We study the wave optics features of gravitational microlensing by a binary lens composed of a planet and a parent star. In this system, the source star near the caustic line produces a pair of images in which they can play the role of secondary sources for the observer. This optical system is similar to the Young double-slit experiment. The coherent wavefronts from a source on the lens plane can form a diffraction pattern on the observer plane. This diffraction pattern has two modes from the close- and wide-pair images. From the observational point of view, we study the possibility of detecting this effect through the Square Kilometre Array (SKA) project in the resonance and high-magnification channels of binary lensing. While the red giant sources do not seem to satisfy the spatial coherency condition, during the caustic crossing a small part of a source traversing the caustic line can produce coherent pair images. Observations of wave optics effects at longer wavelengths accompanied by optical observations of a microlensing event provide extra information on the parameter space of the planet. These observations can provide a new basis for the study of exoplanets.
