Communication and Device Technology

Introducing cutting-edge technologies that realize new services and societies

What is high-capacity optical transmission technology? Infrastructure to support rapidly increasing communication traffic

What is high-capacity optical transmission technology?

High-capacity optical transmission technology expands the transmission capacity per hour compared to conventional optical transmission. Thus far, the transmission capacity per optical fiber has been drastically increased by multiplexing, signal density and multi-leveling, via methods such as “time division multiplexing” “wavelength division multiplexing”, “polarization multiplexing”, “multi-level modulation”, “quadrature amplitude modulation (QAM modulation)”, and “digital coherent technology”.

The following section briefly describes each technology and explains how it increased transmission capacity.

Time division multiplexing is a method of setting a fixed time for transmission and distinguishing information.
Wavelength division multiplexing increases the volume of communication by simultaneously carrying optical signals of different wavelengths on a single optical fiber cable. Putting different information in multiple lights with different wavelengths and sending them on a single cable makes it possible to handle the cable as if it were multiple cables, thereby increasing communication speed.
Polarization multiplexing is a method to increase the amount of information by adding information to the polarization, phase, and amplitude of light. Horizontally polarized waves (which oscillate horizontally) and vertically polarized waves (which oscillate vertically) can be transmitted without interference on the same optical fiber, and by using the same frequency, it doubles the amount of information that can be transmitted.
Multi-level modulation is a method of increasing the number of bits per symbol by modulating the phase of a signal. Quadrature amplitude modulation, further increases the amount of information that can be transmitted by performing phase modulation followed by amplitude modulation.
In addition, ultra-high-speed communication has been achieved with spatial multiplexing element technology and the expansion of transmission bandwidth.

Digital coherent technology is a core technology that incorporates ultra-high-speed digital signal processing into optical communication and dramatically improves optical fiber transmission performance. An optical transceiver equipped with a digital signal processor and a broadband optical front-end circuit are used to increase the amount of information by adding information to the polarization, phase, and amplitude of light.

Social background which demands ultra-high-speed communication technology

Communications traffic is expected to continue increasing due to the spread of ultra-high-definition video, IoT, big data, and AI. In order to respond to this development, it is necessary to economically realize even higher capacity on the backbone optical communication network.
For this reason, NTT and NTT Communications are developing world-class technologies for economically expanding the capacity of existing optical transmission systems.

Current research findings

NTT has constructed a 1,122 km transmission environment for wavelength multiplexed signals with 1 terabit/second optical signal, using a new core-extended low-loss optical fiber cable that reduces optical loss and optical nonlinearity, installed in the NTT Communications commercial environment, and an optical transceiver newly developed by NTT.

As a result of this, it is possible to increase transmission speed to 1 terabit/second per channel, which is 10 times the speed of 100 gigabit/second per channel with the current commercial system. By increasing transmission capacity per wavelength, it is possible to reduce power consumption per bit by more than 80% compared to existing equipment.

What can be done with 1 terabit/second communication speed

How fast is 1 terabit/second communication?
One terabit is equal to 1,000 GB. For example, a 2 hour movie of standard definition fits within 2GB, so 1 terabit is equivalent more than 500 movies. In other words, if communication becomes possible at a speed of 1 terabit/second, 500 movies could be downloaded within 1 second.

When this ultra-high-speed communication is commercialized, it will be possible to exchange high-definition images both ways with no delay on multiple channels. It can also be used in tasks that require quality. Therefore, it can be used for tasks where even slight delays cannot be tolerated and high communication quality is key, such as in telesurgery. In addition, when building and simulating an elaborate and complex virtual society with digital twin computing (DTC), which is included in the IOWN Initiative, information that was previously lost during the digital conversion stage can now be exchanged in a form that is closer to the original signal, enabling more advanced simulation and prediction results.

References

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