Large Optical Telescope Based on High Efficiency Thin Film Planar Diffractive Optics

In future ground-based receivers for deep-space optical communications with spacecraft, aperture diameters of the order of 10 meters are required even with the most sensitive available detectors. Directly applying the technology of 10 meter class ground-based telescopes is cost prohibitive. Also, conventional astronomical telescopes are not compatible with operation within 5 degees of the sun, but such near-sun operation is required with the Ground-based Telescope Assembly to provide consistent and reliable wideband communications with interplanetary spacecraft. BEAM Co. proposes to develop a telescope based on diffractive optics that is expected to be far less expensive to manufacture than a telescope based on conventional reflective optics. Our approach takes advantage of the well-defined wavelength of the optical communications beam, thus allowing a high-efficiency design that is expected to be much lighter than a conventional design, thereby reducing the cost of the system that will be used to point the telescope. At the end of Phase I, we will have fabricated and tested subscale diffractive optical elements and performed tests to validate the technology's scalability to large apertures and its capability to support the <20 microradian object space spot size requirement as well as the requirement for near-sun operation.