May 2026 Vol. 24 No. 5

Front-line Researchers

• Tatsuaki Okamoto, NTT Fellow, Social Informatics Laboratories, NTT, Inc.

  

  Abstract
  As a world-renowned researcher studying cryptography and NTT Fellow at NTT Social Informatics Laboratories, Dr. Tatsuaki Okamoto has formulated the problem of “organized complexity” (a concept he has long contemplated) as “the law of increasing complexity,” informed by cryptographic methodologies. This law provides a unified explanation of the phenomenon of increasing complexity over a long time in subjects such as the universe, living organisms, and human societies. In this interview, we asked him about his thinking behind the formulation of the law of increasing complexity, specific examples demonstrating the validity of the law, and the future direction that the Earth and human society might take if the law is followed.

Rising Researchers

• Ryo Nishimaki, Distinguished Researcher, Social Informatics Laboratories, NTT, Inc.

  

  Abstract
  The practical application of quantum computers carries the risk that many current encryption methods could be compromised. However, it enables the implementation of cryptographic technologies that are only possible through the capabilities of quantum computers. We spoke with Ryo Nishimaki, a distinguished researcher at NTT Social Informatics Laboratories and a leading figure in cryptographic technology that could serve as the core element of information-security systems in the quantum-computing era.

Feature Articles: Research and Development toward Sustainable Infrastructure

• Technologies for Infrastructure Sustainability

  

  Abstract
  At the Sustainable Device Technology Laboratory in NTT Device Technology Laboratories, researchers in a wide variety of technical fields with basic knowledge in chemistry and physics seamlessly combine their skills in engineering and programming to conduct research and development that contributes to a sustainable society. One of our research and development themes is sustainable-infrastructure technologies. We aim to implement infrastructure that is both safe and economical in maintenance and management, not only for the communication infrastructure within the NTT Group but also for the entire social infrastructure.

• Prediction of Corrosion Deterioration Based on State of Individual Facilities for Appropriate Maintenance of Communication Infrastructure

  

  Abstract
  Correctly understanding corrosion behavior under individual environments and predicting deterioration is important in maintaining a communication infrastructure in a sustainable manner. Targeting metal components installed inside maintenance holes, this article introduces efforts for predicting the deterioration of metal inside a maintenance hole by investigating acceleration tests that simulate the maintenance-hole environment.

• Accelerated Aging Testing of Plastic Materials to Extend Service Life of Telecommunications Infrastructure

  

  Abstract
  Plastic materials that are used outdoors deteriorate due to the combined effects of light, heat, water, and stress. Therefore, evaluation techniques that enable the identification and use of materials with excellent weather resistance are essential for extending the lifespan of infrastructure facilities. In this article, we introduce our efforts to establish accelerated aging tests for appropriately evaluating weather resistance, using polypropylene as an example.

• Laser Technology for Extending the Maintenance Interval of Communication Infrastructure: Understanding the Phenomena Occurring between Rust and Steel

  

  Abstract
  Reliable repair methods for suppressing re-deterioration are important for maintaining the long-term integrity of communication-infrastructure facilities. This article focuses on rust removal and steel-surface modification achieved through laser irradiation. It introduces our efforts to evaluate the characteristics of iron oxide, which is formed by laser irradiation, and understand its formation mechanisms, with the goal of establishing surface-preparation techniques that maintain post-repair conditions over extended periods.

• R&D on Telecommunications Infrastructure and Its Expansion to Social Infrastructure

  

  Abstract
  NTT Access Network Service Systems Laboratories conducts research and development (R&D) on telecommunications infrastructure. Its Civil Systems Project focuses on elucidating material- and structure-based deterioration mechanisms, seismic countermeasures, disaster-damage prediction, and artificial-intelligence-based inspection and maintenance technologies. This expertise has also recently been applied to social infrastructure to develop technologies that enhance the efficiency and sophistication of maintenance management. This article outlines the evolution of R&D in telecommunications infrastructure and introduces technologies, including image-based diagnostics, disaster prediction, and early anomaly detection using synthetic aperture radar satellites.

Regular Articles

• High-speed Vertical-illumination Photodiode for Beyond-200-Gbaud Applications

  

  Abstract
  The rapid increase in data traffic is pushing optical communication systems toward higher symbol rates. High-speed, high-responsivity photodiodes (PDs) are therefore essential for next-generation transceivers. We report on our fabricated vertical-illumination InP/InGaAs (indium phosphide/indium gallium arsenide) PD designed for symbol rates beyond 200 Gbaud, offering a 3-dB bandwidth over 100 GHz. By interference-based absorption enhancement, the PD exhibits responsivity exceeding 0.5 A/W over a broad absorption wavelength range. The inverted p-down structure enables electric-field confinement, resulting in a low dark current of approximately 1 pA with small device-to-device variation. These results indicate the suitability of the fabricated PD for future high-symbol-rate receivers.

Global Standardization Activities

• Trends in the Second Plenary Meeting of ITU-T SG15 (Networks, Technologies and Infrastructures for Transport, Access and Home)

  

  Abstract
  The second plenary meeting of ITU-T (International Telecommunication Union - Telecommunication Standardization Sector) Study Group 15 for the 2025–2028 study period was held in Geneva, Switzerland, from 13 to 24 October 2025. This article reports on the outcomes of this meeting, with a particular focus on optical access network standards and optical physical-layer standards.

Practical Field Information about Telecommunication Technologies

• Case Study on Using the α-Command Analysis Support Tool for Handling Problems Occurring during Use of Business Phone Systems

  

  Abstract
  Many problems reported by customers regarding NTT’s “α Series” business phone systems are caused by an unintended operation, due to incorrect operation of telephone terminals, or unexpected behavior due to constrains concerning equipment specifications. Identifying the status of telephone operation when such problems occur is difficult since the control commands (α-commands) exchanged between the α-Series main unit and telephone terminals is not recorded in the system log. This article introduces a method for analyzing α-commands using the α-command analysis support tool and two example cases of its use.

External Awards

• External Awards