A novel method for identifying the order of interference using phase‐shifting digital holography

Summary In this paper, we introduced a mathematical method for measuring the optical path length differences (OPDs), which is suitable for large OPD values where the fringes connections are difficult to detect. The proposed method is based on varying the width of the fringes, without changing the wavelength of the used coherent source. Also, in this work, we discussed the need for such method in off‐axis phase‐shifting digital holography. Low‐resolution off‐axis holograms failed to detect the correct interference order. In general, off‐axis phase‐shifting digital holography is limited by the resolution of the captured holograms. The results obtained using our proposed technique were compared to the results obtained using off‐axis phase‐shifting digital holograms and conventional two‐beam interferometry. Holograms were given for illustration. Lay description Off‐axis phase‐shifting digital holography is limited by the resolution of the captured holograms. Low resolution off‐axis holograms failed to detect the correct interference order. A mathematical method is introduced for measuring the optical path length differences, OPD. The proposed method is suitable for large OPD values where the fringes connections are difficult to detect, as well as, small OPD.