Converting from optical to electrical signals, then back to optical, is the bane of modern networks, often requiring a $10,000 optical-to-electronic converter just to perform some simple signal processing, then another $10,000 electronic-to-optical converter to put the signal back on the fiber-optic cable. Now researchers have invented a method that merges electronics with optics by inserting semiconductor devices inside a hollow optical fiber, potentially integrating the electronic signal-processing functions into the cable carrying the signal. The technique coats the inside of the hollow cores of fiber-optic cables with semiconductors at a rate of tens of nanometers per minute. At the end of the process, the hollow cores--which may measure 100 nm to 5 microns in diameter--close down to as small as 10 nm. So far the researchers have successfully fabricated silicon germanium heterojunctions inside a fiber, demonstrated that the fiber still behaves as a waveguide, then implemented a field-effect transistor (FET) that could modulate the signal passing though the core.