Research On Imaging Through Scattering Media Based On Disordered Laser

The scattering phenomenon exists widely when light beams transmit through disordered media(such as biological tissue,multimode fiber,cloud/smoke,etc),which gives certain challenges to the application of optical information,and also provides potential opportunities.On the one hand,in applications such as biological microscopy,optical remote sensing,and laser projection,the appearance of light scattering would reduce the signal-to-noise ratio of the optical systems and deteriorate the imaging quality,thus it is generally required to suppress the scattering effects.On the other hand,in scenarios such as random laser generation and speckle related imaging,light scattering plays a unique role.In recent years,many physical properties related to scattering media have been discovered,such as the optical memory effect(OME),the Anderson localization,etc.Meanwhile,based on the linear mapping relationship of the scattering effect,researchers have also developed various information extraction methods for light transmitting through scattering media,such as wavefront shaping and deep learning,etc.Among them,OME-based speckle-correlated imaging has advantages such as strong generalization,non-invasive,fast imaging speed,and simple structure,which has been widely studied.However,the existing speckle-correlated imaging methods still face some bottlenecks that need to be solved urgently,as follows.I)Small field of view: The optical memory effect is only valid within a small angle range,which limits the field of view of the speckle-correlated imaging systems.II)Low lighting efficiency: Currently,the major lighting source employs a narrow linewidth laser passing through a fast-rotating ground glass or a narrowband filtered broadband light,which reduces the lighting efficiency of the speckle-correlated imaging systems.III)Limited resolution: Both the limited size of the numerical aperture and the illumination wavelength determine the minimum distinguishable unit,which limits the resolution of the speckle-correlated imaging system.IV)Slow reconstruction speed: Phase retrieval algorithm and iterative deconvolution algorithm require more time to reconstruct the objects,making speckle-correlated imaging system only capable of offline reconstruction and not conducive to real-time imaging.V)Unsuitable for imaging through a thick scattering media: When imaging through a thick scattering media,the object size is generally much larger than the effective range of the OME,making single-shot speckle-correlated imaging methods no longer effective.To address the above issues,this dissertation conducts speckle-correlated imaging research from the aspects of imaging mechanisms,lighting systems,reconstruction algorithms,etc.The main work and contributions are as follows.(1)To improve the field of view and lighting efficiency,speckle-correlated imaging under near-infrared low-spatial-coherence random fiber laser(RFL)illumination is studied.Firstly,a near-infrared RFL illumination source with a central wavelength of1452 nm is designed,which has a high spectral density(3d B spectral bandwidth of 2.4nm),low spatial coherence(speckle contrast of 0.048),and high illumination efficiency,perfectly meeting the requirements of illumination source of the speckle-correlated imaging systems.Secondly,speckle-correlated imaging is realized by using the nearinfrared RFL as the illumination source.Compared to the visible illumination source at635 nm,the field of view is increased by 1.72 times.Furthermore,making full use of the flexible alignment feature of the designed RFL,a local and global illumination method is proposed,which can be used to eliminate the ambiguousness of orientation in the image reconstruction based on phase retrieval algorithm.(2)To improve the resolution,speckle-correlated super-resolution imaging based on multi-dimensional disordered laser illumination is studied.Firstly,a multi-dimensional disordered fiber laser is designed,which exhibits disordered characteristics in the time domain,the spatial domain,and the spectral domain.Secondly,under the dynamic speckle illumination of the designed multi-dimensional disordered laser,non-invasive point spread function(PSF)recovery of a scattering imaging system is realized by introducing non-negative matrix factorization algorithm.Finally,combined with the dynamic speckle illumination characteristic of multi-dimensional disordered laser,a speckle-correlated super-resolution imaging method is proposed.By calculating the highorder accumulation of each pixel in the deconvolution reconstructed image,the resolution is improved by about 2 times.(3)To improve reconstruction speed,real-time speckle-correlated imaging based on deep learning is studied.Firstly,a method for training neural networks using numerical simulation data is proposed.The autocorrelations of the simulated speckle patterns instead of the experimental ones are used to train the network,which greatly saves the time and the hardware costs required for preparing the training set.On this basis,based on the proposed method,real-time imaging through scattering media is achieved with a frame rate of up to 33 fps.Compared with other reconstruction algorithms,the proposed method has advantages such as non-invasive,strong generalization,and high reconstruction image quality.(4)To solve the problem of imaging through thick scattering media,the speckle correlation of moving objects is studied.Firstly,the theory of speckle correlation of moving objects under two illumination mechanisms,i.e.,the spatial coherence illumination and the spatial incoherence one,is established.Through numerical simulation and experimental verification,it is revealed that the speckle correlation of moving objects in the former mechanism is the squared module of field autocorrelation of the object,while for the latter one it is the intensity autocorrelation of the object.This provides a theoretical foundation for imaging through thick scattering media based on different illumination mechanisms.Furthermore,a moving object-based speckle correlation imaging method under spatially incoherent illumination is proposed,which is not restrited by the OME range.Meanwhile,compared with existing coherent illumination method,it is found and verified that this method can alleviate the interference noise in imaging scenes,such as objects embedded in scattering media,and non-uniform objects passing through scattering media,with stronger robustness and higher imaging quality.