Imaging Research Of Threedimensional Computaional Holography

Digital holography is an imaging technique used to record and display threedimensional information of objects.It uses photoelectric sensors instead of dry plates to record holograms,then enters the holograms into a computer,and uses a computer to simulate the optical diffraction process to achieve recording.Holographic reproduction and processing of objects.Low production cost,fast imaging speed,repeatability and flexibility of recording and reproduction are the great advantages of digital holography over traditional optical holography.Compared with computational holography,digital holography is more suitable for engineering applications,and has higher value for recording real-world objects.In recent years,the development of ultra-high-resolution electronic recording devices has made digital holography technology more and more popular.However,in digital holography,laser is usually chosen as the light source.Because of the high coherence of laser,a series of coherent superposition of reflected light on the object will occur,which will cause irregular granular noise on the recorded hologram.This kind of noise is defined as speckle noise.The quality of reconstructed image is much lower than that of incoherent technology due to the introduction of noise.To solve the problem of noise,the speckle noise is effectively suppressed by eliminating the interference of DC light and conjugate light,and the quality of reconstructed image is enhanced.The innovations of this paper are as follows:1.Three wave plates,one 1/2 wave plate and two 1/4 wave plates are used to realize arbitrary polarization in the off-axis digital holographic optical path.Firstly,the coherence between the reference light and the object light is reduced by optical method,and the speckle noise of the hologram is suppressed.Secondly,the independent statistical speckle noise holograms are superposed to average the speckle noise in the hologram One step is to reduce the influence of speckle noise,so as to improve the quality of reconstructed image.2.It is proposed to use liquid crystal wave plate to realize random phase delay.Due to the birefringence of liquid crystal,the phase delay of light can be changed by voltage control.The hologram can be eliminated by any one phase-shifting principle,and then the influence of conjugate term can be eliminated by frequency-domain filtering,so as to improve the quality of reconstructed image.This method does not need mechanical movement,and to a certain extent improves the stability of the system.3.Under the circumstance that the arbitrary polarization state method effectively improves the image quality,a method of reducing the coherence degree in the spatial and time domains is proposed.These two schemes are more stable and time-saving than the arbitrary polarization state scheme.In the airspace depolarization,a quartz wedge depolarizer is used to depolarize the linear polarization state in the object optical path by one step to reduce the coherence degree.The degree of depolarization can be controlled according to the deflection beam radius.Time-domain depolarization adopts a combination of two 1/4 wave plates and a liquid crystal wave plate to achieve depolarization.The frequency sweep signal is output to the liquid crystal to cause continuous phase delay changes,and the final emitted object light has a continuous polarization state.Change to get holograms with different interference levels.After CMOS recording and averaging,the speckle noise of the hologram can be effectively reduced.Both have effectively improved the image quality of the reproduced image.