Research on design of optimum phase mask for wave-front coded imaging system

Wave-front coding is a system level design method which can be used to extend the depth of field of an incoherent optical system. By attaching a phase mask to the aperture, the optical transfer function can not only be made insensitive to misfocus, but also can avoid the isolated zeros caused by defocus. With this modified optical transfer function, a purposely blurred image can be obtained and its corresponding clear one with large depth of focus can be generated through digital processing techniques, such as direct inverse filtering, wiener filtering and maximum entropy restoration and so on. This is why the wave-front coded imaging system is called optical/digital hybrid imaging system as well. The most important part of the system design lies in the design of phase masks. So far, many kinds of phase masks have been suggested; among all those types, two are classical: cubic-phase-mask and logarithmic-phase-mask. However, whether an optimum phase mask exists or not is still a question that is not answered yet. This paper focuses on this question and tries to find one answer. In this paper, considering several critical factors and with the help of a simulation program developed by ourselves, we make a comparison among the performance of different phase masks and finally propose a prototype phase mask whose performance is acceptable in several aspects.