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September 22, 2023


NTT and Tokyo Denki U Innovating Fast, Accurate and Stable Optical Communication

NTT Corporation and Tokyo Denki University have made a breakthrough in the field of optical communication. Through their innovative research, they have stabilized the frequency of a tool known as the optical frequency comb, which is central to the development of high-capacity, high-speed optical communication systems.

To understand their accomplishment, it's important to grasp the concept of the optical frequency comb. It can be likened to a high-tech flashlight, one that emits not one, but many different colors (frequencies) of light simultaneously. On a graph, these frequencies appear as the teeth of a comb--evenly spaced and distinct. It is this distinctive trait that allows the optical frequency comb to measure various frequencies of light with unprecedented precision, serving as a finely tuned ruler for light.

Prior to this achievement, the research partners had attempted to stabilize the optical frequency comb using two lasers with varying frequencies. However, this approach proved insufficiently stable. Their new method involves the use of a single laser and a novel control mechanism. The development has led to a highly precise, high-bandwidth light source that could potentially transform the landscape of data transmission.

In addition to enhancing data transmission speeds, frequency stabilization allows for the generation of microwaves with significantly reduced noise. This can improve the accuracy of microwave generation and measurement tools. Moreover, it holds potential to enhance the reliability of timekeeping devices in areas with weak GPS signals, such as in remote locations or densely built urban areas.

Tokyo Denki University and NTT's new technique is not only groundbreaking, but also versatile. The optical frequency comb can be used to measure frequencies from light to microwave, converting them into a format that can be utilized in various technologies, particularly communication equipment. It's akin to having a universal translator that can convert the language of light into something more widely understood and applied.

In the realm of optical communications, the technology's precision and versatility are key. Typically, optical frequency combs with intervals ranging from tens to hundreds of MHz were difficult to control and individualize. The partners' new approach employs a continuous wave (CW) laser introduced into an electro-optic modulator (EO modulator), which yields larger frequency intervals, making it more fitting for optical communication applications. Furthermore, by selecting the microwave frequency applied to the EO modulator, the frequency interval can be easily adjusted, further enhancing its versatility.

As a result of this research, Tokyo Denki University and NTT have demonstrated that EO combs with larger frequency intervals can be stabilized effectively. The EO comb linewidth is significantly narrower than the laser linewidth necessary for digital coherent communications. As we race towards faster communication speeds, laser linewidth control becomes increasingly vital. Research findings suggest that the EO comb could provide multiple light sources for optical communication within a single system, paving the way for the future of high-speed, high-capacity optical communications.

NTT and Tokyo Denki University have opened the door to a future of high-speed, large-capacity optical communications and have simultaneously increased the accuracy of microwave generation and evaluation equipment. Their work offers promise in various fields that require real-time, accurate data, such as traffic and air traffic control, and financial transactions.

Going forward, NTT plans to further enhance the frequency stability and practicality of the EO comb. The company aims to reduce errors in position measurements and timestamps, and contribute to fields that require real-time, accurate data. The technology's potential is huge and the EO comb's practical applications in optical frequency measurement are significant, with the promise of measuring optical frequencies with high accuracy, marking a significant advancement in the field of precision metrology.

NTT--Innovating the Future of Communication

Picture: Daniel O'Connor

Daniel O'Connor joined the NTT Group in 1999 when he began work as the Public Relations Manager of NTT Europe. While in London, he liaised with the local press, created the company's intranet site, wrote technical copy for industry magazines and managed exhibition stands from initial design to finished displays.

Later seconded to the headquarters of NTT Communications in Tokyo, he contributed to the company's first-ever winning of global telecoms awards and the digitalisation of internal company information exchange.

Since 2015 Daniel has created content for the Group's Global Leadership Institute, the One NTT Network and is currently working with NTT R&D teams to grow public understanding of the cutting-edge research undertaken by the NTT Group.