Research Of Encryption And Imaging Based On The Manipulation Of Light Field Coherence Structure

Coherence is a basic attribute of light field,which is divided into spatial coherence and temporal coherence.In recent years,the partially coherent light with special spatial coherent structure has attracted wide attention of researchers due to its unique characteristics such as self-splitting and self-shaping.In addition,the spatial coherent structure of random light fields also plays a key role in the application research of crystallography,phase imaging,and incoherent light source reconstruction.Therefore,the application research of the spatial coherence structure of the light field is an important topic.In this paper,the development history and theoretical foundations of laser coherence research are reviewed.Based on the spatial coherence structure of random light fields,an information encryption method and an imaging method through the scattering layer are emphatically proposed.Investigate the effect of the spatial coherence structure of the illumination source in the case where the Fourier plane is partially blocked by an opaque obstacle.Firstly,since the light field has many degrees of freedom and is easy to control,optical encryption technology is becoming increasingly relevant.However,the optical encryption methods proposed so far are mainly based on the first-order characteristics of the light field,and they are susceptible to external interference,which makes the encryption system unstable during the interaction between light and matter.Here,we propose an alternative encryption method,which is to encode information into the spatial coherent structure of a random beam through the generalized van Cittert-Zernike theorem.The results reveal that this method offers two unique advantages compared with traditional methods.First,the complexity of the spatial coherence distribution of the measurement light improves the security of encryption.Second,the relative insensitivity of the second-order statistics of light to environmental noise makes the encrypted light field generated by this method robust to environmental fluctuations(such as atmospheric turbulence).Finally,we used the fractional Fourier transform system for encryption,which verified the feasibility of our theory in principle.Secondly,in many imaging processes,the phase information of the light field is lost when the light beam encounters the scattering medium,resulting in poor imaging quality.However,up to now,there never has been a method that can restore the shape and position of dynamic objects without obtaining the point spread function of the system when the target size is not limited by the optical memory effect.This paper proposes a modulated through-scattering imaging approach that relies on the second-order statistical properties of random light fields,that is,measuring the spatial coherence structure of the scattered light field through the generalized Hanbury Brown-Twiss effect,and accurately using the generalized van Cittert-Zernike theorem.The light intensity distribution information on the back surface of the scattering medium is recovered,and the mode of the light field is obtained,and the shape and position of the object are retrieved by combining the phase recovery algorithm in the Fresnel domain.Finally,distortions in the image plane are unavoidable in a classical 4f imaging system where the Fourier plane is partially blocked by an opaque obstacle.we found that although reducing the spatial coherence of the light source could improve the image quality,the image quality would still be affected.Through theoretical analysis that appropriately decomposes a partially coherent light source into a set of coherent pseudo-modes with a large linear phase-shift,we demonstrate that the distortion is mainly caused by modes located at the edges of obstacles.Further investigation showed that by adjusting the spatial coherence structure of the light source,we can make all coherent modes bypass obstacles to ensure the same image quality as if there were no obstacles on the Fourier plane.