Long-haul optical transmission technology for effective use of wavelengths when providing end-to-end optical paths
Developed optical node architecture utilizing wavelength conversion technology with optical and analog electrical signals

News Highlights:

Background

In the IOWN concept, APNs that make maximum use of optical technology will provide users with large-capacity, low-latency end-to-end (E2E) optical paths² while reducing power consumption. This is expected to enable factory DX (digital transformation), interactive live video streaming services, and remote surgery. To provide E2E optical paths widely, connecting optical paths that have different assigned wavelengths is necessary. The connection can be achieved by converting and adapting the wavelength of the optical path with low delay and no jitter in the optical node architecture through which the optical path passes in the APN (Figure 1).
　NTT has been researching and developing Photonic Exchange, an optical node architecture that constitutes APNs. To efficiently provide E2E optical paths over long distances, it is necessary to ensure transmission performance at the same time as the wavelength adapter function that allows Photonic Exchange to convert and adapt the wavelength of the optical path to the desired one. NEC has been conducting research and development on optical-analog-optical (OAO) wavelength conversion technology that can convert the wavelength of each optical path to any other wavelength. This time, we conducted an experimental demonstration of wavelength adapter functions using OAO wavelength conversion technology developed by NEC, for Photonic Exchange developed by NTT.

Figure 1 Overview of the Photonic Exchange Wavelength Adapter Function providing an E2E Optical Path using Unused Wavelengths per Area

Key points of the technology

(1) Photonic Exchange

Conventional optical node architectures have a cross-connect function that physically switches the direction of the optical path according to the connection destination, and a function that allows the optical path to be moved in and out of the network. Photonic Exchange also features a wavelength adapter that adapts the wavelength to a wavelength unused at the destination. To apply the wavelength adapter function to a long-haul E2E optical path, it is necessary to suppress the signal impact caused by wavelength conversion. Therefore, we estimated the signal quality based on the physical phenomena of the wavelength conversion method to be applied, and designed an optical node architecture configuration that suppresses the signal effects caused by wavelength conversion (Figure 2 (A)). This contributes to providing long-haul E2E optical paths that make effective use of unused wavelengths in each area.

(2) OAO wavelength converter

The OAO wavelength converter can convert the wavelength of an optical path to any wavelength, as required to realize the wavelength adapter function of Photonic Exchange. Conventional wavelength conversion techniques cause delays and fluctuations due to the digital signal processing. OAO wavelength converters only convert optical signals to analog electrical signals and can convert wavelengths without converting them to digital electrical signals (Figure 2 (B)). Since the delay and fluctuation caused by digital signal processing can be eliminated, the wavelength of the optical path can be changed without losing the characteristics of the low-delay and no-jitter E2E optical path.

Figure 2 Component Technologies for Implementing Wavelength Adapter Function

Outline of the experiment

NTT and NEC jointly conducted transmission experiments to evaluate E2E optical path transmission performance when the wavelength adapter function of Photonic Exchange is applied. Using a prototype of an OAO wavelength converter, we constructed an experimental setup using a recirculating loop that includes two OAO wavelength converters (Figure 3). Using this experimental setup, we measured 100Gbps/λ optical signal quality with multiple wavelength conversions. As a result, it was confirmed that transmission performance over 3,000km could be ensured even after four wavelength conversions. Furthermore, the OAO wavelength converter used in this experiment reduced the power consumption caused by wavelength conversion by approximately 90% and the amount of delay by approximately 99% compared with the conventional wavelength conversion method.
　The transmission distance confirmed in this experiment corresponds to a distance that can traverse the main island of Japan if used in Japan. This will contribute to the expansion of IOWN service areas such as factory DX, interactive live video distribution services, and remote surgery. Since the possibility of multiple wavelength conversions was confirmed in this experiment, it will also contribute to the realization of E2E optical paths across networks managed by different operators.

Figure 3 Experimental Setup for Evaluating the Transmission Performance of an E2E Optical Path with Wavelength Adapter Function

Roles of each company

NTT:

Outlook

In the future, we will continue to demonstrate use cases for the application of Photonic Exchange with wavelength adapter functions for the development of APN. We will also promote the dissemination of APNs through proposals for the Open APN Functional Architecture defined by the IOWN Global Forum.

^1."NTT R&D FORUM 2024 -IOWN INTEGRAL" Official website: https://www.rd.ntt/e/forum/2024/

^2.Optical path
The path of an optical signal from the transmitter to the receiver is called an optical path. Each optical path has a specified path made up of optical fibers and optical node architectures passing through it, as well as a specified optical signal capacity and assigned wavelength.

About NTT

NTT contributes to a sustainable society through the power of innovation. We are a leading global technology company providing services to consumers and businesses as a mobile operator, infrastructure, networks, applications, and consulting provider. Our offerings include digital business consulting, managed application services, workplace and cloud solutions, data center and edge computing, all supported by our deep global industry expertise. We are over $97B in revenue and 330,000 employees, with $3.6B in annual R&D investments. Our operations span across 80+ countries and regions, allowing us to serve clients in over 190 of them. We serve over 75% of Fortune Global 100 companies, thousands of other enterprise and government clients and millions of consumers.