Distributed Aperture Synthesis Based On Digital Holography

The path synthesis is one of the effective methods to improve the resolution of digital holographic imaging.Holography is detected by using several subapertures with smaller diameter,and then the holograms collected from each subaperture are integrated according to their spatial arrangement,as to obtain a larger numerical aperture.In practice,the influence of atmospheric turbulence,system assembly error and other factors,the direct integration of sub-aperture hologram is usually difficult to achieve the theoretical image quality.For this reason,the aperture synthesis technique based on image index optimization is studied in this paper.For the digital off-axis holography system,the relation between the angle of the local reference light and the pixel size of the photodetector and the angle of the target light are analyzed in detail from the two aspects of digital recording and spectrum separation.The simple and practical design basis is given.In order to solve the high order phase error in single sub-aperture,a calibration method combining diffraction distance scanning,target image correlation and stochastic parallel gradient descent algorithm is studied.Firstly,the basic principle and process of the calibration method are given.The results show that compared with the direct optimization method,the method is not easy to fall into the local extremum and the correction speed is faster.The correction method of target image correlation and stochastic parallel gradient descent algorithm is analyzed for the translation and tilt phase errors between apertures.On this basis,the holograms were divided into 4 and 9 parts respectively,and then the results were validated by the method.Aiming at the relative rotation between the photodetectors and the different magnifications between the sub-apertures,an error calibration and correction method based on the image scale invariant feature transformation algorithm is proposed and verified experimentally.