Common Path Digital Holographic Tomography Based On Grating Diffraction

Digital holographic tomography is a popular technology in recent years.It uses digital holography to obtain the phase data of the object in multiple angles,and reconstruct the three-dimensional refractive index distribution of the object through the reconstruction algorithm.While inheriting the advantages of real-time,quantitative,non-interference,full field of view and high-precision measurement of digital holographic microscopy,it can accurately reconstruct the three-dimensional refractive index distribution of biological cells,micro optical elements,optical fibers and other micro objects,which has a wide range of needs and application prospects in life science,medicine,material detection,micro manufacturing and other fields.Digital holographic tomography need to reconstruct the refractive index distribution of the object by using the phase distribution data of the object at multiple angles.Therefore,the quality of a single hologram and the consistency of multi angle holograms will have a significant impact on the final 3D refractive index reconstruction results.Therefore,how to improve the quality of the obtained multi angle phase data is an important direction in the study of digital holography.Because the traditional digital holographic tomography system is the structure of the separation system,in which the object light and the reference light passes the different optical path.So it is easy to be interfered by the environment,which leads to the large time noise of the phase image and affects the final tomographic reconstruction accuracy.Therefore,in order to improve the reconstruction accuracy of the tomographic image,this paper uses the common-path digital holographic microscopy technology based on grating diffraction to obtain the phase data of each angle.By using the common-path instead of the traditional path,it can obviously overcome the poor stability brought by the traditional digital holographic system to obtain phase data.The main contents of this paper are as follows.(1)In this paper,the basic principle of digital holography micro tomographic technology is described in detail,including tomographic reconstruction algorithm and phase data acquisition method.In addition,the basic principle of grating diffraction common path digital holographic microscopy is also described.These basic theoretical knowledge provide support for the follow-up research.(2)The image quality improvement of rotating digital holography was studied.Firstly,in order to solve the problem of hard cut-off of aperture in off-axis digital hologram reconstruction,the digital toe cutting method is used to effectively suppress the ringing error in the reconstructed phase image and reduce the impact of high-frequency noise.Then,there are different degrees of radial run out and position deviation in the multi angle phase data obtained whenthe object rotates.Using the numerical processing method combined with automatic focus and automatic alignment,the multi angle phase data can be more accurate focus reconstruction and alignment.It lays a foundation for the reconstruction of high precision digital holography.(3)The structural parameters and the parameters of each optical element of the common path digital holography system based on grating diffraction are derived and optimized,and the experimental optical path system is constructed.The single-mode fiber,multi-mode fiber,polarization maintaining fiber and other samples are measured.The results show that the built system and the numerical processing method can significantly improve the quality of multi-angle phase data,so as to achieve high-precision chromatography.