Laser system for data transmission between satellites

2023: Product Announcement

In mid-June 2023, researchers from the University of California at Los Angeles and the Max Planck Institute for Applied Physics in Germany figured out how to transmit data between satellites using lasers. This will create an Internet highway in space that will work faster and more reliably.

To develop a system for transmitting data between satellites, the project partners took a significant step forward in creating a satellite optical communication channel, conducting a successful test between the alpine mountain peak of Jungfraujoch and the Swiss city of Bern. Although the laser system was not tested directly with the orbital satellite, it provided a large amount of data transmission over a distance of 53 km in free space.

Scientists have figured out how to transmit data between satellites using lasers

The laser beam passes through dense layers of the atmosphere near the ground. In this case, many factors affect the movement of light waves and, therefore, data transmission. The flickering of air caused by thermal phenomena disrupts the uniform movement of light and can be visible to the naked eye on hot summer days.

Connecting to the Internet via satellite is nothing new. The most famous example for June 2023 is StarlinkIlona Musk, a network of more than 2,000 satellites orbiting near the Earth, which provides Internet access in almost every corner of the world. However, radio technologies are used to transmit data between satellites and ground stations, which are significantly less powerful. Technologies such as wireless LAN ([[WiNG5 WLAN WLAN (Wireless LAN) - wireless local area network 'WLAN]]) or mobile communication, operate in the microwave spectrum and therefore have a wavelength of several centimeters.

Laser optical systems, on the contrary, operate in the near infrared range with a wavelength of several micrometers, which is about 10 thousand times shorter. As a result, they can transmit more information per unit time. To provide a strong enough signal by the time it reaches the remote receiver, the laser's parallel light waves are guided through a telescope that can reach several tens of centimeters in diameter. This wide beam of light must be accurately directed at the receiving telescope with a diameter of the same order of magnitude as the width of the transmitted beam of light upon arrival.

To achieve the maximum possible data rate, the laser light wave is modulated so that the receiver can detect different states encoded in one symbol. This means that each symbol transmits more than one bit of information. In practice, this implies different amplitudes and phase angles of the light wave. Each combination of phase angle and amplitude forms a different information symbol that can be encoded in the transmitted symbol. Thus, with a scheme consisting of 16 states (16 QAM), each wave can transmit 4 bits, and with a scheme consisting of 64 states (64 QAM) - 6 bits.

Fluctuations in the turbulence of air particles lead to a change in the speed of light waves both inside the light cone and at its edges. As a result, when light waves hit the detector of the receiving station, the amplitudes and phase angles either fold or cancel each other, giving false values. To prevent these errors, the project scientists installed a microelectromechanical system (MEMS) chip from ONERA with a matrix of 97 adjustable mirrors. Mirror deformations correct the phase shift of the beam on the intersection surface along the measured gradient 1.5 thousand times per second, eventually improving the signals by about 500 times. This improvement was important to achieve a capacity of 1 Tb per second at a distance of 53 km.

The system also uses special algorithms to correct distortion of laser beams due to air. Scientists tested their system on a computer and showed that it can provide high beam targeting accuracy and high data transfer rates up to 10 GB per second.

Their system could be used to create a global internet backbone through satellites that would connect different regions of the Earth and provide communications with spacecraft in deep space, the researchers said. Such a highway can improve the efficiency and security of communications in various areas, such as medicine, science and education. In the future, the modulation format developed by scientists is likely to increase the throughput of other data transmission methods, where beam energy can become a limiting factor.^[1]

Notes