High-density grating pair for displacement measurement

A novel method of displacement measurement based on a high density grating pair is proposed. When a laser beam is incident normal to a closely placed high density grating pair, efficiencies of transmission diffraction orders will change periodically along with the relative displacement of the two gratings in the grating period direction. The period of efficiency changing is equal to the grating period, thus measurement of displacement in the grating period direction can be achieved by detecting the power of diffraction orders.