Networking

Twisted light encoding may boost fiber optic bandwidth in a big way

To match the onslaught of data, every conceivable way of increasing fiber optic's data transfer rate is under scrutiny--even twisting light.

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Image: iStockphoto.com/Streager
One has to wonder if or when scientists and engineers will finally run out of ways to coax more bandwidth from fiber optic transmission systems. The current record, described in this University College London (UCL) press release, is an incredible 1.125 Terabytes per second set by a research team under the direction of Dr. Robert Maher (lead researcher, UCL Electronic & Electrical Engineering).
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Image: University College London

Maher and his fellow team members are no strangers to high-speed fiber optic research. They doubled the data transfer rate last year, as mentioned in the TechRepublic article Researchers double throughput of long-distance fiber optics. Maher describes the team's latest accomplishment:

"While current state-of-the-art commercial optical transmission systems are capable of receiving single channel data rates of up to 100 gigabits per second, we are working with sophisticated equipment in our lab to design the next generation core networking and communications systems that can handle data signals at rates in excess of 1 terabit per second."

To obtain those data transfer rates, the UCL team optimized how data is encoded in optical signals. Then, the researchers employed coding techniques used in wireless communications to allow the optical transmissions to ignore bandwidth-robbing distortion created in the system's electronics.

Another unique encoding method

How information, prior to transmission, is encoded plays a huge role in determining the data transfer rate, which explains why Min Gu (associate deputy vice chancellor for research innovation and entrepreneurship at RMIT University), Qiming Zhang (senior research fellow, RMIT University), and Haoran Ren (Ph.D. candidate, Swinburne University of Technology) are also looking into new ways to encode fiber optic traffic.

"Currently, optic-fiber technology uses several different properties of light to encode information, including brightness, color, polarization, and direction of propagation," Gu, Zhang and Ren said in The Conversation commentary Twisted light could dramatically boost internet speeds. "But if we want to cram even more information through optic fiber, we need to use other features of light to encode more information, without disrupting currently used properties."

SEE: How shark attacks, shipwrecks, and earthquakes threaten global communications

Angular momentum encoding

The area of encoding being looked at by the RMIT and Swinburne research team is angular momentum division, the orthogonal multiplexing method of choice in high-capacity optical information technologies.

"If the light wave traveling through the optic fiber is twisted helically—like a spring—then it has angular momentum, which is a measure of its momentum when it rotates around a point," the researchers said. To carry the twisted light, a new type of optical fiber and the associated encoding and decoding technologies were created.

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Image: Wikipedia

Problem with existing encoding technology

Current angular momentum division multiplexing devices are not acceptable to the RMIT and Swinburne authors, who wrote, "The typical bulky elements used for information retrieval from the overall diffracted field based on the interference method imposes a fundamental limit toward realizing on-chip multiplexing."

The team's preference was a tiny nanoscale helical structure that could detect and control the twisted light at nanoscale, using an integrated photonic chip.

Figure A shows the nanoscale helical structure the team created. "Each indentation on the image is a single unit of the chip, like a single pixel in a display panel, made up of semi-circle nano-grooves and nano-apertures engraved in a metallic film," the authors said.

Figure A

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Image: RMIT University

Figure B shows Professor Min Gu with one of the team's nanophotonic chips.

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Figure B
Image: RMIT University

What is especially interesting is how this research moves toward the goal of replacing electrons with photons at the chip level. Besides replacing electrons, the team's nanophotonic chip permits:

  • Precise guidance of the twisted light data signals, eliminating data loss.
  • Multiple twisted light signals to be processed at the same time.
  • Means to achieve ultra-wide bandwidth (an increase of six orders of magnitude over current technology).
  • The creation of an ultra-wide bandwidth device.

SEE: 3D printing is helping UK researchers create complex fiber optics

What this means

"Owing to the rapid development of nano-fabrication technology, we believe there is no technical challenge to the mass production of this chip today," Gu, Zhang, and Ren said.

Besides few if any manufacturing problems, the researchers believe their nanophotonic chip:

  • Opens a new perspective in employing light for chip-scale information generation, transmission, and retrieval of images, videos, sounds, and so on.
  • Could be used in applications such as data transmission, ultra-high definition displays, ultra-high capacity optical communications and ultra-secure optical encryption.

Another big advantage of the team's nanophotonic chip is its ability to parallel process optical information. "A large number of optical fibers in one fiber bundle can be processed through the chip in parallel, which means the processing speed can be significantly increased by considering how large the array is," they said. "For example, if we take 100 by 100 of such units in the array for the chip, then the speed could be boosted by four orders of magnitude."

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About Michael Kassner

Information is my field...Writing is my passion...Coupling the two is my mission.

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