Chalmers and Nokia Bell Labs refine prediction of network failures…

20 Feb 2024

…and NTT Innovative Devices “breaks data speed record” on optical links.

Researchers based in Sweden and the USA have successfully used a coherent transceiver prototype to detect polarization changes that preceded a cable break in a live optical network. The work by Chalmers University and Nokia Bell Labs, which is one of the first demonstrations of field-based measurements for an active cable break, shows the potential of transceiver-based sensing for actively monitoring and improving the stability of fiber networks.

Using the global fiber network as a sensor could help improve network robustness and reliability by providing network management and control systems with real-time information about the environment around each fiber path or link. When a significant change is detected, preventive measures could be used to reroute data or to send early warnings that prevent damage to the network.

“We all are exposed and easily frustrated by connectivity disruptions, and protecting the fiber network is therefore of outmost importance,” said Mikael Mazur, member of the technical staff in the Advanced Photonic Research department at Nokia Bell Labs.

“Today, our ability to mitigate the effects of fiber breaks are limited due to the lack of sensors capable of monitoring the physical environment in real-time. Without these, network-level management is limited to post outage mitigations rather than taking preventative actions,” Mazur said.

“This holds for any outages either caused by human factors such as faulty construction work, and uncontrollable events like bad weather. Our results demonstrate that coherent transceivers with added sensing capabilities can fill this gap, providing a scalable path to implement the smart fiber networks of the future,” he said.

Mazur will present this research, which was a collaboration between Nokia Bell Labs US and Chalmers University of Technology & Sunet, both in Sweden, at OFC, the optical communications and networking expo, between 24 – 28 March 2024 at the San Diego Convention Center, Ca., USA.

The researchers used coherent receiver monitoring to analyze results captured in a live network during a fiber break that occurred when an excavator accidentally exposed the cable during construction. The 524-km link included five reconfigurable optical add-drop multiplexers and primarily consisted of aerial fiber.

The fiber was monitored by transmitting a co-propagating signal from a field programmable gate array-based coherent transceiver prototype along the live coherent data channels on the network. Baseline measurements showed that most polarization changes occur at frequencies around 1 Hz, matching well with environmental changes.

… and NTT Innovative Devices ‘breaks data speed record’

As data traffic continues to increase, there is a critical need for miniaturized optical transmitters and receivers that operate with high-order multi-level modulation formats and faster data transmission rates.

In an important step toward fulfilling this requirement, researchers developed a new compact indium phosphide-based coherent driver modulator (CDM) and showed that it can achieve a record high baud rate and transmission capacity per wavelength compared to other CDMs.

“Services that require data capacity, such as video distribution and web conferencing services, have become widespread, and services that more enrich our lives are expected to be introduced in the future,” said Josuke Ozaki from NTT Innovative Devices, in Japan.

“To realize the new services, it is very important to increase the total data rate of optical transmission systems that support the background. If the optical transmission capacity is insufficient, it will be difficult to realize new convenient services and data society. In addition, the development of an optical transmitter that covers the C+L band in a single module enables flexible network operation and reduces equipment costs.

One measure of the speed of data transmission is the baud rate, which indicates the number of signal changes that occur every second in a communication channel. With higher baud rates, the bandwidth of the modulation signal required for each channel increases and fewer channels can be transmitted in the conventional C-band.

Although modulators made from InP have excellent optical and radio frequency characteristics, they exhibit strong wavelength dependence that has made it difficult to extend their wavelength range. To overcome this challenge, the researchers developed a novel InP modulator chip with an optimized semiconductor layer and waveguide structure that can operate over a wide wavelength range.

By using the new modulator chip, they achieved the world’s first CDM with an InP modulator chip that can transmit in C+L band and has a package body measuring just 11.9×29.8×4.4 mm.

“The next step is to further increase the baud rate for a higher transmission speed, “ said Ozaki. “In doing so, it is important to find new modulator’s structure and assembly configuration, including a driver die and a package, that can achieve higher EO bandwidth with both lower power consumption and smaller form factor.

Alpha samples of the CDM are ready for shipping from NTT Innovative Devices. Ozaki will present this research at OFC, as detailed above.