Dry fiber study boosts data transmission

17 Jun 2002

Understanding the origin of water in optical fibers is opening up routes for improving the efficiency of future telecommunications. Gordon Thomas and colleagues at Bell Labs have discovered that optical fibers become contaminated with water mainly through the heat source employed in drawing the rods into fibers, rather than from the atmosphere or from the starting materials in the glass manufacture. They have published a patent for alternative heat sources that do not produce significant amounts of water.

This discovery has also led Bell Labs to develop dry fibers that enable a much wider range of wavelengths to be exploited for telecommunications.

Optical communications are limited by the clarity of the wavelength transmission window in the SiO₂ glass. Currently data are only transmitted in a narrow band of wavelengths at around 1550 nanometers because there is a large optical loss at lower wavelengths (peaking at around 1400) associated with OH contamination.

Thomas, who now works at Massachusetts Institute of Technology, explains that his research was involved in understanding the fundamental physics behind the process of making optical fibers so that Bell Labs could plan for future developments and be ahead of the technology.

Following the Bell Labs research, Lucent Technologies has released AllWave, a dry fiber which has a wavelength transmission range about five times bigger than existing fibers. Thomas says that this fiber is yet to become fully utilized because the technology to send the signal over the whole range of wavelengths is not yet available. He predicts that there will soon be a rush of new lasers and amplifiers to work with wavelengths from lower then 1300 nanometers to about 1600 nanometers. He says that Lucent has had a head start in making devices because of the Bell Labs research but predicts that other manufacturers will follow very soon.

Thomas says that the patented technology simply states the use of a heat source that does not produce significant quantities of water. Most manufacturing techniques currently employ an OH torch, as this is very inexpensive. He says that other methods, like RF-ovens and oxygen plasma, are more expensive but do not produce water.

Previously people suspected that the water originated from impurities in the chemicals used as starting materials. "We've found out that the chemists were doing a really good job," said Thomas, explaining that chlorine is pumped through the system during manufacture of the glass in order to pick up any residual hydrogen before it could form water.

The research was reported in the latest issue of the journal Nature.

SH