Two-point diffraction interferometer for absolute distance measurement

We describe a novel method of measuring absolute distances by using a two-point diffraction source specially devised to generate two high quality spherical waves simultaneously with a small lateral offset. Interference of the generated two spherical waves produces a unique ellipsoidal phase distribution in the measurement space. A partial map of the resulted interference phase field is sampled and fitted to a geometric model of multilateration that allows absolute-distance measurements to be performed without 2π-ambiguity. The partial phase map may be obtained by use of either homodyne or heterodyne phase measuring technique. Test results demonstrate that high precision with 1 part in 10⁶ uncertainty can be achieved over 1 meter distance range.