June 2026 Vol. 24 No. 6

Front-line Researchers

• Takahiro Kawabe, Senior Distinguished Researcher, Communication Science Laboratories, NTT, Inc.

  

  Abstract
  Objects that look so soft they almost invite touch as they move. Images that seem ready to spring into motion at any moment. What perceptual mechanisms enable the human visual system to evoke such vivid impressions? Takahiro Kawabe, a senior distinguished researcher at NTT Communication Science Laboratories, approaches this question from a unique vantage point. With a background in psychology, he leverages computational methodologies to uncover the underlying principles of visual information processing in the brain. He is also driving efforts toward the real-world deployment of technologies capable of transmitting the visual sense of materiality across distance. In this interview, we explore his latest research achievements and the future directions of his work.

Rising Researchers

• Haruki Sanada, Distinguished Researcher, Basic Research Laboratories, NTT, Inc.

  

  Abstract
  Current information and communication technologies form the foundation of people’s lives and economic activities, and much of the information processing involved in those activities is carried out by electrons. Research has focused on properties of electrons other than electric charge, and with the advent of two-dimensional semiconductors, a new degree of freedom called “valleys” has attracted attention. Strongly linked to the polarization of light, valleys have the potential to lead to the creation of new means of information processing and optical functions. We interviewed Haruki Sanada, a distinguished researcher who is taking on the challenge of identifying and controlling valleys in two-dimensional semiconductors.

Feature Articles: Forefront Research on Ultrawide-bandgap Semiconductors

• Overview of Ultrawide-bandgap Semiconductor Research at NTT

  

  Abstract
  Ultrawide-bandgap semiconductors exhibit high breakdown voltage, high-frequency operation, and excellent environmental robustness. They therefore have attracted significant attention as key materials for attaining a sustainable society and enabling next-generation innovative devices and systems. At NTT Basic Research Laboratories, we have been promoting research and development on aluminum nitride, cubic boron nitride, and diamond, using advanced crystal growth technologies developed through long-term studies on fundamental materials. We present the recent progress and future prospects of ultrawide-bandgap semiconductors.

• AlN Transistors for Ultrahigh-temperature Electronics

  

  Abstract
  Aluminum nitride (AlN) is attracting significant attention as a semiconductor material able to operate in ultrahigh-temperature environments. We outline potential applications of high-temperature electronics and highlight the advantages of AlN for such applications. We also describe the development of AlN metal-semiconductor field-effect transistors at NTT, which can operate stably at temperatures as high as 1000°C. These devices exhibit the highest current on/off ratio reported to date for semiconductor transistors operating at such high temperatures, highlighting the strong potential of AlN for electronics in harsh environments.

• High-frequency Operation of AlN-based Polarization-doped Transistors

  

  Abstract
  Aluminum nitride (AlN)-based nitride semiconductors exhibit an extremely high critical electric field and promising materials for the high-power and high-frequency devices required in next-generation wireless communications. However, in the high-Al-composition region, conventional impurity doping cannot provide sufficiently high carrier concentrations, which has hindered high-frequency transistor operation. We present polarization doping, a novel conductivity control technique that uses the polarization properties of nitride semiconductors, and introduce our latest research demonstrating the high-frequency operation of AlN-based transistors enabled with this technique.

• AlN-based Deep-ultraviolet Laser Diodes

  

  Abstract
  Deep-ultraviolet (UV) laser diodes are promising light sources for applications such as virus inactivation, spectroscopic analysis, and next-generation communications. We focus on aluminum nitride (AlN)-based semiconductors suitable for deep-UV light emission and summarize the current technical challenges associated with applying these materials to laser diodes. We also present our unique approach to improving electron injection characteristics by using n-type contact layers, which contributes to deep-UV laser oscillation in our AlN-based laser diodes.

• Gigahertz Acoustic Wave Devices Using AlN Piezoelectric Thin Films

  

  Abstract
  Aluminum nitride (AlN), an ultrawide-bandgap semiconductor, exhibits excellent electrical insulation properties as well as high piezoelectricity. Its low mass density compared with other piezoelectric materials makes it a promising candidate for piezoelectric transducers capable of electrically exciting and detecting high-frequency acoustic waves in the gigahertz range. This article introduces NTT’s research on the development of gigahertz acoustic wave devices using high-quality AlN piezoelectric transducers and on the exploration of novel physical phenomena enabled by high-speed acoustic waves.

• Engineering of Novel Ultrawide-bandgap Nitride Semiconductors

  

  Abstract
  We describe the world’s first epitaxial growth of cubic boron scandium nitride (c-BScN) layers by magnetron sputtering. The Sc composition can be controlled by changing the growth temperature. From X-ray absorption fine structure measurements using synchrotron radiation and first-principles calculations, we found that Sc atoms substitute for B atoms. These results open the way for the development and application of c-BN-based heterostructures in power devices.

• Diamond Semiconductors for Spintronic Device Applications

  

  Abstract
  Diamond is a promising platform material for next-generation spintronic device applications due to its outstanding semiconductor and spin properties. The injection of spin-polarized carriers from a ferromagnetic metal into a diamond semiconductor through a tunnel barrier is a key technique for diamond spintronic devices. A Schottky barrier formed at a ferromagnetic metal/diamond interface is a candidate for such a tunnel barrier. We explain the carrier transport mechanism in ferromagnetic permalloy/p-type boron-doped diamond Schottky barrier diodes toward spintronic device applications.

Regular Articles

• Reliable Operation Technologies for Datacenter Networks Composed of Optical Circuit Switches

  

  Abstract
  Optical circuit switches (OCSs) are attracting considerable attention as a key enabler for next-generation datacenter networks (DCNs), as they allow networks to improve capacity, latency, and energy efficiency by eliminating optical–electrical–optical conversions. However, the adoption of OCS-based architectures fundamentally changes network operations, particularly with respect to the verification of fiber connectivity and link quality prior to service deployment. Unlike conventional electrical packet-switched networks, OCS-based networks do not inherently support packet-based probing, topology discovery, or continuous link monitoring. The fiber-layer connectivity and quality of optical fibers, both between OCSs and between OCSs and terminal nodes, must therefore be verified through optical signal probing and power measurements. This article presents a unified technical framework that integrates two fiber-layer verification methods: (i) efficient inspection and certification of inter-OCS fibers and (ii) scalable topology and quality verification of terminal–OCS fibers in OCS-based DCNs. Both methods combine signal propagation modeling, link-budget-aware fiber-loss evaluation, and probing algorithms designed to resolve observational ambiguities. By leveraging these techniques, our methods substantially reduce inspection time while maintaining verification accuracy, enabling the practical deployment of large-scale OCS-based DCNs.

Global Standardization Activities

• Recent Trends in Optical Fiber and Cable Technologies within IEC TC86

  

  Abstract
  The International Electrotechnical Commission (IEC) Technical Committee 86 (TC86) is the standardization body responsible for developing international standards related to optical fiber communications. This article provides an overview of the standardization activities conducted in IEC TC86, with particular focus on optical fiber and cable technologies that have been discussed in recent meetings as well as their future directions. Emphasis is placed on emerging topics reflecting technological advances and market demands and on how these discussions contribute to the establishment of international standards that ensure performance, quality, and interoperability of optical fiber products and systems.

External Awards

• External Awards