Researchers have designed a Fresnel hologram to focus light in the transverse direction (x–y plane) and disperse it in a linear fashion along the optical axis (z-axis). It functions not only as a focusing but also a dispersive element along an optical axis. The computational method uses wave-optics principle.
The hologram disperses broad wavelengths over a long distance on axis. This Fresnel hologram constitutes the primary diffractive optics in a Dual Use Exoplanet Telescope (DUET) system. The main function of the hologram is to collect the collimated star-light source and focus it into the detector.
When a broad-band light source passes through an annulus diffractive optic, the incident light with different wavelengths will be focused into different positions along the optical axis. It is called dispersive behavior and can be applied for high resolution spectroscopy applications.