Nanomechanical Dual-Core Optical Fiber May Enable Optical Buffering
As the Autobahn of the Internet, optical fibers carry text, movies, and music at the speed of light. Even with their rapid efficiency, these thin filaments of glass are hooked up to slower routers, signal switches, and buffers in order to relay and package data. Researchers at the University of Southampton in the UK have now developed a dual-core optical fiber able to perform the same functions just by applying a little mechanical pressure.
These novel nanomechanical fibers have two light-carrying cores suspended less than 1 micrometer apart from each other. They could greatly improve data processing and could also be used as sensors in electronic devices.
“Nanomechanical optical fibers do not just transmit light like previous optical fibers,” says University of Southampton researcher Wei H. Loh, “Their internal core structure is designed to be dynamic and capable of precise mechanical motion. This mechanical motion, created by applying a tiny bit of pressure, can harness some of the fundamental properties of light to give the fiber new functions and capabilities.”
To create the new fibers, the researchers heated and stretched a specially shaped tube of optical glass with a hollow center containing two cores suspended from the inside wall, as shown in the illustration above. The fibers keep the original structure as they are drawn and stretched to the required thickness.
The next phase in the researcher’s work will be to test the fibers at longer lengths and to optimize the precision in switching and other functions. The researchers anticipate that nanomechanical fibers could begin to enhance telecommunications and industrial systems in the next three to five years.
Changing Optical Coupling
The advance was attained by fabricating fibers with two cores (the pathways that carry light) which are close enough to each other to be optically coupled. Optical coupling is a characteristic of light whereby a photon’s influence can extend beyond the fiber’s core, even though the light itself remains inside. Through the shifting of the position of one of the cores by a few nanometers, the researchers altered how strongly the light responded to this coupling effect.
Given a strong enough coupling effect, the light immediately jumps from one fiber to the other. “Think of having a train traveling down a two-track tunnel and jumping the tracks and continuing along its way at the same speed,” explained Loh.
The flexible suspension of the fiber responds to the slightest bit of pressure, bringing the two cores closer together or moving them apart. Controlling when and how the signals hop from one core to the other reproduced, for the first time, the function of an optical switch inside the actual fiber.
This capability could also allow for optical buffering. According to the researchers, optical buffering has been very hard to achieve. Buffers are indispensable when multiple data streams arrive at a router at the same time. They delay one data stream so another can travel freely.
“With our nanomechanical fiber structure, we can control the propagation time of light through the fiber by moving the two cores closer together, thereby delaying, or buffering, the data as light,” says Loh.
Integrated Fiber Backbone MEMS
In the photo, you can see the actual cross-section at high magnification of the nanomechanical fiber. In the center are shown the dual cores, each only 0.5 micrometers in diameter, with the supporting glass filament being just about 0.2 micrometers across.
This is the first time, according to the researchers, that nanomechanical dual-core fibers have been directly fabricated. Other types of multicore fibers have previously been fabricated, but with cores encased in glass and thus mechanically locked. This meant that routing, switching, or buffering data involved taking the light out of the optical fiber for processing in the electronic domain before reinsertion back into the fiber, which is cumbersome and costly.
“An implication of our work is that we would integrate more of these functions within the fiber backbone,” says Loh, “through the introduction of MEMS (microelectromechanical systems) functionality in the fibers.”
Because this process uses traditional fiber optic manufacturing technology, it’s possible to create dual-core fibers that are hundreds of meters to several kilometers long, which is vital for telecommunications.
This introduction of MEMS functionality into the optical fiber is also expected by Loh and his colleagues to have applications in other fields, such as sensing. “Nanomechanical fibers could one day take the place of silicon-based MEMS chips, which are used in automobile sensors, video game controllers, projection displays, and other every-day applications,” says Loh. They could also be used in the aerospace industry for stress corrosion dynamic monitoring.
Because the fibers are so sensitive to pressure and may be easily made in very long lengths, they could be integrated into bridges, dams, and other buildings to signal subtle changes that could indicate structural damage.