While there are many technical hurdles (especially regarding focusing) to overcome, this is an interesting project.

Telescope could focus light without a mirror or lens

"A proposed space telescope would focus light primarily with a patterned sheet of metal rather than a large mirror or lens. The telescope would have amazingly sharp vision and could spot Earth-size planets around other stars, its backers say.
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A 30-metre Fresnel imager would be powerful enough to see Earth-sized planets within 30 light years of Earth, and measure the planets' light spectrum to look for signs of life, such as atmospheric oxygen. The Fresnel imager could also measure the properties of very young galaxies in the distant universe and take detailed images of objects in our own solar system."

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I had thought that Fresnel lenses, even though flat and thin, had concentric zones that had progressively steeper inclines to duplicate the function of a heavy thick lens. Maybe the ones in this discussion are completely different.

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This is what makes me so absolutely 100% certain that any older civilization in our galaxy (if they exist) would have to be aware of the fact that there's life on Earth right this very minute as you read this;

We more or less have the technology to detect the same fact in other star systems right now!

I had thought that Fresnel lenses, even though flat and thin, had concentric zones that had progressively steeper inclines to duplicate the function of a heavy thick lens. Maybe the ones in this discussion are completely different.

Correct... they're Fresnel zone plates that use diffraction so are flat.

This is what makes me so absolutely 100% certain that any older civilization in our galaxy (if they exist) would have to be aware of the fact that there's life on Earth right this very minute as you read this;

We more or less have the technology to detect the same fact in other star systems right now!

Good point. And an older civilization might want to send a beacon to any planets like this that they find. I'm glad we're finally listening.

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