Northrop Grumman’s 11th commercial resupply services mission, scheduled to launch from Wallops Island Flight Facility in Virginia later today, includes two ISS National Lab investigations focused on the production of ZBLAN optical fiber on the space station—one project from FOMS, Inc. and one from Physical Optics Corporation.
First off, what are optical fibers? Optical fibers are remarkably fine glass or plastic fibers (imagine a thread thinner than a strand of your hair) capable of transporting vast amounts of information such as light signals over great distances. There are currently three experiments sponsored by the ISS National Lab focused on the manufacture of a specific kind of optical fiber using a type of fluoride glass called ZrF4-BaF2-LaF3-AlF3-NaF, or ZBLAN for short. These ZBLAN optical fibers may offer dramatic improvements over current silica fibers, but there’s a catch: ZBLAN fibers are notoriously difficult to make on Earth.
The most recent issue of Upward, the official magazine of the ISS National Lab, includes a feature article that describes the challenges of producing ZBLAN optical fiber on Earth and explores the benefits of manufacturing ZBLAN in microgravity. Not only can microgravity improve the production quality of regular ZBLAN optical fibers, it could also potentially improve the quality of ZBLAN fibers doped with rare-earth elements such as erbium or holmium, which are used to amplify weak optical signals. Scientific and commercial applications of these doped fibers abound in fiber amplifiers and lasers, smart sensors, nonlinear optics, and many others.
Because rare-earth ions are atomically much heavier than most atoms found in silica and ZBLAN fibers, they tend to form clusters, a process similar to crystallization, in normal gravity conditions. Clusters can reduce gain efficiency in the optical fiber, thereby negatively affecting optical amplifier performance. The problem worsens at higher doping concentrations, which are desirable for making high-power and high-gain amplifiers.
“Microgravity helps you here,” said Dimitri Starodubov, chief scientist at Fiber Optics Manufacturing in Space (FOMS), one of the companies producing ZBLAN fibers on the ISS National Lab. “You can increase the concentration of doping elements and at the same time still produce a material that has high optical quality.”
These are exciting times in the history of optical fibers, as ZBLAN optical fibers produced onboard the ISS National Lab could lead to dramatic improvements in optical communications and numerous other scientific and commercial uses here on Earth.