A few groups of HAM Radio operators have been experimenting with what they call terahertz communication for quite some time now.

The transceivers got pretty sophisticated, with very complex optics. There are reports of successful conversations over distances of >150km.

Apparently, many of them are in Germany so quite a few of the sources are in German.

http://modulatedlight.org/optical_comms/optical_index.html

http://www.db6nt.de/laser.html

http://modulatedlight.org/optical_comms/SDIM8379h.jpg

http://www.dd1wks.de/laser.html

http://www.dl2dr.de/6.html