Patent ID: 7375820

Claim:
An interference measuring apparatus comprising: an optical system for dividing a coherent light beam into two light beams, causing the divided two light beams to pass along discrete optical paths and making the two light beams into linearly polarized light beams orthogonal to each other and giving modulation to the phase of the wavefront of at least one of them, and again superposing the wavefronts of the linearly polarized light beams one upon the other; a light dividing member for dividing the light beams superposed one upon the other by said optical system into a plurality of light beams; a light-transmissive element including a plurality of light passing areas, wherein said plurality of light passing areas have different optical path lengths so as to give the light beams a phase difference of integral multiples of a quarter wavelength; and a plurality of light receiving elements for individually receiving the light beams polarized by said light-transmissive element, a plurality of different interference phase signals being provided by the reception of light by said light receiving elements, wherein the light-transmissive element comprises a single substrate and thicknesses at the respective light passing areas in the light-transmissive element are different from each other.