Research On Focusing And Imaging Through Scattering Medium Based On Optical Transmission Matrix

The light scattering phenomenon has always been considered as a factor which reduces imaging quality in the process of traditional optical imaging.Therefore,scattering should be suppressed by means of a great deal of methods as much as possible.However,the scattering medium is found to be able to replace the traditional lens to achieve super-diffraction limit focusing and imaging in recent years,which makes scattering imaging a hot topic in optics.Speckle correlation,feedback control optimization and optical phase conjugation are the common methods used to image through scattering medium.However,there are plenty of shortcomings for these methods,such as limited field of view,time consuming,and limited imaging bandwidth.To this end,this thesis has studied the measurement methods of optical transmission matrix(OTM)of scattering medium.In addition,various focusing and imaging effects through the scattering medium were realized.Innovations at the aspects of focusing at single point and uniform multi-point,vortex focusing as well as gray-scale target imaging,moving target imaging and color 3D focusing were achieved.The specific work includes:(1)A random step phase shifting method which can shorten the measurement time of the OTM was proposed.The random step phase shifting(RSPS)interferometry was more efficiently compared to the existing full field three-step phase shifting interferometry method and the full field four-step phase shifting interferometry method.Under the premise of no substantial changes to the properties of OTM,the measurement time of the mathods proposed in this thesis was reduced to 2/3 times and 1/2 times,which is quite promising to achieve dynamic scattering imaging.(2)Focusing at single point,uniform multi-point and vortex focusing through the scattering medium were conducted.The above results was complished tcombining the OTM with TVAL3 in numerical simulation and experiment.For a 64~2×64~2 OTM,the maximum enhancement factor of focusing at single point reached 862.Besides,it verifies the lens-like properties of scattering medium with the known OTM because that depth of focusing attained 5mm.Moreover,focusing at uniform multi-point for complex targets and vortex focusing were obtained by utilizing pseudo-inverse,point-by-point average focusing and vortex phase.(3)Binary target imaging,gray-scale target imaging and moving target reconstruction through the scattering medium were realized.Two phase masks and a 64~2×64~2 OTM were used to reconstruct gray-scale target,which make up for the inadequacy of binary target imaging.A 141 pixels gray-scale target was reconstructed,whose similarity and peak signal-to-noise ratio(PSNR)were 0.5625 and 39.68dB,respectively.The maximum similarity and PSNR for tracking moving targets achieved 0.97 and 28.85dB,which embodies the ability of OTM method to track moving targets.(4)The multi-wavelength OTM of the scattering medium was measured in numerical simulation and the color focusing,color imaging through the scattering medium were fulfilled as well.The multi-wavelength OTM adapted to 478nm,532nm and 633nm was acquired based on the RSPS method.The average value of the enhancement factor of color focusing at single-point by a 16~2×16~2 multi-wavelength OTM was 75 and the depth of color focusing was 2mm.Finally,the reconstruction of the color 3D focusing target and color imaging targets were completed.In summary,the measurement OTM of scattering medium,focusing and imaging based on the OTM were studied.On the other hand,the OTM was further discussed and studied from the perspectives of spectrum and experimental setup.The above results are of significance for the development and application of the OTM.