Increasing transmission distance 1.5 times and communications capacity by 25%, improving disaster recovery performance

Tokyo, March 17, 2017 - NEC Corporation (NEC; TSE: 6701) today announced the development of next-generation optical node technology capable of both extending the transmission length of the optical path (the path of optical signals) and increasing the capacity of communications. This technology will improve the robustness of next-generation ultra-high capacity optical networks through effective network utilization.

NEC has developed an optical filter technology that broadens the filter's bandwidth within the optical node, which is the communication path switching unit, and drastically reduces the pass band narrowing effect, which decreases the transmission length. It has also developed an optical wavelength control technology that improves the transmission length of optical paths by balancing signal loss and crosstalk through the high-precision control of optical signals that pass the optical filters with wider bandwidth.

Moreover, it has developed a guard band control technology that increases the number of optical paths in a limited band by controlling the allocation of guard bands (empty bands) set in the optical signals to be transmitted in the network controller that controls the communication centrally.

These technologies have made the transmission distance of optical signals 1.5 times longer than before and increased the free capacity of bandwidth by 25% (*1) by increasing the number of optical paths.

"These technologies enable the additional allocation of optical paths with high transmittance to the free bandwidth capacity in the event of emergency situations such as demand fluctuations and failures at the time of a disaster, contributing to the implementation of a robust network environment that ensures uninterrupted communication, even at the time of a disaster, and has excellent disaster recovery performance," said Soichi Tsumura, general manager, IoT Devices Research Laboratories NEC Corporation.

Background

The rapid increase in video content on the Internet, the increase in IoT devices and the spread of cloud services have led to the further acceleration of the expansion and diversification of network demand. In order to provide suitable network environments in a sustainable manner in response to these changes, it is necessary to develop high capacity optical network technologies that are extremely resilient to demand fluctuations and failures.

Optical networks have adopted ultra-high density wavelength division multiplexing (WDM) implemented through digital coherent technology (*2), which achieves a large capacity for communications, and optical path network technology, which efficiently reconfigures high capacity optical signals without optical-electrical signal conversion. However, challenges remain in terms of the deterioration of signal quality, the extension of the transmission length of optical paths and the increase in capacity of communications. Particularly in WDM optical path networks, which are next-generation large capacity networks offering ultra-high speed such as 400Gbps per channel, the challenge lies in the development of a technology that implements optical communication quality equivalent to the current quality by efficiently using existing communication network resources.

In this latest advancement, NEC has developed optical node technology capable of both extending the transmission length of optical paths and increasing the capacity of communications by using the optical networks efficiently.

NEC's Optical Node Technology

Primary technology features

• Wider bandwidth of optical filters within optical nodes

A wider bandwidth was implemented by broadening the bandwidth of the optical filter within the optical node while fixing the center frequency at the Dense Wavelength Division Multiplexing (DWDM) frequency grid (*3) and by allocating the edges while overlapping them. The pass band narrowing effect was drastically reduced by broadening the pass band of each filter. This enabled the minimization of loss to available optical signal bandwidth which occurs with the influence of the pass band narrowing effect when passing through the optical filters.

This technology is capable of minimizing optical signal loss in the ultra-high density WDM optical path network, thereby increasing the transmittance in optical communication to transmit through cascaded optical nodes.

• High-precision control of transmitted optical wavelength within the optical node

While the pass band narrowing effect was drastically reduced by broadening the pass band of optical filters, interference with adjacent optical signals (crosstalk) occurs. With the aim of improving the transmission characteristics by maintaining the balance of the loss due to the pass band narrowing effect caused by filters and crosstalk, NEC has developed a technology that controls the wavelength with precision according to the cumulative pass band characteristics of cascaded filters. This technology has enabled communication capable of minimizing the impact of crosstalk and loss of available signal bandwidth even when it occurs.

By applying this technology against the pass band narrowing effect of optical filters that is generated especially when transmitting through cascaded optical nodes, it is possible to achieve optical signal transmission through optimal wavelength control that results in no crosstalk between adjacent wavelengths without causing loss in the necessary wavelength. As a result, the transmittance of the optical signals increases.

Technologies 1 and 2 above have made the transmission distance of optical signals 1.5 times longer than before in transmission through cascaded optical nodes in the ultra-high density WDM optical path network.

• Appropriate guard band allocation by the network controller

The network controller estimates the optical path quality (the amount of quality deterioration of optical signals to be transmitted and transmittance of the optical paths) from the transmission distance, the number of optical nodes in the path and the optical modulation format, and determines the guard band (*4) width to be inserted between the wavelengths of the optical signals in accordance with the estimated quality. Since this enables the setting of the guard band width, which used to be fixed, at a minimum value, the width of the entire guard band can be drastically reduced, improving the accommodation rate of the optical wavelength. This frees up bands that were unnecessarily occupied, thus increasing the capacity of communications by 25% over the conventional capacity.

This technology enables the allocation of new optical paths in empty bands, which can be used in the case of sudden demand fluctuation and recovery from disaster.

Some of the technologies developed on this occasion have been pursued as part of the R&D of elastic optical networking technologies, a project commissioned by the National Institute of Information and Communications Technology (NICT) with which NEC has been involved since 2013.

NEC will present these technologies on March 23 at The Optical Networking and Communication Conference & Exhibition (OFC), which will be held in Los Angeles from Sunday, March 19 to Thursday, March 23.

• (*1) In a 4x4 mesh optical network topology model
• (*2) Digital coherent technology: Optical transmission technology for long distance and large capacity transmission using optical amplitude and phase achieved by combining coherent reception and digital signal processing
• (*3) DWDM frequency grid: Optical center frequency defined for wavelength division multiplexing Specified by ITU-T Recommendations G.694.1.
• (*4) Guard band: Empty band to avoid crosstalk between signals and deterioration of signal quality due to optical band loss