, 1D and 2D in-plane displacements can be measured, respectively.