Two-dimensional encoder with independent in-plane and out-of-plane detection for nanometric measurement

We propose and demonstrate a new, to the best of our knowledge, optical encoder, which can measure in-plane and out-of-plane displacements simultaneously and independently. The symmetrical structure of the optical path can eliminate the impact from out-of-plane displacement on the measurement of in-plane displacement. The innovative new geometry also facilitates the multi-reflected diffracted beam to interfere with the same-order diffracted beam, so as to eliminate the impact from in-plane displacement on the measurement of out-of-plane displacement. An experimental setup is established to verify the two-dimensional independent measurement. The experiment result coincides with the one measured by two independent interferometers. The output of spectrum analysis shows that the two-dimensional independent encoder can be used for nanometric measurement.