| Digital holography is a new emerging field of holographic technique, which uses a photoelectric imaging device (CCD sensors) to instead of the traditional holographic material for hologram and uses a computer to simulate the optical diffraction process, in order to reconstruct the original object wave front, so we can realize the recording and reconstruction holograms in digitalize.Digital holography is a non-contact, high resolution, and quantitative technique which can get amplitude and phase of object wave. Due to this advantage, now digital holography has become widely used in various aspects, including particle field observation, MEMS/MOEMS dynamic analysis, micro-optics, semiconductor, nanophase material, biology, biochip, and biosensor.In allusion to the key problems to affect the precision of digital holographic technology (DH), this paper first analyze essence of the noise in the DH by theoretical, and then we propose a new digital holographic technique with noise free based on imaging of low-pass filter to obtain 3-D shape of macro-object in low resolution. It should be decline the precision and view angle of reconstructed image, but our method would be useful when we test the object that have slow shape change or low resolution. In order to remove the noise, but resolution or view angle of reconstructed image is un-decline, we proposal a digital holographic technique with large view angle and noise free based on spectrum mapping. To record the image plane holograms that contain different parts of frequency of object wave one by one, we use a filter in the optical Fourier Transform imaging system. We can get each parts of frequency about object by numerical Fourier transform. And auto stitch them to obtain whole spectrum of object by use the phase shifting properties of Fourier transform. Thus, the large viewing angel result can be get by this technology and also prompt the resolution. Experiment results for objects which have smooth surface shape (sewing needle, micro-lens array) showing the capabilities of the proposed approach are presented. This paper includes six parts:First of all, summarize the basic characters of DH and its research actuality inside and outside, then we also analysis the main problems in DH. Besides all of these, we propose the main idea and direction of our work in recoding hologram with noise free and promote view angle in the digital holographic technology.Secondly, we retrospect the recording and reconstruction principles of DH in briefly and discuss three diffraction algorithms by theory and MATLAB stimulation.Thirdly, we analyze the cause of noise in reconstructed image in digital holography. If the frequency of holograms that contains light scattered of object have twice larger than the maximum frequency of recoding device, the high frequency of hologram can not be recorded efficiency, but the distribution of this light intensity will still exist and will have a bad effect to our reconstructed image. We also use MATLAB as a tool to stimulate this process. The results of stimulate have been verify the correct of our theory.Fourthly, we propose to set a rational optical path structure to record holograms without noise, just as what we said a digital holographic technique with noise free based on imaging of low-pass filter to obtain 3-D shape of macro-object. We discus the theory of this optical path structure in detail, experiment results have been certify the advantage of this technology in test the outline of macro-object.Fifthly, we proposal a digital holographic technique with large view angle and noise free based on spectrum mapping. Use this method can no only remove noise but also ensure the resolution and view angle of reconstructed image. Experiment results for objects which have smooth surface shape (sewing needle, micro-lens array) showing the capabilities of the proposed approach are presented. We also have a satisfied result of high resolution object (grating).Last is the conclusion of this paper and the problems to be further resolve. |
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