Study Of Incoherent Light Self-interference Digital Holographic Imaging System Based On Structured Light Illumination

Incoherent optical self-interference digital holography is a high-quality imaging technology that combines holography,optoelectronic technology,and computer technology.It has the characteristics of no mark,non-contact,fast real-time,three-dimensional imaging,etc.On the one hand,as an incoherent imaging technology,it records holograms of self-luminous objects or objects illuminated by incoherent light sources,solving the edge artifact problem existing in coherent imaging systems,reducing coherent speckle noise and improving imaging quality.On the other hand,as a kind of digital holography,the holograms are recorded by CCD or CMOS sensor and other components instead of traditional photosensitive materials.Then they are numerically reproduced by computer simulation of lightwave diffraction process,which not only reduces the complicated and tedious processing process during recording and reproduction,and can be combined with a variety of image processing technologies to improve the quality of reproduced images,and has a wide range of applications in surface topography detection,biomedical imaging,color holographic imaging,etc.However,due to diffraction phenomena,the resolution of the optical imaging system is limited by the numerical aperture(NA).The systems allow only the low-frequency part of the objects’ spectrum to be transmitted and then recorded by the sensor,so the corresponding reconstructed image is band-limited in the frequency domain.As a super-resolution optical imaging technology,structured light illumination technology,based on the theory of information optical imaging,collects information about different frequencies of objects.It increases the numerical aperture,improves the system’s resolution,and more easily meets the performance requirements of actual detection.This paper systematically analyzes incoherent light self-interference digital holography technology and the super-resolution imaging technology based on structured light illumination.It combines the two to realize super-resolution digital holography imaging based on structured light illumination.The main contents include the following three aspects:(1)Expound the principle of optical imaging of incoherent optical self-interference digital holographic imaging system based on Michelson interferometer,and derive mathematical expressions such as system lateral magnification,point spread function,and system resolution.Perform imaging simulations and performance studies on the system: Simulation of the effects of parameters such as numerical aperture,recording wavelength,and reproduction distance on system resolution;Carry out the imaging experiments on the resolution target USAF1951 and two steel rulers at different positions to verify the planar and three-dimensional imaging properties of the system,respectively.(2)Analyze the principle of realizing super-resolution imaging by incoherent light self-interference digital holographic imaging system based on structured light illumination,and carry out imaging simulation research.The specific way is to place a transmissive amplitude spatial light modulator(SLM)between the light source and the object in the holographic imaging optical path and use the computer to control the spatial light modulator to replace the grating masks of different directions and different frequencies to achieve the purpose of illuminating objects with structured light.The high-frequency object light wave initially confined outside the CCD is deflected by the diffraction effect of the grating on the light wave and collected by the CCD again.By selecting the appropriate grating frequency and recording distance,the three holograms corresponding to the grating 0,±1 diffraction orders can be recorded into one hologram simultaneously.The three-order diffracted waves are separated,shifted,are reconstructed by the three-phase spectrum separation and Fourier transform displacement theorem to realize super-resolution imaging.Taking the resolution target as the object to be measured,the simulation results of the super-resolution digital holographic imaging system based on structured light illumination are compared with the simulation results of the conventional Michelson digital holographic imaging system.The results show that the system’s resolution has been increased from 20.16 lp/mm to 35.92 lp/mm,and the overall resolution enhancement factor is 0.78.(3)Build a Michelson digital holographic imaging system based on conventional incoherent light-illuminated and a super-resolution digital holographic imaging system based on structured light illumination,respectively to experimentally verify the feasibility of the super-resolution imaging method based on structured light illumination.When using structured light illumination at frequencies of 20 lp/mm,30lp/mm and 40 lp/mm,the system resolutions can reach 64 lp/mm,71.84 lp/mm,and90.51 lp/mm,and the overall resolution enhancement factors are 1.41,1.59,and 2,respectively.The experimental results show that the super-resolution imaging method based on structured light illumination can effectively improve the imaging system’s resolution.The way can realize the multi-mode structured illumination function by flexibly controlling the spatial light modulator,has strong controllability of the imaging light path,and has low requirements on the stability of the experimental device.