As of today, satellites use radio signals to communicate with each other. However, the radio frequency spectrum is limited and as the number of satellites increases, they begin to interfere with each other. In order to solve this problem, researchers study optical communication, which uses precise laser beams instead of radio waves. Laser communication can transmit much more data, than the radio. The main difficulty lies in the creation of equipment, capable of accurately aligning with the laser beam, while the satellites are moving at high speeds, and at the same time process large flows of information.
NTT company (a Japanese telecommunications giant, which is one of the world leaders in the development of optical networks) investigates, can technology, designed for terrestrial Internet networks, work in space. They are adapting tools from the Innovative Optical and Wireless Network initiative (IOWN), which are commonly used in fiber optic cables on Earth, to test their suitability for working on the planet. One of the company's key ideas is the Optical Inter-Satellite Link (OISL) — optical intersatellite communication. In NTT's proposed system, satellites use laser transmitters and receivers, so-called "optical terminals", which transmit data through the vacuum of space using light, creating a high-speed communication channel between satellites in different orbits. To achieve such speeds, researchers use a method called digital coherent transmission. It's the same technology, which is used in long-distance fiber optic cables, but instead of simply turning the light on and off, it encodes data through the shape and direction of the light wave. At the receiving end, digital processing restores the signal and corrects distortion. This approach allows you to transfer much more information, than standard light signals.
Using IOWN technologies in space adds a new factor — speed. Because satellites move very fast, the frequency of the light signal varies depending on, they are approaching or moving away from each other. If the system does not take these changes into account, the connection is interrupted. A significant part of NTT's research is aimed at that, so that the equipment can automatically compensate for these shifts and maintain a stable connection. Another challenge
there is the equipment itself, which must be compact and consume a minimum of energy due to the limited resources of spacecraft. To reduce size and energy consumption, NTT is working on processor integration, optical circuits and amplifiers in one compact module. This shortens the signal path, saves energy and makes the device lighter.
NTT's ultimate goal is to create a multi-layered communications network, connecting ground stations, stratospheric platforms and satellites in various orbits. Such laser channels will allow data to move quickly through space, before they are transmitted to users on Earth.
NTT's current plans include development during 2026 year with possible commercial implementation at the end of the decade. It can find application in the military sphere, national security and in global Internet providers.
Source: https://group.ntt