The irradiance in the exit pupil of a typical optical data storage system (i.e., the detector pattern) consists of fringes formed by the interference of fields reflected from the optical disk. The reflected fields are decomposed using Babinet's principle into desired and undesired components. The behavior of the fringes depends on the interaction of the focused light spot with the features on the optical disk and media parameters, such as mark and land reflectivities, groove depth, and mark pattern. The behavior of the desired and of the undesired fringes are determined for both write-bright media (bright data marks written on a dark background) and write-dark media (dark marks written on a bright background). Both a theoretical development and a scalar diffraction simulation tool are used in the analysis.