Characteristic And Experimental Study On Wavefront-Coding Imaging

Due to many advantages of the large depth-of-focus of an imaging optical system, various methods to extend depth-of-focus of optical imaging system were proposed. Among those methods, a close attention was paid to wavefront coding(WFC) imaging technology because of its superior performance. In wavefront coding technology, the optical design is combined with digital image processing. The technique is based on the modification of the wavefront (or wavefront coding) by means of a suitable phase mask (such as a cubic phase mask) placed at the aperture stop of the system. The major function of the WFC is to modify the point spread function (PSF) of the system in such a way that it becomes invariant over a range of distances around the image plane. The final image with diffraction-limited quality is obtained by using digital filtering process from the coded images.In this thesis, we present a characteristic and experimental study on the wavefront coding imaging with different phase masks, in which comparative study on the performances of two major different categories of the phase mask, i.e., rotational symmetric and asymmetric type phase masks are presented, and the suppression effects of various imaging aberrations of the WFC system with a cubic phase mask is analyzed. The major works are as follows:1. Based on the theoretical analysis and numerical calculation, the depth of focus and the extension rate of depth-of-focus in the wavefront coding system with a cubic phase mask is reviewed and analyzed.2. The imaging characteristics and the invariant behavior of the imaging with different defocuses of the WFC system with a cubic phase mask are investigated with the optical design software ZEMAX. The imaging recovery with inverse filtering technique is implemented and clear images are obtained and evaluated. The suppression effects of various imaging aberrations of the WFC system with a cubic phase mask is analyzed.3. Comparative study on the performances of two major different categories of the phase mask, i.e., rotational symmetric and asymmetric type phase masks are presented, which shows that the extension of depth of focus of the WFC system with rotational asymmetric phase mask is much larger than that of those symmetric types.4. Experimental fabrication and metrology of cubic phase masks and WFC experimental imaging system are performed. Clearly recovered WFC images are obtained which demonstrates the feasibility of the WFC technique.