Normally light waves cannot penetrate structures smaller than their length. But a length of nanotube protrudes from the end of the cable and acts as an optical antenna to guide the light into the structure. The longest of these nanocables is only 20 micrometers, and longer cables will only carry light a maximum of about 50 micrometers – roughly 100 wavelengths.
The first target application is to increase the efficiency of energy conversion in solar cells by tightly packing together arrays of nano-coax filled with photovoltaic material rather than aluminium oxide.
Another possibility is to assemble arrays with optical antennas on one end and electrical output at the other to serve as artificial retinas for people with impaired vision.