MURRAY HILL, N.J.
Bell Labs (part of Alcatel-Lucent) has just announced a new world speed record for fiber-optic transport. This record, 100 petabits per second kilometer, exceeds previous records such as one achieved in May 2009 of 19 petabyes per second per kilometer (Pbps/km) claimed by AT&T, NEC and Corning.
This new record was achieved by transmitting 155 simultaneous wavelengths of light over a single 7000 km fiber, with optical repeaters every 90 km along the link. Each wavelength carried 100 gigabits per second of traffic to give the fiber a total payload of 15.5 terabits (trillion bits) per second. This is enough capacity to carry 10,430 simultaneous uncompressed HD video signals.
These types of technological advancements are good news for broadcasters and content aggregators who want to deliver their programming to the largest possible audiences. Because optical fibers are so expensive to install and maintain on transoceanic connections, achieving more capacity per fiber will help meet the growing worldwide demands for Internet and private network bandwidth.
Fig. 1: Fiber-optic landspeed transmission records since 2000 “The key benefit of increased capacity is driving down the cost per megabit,” said Jeremy Dujardin CTO of Genesis Networks, a New York-based provider of global transmission services. “This allows customers to do more—when they have more bandwidth, they deliver more services, or they can increase the quality of existing services.”
Andrew Dugan, Senior Vice President of Architecture and Engineering for Level 3 commented, “Level 3 is interested in and supportive of research and experimentation that leads to increased capacity and speeds in the global delivery of data. Although we are not aware of the specific technology used by Bell Labs for this experiment, we believe investment in this type of research benefits Level 3 and the entire industry.
“Increased capacity for WDM systems is something Level 3 generally likes to support because it has historically tended to drive down cost per bit of transmitting data, a key economic component as demand continues to grow.”
UNDERSTANDING SPEED RECORDS
Fiber optic speed records can be a bit tricky to understand, particularly because of the way they are measured. With fiber optics, there is a tradeoff between signal speed and fiber length, due to dispersion. Higher speed signals tend to disperse more over longer distances, and even though signals are regenerated periodically along the fiber (every 70 to 90 km), these effects can build up across a long link. So, most results are measured in terms of the Bandwidth-Distance product, which is simply the result of multiplying the bit rate of the signal by the distance that it travels. This permits records to be broken in two ways—first, by increasing the raw bandwidth of the transmission system or secondly, by increasing the distance traveled by the signals. Both of these are worthy goals—long transoceanic links benefit from increases in bit as well as increases in link distances.
There have been a number of claims for the fiber optic data transmission speed record over the last decade. Fig. 1 shows some of the records that have been claimed by various manufacturers since 2000.
It is quite likely that new records will continue to be set in coming years, because the spectral density of fiber-optic systems can be improved significantly as new technologies become available. For example, most of the optical terminal gear that can be purchased today offers a spectral density of less that 1 bit per second per Hertz. Some lab experiments have shown high-speed fiber optic gear running at 3 bits per second per Hertz, but there is room for improvement. After all, every consumer grade TV receiver sold in the United States today has the ability to receive a 19.39 Mbps signal in a 6 MHz channel, which has a spectral density of 3.2 bits per second per Hertz, and professional satellite gear can achieve much more. So, it is likely that fiber-optic bandwidth distance records will continue to be set as technology continues to improve.
IN THE REAL WORLD
Of course, these speed records are achieved with equipment that is not yet available on the market. There are a number of reasons why this is so. To begin with, most of the records are achieved in a laboratory, which means that environmental conditions can be tightly controlled, and hand-selected components can be used. Second, the systems don’t need to be designed for the kind of reliability that we have come to expect from our communications systems—particularly considering the cost of dispatching a repair vessel to the middle of an ocean. And finally, the cost of manufacturing is not a significant issue when in the research phase, but certainly has a big impact on any deployable system. If the past is an accurate guide, these newly achieved technologies will begin to appear on the market inside commercially available products within the next 10-20 years.
It seems particularly fitting that this record was announced on the eve of the Nobel Prize in physics being awarded to Charles K. Kao, who is widely regarded as the “Father of Fiber Optic Communications.” His groundbreaking work in the mid-1960’s made it possible for all the subsequent developments that have formed the backbone of the modern communications network, and brought benefits to people around the world. In the four-and-a-half decades since Dr. Kao performed his work, there have been a startling number of advances. It will be interesting to see what the future will bring in this incredibly important field.