Theory Analysis, Design And Realization Of Imaging System With Deep-Field Depth And Large-Viewing Angle Based On Wavefront Coding

Wavefront coding system, a two-step imaging system including optical encoding and digital decoding, can achieve deep depth of field which is impossible for traditional optical imaging systems. Firstly, intermediate blur images will be obtained in the image plane by the imaging system with a CPM (Cubic Phase Mask) added in the pupil plane. The wavefront coding system has almost the same PSFs (Point Spread Function) within the deep depth of field due to the CPM. Then final sharp images will be obtained based on various image restoration algorithms by using the PSF as the decoding core in frequency or space domain. This technique will be widely used in optical imaging systems for either military or civil use.Firstly, pupil with arbitrary incidence is analyzed for the first time based on Fourier optics theory. The results show that the wide viewing incident angle leads to side-extension and skew-effect for the PSF; it also leads to the decrease of MTF (Modulation Transfer Function). Therefore, it will cause bad effect on the final decoded images.Secondly, we proposed a novel design method for wavefront coding system based on widely-used optical design software. In order to suppress the wide viewing angle effect, we proposed a new method for the first time to control the maximum incident angle of chief rays on the pupil plane. Two design examples show that the wide viewing angle effect is obvious in practical system; and the method we proposed is effective and obvious in practical system design.Thirdly, two novel wavefront decoding algorithms in space domain are proposed. One is image restoration based on TSVD (Truncated Singular Values Decomposition) by using MTF as singular values, and the other is Bi-CGSTAB (BiConjugate Gradient Square Stable Methods) image restoration algorithm based on anti-reflective boundary conditions and Kronecker production approximation. Compared to traditional method, both of them reduce the computation and have better restoration results. The former belongs to direct method, which is suited for real-time restoration; while the latter is iteration method, which suppresses the ringing effect of the image borders and edges with more details maintained.Fourthly, we introduce the hardware and software of the system. Optical-mechanical system and circuit are introduced as hardware; while image process with wavefront decoding as the core is introduced as the software.Finally, we give the experiment results of a wavefront coding system with deep depth of field and large viewing angle. The results show that a wavefront coding imaging system with deep depth of field and large viewing-angle can be obtained successfully by using the design method based on optical design software. Compared to Wiener filter, better restored image has been obtained based on Bi-CGSTAB with ringing effect suppressed and details maintained.