The objective is to assess the most optimum and cost-efficient spectral filtering technique with a bandwidth of a few Angstroem (potentially a narrower, tunable bandwidth to account for the Doppler shift) with high throughput (> 60%) best adapted to a given design of an optical ground antenna and develop a demonstrator prototype for the 1550nm wavelength band. The benefit consists in maximizing the contact duration with the satellite by being able to operate as close to the Sun as possible.

The spectral filter is a critical element to reject unwanted background and straylight onto the receive detector during day and night operation. The activity consists in elaborating its optimized design (interference filters vs. fiber Bragg gratings vs. volume Bragg gratings) after trade-offs taking into account the overall design of the optical antenna (e.g. numerical aperture of the beam, tunability vs. spectral width, etc.). The overall cost will depend on the performance(selectivity, out-of-band rejection and in-band throughput) of the filter system, which is a significant driver for the surface quality requirements mainly of the primary mirror. It is a fundamental building block for optical antennas serving (future) missions in all domains (Earth Observations, Science, Telecommunications) that would employ optical links. Asteroid Impact Mission (AIM; launch 2020, Didymos rendez-vous 2022) presents a strategic demonstration opportunity either on ESA's OGS on Tenerife, or on an existing astronomical telescope by providing the optical receiver chain to the site (including the optical filter as one key element).