Apparatus and method for high-speed phase shifting for interferometric measurement systems

A method for modulating a phase difference of a pair of coherent optical beams, the method comprising:

• illuminating a transparent plate at a first time with a pair of coherent optical beams, the transparent plate having a first region having a first optical thickness and a second region having a second optical thickness, each of the coherent optical beams being incident at the transparent plate at one of the first and second regions wherein a phase difference of the pair of coherent optical beams exiting the transparent plate has a first value;
• illuminating the transparent plate at a second time with the pair of coherent optical beams so that one of the coherent optical beams is incident at the transparent plate in a region different from the respective region for the coherent optical beam for the first time, wherein the phase difference of the pair of coherent optical beams exiting the transparent plate has a second value;
• and
• illuminating the transparent plate at a third time with the pair of coherent optical beams so that one of the coherent optical beams is incident at the transparent plate in a region different from the respective region for the coherent optical beam for the second time, wherein the phase difference of the pair of coherent optical beams exiting the transparent plate has a third value.

A fringe projection and imaging system, comprising:

• a transparent plate having a first region having a first optical thickness and a second region having a second optical thickness, and adapted to receive a pair of coherent optical beams;
• a cyclical motion mechanism coupled to the transparent plate and adapted for planar translation, each of the coherent optical beams being incident at the transparent plate at one of the first and second regions and being phase delayed according to the optical thickness at the respective region, wherein the location of incidence of each of the coherent optical beams traverses a cyclical path defined by the planar translation so that a phase difference of the coherent optical beams is periodically modulated according to a difference in the optical thicknesses as the locations of incidence of the coherent optical beams transition between the first and second regions;
• an imager configured to acquire an image of a fringe pattern generated on a surface illuminated by the coherent optical beams after exiting the phase plate for a plurality of values of phase difference for the coherent optical beams;
• and
• a control module in electrical communication with the cyclical motion mechanism and the imager to synchronize the acquisition of the image of the fringe pattern at each of the phase differences.