A Compact Dual-Oblique-Fiber Heterodyne Phase-Shifting Point Diffraction Interferometer.

Point diffraction interferometers (PDIs) utilize a near-ideal spherical wavefront generated by point diffraction as the reference, providing a high-quality measurement benchmark independent of reference surface quality. In this work, a compact dual-oblique-fiber heterodyne phase-shifting point diffraction interferometer (DOF-HPSPDI) is proposed. A dual-oblique-fiber point diffraction wavefront generator (DOF-PDWG) is designed to generate the reference and measurement beams separately. The proposed configuration enables efficient utilization of the divergence of the fiber-generated diffracted wavefront, while the reflective structure at the fiber end faces allows the two beams to propagate along a common path. In addition, the close spacing between the two oblique fibers minimizes system errors. Heterodyne phase-shifting interferometry (HPSI) is employed to retrieve the wavefront phase from the interferograms. Theoretical system errors are analyzed through simulations, and experiments verify the feasibility and stability of the proposed system. This work provides a low-cost, compact, and highly stable point diffraction interferometer, offering a promising device for high-precision optical testing and sub-aperture stitching of large-aperture optical components.