We cost-effectively achieved 4 fold higher speed optical communications in an existing 100-Gbps-based optical network~
Tokyo, March 19, 2015 -
The NTT Corporation and NTT Communications Corporation today announced confirmation of stable transmission of 400-G optical signals without affecting the existing 100-G channels during the addition and removal of 400-G channels in a 100-G-based wavelength division multiplexing (WDM) system comprising installed dispersion-shifted fiber (DSF) (*1) cables with high polarization mode dispersion (PMD) (*2) that could cause degradation in communications performance.
We applied advanced 400-G digital coherent optical transmission techniques  with novel world-top-level waveform distortion compensation techniques, and confirmed the high performance in 400-G optical transmission compared to our conventional digital signal processing techniques.
This success is a step toward expanding the optical communication capacity by four times that of the currently installed 100-Gbps systems by using 400-G advanced digital coherent optical transmission technologies. This advancement will meet in a timely manner the rapidly increasing demand represented by the distribution of high definition 4K / 8K movies or an increase of the Internet of Things (IoT) toward the opening of the Tokyo Olympics and Paralympics.
To accommodate the explosive growth in data communications traffic stemming from the widespread use of movie data delivery services and cloud computing technology, the NTT Group has just developed and proactively deployed 100-Gbps transmission systems that adopt digital coherent optical communication technology (*3) into commercial use. Progress is now being made in the global market to increase the capacity of 100-Gbps optical transmission systems.
However, the spread of 4K/8K high definition movies and the surging demand for M2M communications have increasingly necessitated that the next-generation optical core networks be able to transmit ultra-high-speed, high-capacity data both flexibly and economically.
Accordingly, the NTT and NTT Com have engaged themselves in diligently developing the world's top level 400-Gbps-class digital coherent optical transmissions technology in order to develop expanded existing 100G-based optical transport systems timely and cost-effectively.
Experimental Configurations (Fig.1)
Both the 16 Quadrature Amplitude Modulation (16QAM) (*4) and Sub-Carrier Wavelength Multiplexing (*5) techniques were applied in this field trial, which superimposed 200-Gbps information on the amplitude and phase of the light per sub-carrier, and integrated two sub-carrier wavelengths to compose a single 400-Gbps channel. These key technologies enable us to expand the optical communication capacity of the installed 100-Gbps systems up to four fold.
NTT Communications intentionally configured the field-test transmission line with a very high PMD, which occasionally fluctuates over time, from its own installed commercial DSF cable, in order to examine the transmission characteristics under every conceivable condition in the commercial field.
A single 100-Gbps optical channel with eleven other adjacent 400-Gbps channels, or a single 400-Gbps optical channel with eleven other adjacent 100-Gbps, was set, and the channel was examined during transmission through the optical fiber. We examined the transmission performance of an existing 100-G channel while adding and removing the 400-G channels.
Based on the following experimental results in the field trial, we confirmed that 400-Gbps channels can be additionally equipped in an in-service state into the installed 100-Gbps optical transmission equipment that is currently in commercial use.
(1)Successful transmission of 100-Gbps channels and 400-Gbps channels simultaneously in the optical transport system
The additional 400-Gbps channels and the existing 100-Gbps channels did not cause mutual degradation from the viewpoint of the transmission characteristics. We also confirmed that the addition and removal of the 400-G channels in the existing 100-G-based WDM system did not affect the communication performance of the other channels, although the communication performance was anticipated to degrade.
(2) Successful verification of long distance transmission using world's top-level advanced digital coherent optical transmission techniques
NTT's advanced 400-Gbps-class digital coherent optical communication technology experimentally proved in this test that the complicated distorted waveform caused by nonlinear effects (*6) could be removed. Thus, further extension of transmission performances up to two fold could be achieved using the digital backward propagation signal processing technique (*7) [1,2] with a high-performance error-correction code technique [1,2] . The transmission performance results showed that 400-G channels could transmit a signal over 750 km under the field trial environmental conditions using the fibers with a high PMD.
*Parts of this research use results from research commissioned by the Ministry of Internal Affairs and Communications (MIC) entitled "Research and Development Project for the Ultra-high Speed and Green Photonic Networks " and by the National Institute of Information and Communications Technology (NICT) entitled "R&D of optical transparent transmission technology for transparent metro/access network "
Based on these results, the companies will move forward to establish world top-level optical transport systems including high performance optical fiber cables and apply them commercially, i.e., 400-Gbps and beyond 400-Gbps-class optical transmission technology, advanced flexible optical network technology, and super-high-speed Ethernet technology including 400-GE (*8) to compose 400-Gbps-class optical signals. In addition, they will collaborate with institutions inside and outside Japan with the aim to deploy these technologies on a global scale.
 K. Yonenaga, et al., "Research and Development on Photonic Transparent Transmission Technologies (λ-Reach Project)," IEICE, OCS2011-110, 2011 (in Japanese)
Glossary and Notes
1. Dispersion-shifted fiber (DSF)
Single mode optical fiber with shifted wavelength-dispersion into 1.5 um-band defined in ITU-T G.653.
2. Polarization Mode Dispersion (PMD)
PMD is a form of modal dispersion where two different polarizations of light exist in a waveguide that travel at different speeds due to random imperfections and asymmetries in an optical fiber.
3. Digital coherent optical transmission technology
This technology is a cutting-edged optical transmission method that combines coherent reception and digital signal processing. In addition to streamlining frequency usage through modulation methods such as polarization division multiplexing and phase modulation, the technology enables significant improvements in receiver sensitivity.
4. 16 Quadrature Amplitude Modulation (16 QAM)
QAM is a digital modulation scheme to convey data by changing the amplitude of two waves, 90° out-of-phase with each other (in quadrature). 16QAM can convey 4 bits per symbol.
5. Sub-carrier multiplexingThis is a method to configure a high-speed channel by densely multiplexing several wavelengths of optical signals with hardly any gaps.
6. Nonlinear optical effect
The nonlinear optical effect is a change in the refractive index of an optical fiber in response to an applied electric field. The waveform of one optical channel may be distorted due to this effect caused by electric fields from other channels in the case of wavelength-division multiplexing (WDM) transmission.
7. Digital backward propagationTechnology that simultaneously converts received optical signals into digital signals and then compensates for linear and nonlinear distortions in the optical fiber by virtually reversing the transmission using digital signal processing.
This is a high-speed Ethernet packet frame format that is under discussion for IEEE802.3bs for beyond 100-G next-generation standardization.
Figure.1 Experimental Configuration
NTT (Nippon Telegraph and Telephone Corporation) is the world’s largest global IT and telecommunications services company. The company’s roots go back over 100 years to the introduction of the telegraph in Japan and focuses today on innovation in the cloud, mobility, network and communications. The company had operating revenues of US$112 billion for the fiscal year ended March 31, 2014 and employs more than 240,000 people worldwide. The company’s subsidiaries include Regional Communications Businesses: NTT EAST, NTT WEST; Mobile Communications Businesses: NTT DOCOMO; Long-Distance and International Communication Businesses: NTT Communications and Dimension Data; and Data Communication Businesses: NTT DATA. For more information, visit http://www.ntt.co.jp/index_e.html
About NTT Communications Corporation
NTT Communications provides consultancy, architecture, security and cloud services to optimize the information and communications technology (ICT) environments of enterprises. These offerings are backed by the company’s worldwide infrastructure, including the leading global tier-1 IP network, the Arcstar Universal One™ VPN network reaching 196 countries/regions, and 130 secure data centers worldwide. NTT Communications’ solutions leverage the global resources of NTT Group companies including Dimension Data, NTT DOCOMO and NTT DATA.
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