Manufacturing Fibre Optic Strands In Space: .001 dB Loss Per Kilometer

ZBLAN is the acronym for a flouride-based optical fibre that uses a combination of zirconium, lathanum, barium, sodium, and flouride that has a theoretical optical loss of only .001 dB loss per kilometer in the infrared frequencies. Good silicon-based fibre generally lies in the .15 to .20 range. Obviously, if perfected, this would constitute a major fibre optic revolution. The theoretical dB loss of 2000 kilometers of ZBLAN fibre, a French invention, would be equivalent to ten kilometers of standard silica fibre. Optical amplifiers would become obsolete for terrestrial networks and many subsea spans.

The challenge is that earth's gravity leads to crystals forming when the glass is drawn and allowed to cool. Unlike standard fibre optic glass which is SiO2, silicon dioxide, ZBLAN is a complex mixture of elements with different molecular weights. Convection during the drawing process results in these elements separating into crystals. The glass also becomes extremely brittle as a result. The realized dB loss is as high as .7 dB. It was discovered many years that ZBLAN manufacturing in minor gravity where objects float eliminates the vast bulk of the defects that prevent this material from achieving its full potential. These low weight experiments suggest that 1 to 10 dB is easily achievable. The first experiments involved drawing ZBLAN aboard zero G aircraft or rockets. The two photos below the difference in the degree of geometric imperfections.

Recently 11 kilometers of ZBLAN was manufactured above the International Space Station and returned to earth for analysis. Flawless Photonics supplied the raw materials and manufacturing platform. The spooled fibre has been given to the University of Adelaide for analysis. Results are scheduled to be released this month or early 2025.