Research On Element And Algorithm In Division Of Focal-Plane Array Approach

In phase shifting interferometer and imaging polarimeter, multiple images need to be captured in order to reconstruct the measured phase or Stokes vector. The commonly used approach is capture these images sequentially, which suffer from the sensitivity to the environment, both vibration and air turbulence. Based on the pixeled-mask, the division of focal-plane array approach can complete the measurement by captureing only one image, which can be used to the measurement of dynamic target. Many measurements can be averaged to reduce the effects of air turbulence.The key element of the division of focal-plane array approach is pixeled-mask, which is a polarization element array. Up to now, the pixeled-mask is fabricated by complex micro-nano processing technology. In this paper, the azo-polymer orientation array has been fabricated by simple photolithography technique. Due to the photo-induced optical anisotropy of azo-polymer, the azo-polymer orientation array is a retarder array, which can be used as a pixeled-mask. Experimental results are provided to verify its application in the division of focal-plane array measurement.Detailed research contents are shown as follows:(1) The photo-induced birefringence of azo-polymer film is measured based on the photoelastic modulator. Upon illumination by polarized light at405nm, The photo-induced birefringence of azo-polymer film will increase and reach a stable value. After the inducing light is turned off, the birefringence will decrease a little and reach a new stable value, which is121degree in our test.(2) The polarization phase-shifting interferometer by rotating the azo-polymer film with photo-induced optical anisotropy has been designed. By changing the angle of the optical axis of the azo-polymer film to π/3,π/6,-π/6and-π/3, four phase-shifted fringe patterns were obtained sequentially, from which phase difference between orthogonal polarized light could be calculated.(3) Four exposures are needed to fabricate of the azo-polymer orientation array, which is is a retarder array. The size of a retarder is10μm×10μm, and its retardance is120degree. Based on the azo-polymer orientation array, a single-exposure polarization phase-shifting interferometer has been designed, which has been experimentally verified by measuring the interference of two plane mirrors. Furtherly a simultaneous imaging polarimeter of coherent light has also been realized.(4) The algorithm error of the retader array-based simultaneous phase-shifting interferometer has been studied. The pixel-to-pixel registration error of average algorithm, interpolation algorithm and frequency domain reconstruction algorithm has been compared. The frequency domain reconstruction algorithm has the minimum error and the average algorithm has the maximum one. The frequency domain reconstruction algorithm requires the retaedance of the retader array to be126.9degree, while the cubic spline interpolation does not.(5) The algorithm error of the retader array-based simultaneous imaging polarimeter has been studied. The pixel-to-pixel registration error of interpolation algorithm and frequency domain reconstruction algorithm has been compared. When the polarization image is band limited, the error of frequency domain reconstruction algorithm is less than the cubic spline interpolation. In general, polarization image has many boundaries. When the boundary is fuzzy, both the frequency domain reconstruction algorithm and the cubic spline interpolation has small errors. When the boundary is sharp, errors of the frequency domain reconstruction algorithm is less than the cubic spline interpolation, but the cubic spline interpolation has smaller oscillation.