August 2022 Vol. 20 No. 8

View from the Top

• Akira Shimada, President and Chief Executive Officer, NTT

  

  Abstract
  With people at its core, the NTT Group defines the capabilities it aims to achieve as service expertise, technical expertise, and intelligence. All 330,000 NTT Group employees—working in approximately 90 countries and regions—are accelerating the group's self-transformation into a new NTT that is open, global, and innovative to be valuable to all stakeholders, including customers, shareholders, local communities, and employees. We asked Akira Shimada, president and chief executive officer of NTT, who took up the post in June 2022, about the details of the guidelines that he announced at his inaugural press conference and his thoughts on what it means to be a top executive.

Front-line Researchers

• Mitsuaki Akiyama, Senior Distinguished Researcher, NTT Social Informatics Laboratories

  

  Abstract
  NTT laboratories have a long history of research and development (R&D) in the field of computer science, including the world’s most-advanced cryptography and cybersecurity. Senior Distinguished Researcher Mitsuaki Akiyama is conducting R&D on cybersecurity by incorporating social science, such as social value, people’s happiness, legal systems, and social acceptability, to transform and develop society. We asked him about the progress of his research and attitude as a researcher.

Rising Researchers

• Hiroshi Yamazaki, Distinguished Researcher, NTT Device Technology Laboratories

  

  Abstract
  In communication systems that involve signal processing using digital circuits, the bandwidth at the interface between digital and analogue is a bottleneck to improving communication speed. We spoke to Distinguished Researcher Hiroshi Yamazaki, who developed the principles of the bandwidth-doubler technology for solving this bottleneck.

Feature Articles: Device Technologies for Enabling the All-Photonics Network

• High-output Optical Transmitter and High-sensitivity Optical Receiver for 400-Gbit/s 40-km Fiber-amplifier-less Transmission

  

  Abstract
  We developed a high-output optical transmitter and a high-sensitivity optical receiver for long-distance transmission in the All-Photonics Network that is being promoted under IOWN (the Innovative Optical and Wireless Network). This article introduces the 400-Gbit/s optical transmitter with a semiconductor optical amplifier-assisted extended-reach electro-absorption modulator integrated distributed feedback laser called AXEL, a key device for higher optical output, and the 400-Gbit/s optical receiver with an avalanche photodiode, a key device for higher sensitivity.

• C+L-band Colorless, Directionless, Contentionless Reconfigurable Optical Add/Drop Multiplexing for High-capacity Network Flexibility

  

  Abstract
  We investigated the possibility of expanding the operating wavelength range of one of the most flexible optical networks, i.e., colorless, directionless, contentionless reconfigurable optical add/drop multiplexing (CDC-ROADM), to the C+L-band. By expanding the operating wavelength range of multicast switches, which are indispensable for CDC-ROADM, to the two bands of C+L, a seamless optical node can be achieved. This concept reduces the complexity in network equipment as well as network operation because it enables operation without operators having to be aware of the bands.

• Development of Membrane Optical Modulators for IOWN

  

  Abstract
  To develop a high-speed, large-capacity optical network with low power consumption, which is important for IOWN (the Innovative Optical and Wireless Network), we are conducting research and development on membrane optical devices that integrate III-V compound semiconductors on silicon-photonics circuits. Membrane optical devices are expected to be used for high-modulation efficient lasers and optical modulators because they can achieve high optical confinement in the core layer. This article introduces the current state of research and development focusing on optical modulators and the integration of such modulators and lasers on the basis of membrane-device technologies.

• Observation of Exceptional Point Degeneracy with Current-injected Photonic Crystal Lasers

  

  Abstract
  Coupled resonators and coupled waveguides with contrast of their gain and loss are non-Hermitian optical systems, which are based on energy-non-conserving processes. They have been reported to exhibit a number of unconventional phenomena that are expected to contribute to practical applications. We developed a coupled system of two current-injected photonic crystal lasers that enable precise control of gain and loss, thus establishing a promising non-Hermitian nanophotonic platform. We introduce our demonstration of a peculiar non-Hermitian mode degeneracy called an exceptional point (EP) and the EP-based enhancement of spontaneous emission with this system.

Feature Articles: Optical Device Technologies for Next-generation Computing Using Light

• Optical Device Technology for Next-generation Computing Using Light

  

  Abstract
  The performance of conventional computers, which have supported the infrastructure of our digital society and developed in accordance with Moore’s law, seems to be approaching its limits. To solve many social issues and achieve a safe, secure, and prosperous society, next-generation computers with performance far beyond that of conventional computers, such as quantum computers, are expected. This article outlines the possibilities of next-generation computers that compute using light and optical device technologies introduced in the Feature Articles of this issue.

• Broadband Continuous-wave Optical Quadrature Squeezer for Ultra-fast Optical Quantum Computers

  

  Abstract
  An optical quadrature squeezer is expected to be a key device for high-speed optical quantum computing. We developed a high-gain and broadband optical quadrature squeezer by using a periodically poled lithium niobate (PPLN) waveguide. The squeezer is assembled as a pump-combiner-integrated module with four optical-fiber input/output ports. By improving the fabrication processes of the PPLN waveguide, we achieved a low-loss module that exhibits about 1-dB optical loss. By using this module, we successfully obtained continuous-wave 6-dB-squeezed light at over-6-THz sideband frequency even in a fiber-closed optical system with commercially available optical components. This fiber-compatible broadband quadrature squeezer will accelerate the development of optical quantum computers.

• Optical Circuit Technologies for Next-generation Computing Using Light

  

  Abstract
  To sustainably achieve a society in which digital technologies have penetrated in various forms such as smartphones and cloud services, computing technologies that greatly exceed the current performances are becoming important. NTT is advancing research and development of computing technology using lightwaves/photons by applying device technology for communications using optical waveguides. In this article, we introduce optical circuit technology mainly for optical quantum computing as an example.

• Photonic Implementation of Reservoir Computing

  

  Abstract
  Today’s computing for machine learning is carried out with digital electric processors, which have issues regarding energy consumption and processing speed, by emulating brain-inspired information processing. To address these issues, photonic devices, comprising a photonic neural network, are gaining much attention for achieving high-speed and energy efficient brain-inspired computations. We report on the photonic implementation of a simplified recurrent neural network called reservoir computing.

Regular Articles

• Business Design Support Technology to Promote Digital Transformation

  

  Abstract
  Business processes for providing services and products are becoming increasingly complicated to meet the diverse needs of customers brought on by dramatic changes in the social environment. To make improvements to these complicated processes, it is important to accurately understand and analyze business processes on the basis of comprehensive and objective data. This article introduces the business design support technology we developed that can be used immediately on-site to effectively understand and analyze the current state of business processes and the NTT technologies at the core of this technology.

Global Standardization Activities

• Report on WTSA-20 (World Telecommunication Standardization Assembly)

  

  Abstract
  Due to the impact of COVID-19, the World Telecommunication Standardization Assembly (WTSA-20), which was scheduled to be held in 2020, was held locally and online in Geneva, Switzerland, from March 1 to 9, 2022. This article provides an overview of WTSA-20 and the main deliberations.

Practical Field Information about Telecommunication Technologies

• Development of the Hikari Denwa Fault-isolation Tool for Voice Over IP Services

  

  Abstract
  Internet Protocol (IP)-based communication systems have become more sophisticated, and the details/causes of problems are becoming more complex and diverse. This article introduces a tool developed by the Technical Assistance and Support Center, NTT EAST that is efficient in identifying the faults in voice over IP services and connected equipment. This is the seventy-first article in a series on telecommunication technologies.

External Awards/Papers Published in Technical Journals and Conference Proceedings

• External Awards/Papers Published in Technical Journals and Conference Proceedings