Polarization cameras integrated with conventional four-channel Micro-Polarization Arrays (MPA) are usually used as phase shift devices in focal plane-type interferometric systems to achieve simultaneous phase shifts. However, such phase shift devices suffer from low sampling rates and a lack of mature resolution reconstruction techniques to resolve pixel-level alignment errors. To solve such problems and further improve the phase reconstruction accuracy of the focal plane interferometric system, this paper proposes to apply the "Bayer-like" three-channel MPA to the interferometric system to realize the simultaneous phase shift. The arrangement of the three-channel MPA can reduce the processing complexity of the element and improve the inter-channel sampling rate. In addition, this structure can better utilize the resolution reconstruction idea of Color Filter Array (CFA) to solve the inherent pixel-level alignment error problem between simultaneous phase shift interferograms. Taking lateral shearing interferometry as an example, the process of acquiring simultaneous phase-shifted interferograms and phase reconstruction in an interferometric system with three-channel MPA is verified by simulation. The experiment results shows that the proposed three-channel MPA structure performs better than the traditional four-channel MPA structure in terms of visual reconstruction effect and quantitative index of phase reconstruction.
The aspheric surface testing system based on the shearing interference principle is used to better analyze how the installation and fabrication errors of linear polarizer affects the precision of the aspheric surface. The effects of the angle error of the linear polarizer and the phase-shifting error of the wave plate on the reconstruction of the aspheric surface are studied. Constructing the model of the Jones matrix with the error term system, the reconstruction surface and residual after the corresponding error system are obtained using the four-step phase-shifting and differential Zernike method. The polarizer array of an angle of θ was varied from ( θ − 1 deg ) to ( θ + 2 deg ) every 0.2 deg, and the changes of the fitting surface and the residual surface were simulated. The phase-shifting error of the simulated one-fourth wave plate was <λ / 300. Then, the change of the fitting surface and residual surface when these two errors exist at the same time were simulated. The simulation results show that the influence of the phase-shifting error of the wave plate on the fitting surface is much greater than the angle error of the polarizer array. When assembling the interference system, the phase-shifting error of the wave plate should be <λ / 300 when the light transmission angle error of the polarizer array is between −0.2 deg and 0.2 deg, which will ensure the testing precision of the aspheric surface testing system.
Based on birefringence theory and polarization-synchronized phase-shifting lateral shearing interferometry technology, we proposed a compact and simple polarization phase-shifting lateral shearing interferometer using a polarization camera integrated with a phase-shifting array of micro-polarizers. This interferometer is designed to realize a common optical path synchronous phase-shifting lateral shearing interference for aspheric surface testing system. This interferometer is composed of a polarization beam displacer (PBD), a quarter-wave plate (QWP), polarization camera (PCam). With the polarization birefringent crystal used as the PBD to realize the lateral shearing, and the parallel beam is divided into linearly polarized light whose polarization directions are orthogonal to each other. With the QWP changed the shear beam formed by the interference of the measuring beam and the self-copy beam into circularly polarized light with the opposite rotation direction. Next, with the micro-polarizer phase-shifting array on the PCam obtained four shearing interferograms with a phase-shifting difference is π/2, which allows for the implement of aplanatic and common optical path shearing interferometer. Therefore, the system possesses significant advantages of simple structure, compact and strong antiinterference ability. Then, by the four-step phase-shifting algorithm demodulated the measurement light field distribution on the shearing interferograms. Finally, using the Zernike polynomial fitting method realized the surface shape reconstruction of the interferogram wavefront. The effectiveness of the interferometer is demonstrated by simulations and experiments, which research results showed that the optical measurement method can extract interferogram information in real time and directly measure the wavefront phase distribution.
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