One of the biggest challenges for 5G and last mile 10 Gig deployments is not raw data speeds, but middle mile and core networks. Currently, top speeds for core networks are between 200 Gbps and 400 Gbps, depending on the carrier and day of the week. Optical systems with advent the laser and optical fiber have been attracted a lot of concerns for optical communications, which support unlimited bandwidth and very low losses for long distance. Companies are racing to introduce new fiber technologies to enahance the speed to terrabit / sec and petabits/sec.
Nowadays, the commercial system can carry more than 1 Tbps (128 channels) over unregenerated distances of thousands of kilometers. Long distance, as well as regional networks, are based on fiber optic cables. Nokia and Etisalat (UAE) report the completion of a multi-terabit-per-second, single-carrier data transmission over an operator-deployed fiber network in a field trial. Nokia Bell Labs reported a record single-stream data rate of 1.52 terabits per second, close to four times the 400 gigabits per second achieved by the fastest links now used in data centers. Nokia said in a press release that a terabit-per-second is enough bandwidth to download the entire “Game of Thrones” video series in HD in under two seconds. The Nokia field trial showed that Etisalat’s existing network could support the higher optical wavelength bit rates that will be required to support high-bandwidth services such as 5G extreme mobile broadband, fiber-to-the-home (FTTH) and data center interconnect (DCI) cloud services.
In August 202, a team from Japan’s National Institute for Communications Technology (NICT) has sent a staggering 172 terabits per second through a single multicore fiber—more than the combined throughput of all the fibers in the world’s highest-capacity submarine cable.
Optical Fiber communication network technologies
Telecommunications traffic has increased relentlessly over recent decades, made possible by tremendous increases in the data rates that fiber-optic transmitters can push through the standard single-mode fibers that have been used since the 1990s.
The main driver of optical communication networks is advancement on optical fibers and optical components. The Bit rate-Distance (BL) has increased to meet the requirements of high-speed communication networks, where B is the bit rate and L is the repeater spacing. The first generation of lightwave systems employed lasers operating near 0.8 microns and used a multi-mode fibers for a bit rate of 45 Mbps, with repeater spacings of up to 10 km.
Then, lasers working at wavelength of 1.3 microns were used in the second generation of optical networks, and the data rates transmitted through single-mode fiber were up to 1.7 Gbps for 50 Km of a repeater spacing. Afterwards, developments were obtained a single longitudinal mode laser and very low losses of optical fiber. The third generation commercially operated at 1.55 microns with single longitudinal modes where the bit rates achieved up to 10 Gbps, and the distance between electronic repeaters was limited to 60-70 km.
Then, optical fiber amplifiers were invented in 1989 for high expanded transmission distance while operating over the C-band, with low cost and very low noise. Electronic repeaters were replaced by optical amplifiers, allowing to be the signal in the optical domain. The fourth generation of lightwave systems using optical amplifiers and the lithium niobate external modulator, transmission distances of nearly 1000 km could be reacted at 2.5 and 10 Gbps.
Wavelength Division Multiplexing (WDM) is a widespread technology deployed for the internet to reduce traffic induced by increasing number of applications. Along advent a WDM in 1992, the data rates increased for network throughput, and bit rate of 10 Tbps was achieved in 2001. WDM exploits a multiplexing technique similar to FDM in the radio communications in order to increase the network capacity. This system combines (muxing) multiple optical signals so that they can be transported as a group, over a single fiber, and separates (demuxing) the wavelength channels in the receiving end. The DWDM systems from the beginning of 1995 could transmit 2-16 wavelength channels at the same time. The early DWDM transported optical signals point to point. In the late 1990’s, advances in the fiber optic technology provided the basis to increase the DWDM capacity to 40-120 wavelengths and extended the transmission distances to 1000 km.
Advances in the optical waveguide technology made it possible to enhance the capability. Improvements in both EDFA and fiber optic technology contributed to the significant increase in the number of wavelengths that could be transported. In 2017, CableLabs demonstrated the ability to deliver 256 Gbps over 80 kilometers on a single wavelength with 16 QAM “using electronics bought on eBay,” said McKinney. By multiplexing eight wavelengths, speeds of 2048 Gbps — 2 Tbps — were achieved. By tweaking up encoding and modulation, 4 Tbps should be reachable in the near term while speeds of up to 50 Tbps are possible.
CableLabs President and CEO Phil McKinney, conducting interviews at CES 2018, says the path forward to boost fiber capacity is by borrowing techniques from long-haul networks and getting rid of unnecessary overhead to increase speed. Coherent optics utilizes the ability to transmit multiple bits of information using light, including amplitude and phase modulation, instead of a simple binary on-off approach. Adding QPSK and QAM, plus polarization means you can move a lot more data onto a single strand of fiber.
But fiber throughputs are now approaching the nonlinear Shannon limit on information transfer, so developers are exploring ways to expand the number of parallel optical paths via spatial-division multiplexing. Spatial-division multiplexing is an optical counterpart of MIMO, which uses multiple input and output antennas for high-capacity microwave transmission. The leading approaches: packing many light-guiding cores into optical fibers or redesigning fiber cores to transmit light along multiple parallel paths through the core that can be isolated at the end of the fiber.
Yet multiplying the number of cores has limits. They must be separated by at least 40 micrometers to prevent noise-inducing crosstalk between them. As a result, no more than five cores can fit into fibers based on the 125-micrometer diameter standard for long-haul and submarine networks. Adding more cores can allow higher data rates, but that leads to fiber diameters up to 300 µm, which are stiff and would require expensive new designs for cables meant for submarine applications.
In a late paper, Georg Rademacher of NTIC described a new design called close-coupled multi-core fibers. He explains that the key difference in that design is that “The cores are close to each other so that the signals intentionally couple with each other. Ideally, the light that is coupled into one core should spread to all other cores after only a few meters.” The signals resemble those from fibers in which individual cores carry multiple modes, and require MIMO processing to extract the output signal. However, because signals couple between cores over a much shorter distance in the new fibers than in earlier few-mode fibers, the processing required is much simpler.
Earlier demonstrations of close-coupling were limited to narrow wavelength ranges of less than 5 nanometers. In San Diego, Rademacher reported testing an 80-km length of three-core 125-nm fiber with signals from a frequency comb light source. The team transmitted 24.5 gigabaud 16-quadrature amplitude modulated (16-QAM) signals to sample performance on 359 optical channels in the C and L fiber bands spanning a 75-nm bandwidth. Signals were looped repeatedly through the test fiber and an optical amplifier to simulate a total distance of 2040 kilometers.
Russian fiber optic breakthrough offers 200 gigabits per second over more than 300 miles.
The Moscow Institute of Physics and Technology announced this week they have successfully transmitted a signal over the high-tech wires at a distance of 323 miles at 200 gigabits per second. That beats current real-world transmission systems that can manage 100 gigabits per second over 311 miles. It also brings the sort of high speeds previously demonstrated in research labs out into commercial cables. The team’s findings were published in IEEE Photonics Technology Letters.
The breakthrough could help connect up rural areas that might otherwise struggle to get online. Alzbeta Fellenbaum, principal analyst for IHS Markit, a London-based data broker, tells Inverse that fiber optics could offer a better means of plugging the gap than other options like cellular towers.
“There have been some hopes recently that fixed wireless access (FWA) over LTE/4G (or 5G in the near future) could solve the poor rural connectivity issues, but for very large countries like Russia or Canada with vast sparsely populated areas, this might be a more suitable solution,” Fellenbaum says.
The team used commercial cables developed by Corning. The connection comprised three sections, with each one packing two kinds of fiber optic cables in series. Remote optically pumped erbium amplifiers were used in between each section, the first one placed 76 miles from the transmitter and the other 81 miles from the receiver.
Nokia successful field trial of single-carrier, 50.8 terabit-per-second on Etisalat’s WDM fiber optic network
Using Etisalat’s wavelength division multiplexing network, the companies were able to reach a transmission speed of 50.8 terabits per second over 93 kilometers of optical fiber.
In addition to the speeds, higher bit rates per wavelength enable power and space savings, improved network simplicity, as well as increased spectral efficiency and capacity. It also enables reduced cost per bit compared to optical networks composed of lower rate channels, according to Nokia.
Using a single optical carrier operating at 100 Gigabaud, the terabit wavelengths tapped into Nokia Bell Labs’ probabilistic constellation shaping (PCS) to intelligently shape the signal to achieve maximum capacity for the specific fiber route. Nokia said its Photonic Service Engine 3 was the first coherent digital signal processor to implement PCS.
German Researchers realize 1 Tbps Optical Fiber Transmission
Nokia Bell Labs, Deutsche Telekom T-Labs and the Technical University of Munich TUM have achieved unprecedented transmission capacity and spectral efficiency in an optical communications field trial with a new modulation technique. The breakthrough research could extend the capability of optical networks to meet surging data traffic demands.
In an optical communications field trial Nokia Bell Labs, Deutsche Telekom T-Labs and the TU Munich showed that the flexibility and performance of optical networks can be maximized when adjustable transmission rates are dynamically adapted to channel conditions and traffic demands. As part of the Safe and Secure European Routing project SASER, the experiment over a deployed optical fiber network of Deutsche Telekom achieved a net transmission rate of one Terabit per second.
This is close to the theoretical maximum information transfer rate of that channel and thus approaching the Shannon Limit of the fiber link. The Shannon Limit was discovered in 1948 by Claude Shannon, Bell Labs pioneer and the “father of information theory”. The trial of the novel modulation approach, known as Probabilistic Constellation Shaping PCS, uses quadrature amplitude modulation (QAM) formats to achieve higher transmission capacity over a given channel to significantly improve the spectral efficiency of optical communications.
PCS modifies the probability with which constellation points – the alphabet of the transmission – are used. Traditionally, all constellation points are used with the same frequency. PCS cleverly uses constellation points with high amplitude less frequently than those with lesser amplitude to transmit signals that, on average, are more resilient to noise and other impairments. This allows the transmission rate to be tailored to ideally fit the transmission channel, delivering up to thirty percent greater reach.
It was fifty years ago when optical fiber was introduced. With the promise of 5G wireless technology on the horizon, optical transport systems today continue to evolve to help telecommunications operators and enterprises meet network data traffic growing at a cumulative annual rate of up to one hundred percent. PCS is now part of this evolution by enabling increases in optical fiber flexibility and performance that can move data traffic faster and over greater distances without increasing the optical network complexity.
The research is a key milestone in proving PCS could be used in the future to extend optical communication technologies. The results of this joint experiment will be presented today at the European Conference on Optical Communication ECOC in Düsseldorf, Germany.
“Increased capacities, reach and flexibility over deployed fiber infrastructures,” said Bruno Jacobfeuerborn, Director Technology Telekom Deutschland and CTO Deutsche Telekom. “We provide a unique network infrastructure to evaluate and demonstrate such highly innovative transmission technologies for example. Furthermore, it also supports higher layer test scenarios and technologies.”
“Information theory is the mathematics of digital technology, and during the Claude E. Shannon centenary year 2016 it is thrilling to see his ideas continue to transform industries and society,” said Gerhard Kramer, Head of the Institute for Communications Engineering at TU Munich.
“Probabilistic constellation shaping, an idea that won a Bell Labs Prize, directly applies Shannon’s principles and lets fiber optic systems transmit data faster, further, and with unparalleled flexibility,” added Kramer. “The success of the close collaboration with Nokia Bell Labs, who further developed the technology, and Deutsche Telekom T-Labs, who tested it under real conditions, is satisfying confirmation that TUM Engineering is a label of outstanding quality, and that TUM teaching gives our students the intellectual tools to compete, succeed and lead globally.”
Marcus Weldon, president Nokia Bell Labs & Nokia CTO, said: “Future optical networks not only need to support orders of magnitude higher capacity, but also the ability to dynamically adapt to channel conditions and traffic demand. Probabilistic Constellation Shaping offers great benefits to service providers and enterprises by enabling optical networks to operate closer to the Shannon Limit to support massive datacenter interconnectivity and provide the flexibility and performance required for modern networking in the digital era.” (Source: TUM)
ZTE Demos 1.7Tbps Fiber Transmission
IN A MOVE sure to be lauded, Chinese telecommunications provider ZTE held a field demonstration of an optical network capable of transmitting 1.7Tbps, the company announced today.
The network used Wavelength Division Multiplexing to achieve the thousand-gigabit speeds, which separates data into different wavelengths and transmits those wavelengths over the same optical fiber. In ZTE’s demonstration, the company used 8 different channels, each transmitting 216.4Gbps. The transmission was conducted in China over 1,087 miles, on a standard fiber-optic cable.
While the 1.7Tbps number will mostly intrigue network operators (there’s not yet a future where you’ll get terabits of information to your home network), the channels delivering 200Gbps will mean a lower cost per bit for operators, which could possibly be passed on to consumers whose data demands will invariably grow.
Still, ZTE’s demonstration was just a field test, and there’s no saying when the technology will be available in any practical sense. ZTE’s press release implies that the demonstration was less about a specific product than proving an upgrade from a 100Gbps to a 200Gbps network was possible. The company reported “a 25 percent increase in spectrum efficiency” from the test.
Currently, networks delivering 40Gbps and 100Gbps are considered advanced, and although ZTE isn’t the only company in the terabit ring — according to Computerworld Huawei displayed a prototype optical system that could transmit 20Tbps over multiple 400Gbps channels — it does move closer to a world in which 200Gbps could become the norm.
Internet speed record shattered at 178 terabits per second
The fastest internet speed in the world has been clocked at an incredible 178 terabits per second (Tb/s) – fast enough to download the entire Netflix library in under a second. Engineers in the UK and Japan have developed new ways to modulate light before it’s beamed down optical fibers, allowing for much wider bandwidths than usual.That new top speed is an insane feat. It’s 17,800 times faster than the current fastest internet connections available to consumers – 10 Gb/s in parts of places like Japan, the US and New Zealand. Even NASA can’t compete, with its 400 Gb/s ESnet.
It also leaves other experimental devices in the dust, including a photonic chip developed in Australia that clocked a still-impressive 44 Tb/s just a few months ago, and beats the previous record holder – a Japanese team with 150 Tb/s – by almost 20 percent. “While current state-of-the-art cloud data-centre interconnections are capable of transporting up to 35 terabits a second, we are working with new technologies that utilize more efficiently the existing infrastructure, making better use of optical fiber bandwidth and enabling a world record transmission rate of 178 terabits a second,” says Lidia Galdino, lead researcher on the study.
To hit these speeds, engineers at University College London (UCL), Xtera and KDDI Research developed new technologies to essentially squeeze more information through the existing fiber optic infrastructure. Most are currently capable of a bandwidth of up to 4.5 THz, with some new technologies approaching 9 THz. The team’s new system, however, raises the bar to 16.8 THz.
To get this much extra “room,” the researchers develop new Geometric Shaping (GS) constellations. Basically, these are patterns of signal combinations that alter the phase, brightness and polarization of the wavelengths, in order to fit more information into light without the wavelengths interfering with each other. This was done by combining different existing amplifier technologies into a hybrid system.
Perhaps the best news is that because it uses the fiber optic cables already in place in many parts of the world, this technology could be integrated into existing infrastructure relatively easily. Instead of replacing miles and miles of cable, it would only require upgrades to the amplifiers, which appear every 40 to 100 km (25 to 62 mi) or so.
NICT demonstrates a 1 petabit per second optical network node
The Network System Research Institute at the National Institute of Information and Communications Technology (NICT; Tokyo, Japan) has developed and demonstrated the first large-scale optical switching testbed capable of handling 1 petabit per second (Pbit/s) optical signals; this data rate is equivalent to sending 8K video to 10 million people simultaneously.
This demonstration made use of state-of-the-art large-scale and low-loss optical switches based on MEMS technology, three types of next-generation spatial-division multiplexing fibers, and included the routing of signals with capacities from 10 terabit per second (Tbit/s) to 1 Pbit/s, which corresponds to more than 100 times the capacity of currently available networks.
NICT states that this is a major step forward towards the early implementation of petabit-class backbone optical networks capable of supporting the increasing requirements of internet services such as broadband video streaming, 5G mobile networks, and the Internet of Things (Iot). The results of this demonstration were unveiled at a postdeadline presentation at the 45th European Conference on Optical Communication (ECOC 2019; 22-26 Sept. 2019; Dublin, Ireland).
NICT has collaborated extensively with academia and industry to develop new types of optical fiber technologies and provide petabit-class communications for short- and long-reach backbone networks as well as datacenter networks. These included achievements such as the record petabit-class transmission in a single fiber (September 2015 and September 2018) and the longest link using spatial-division-multiplexing amplifiers (March 2019).
However, petabit-class transmission requires petabit-class switching technologies to manage and reliably direct large amounts of data through complex networks. Up to now, such technologies have been beyond reach because the existing approaches are limited by complexity and/or performance.
With its state-of-the-art large-scale spatial optical switching, NICT’s 1 Pbit/s network demonstration aims at petabit-class next-generation optical networks that use spatial-division multiplexing. The experimental network testbed used three types of multicore fibers and included practical requirements of real networks, such as protection switching. The system was demonstrated in four fundamental scenarios that constitute the building blocks of next-generation optical fiber networks:
1. Optical switching of 1 Pbit/s of data
2. Redundant configuration to support network failures or fiber breaks
3. Branching of 1 Pbit/s signals into different types of optical fibers with various capacities
4. Management of lower-capacity 10 Tbit/s signals within the 1 Pbit/s network