Resolution-enhanced phase retrieval for fringe reflection technology with structured light illumination

Owing to its advantages of simple system structure, large dynamic range and high measurement accuracy, fringe reflection technique (FRT) is becoming a powerful tool for specular free-form surface testing in the fields of reverse engineering, defect inspection, optical manufacturing, etc. However, due to the optical transfer function (OTF) of the FRT optical system, high-frequency information on the surface of an element under test is easily lost, which affects the high-precision acquisition of three-dimensional (3D) topography especially in microscopic measurement. Although the above problem can be suppressed to some extent by using or designing high-performance optical systems, the significant increase in the complexity and cost of the measurement system is sometimes unacceptable. To overcome the afore mentioned issue, a resolution-enhanced phase retrieval algorithm based on structured illumination microscopy (SIM) for FRT with an ordinary optical system is proposed in this paper. The combination of FRT and SIM is realized by projecting conventional phase-shifting fringe patterns in multiple directions. In principle, resolution-enhanced phase retrieval with super-diffraction limitation (up to twice the pass band of OTF) can be realized through spectrum extraction, stitching and shifting. A low-cost, compact, coaxial FRT setup based on open-source hardware is designed and built for experimental verification. Simulations and experimental results demonstrate the effectiveness of the proposed technique.