Wireless optical communication is booming with the development of satellite field

Wireless optical communication (FSO) and system realize fast and safe connection, whether in ground or non-ground networks. With the significant progress of space optical technology in the past 20 years, ultra-high bandwidth signals are now often transmitted back and forth over a long distance, providing a global communication canopy.

The application of a typical wireless communication concept in low earth orbit satellite constellation. Each satellite carries four optical communication terminals, which are connected with adjacent satellites in all directions to form a mesh network.

 

From transmitter to receiver to all relevant optical equipment in the middle, every technological leap in the past 20 years has helped wireless communication become cheaper, faster, easier to deploy, and ultimately more commercially feasible. Global Market Estimates, a research firm, predicts that the value of the FSO industry will increase from $4.4 billion in 2022 to $47.5 billion in 2027, with a CAGR of 34.1%.

 

A variety of advanced technologies are playing a role. Including high power small linewidth laser; Complex opto-mechanical control systems, such as fine steering mirrors, can accurately shape and guide the laser; High sensitivity detector; Adaptive and coherent optics for compensating atmospheric aberration; High-speed digital processing device for signal encoding and decoding; And photonic integrated chips (PICs) that help to reduce the size of optical signal processing components.

 

With the progress of technology, the demand for more and more data bandwidth has also promoted people's interest in wireless networks, whether over the earth or on the earth's surface.

 

The demand for greater bandwidth around the world has prompted several companies to deploy large "constellations", which sometimes consist of thousands of satellites, most of which are connected by wireless optical systems and can exchange optical data signals with ground terminals.

 

Compared with the traditional point-to-point microwave link, the wireless optical network provides a wireless access solution that can be rapidly deployed, with higher bandwidth, security, and lower power consumption.

 

John Reid, the scientific director and co-founder of the Airvision Company in Eindhoven, the Netherlands, said: "In the satellite system, the laser signal from the earth terminal must lock the satellite when it flies over the horizon, and then wait for the line of sight to reduce to an acceptable level, and then transmit data at the maximum speed." "Reducing the line of sight can reduce the distortion of optical signals through atmospheric turbulence."

 

The first research group to report gigabit speed laser satellite communication is the European Data Relay System (EDRS), which is a commercial cooperation agreement between Airbus and the European Space Agency (ESA). Part of the purpose of the network is to support the Copernicus plan, which is jointly managed by ESA and the European Commission. It is estimated that the Copernicus plan will require the spaceborne telecommunications infrastructure to transmit terabytes of Earth observation data from space to the ground every day. Providing these data to ground stations in real time is very useful for land, sea and ice monitoring, as well as government and security services.

 

SpaceX's "star chain" has 12000 satellites, which may be the most eye-catching giant constellation and the largest low-Earth orbit satellite constellation. Its satellite operates in an orbit around 550 kilometers above sea level - relatively close to the Earth - to reduce the delay to about 20 milliseconds, and supports high data rate activities such as games and streaming media with a speed of 50 to 500 Mbit/s.

The optical communication link network shows the inter-satellite links in the LEO and GEO layers, as well as the wireless links with aircraft, balloons and ground stations.

 

According to TESAT, its CubeL is the smallest optical communication terminal of the cube satellite used for wireless communication.

Unlike fixed underground telecommunication optical fiber, these constellations can be moved to any desired place. For example, these needs may include communications during natural or man-made disasters. At the beginning of last year, the plug-in terminals of several trucks were transported to Ukraine to compensate for the damage of the communication link caused by the Russian bombing.

 

The ground antenna also provides an important lifeline for the Ukrainian army. Through it, users can connect to the nearest satellite chain and then communicate with the nearest ground station in neighboring Poland.

 

The key to the success of such large constellations is a high-performance but affordable optical system that can withstand strict mechanical, thermal and radiation conditions. "These systems will include optical amplifiers that meet space conditions, electronic equipment with sufficient optical output power, high data rate capability, and space-proven pointing, acquisition and tracking algorithms to establish links between remote satellites."

In addition to the interference of the earth's atmosphere, the optical links between satellites send signals back and forth across the earth (above).

TNO optical ground station in The Hague, the Netherlands. The company said that in cooperation with Airbus Defense and Dutch Space, TNO recently demonstrated a ground-based laser communication link of more than 10 kilometers in the Netherlands, which is the first optical data connection operated using traditional infrastructure under realistic conditions.

 

In quantum optical technology, single photon source and detector are used to encrypt data and transmit data safely and remotely. In fact, the FSO link will not cause the same transmission loss and limited distance as the quantum key distribution (QKD) technology on the optical network. FSO can further use the traditional wavelength division multiplexing technology to send encrypted data at a higher rate.

 

At present, due to the lack of appropriate optical amplifiers to overcome the limitations of optical fiber transmission, QKD is limited, but FSO may provide a solution.

 

Atmospheric constraints applicable to ground-to-air networks also hinder ground-based FSO communications. However, with the decline of the cost of key optical components, there are more opportunities for ground-based FSO systems to replace fiber-based networks.

 

The demand for faster, large-capacity communication and data rate guarantees the strong development prospect of FSO. The future trend is the more and more popular Internet of Things, from cars and containers to lighting and surveillance cameras, and billions of devices are connected and communicated with each other. FSO's ability to extend data exchange beyond the cable infrastructure will ensure that this technology plays a key role.

 

Optical wireless communication technology has made great progress, especially above the atmosphere, but on the ground, safe and high-bandwidth information transmission still has a way to go.

 

In the future, the 6G mobile system will be launched in succession, and the standardization committee is formulating specifications. But one thing is clear: the proposed 6G requirement will require more bandwidth.

 

Article source:https://www.photonics.com/Articles/Free-Space_Optical_Communications_Soar_with_the/p5/vo221/i1428/a68666