Infinera, a supplier of optical network platforms with 135 customers in over 70 countries, recently announced exciting news. "Facebook deployed an Infinera Intelligent Transport Network to light the world's longest terrestrial optical network route capable of delivering up to eight terabits per second of data transmission capacity. The new route spans 3,998 kilometers and is deployed without any regeneration."
There are three important tech concepts in the press release:
- Eight terabits per second is equivalent to streaming one million high-def videos at the same time.
- 3,998 kilometers is unofficially the longest 8 Tb/sec-capable production route in existence.
- No regeneration required.
Photonic Integrated Circuit (PIC) technology
PIC technology is one reason eight terabits per second can be transmitted over a 3,998 kilometer fiber-optic run. PICs, like the tiny chip on the technician's fingertip above, are devices that integrate functions using photons rather than electrons like the more familiar integrated circuits. This MIT Technology Review article explains why photonics is more in favor. Simply put, electrical resistance unacceptably slows data throughput and degrades the information being transported in electronic integrated circuits.
After some digging, I learned that Infinera's PICs were fabricated using Indium Phosphide (InP). This Infinera white paper adds, "While other optically-active materials are available (silicon), none of the materials offer the same advantages as InP when applied to the long-haul dense wavelength division multiplexing (DWDM) market."
500 Gb/sec "super-channels"
Not unlike chip manufacturers who are battling Moore's Law, fabricating PICs to work with data rates above 100 Gb/sec creates similar manufacturing headaches. As the data rate increases so does the complexity of the transmit and receive circuits and increased complexity translates into higher costs and increased customer prices.
According to Infinera, the answer to increased complexity and higher prices is the "super-channel," which is large-scale PIC technology that uses two chips: one for transmitting and one for receiving. The idea is to mix multiple lower data-rate carriers into a composite channel that can be considered a unit of "operational capacity" — in this case 500 Gb/sec. Infinera states in the white paper that the line card can support 12 Tb/sec of non-blocking Optical-Transport Network (OTN) switching.
No regeneration required
"No regeneration required" captured my attention, as I was unsure of the difference between amplification and regeneration. I also wondered if amplification was needed. I contacted Infinera to find out.
"In long-distance optical transmission it's necessary to amplify the signal every 80-120 km to compensate for optical-fiber loss," writes Matt Mitchell, vice-president of optical-system architecture at Infinera. "Amplification can be done for all the wavelengths in a given optical fiber using one amplifier, making it very cost-effective. But each time the signal is amplified it adds optical noise to the fiber and eventually the signal needs to be electrically cleaned up or regenerated."
Next, Mitchell clarified regeneration: "Unlike amplification, regeneration has to be done per wavelength, and this means it's much more expensive and uses more equipment than optical amplification. That Infinera could transmit the signal for almost 4,000 km without digital regeneration makes it extremely cost-effective for Facebook."
Fiber-optic technology was reaching practical and theoretical limits for an individual channel or wavelength. Coherent super-channels provide a solution for companies to get past the 100 Gb/sec barrier and send eight (possibly 12) terabits of data every second through a tiny optical fiber.
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- Facebook open sources new data-center tech at the 2015 OCP summit
- Facebook's 6-pack: The main ingredient in its data center network redesign
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