Light can cross galaxy's and maintain it's original form (more or less). Crossing a few hundred miles isn't hard to do. Single mode fiber has no known maximum length, neither do the transceivers attached to the fiber. You could just as easily make this work at 100 miles are you could at 10 feet. That being said, the fiber must be of a high enough quality that it doesn't introduce errors. It they try to use multi-mode fiber for this then you'll get vastly limited length.
In short, if they can develop an optic capable of sending / receiving at 50Gbps, then it can send / receive at 10, 100, 1000, or 100,000 feet.