Researches On Far Field High Resolution Optical Imaging Technology Based On Phase Information

Improving the object's spatial resolution has always been a research focus in the advanced optical remote sensing and high-performance imaging.The diffraction limit is a key obstacle to improve the system's spatial resolution.As a novel phase imaging technology,ptychography shows great advantages in microscopic imaging.It can achieve a resolution enhancement of more than 5 times.Moreover,its idea of improving resolution is similar to synthetic aperture technology.Therefore,ptychography is a promising high-resolution phase imaging technology for long-range scenes.Ptychography does not need direct measurement of phase information or strict co-phase between sub apertures,but relies on the acquired intensity image to recover the object's phase information.It uses the recovered phase information to realize the splicing extension of the spectrum,thereby improving the resolution of the imaging system.At present,there is very little research on the application of ptychography in the far field imaging scenes,especially in China.This paper focuses on the application of ptychography in the far field scenes.The main research work is summarized as follows:1.The ambiguity resolution of phase retrieval algorithm is analyzed.And then explain that ptychography can effectively suppress this problem.The theoretical model of the far field scanning Fourier ptychography(FP)system is carried out in detail.The amplitude point spread function,the coherence transfer function,the signal-to-noise ratio,and the evaluation criteria of the reconstructed image are given.The key influencing factors of the phase for far field scanning FP system are analyzed,which can provide theoretical basis for the design of reconstruction methods and experiments.2.A comprehensive preprocessing method is proposed to solve the field of view changing and noise pollution for far field scanning FP imaging system.First,the sequence image registration method based on transforming domain can realize sub-pixel registration accuracy between the adjacent measurements.Secondly,the global noise reduction method and the speckle noise suppression method based on gamma correction are used to effectively suppress the mixed noises including Gaussian noise,Poisson noise and speckle noise.The simulation results show that the PSNR of the reconstructed image can be improved by 4.42 d B,which proves the effectiveness of this comprehensive preprocessing method.3.A novel FP reconstruction framework RAFP-RED is proposed,which can greatly improve the quality of reconstructed images.The cost function suitable for Poisson noise is selected,a special initialization method is adopted,and the gradient descent direction is revised step by step,so that the estimated data can point to the true value with high probability.Finally,the RED regular term is added to further filter the noise in reconstruction process.Compared with the existing reconstruction algorithms,RAFP-RED has the best noise robustness and reconstruction performance.Compared to the traditional AP algorithm,the RAFP-RED algorithm can improve the PSNR by 8.47 d B,the SSIM by 0.36.At the same time,it has better visual fidelity.4.The transmission and reflection laboratory platforms for the far field scanning FP imaging system are constructed.We successfully verify the resolution improvement performance of the proposed RAFP-RED algorithm with analyzing the main system errors and correcting them.On the transmission platform,the resolution is improved by 4 times at 1.6m imaging distance.On the reflective platform,the resolution is improved by 3.2 times at 1.75 m imaging distance.5.An imaging method named imaging correlography using ptychography is proposed to bypass the obstacles in the far field scanning FP imaging system,such as speckle noise and coherence destruction.It combines the ptychography with traditional imaging correlography to improve the reconstruction quality.Compared with traditional imaging correlography,the imaging correlography using ptychography can increase the resolution of reconstructed images by 4 times with only 1/6 measurements at each scanning position.