Absolute measurement method for the phase of the complex coherence coefficient

A method for measuring an absolute phase of a complex coherence coefficient of an extended light source based on minimum light intensity values, comprising

• providing an optical system comprising an equivalent pupil plane with a plurality of baselines, wherein each of the baselines comprises a pair of apertures at two end points P1 and P2 on the equivalent pupil plane,
• emitting optical signals from the extended light source through optical paths to the equivalent pupil plane, wherein the optical signals pass through the pair of the apertures at the two end points P1 and P2 on the equivalent pupil plane,
• obtaining interference fringes through interference coupling for the optical signals received through the pair of the apertures at the two end points P1 and P2 of the baseline on the equivalent pupil plane, wherein one of the optical signals passes through one of the two optical paths comprising an optical fiber retarder,
• controlling the optical fiber retarder by a computer to sweep optical path differences of the two optical paths such that a position of zero optical path difference of the two optical paths is included,
• performing DC removal and denoising on an interference curve of the interference fringes and obtaining an interference term, an envelope, and extreme values of the interference curve,
• obtaining the absolute phase φ of the complex coherence coefficient based on selection and comparison of the extreme values on the interference curve, wherein the absolute phase φ is the absolute phase of the complex coherence coefficient of any of the baselines on the equivalent pupil plane of the optical system,
• selecting a relative minimum light intensity value A in a first interval, wherein the first interval is at one side of a main lobe of the zero optical path difference of the interference curve, and change in the relative minimum light intensity values in the first interval is stable,
• selecting two extreme light intensity values B and C that are closest to the relative minimum value A from a second interval, wherein the second interval is at the other side of the main lobe of the zero optical path difference of the interference curve, and change in the extreme light intensity values in the second interval is stable, and, where C>A≥B, and
• counting the number of fringe periods between A and C, and when the number of fringe periods is an odd number, calculating and obtaining the absolute phase
• ϕ
• =
• ❘
• "\[LeftBracketingBar]"
• A
• -
• C
• B
• -
• C
• ❘
• "\[RightBracketingBar]"
• ⁢
• π
• ,
• and when the number of fringe periods is an even number, calculating and obtaining the absolute phase
• ϕ
• =
• (
• 1
• +
• ❘
• "\[LeftBracketingBar]"
• A
• -
• C
• B
• -
• C
• ❘
• "\[RightBracketingBar]"
• )
• ⁢
• π
• .