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Why is Quantitatively, why will optical communication be better than X-band for deep-space communications?

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Why is optical communication better?

In a question about communicating with Voyager, an answer asserts:

[70 meter dish antennas deployed in space] just isn't done, and it probably won't be, since optical communication is definitely the way to go in the near future. We've already had demonstrations from Earth to the Moon, and there are no known roadblocks to extending optical communications to deep space. Since the wavelength of light (about 1 micron) is so much smaller than the wavelengths used in deep space (centimeters, perhaps millimeters in the future) the "dish" shrinks from a huge steel monstrosity to the mirror of an optical telescope tens of centimeters in diameter. This can be managed quite nicely on a deep space probe.

In more detail, considering also path loss and technological considerations in the construction of the receivers and transmitters, just what is it that makes optical communication favorable?