Speckle Illuminated Ghost Imaging Based On Multimode Fiber

As a typical optical transmission medium,multimode fiber plays an important role in information transmission applications such as space division multiplexing and new imaging,due to the existence of a large number of modes in it,and has received extensive attention and research in recent years.Ghost imaging technology is a non-line-of-sight correlation imaging,which can be combined with multimode fiber to realize ghost imaging of a single multimode fiber.It has broad application prospects in military,medical and industrial fields..In this thesis,an illumination speckle ghost imaging technology based on multimode fiber is proposed,a tunable laser is used as the illumination light source,and the wavelength-independent characteristics of the speckle at the output end of the multimode fiber are used to solve the problem of the need to use rotating frosted glass in traditional ghost imaging.Mechanical methods to reduce the problem of spatial coherence.At the same time,a wavelength-dependent speckle multiplexing technique is also proposed,which reduces the number of acquisition samples required for imaging and reduces the image reconstruction time.Firstly,the theoretical simulation of speckle illumination ghost imaging is carried out,the influence of the correlation between the illumination speckle fields on the reconstructed object is analyzed,and a wavelength modulation-based multimode fiber ghost imaging scheme is proposed.Based on the Lab VIEW platform,the automatic joint debugging of imaging equipment and instruments is realized.The advantages and disadvantages of the second-order intensity correlation algorithm and the compressed sensing TVAL3 algorithm in reconstructing objects are compared and analyzed through experimental data.The research results show that in the case of no scattering medium,the reconstruction effect of the TVAL3 algorithm is better than that of the second-order intensity correlation algorithm.In the presence of scattering medium,the reconstructed image quality of the second-order intensity correlation algorithm is slightly higher than that of the TVAL3 algorithm.As the sampling rate of the TVAL3 algorithm decreases,the structure of the reconstructed image becomes less obvious.On the basis of the above research,the system performance and optimization method of illumination speckle ghost imaging based on multimode fiber are studied.On the basis of simultaneous measurement,the idea of speckle-wavelength pre-calibration is introduced to realize single-point detection in the true sense.Firstly,the time de-correlation characteristics and length de-correlation characteristics of the output speckle of the multimode fiber are analyzed,and then the appropriate multimode fiber length is selected based on this to improve the stability of the output speckle.Compared with the traditional point scanning imaging technology,the robustness of the imaging system is improved,and the imaging system can be stabilized for more than 90 minutes.Finally,a wavelength-dependent speckle multiplexing technology is proposed,which reduces the number of speckles/wavelengths required for imaging,greatly improves the image reconstruction speed while ensuring image quality,and reduces the amount of data collection by 70%.On the premise of increasing the bandwidth of the tunable light source,it provides an effective method to shorten the length of the multimode fiber and improve the stability of the system..