Twist Beam Can Improve The Fiber Information Carrying Capacity
Internet traffic is growing exponentially, researchers have been trying to enhance the communication capacity of fiber optic cable. A successful method used in the past 20 years, basically is to rely on the more "lane", refers to use a different color or wavelength to transmit different signals. But just like in the real highway, since the amount of "lane" is increased, each width is narrower, so the data stream can only be mixed together.
From past few years, there are a number of research teams trying to get through the shape of light beam to encode the information, in order to ease network traffic congestion, the technology used the called light property of orbital angular momentum. Currently, the network signal is the use of straight spread light beam to transmit, but the specific filters can make the beam distortions in varying degrees in the process of moving. However, the experiments results using this effect are not ideal: different shapes of light beam often mix with each other in advance distance of less than 1 metre.
But now, researchers at Boston University and the University of Southern California cooperated, found a way to make the different shapes of light beam travel separately, the transmission distance reached a record of 1.1 km.
In the experiment, the researchers designed and built a 1.1 km long glass fiber cable, the cross section has a different refractive index (used to measure the travel speed of light in a specific medium). Then, they sent beam of winding and straight along the cable.
The research team found, light output and input can be matched, show that the various shapes beam does not appear mixed. Different refractive index significantly affects only a certain shape of beam, so these different shapes of beams are moving at different speeds in the cable. "This means we can keep them separate." Research team leader, Boston University Electrical Engineer Saida Si Rama Ramachandran said.
The researchers carried out several tests using beam of clockwise and counterclockwise with varying distortion degrees, and found there are about 10 different shapes of beams can be used to transmit information. The results are exciting, because every shapes may presage the "information highway" traffic is expected to reach a whole new level. Based on this, the data stream is is further divided into narrow "lane" according to the different colors, thereby maximize the flow.
However, the laboratory results applied to real world still need time, in part because the current Internet fiber optic cable only transport straight beams. Ramachandran said, a more direct goal, may be used in server farm between servers by some large network companies like Facebook, install cables which can transmit twisted beam in short distance.