Free-space Optical Communication Outlook: Chapter 3 “History and Future of Free Space Optical Communication”
The Beginning of Free-Space Optical Communication (FSO) Development
FSO has been a subject of research and development primarily in the United States, Europe, and Japan since the 1960s.
In 1965, the United States initiated the development of optical communication systems for deep-space communication purposes, marking the world’s first foray into FSO technology. By 1975, they had completed an inter-satellite communication system (though no space experiments were conducted). In Europe, the European Space Agency (ESA) embarked on research into laser communication for geostationary satellite communication in 1979. In 2001, a significant milestone was achieved when the first-ever inter-satellite optical communication took place between France’s Earth-observation satellite SPOT-4 and ESA’s geostationary communication experimental satellite ARTEMIS.
Japan has also actively pursued the development of FSO technology. In 1994, the National Institute of Information and Communications Technology (NICT) and the Japan Aerospace Exploration Agency (JAXA) successfully conducted the world’s first satellite-to-ground optical communication using the Laser Communication Equipment (LCE) aboard the Engineering Test Satellite 6 (ETS-6). Furthermore, in 2005, a groundbreaking achievement in inter-satellite optical communication was reached when communication took place between JAXA’s Optical Inter-Orbit Communications Engineering Test Satellite “Kirari” (OICETS) and ARTEMIS, representing the first inter-satellite optical communication between different agencies.
Delays in FSO Development
From the mid-2000s to the mid-2010s, there were noticeable delays in the practical application of FSO. Several factors contributed to these delays.
Demand for Optical Communication: One of the factors was that the demand for optical communication during that period was not as significant as it is today. In the early 2000s, optical discs and semiconductor memory began to be used, leading to increased storage capacity. However, the communication capacity of satellite data at that time was still at a level where conventional radio communication methods were sufficient for transmitting and receiving data.
Technical Challenges: Additionally, another reason for the delay in practical application was the existence of numerous technical challenges in FSO technology. FSO is sensitive to atmospheric fluctuations and water vapor. Especially, the presence of clouds or fog between ground stations and satellites could disrupt the optical signal, making it challenging to establish a high-capacity and reliable communication link directly between low Earth orbit satellites and ground stations.
Resurgence in FSO Development
However, from the mid-2010s to the present, there has been a resurgence in the development of FSO technology. Several factors have contributed to this resurgence.
Increased Demand: One factor is the expanding need for FSO. With the growth of large satellites for data observation and the development of global satellite constellations, the importance of high-capacity communication links has increased. As data transmission from satellites becomes more common, the demand for fast and highly reliable communication methods has risen.
Technological Advancements: Another factor is the miniaturization and weight reduction of devices used in FSO, particularly laser transceivers and optical modulators. These devices were previously large and heavy, making them expensive to launch and challenging to integrate into small satellites. However, the miniaturization and weight reduction of these devices have enabled payload capacity savings on spacecraft and reduced launch costs. Additionally, their compatibility with small satellites has improved, making it easier to establish multiple communication links between satellites and ground stations. This has enhanced the feasibility of satellite optical communication networks that are less susceptible to the effects of clouds and atmospheres.
In recent years, the United States has accelerated feasibility studies and implementation aimed at practicalizing optical communication for the purpose of enhancing defense capabilities. In 2019, the United States Department of Defense (DOD) established the Space Development Agency (SDA). One of the projects led by the SDA is the creation of the Proliferated Warfighter Space Architecture (PWSA), a national defense space system concept based on a satellite constellation.
By 2022, contracts had already been awarded to three U.S. companies — Lockheed Martin, York Space Systems, and Northrop Grumman Strategic Space — to develop satellites equipped with optical satellite communication for the SDA. The primary objective is the detection and tracking of hypersonic weapons. Traditional early warning satellites in geostationary orbits cannot accurately track these hypersonic weapons due to their extended distance. SDA aims to use a satellite constellation in low Earth orbit to detect and track these weapons and transmit real-time information to the ground, employing optical satellite communication.
In Europe, the European Commission (EC) submitted a draft regulation in 2022 for the establishment of a European Union (EU) proprietary satellite communication network. This plan, set to commence development in 2023, partial service delivery, and in-orbit testing of quantum encryption technology by 2025, aiming to provide all communication services, including quantum encryption technology, by 2028. Airbus is slated to lead the consortium, with the participation of Thales Alenia Space, Arianespace, and others.
Japan is also striving to establish a global satellite optical communication network system. In 2022, the Ministry of Economy, Trade and Industry submitted a research and development concept for the development and verification of satellite constellation infrastructure technology, including optical communication, as part of the “Critical Technology Development for Economic Security Program.” The New Energy and Industrial Technology Development Organization (NEDO) issued a public offering for this project, and four companies — Space Compass, NICT, Axelspace, and NEC — were selected.
Thus, various countries are promoting satellite optical communication networks as critical projects for national security and communication infrastructure enhancement. This is expected to lead to the rapid advancement of FSO technology research and practical application.