In order to know the ability of the hybrid refractive-diffractive element for extending focal depth

the logarithmic phase function based on uniform-intensity principle is analyzed and the relationship is set up between focal depth

optical f/# and fabrication parameters of the hybrid refractive-diffractive element with logarithmic phase function. The simulation analysis of on-axis intensity distribution of the element is performed based on Fresnel diffraction formula with different parameters. Simulation results indicate that for determinate focal length and wavelength

the factor in focal depth compared with same f/# spherical refractive lens is determined by profile depth of diffractive element: when the profile depth is increased

the factor is larger and the on-axis intensity distribution in focal depth offers great uniform characters. For determinate focal depth value

when the optical f/# is decreased

the uniform character of on-axis intensity distribution in focal depth is better.