Interferometric autocollimator based on full-field heterodyne phase-shifting interferometry

This paper presents an interferometric autocollimator based on full-field heterodyne phase-shifting interferometry (HPSI) for high-precision small-angle measurement. An oblique fiber in combination with an autocollimating objective lens is employed as the autocollimation module to generate both the reference and measurement beams. The oblique fiber serves not only as a point light source and a beam splitter, but also as a position-sensing element that ensures the reference beam retraces the incident path, thereby establishing the autocollimation condition and resulting in a compact and self-consistent system architecture. Heterodyne phase-shifting interferometry is incorporated to retrieve the wavefront difference between the reference and measurement beams, enabling accurate determination of angular deviations. In addition, a fiber-coupling efficiency model is developed to evaluate the system error, and experiments are conducted to verify the feasibility and high-resolution performance of the proposed system.