The proposal, entitled "Basic technologies for wireless and optical convergence toward advancing next-generation communication", discusses how to create and establish innovative basic technologies for next-generation high-performance communication allowing the smooth connection between physical and cyber space. The key approach toward the goal is to combine the existing concepts and technologies from the fields of wireless and optical communications, or electronics and photonics in other words, which have been so far developed without intensive interactions. The converging of the concepts and technologies will initiate the developments of novel science and technologies that will be crucial for next-generation communication. In the proposal, we focus on the terahertz (THz) region, the frequency range between the current communication bands in wireless and optical networks, which has not been well explored. For the advanced use of this unexplored frequency band of electromagnetic waves, we discuss some of the strategic research areas. One of the strategic areas is the development of core technologies converging wireless and optics, based on Japan's advanced science and technology, such as photonic technology, hybrid integration technology, and meta-materials. Developing technologies aimed at obtaining lower energy consumption with unique functional materials, higher reliability, and further cost reduction of devices and modules for communication, is another important direction we should aim for. Thereby, those devices and modules would be used not only in communication but also in a wide variety of applications such as computer networks, radars, and sensors. For promoting such strategic research, we propose measures to strengthen the R&D systems, including the development of shared facilities such as high-frequency measurement equipment, funding to accelerate wireless and optical fusion research, the formation of a new research community based on wireless and optical convergence, and coordination with existing projects and international standardization activities.

In the coming years, high data rate / large capacity, low latency, massive connection, low power consumption, and secure next-generation communication technologies are expected to contribute toward the realization of an advanced digital society in which physical and cyber spaces are highly integrated. Not only the conventional personal use such as telephone calls, emails, SNS, photo / video email, and video calls, but other use areas are also becoming important. For example, industrial use such as in factories, agriculture, and services, as well as the roles played in the social infrastructure, such as in telemedicine or communication in case of disaster. In particular, in distributed computing and multi-access edge computing, which are important to provide various services utilizing IoT, it is expected to build various forms of networks in accordance with applications and services. In addition, wireless communication that connects the cloud and edge mobile terminals involves increasingly higher data rate and larger capacity, as represented by 5G in recent years. As a result, the difference between wireless communication and optical communication in terms of communication capacity is becoming smaller. Therefore, there is a demand for technological development and system design for networks that makes the best use of the features and advantages of wireless communication and optical communication technology. For this reason, with the trend moving toward open base stations, the research and development for "Beyond 5G / 6G" is accelerated worldwide, involving various technological layers and stakeholders.

On the other hand, up to now, the data rate and capacity of wireless communication have been increased in the frequency range of several hundred MHz to several GHz mainly by improving the radio access methods and by multiplexing in the limited frequency bandwidth. However, when looking at "Beyond 5G / 6G" and the subsequent generation (7G), it is necessary to develop technology that uses the frequency region of several tens of GHz (millimeter wave band) to the THz frequency region (terahertz band) from the standpoint of wider frequency utilization, in addition to technology for further improving frequency utilization efficiency. The terahertz band is the frequency region between radio (microwave band) and light (visible light / infrared light) so far. However, this region is called "terahertz gap," and the development of practical devices is difficult for both electronics technology and optical (photonics) technology. For communication application, there are various technical issues related to hardware, such as devices / circuits that can oscillate, amplify, and detect with high efficiency and low power consumption, and array antennas that enable longer distance transmission. In order to solve these issues, it is important to create new technology (basic technologies for wireless and optical convergence) by making good use of the knowledge and technology of wireless communication and optical communication, as well as electronics and photonics. Since hardware research takes a long time to be achieved, it is necessary to initiate the creation of new basic technology to overcome these issues, and related basic science and materials science at an early stage.

Projects on basic technology of next-generation communication and photonics-electronics convergence technology that integrate electronic devices and photonic devices are ongoing, with the aim of putting them into practical use in "Beyond 5G / 6G" around 2030, all over the world including the United States, Europe, China, and Japan. However, since the strategies and activities, including long-term research and development of the subsequent generation (7G) are not yet visible, we should lead the world toward clarifying the long-term research and development issues of basic hardware technology related to communication and strategically promote research and development.

The research and development issues to be addressed in the future include the use of unexplored frequency regions, advanced use of wireless and optical communication, low energy consumption, high reliability, and low price of the communication systems, side by side with basic science and materials research that supports technological evolution, each of which are shown below.

• (1) Research and development for the use of unexplored frequency regions

  In order to significantly increase the data rate and capacity, it is desirable to use the terahertz band (100 GHz to 1 THz), which is a frequency region above the millimeter wave band of several tens of GHz. However, in such a high-frequency region, there will be problems such as suppressed diffraction, an increase in absorption of electromagnetic waves in the atmosphere, a decrease in power efficiency of radio wave generation, difficulty in signal amplification, and an increase in transmission loss of conductors and dielectrics. Thus, it will be difficult to transmit radio waves for long distances. To overcome these potential issues, research and development is necessary on array antenna technology that transmits radio waves only to the desired direction, active use of radio wave reflection / transmission, high-efficiency terahertz wave oscillators / detection elements / amplifier circuits, new substrate material / conductor structure / dielectric material for low transmission loss, and high-frequency material characteristic evaluation method / evaluation tools.

• (2) Research and development for advanced use of wireless communication and optical communication

  Within the limited frequency band, it is necessary to develop technology that achieves higher speed and larger capacity with various multiplexing technologies. In addition, we will also work on extreme massive connectivity technology that makes possible the simultaneous connection to a large number of terminals including automobiles and IoT sensors, which will be required as a future communication system, and technology for extreme high reliable communication of information with extreme low latency to ensure real-time control. Furthermore, to produce various system configurations that take advantage of the features of wireless and optical communication, we will also work on technology that performs mutual conversion between wireless signals and optical signals and analog-digital conversion at high speed and efficiency. Since software technology plays an important role in the configuration of various systems, it is important to consider the cooperation with software when conducting research and development of these hardware technologies.

• (3) Research and development for low energy consumption, high reliability, and low price

  The functional requirements as the basic technology for next-generation communication are the above (1) and (2). However, in response to social requirements such as CO2 reduction of network equipment, and reliability and resilience as social infrastructure, as well as utilizing the basic technology not only in communication systems but also in application fields such as computer networks including data centers and edge computing, radar systems, and IoT sensors, it is necessary to conduct research and development corresponding to low energy consumption, high reliability, and low price. This requires not only the pursuit of characteristics at the material and device level, but also the implementation of functional modules through the integration of devices and components. Therefore, we will conduct research and development of hybrid integration technology that integrates different materials and devices such as optical devices, advanced CMOS digital devices / circuits, high-frequency analog circuits, and compact antennas for advanced massive MIMO.

• (4) Basic science and materials research that support technological evolution

  In the above research and development, in addition to the items that can be produced by technological development making the best use of existing science and technology, there are also goals that are difficult to achieve just by the simple extension of existing technology. In addition, to respond to further demands of the communication technology, discontinuous evolution of technology will be required. To respond to these requirements, it is extremely important to promote research in a wide range of related basic fields, such as basic research in condensed matter physics, optical science, and research on emerging materials and process technologies.

In order to proceed efficiently with the above research and development on a long-term perspective, we would like to propose the establishment of shared research facilities capable of advanced high-frequency characteristic evaluation, device fabrication facilities capable of producing in cooperation prototypes of devices and modules, and research facilities capable of verifying functions of devices and systems, as well as the establishment of a new research community which enables industry-academia-government collaboration, international collaboration, and interdisciplinary collaboration for the wireless and optical convergence (wireless and optical communications, analog and digital circuits, silicon and compound semiconductor devices, integrated processes, materials, measurement and evaluation, etc.), thus looking ahead to long-term funding and international standardization. In particular, the high-frequency characteristic evaluation tools and equipment related to the production of devices are expensive, and it is difficult for a single university to purchase and own them. Therefore, it is essential to develop shared facilities that can be used in common, and to build facilities and their operational structure that allow prototypes and evaluations of devices and integrated circuits. In addition, we envision the implementation of long-term research and development projects funded by MEXT (Ministry of Education, Culture, Sports, Science and Technology) and JST, aiming at the next generation (7G) of "Beyond 5G / 6G" which is expected to be implemented around 2040 and later, as well as the cooperation with the "Beyond 5G / 6G" projects conducted by MIC (Ministry of Internal Affairs and Communications) and METI (Ministry of Economy, Trade and Industry). The process of establishing a new community of wireless and optical convergence, requires the fusion area of communication and circuits, elements, and materials at IEICE (The Institute of Electronics, Information and Communication Engineers) and JSAP (The Japan Society of Applied Physics) to be newly established or expanded. It is expected that those concerned will match the seeds of research from academia with the future needs of industry, and create short-term and long-term roadmaps to obtain common goals.