Is this a similar principle to the concept in the 3 Body Problem series of books? As in, how one of the main characters is able to boost the transmission power of an earth bound antenna
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The gravitational lens idea is different, it makes use of a known phenomenom where the Sun's gravity "bends" light rays moving around it, which can amplify the light coming from far away objects. In principle you could run it backwards, so the lens could amplify signals we send as well.