Wavefront Coding Technology Theory And Its Applications

WFC is the fundamental technique that the Optical Transfer Function (OTF) or Point Spread Function (PSF) is invariant, or substantially insensitive over a broad spatial region in the object distance by placing a special-purpose optical phase mask to encode the wavefront of the optical system, as a result, the intermediate image received by the detector is almost invariant but not clear, however, the clear sharp image can be restored from the intermediate image by digital processing. By combining traditional optical design with digital image processing creatively, the depth of filed can be greatly increased, moreover, all defocus-related aberrations, such as spherical aberration, chromatic aberration, astigmatism, Ptzvel(field) curvature, distortion, and other defocus induced by the error of assembling and temperature change, can be corrected or minimized. WFC technique has the predominant imaging performance which traditional optical imaging system is absent. Consequently, the WFC technique has a promising application prospect in all kinds of optical systems.In this paper, the asymptotic expressions of ray aberrations are achieved by the ray tracing method in geometric optics for arbitrary form phase mask. According to the asymptotic expressions of ray aberrations, the spot diagram characteristics of asymmetric phase plates are analyzed, including the spot size, boundaries and ray structures. The results are also compared with those derived from Fourier optics, which shows that both are in great agreements. Through the spot diagram characteristics analysis, a deeper insight into the wavefront coding imaging systems can be obtained.Then, one method based on Genetic Algorithm to optimize the pupil phase mask are proposed firstly, and the method is applied on a cemented doublet system separately which is chosen as the optical system for imaging simulation. The results of imaging simulations for the cemented doublet system with and without pupil phase mask are compared and analyzed. The results also illustrate that this method is simple as well as practical, and all pupil phase mask optimized by this method show novel properties both in improving the image quality and in extending the depth of focus.In addition, WFC technique applied on Infrared imaging simulation is described. The cubic phase mask is employed for an infrared imaging system to encode wavefront. The final clear sharp image is achieved by applying simple Wiener filers on the intermediate image. The simulation results of infrared system with phase mask show that the MTF curvatures are almost coincident with each other with different temperatures, object distances and field of views, which demonstrate that the infrared system is insensitive to defocus-relate aberrations induced by temperature shift. Meanwhile, the depth of field of this system is also extended, and the field effect is eliminated in some extend, which is very useful to extend the field of views of infrared imaging system.At the end of this paper, two solutions are provided to eliminate the field effect which the edges of the image become distorted and hard to be restored when the incident angle gets larger. One solution is to move the phase mask to the plane where the ray gently incident on the phase mask but not the pupil plane of the system, another is to optimize the whole optical system to make the ray gently incident on the phase mask which is on the pupil plane. The simulation results show that the second method is very effective to eliminate the effect which is caused by the large field.