Study On Odd-Symmetrical Phase Plate In Wavefront Coding Imaging Systems

For imaging system, larger depth of field means obtaining larger imaging space.Meanwhile it can correct or minimize defocus-related aberrations, such as sphericalaberration, chromatic aberration, Ptzvel (field) curvature and other defocus inducedbythe error of assembling and temperature, reducing the loss of objective informationduring the imaging process. Bymatching traditional optical design with digital imageprocessing creatively. Wavefront coding (WFC) is the fundamental technique that theoptical transfer function (OTF) or point spread function (PSF) is invariant, orsubstantiallyinsensitive over a broad spatial region in the object distance by placing aspecial-purpose optical phase mask to encode the wavefront of the optical system, as aresult the intermediate image received bythe detector is almost invariant but not clear,however, the clear sharp image can be restored from the intermediate image bydigitalprocessing. In this paper , the WFC Imaging Systems with odd-symmetrical phaseplate has been studied by theories deduce and imitate experiment. And the gist of thecubic phase plate's coefficient is determined. Finally, the intermediate image wasreconstructed.Some researches in this dissertation have been carried out as following:1. The focus invariance of WFC system is characterized bythe mean squaredeviation between out-of-focus's MTF and in-focus's MTF, and the focusinvariance of WFC system with the cubic phase plate is analyzed, then theeffective range of the cubic phase plate's coefficient is determined.2. Analyses the abilityof WFC to depress the spherical aberration, chromaticaberration, Ptzvel (field) curvature.3. The asymptotic solution of OTF and PSF for the WFC system withfive-times phase mask was derived with the stationary-phase method. Cometo the conclusion that the spherical aberration invariance bring bythefive-times phase mask is better than cubic phase plate. Make use of themethod of simulation, add the five-times phase and cubic phase plate. It wasbe found that the mulriple phase mask is invariable to defocus and sphericalaberration. 4. The intermediate image was reconstructed by emulator. The final clear sharpimages is achieved by applying Inverse filters Wiener filers and integrationfilers on the intermediate image.