Research On TMC Space Optical System Based On Wavefront Coding Technology

The depth of field or focus of an optical system is ensured by optical and structure parameter, such as enter diameter, aperture stop and focal length. Large depth of field or focus can obtain more information in the objective space, and prevent image quality declining due to defocus. People have researched the technology of extension of depth of field or focus from the beginning of the last century. In 1995, Dowski and Cathy of the Colorado University present the wavefront coding(WFC) technology which could extend depth of field or focus easily. Since then researchers have paid more attention to WFC and have made it applied in various optics and optical field.The objectives of this topic are the research on the application in the space optical system based on WFC, and the multiple wavefront coding technology. In the space optical system, WFC can prevent the image quality declining due to temperature difference or the satellite vibration, which is equivalent to extension of depth of field or focus. The theoretical model of the phase function expression with the position error of the phase plate can logically explain the influence of phase plate to the imaging and extension of depth of field or focus. It is much helpful to alignment of phase plate in the TMC system. In addition, it presents the new concept of multiple wavefront coding based on the traditional WFC technology, explained by geometric imaging, Fourier Optics and ray tracing. It also presents a multiple WFC optical system which could be able to extend the aperture and the depth of field or focus.In this paper, it involves theoretical principle, calculation process, technical proposal, and performance of the WFC technology. The experimental platform of WFC technology TMC system is established. There are many effective works in optical design, optical elements alignment, and theoretical analysis, which enhance the theory and accumulate the experimental data in the research of the extension of depth of focus by cubic phase mask plate. What is more, we design a multiple wavefront coding system.In this paper, research mainly includes as below:Firstly, it shows theoretical description and mathematic analysis on wavefront coding technology. It analyzes the imaging features of cubic, circular symmetry and user defined surface types. It also analyzes the working about space optical system and the focus extended effects. The TMC system experimental platform based on the cubic phase mask plate has been established. It makes test and experiment on the imaging and the image restoration.Secondly, it presents the research method about the user defined surface type. Compared with the cubic odd asymmetrical and the even symmetrical phase plate, and according to their modulation on rays and difference in imaging, we create a kind of user defined surface phase plate. With the features of subsection and circle symmetrical surface, this surface type combines large extended ratio of depth of focus by cubic phase plate and easily mechanical processing by circle symmetrical plate. Compared with the phase plate of simple surface type, subsection type weakens or eliminates spherical aberration less invariant because of different field of views and aperture in the traditional phase plate. In addition, subsection type decreases distortion and increases the capability of application. What is more, this surface type is able to be mechanical processed. The simulation results present that the user defined surface type can extend the depth of field or focus.Thirdly, we analyze and research the effects on WFC imaging and extension of depth of focus by plate position error. According to the structure of WFC system, the position of the phase element is the key to the imaging result. We calculate the expression of phase function with decenter and tilt. Then, we test the effect by the position decenter error for experiment. The results of simulation and experiment show that the z-direction decenter tolerance is greater than that of x or y-direction, and the decenter error can declines a third extension ratio within the decenter tolerance.At last, we propose the concept the multiple wavefront coding technology. According to the geometrical imaging and Fourier Optics features of the traditional WFC system, we also present the co-mask lens and the diff-mask lens in the multiple WFC system. The former makes the uniform modulation on the rays which pass through it. The latter makes the different modulations on the rays which pass through it as different aperture or field of view. With the modulations of these two kinds of lens, the multiple WFC system also can extend depth of field as the same of the traditional WFC system. What is more, this new technology is capable to extend the aperture and depth of field, and apply to more optical field.The phase plate is the optical element that has the ability to change the trace of imaging rays based on the theory of ambiguity function and Fourier Optics, which can extend the depth of field or focus of the original system combining the digital image processing. The application to the space optical system makes the system insensitive to the defocus due to the satellite temperature difference and vibration, and prevents the fast decline of the imaging quality. The application also replaces the temperature controlled device and mechanical focusing mechanism, which enhances the reliability and stability of system, and reduces the load and the cost of launching. With the action of the co-mask lens and the diff-mask lens, the multiple WFC system holding the traditional WFC imaging features has the ability to extend the aperture and the depth of field.