China’s 2-Watt Laser from 36,000 Kilometres Challenges Starlink

At an altitude of 000 kilometres, familiar limits of satellite communications are suddenly being radically challenged.

In south-western China, a research team has achieved a feat that has caught the attention of many specialists: using a seemingly tiny 2-watt laser, a geostationary satellite transmitted a data stream to Earth that makes conventional radio links and even Starlink look outdated. The record was not made possible by a space-based trick, but by an intelligently designed ground system that technically counteracts the troublesome effects of Earth’s atmosphere.

What happened in the experiment

The test took place at Lijiang Observatory in Yunnan Province. A Chinese satellite in geostationary orbit - around 36,000 kilometres above Earth - directed a laser beam towards a telescope mirror measuring 1.8 metres.

Along the way, the light encountered everything that normally makes optical communications so difficult. Layers of air at varying temperatures bend and disturb the beam; the signal flickers and fragments, arriving on the ground not as a clean beam but as a ragged carpet of light.

“From precisely this chaotic light pattern, the researchers recovered a stable 1-Gbit/s data stream using only 2 watts of transmitting power.”

For comparison, that is broadly comparable with the data rate of a fast fibre-optic connection in a living room, except that this link runs across orbital space. The flow of data would be sufficient to transfer an HD film from Shanghai to Los Angeles in under five seconds.

Why the comparison with Starlink matters

SpaceX’s Starlink relies on thousands of satellites in low Earth orbit, generally a few hundred kilometres above the planet. This brings clear advantages: shorter transmission distances, comparatively low signal losses and fast latency times.

The Chinese test operated under entirely different conditions. Its transmitter was located 36,000 kilometres above Earth - more than 60 times farther away than typical Starlink satellites. Nevertheless, the reported downlink speed was roughly five times what many Starlink users realistically experience.

• Starlink orbital altitude: approx. 500–600 km
• GEO satellite orbital altitude: approx. 36,000 km
• Laser transmitting power: 2 watts
• Reported data rate: 1 Gbit/s downlink

In power terms, a 2-watt transmitter is closer to a night light than to the kilowatt-class equipment used for traditional radio links. Achieving a gigabit connection over this distance sends a clear message: when the optics are controlled effectively, enormous volumes of data can be moved using remarkably little energy.

First technique: adaptive optics with 357 micro-mirrors

At the heart of the Lijiang installation is a large telescope fitted with a specialised correction system. It contains 357 tiny mirrors that continually flex and tilt, doing so many hundreds of times every second.

This adaptive-optics system aims to counteract, in real time, the distorted wavefronts caused by the atmosphere. Put differently, the mirrors alter their shape so that a reasonably straight wavefront reaches the receiver again.

Such systems are familiar from astronomy, where they are used to capture sharper images of stars. In this case, however, they are not intended to improve a picture; they are used directly to recover data.

Second technique: splitting the signal and using only the best parts

Correction alone is still insufficient in severe turbulence. The installation therefore adds another stage after adaptive optics: a so-called Multi-Plane Light Converter.

This optical component divides the incoming light into eight distinct “basis modes”, or eight separate channels. They carry the same data signal, but their strength and the degree of interference affecting them differ.

“The receiver selects the three strongest channels, overlays them and extracts the data from them - the rest is ignored.”

The combination of these two methods - adaptive optics and multi-channel reception - is known in technical terminology as AO-MDR synergy. The key results concern not only speed, but also quality:

• Usable signal before AO-MDR: 72 %
• Usable signal with AO-MDR: 91.1 %

The objective, then, is not merely to achieve a brief burst of exceptional speed, but to sustain a stable connection in adverse conditions.

Why geostationary orbit is far more difficult

A geostationary satellite appears to remain fixed above one point on Earth’s surface. For communications networks, this is highly attractive: dishes and ground stations do not need to track the satellite because it stays in the same apparent position.

The trade-off is the vast distance involved. The signal must not only travel through the long stretch of vacuum, but must also pass through the thickest and most turbulent part of the atmosphere at the end of its journey - precisely where the air is most heavily disturbed.

This final section above the observatory in Yunnan was the real obstacle. Temperature differences, wind and humidity distort the laser beam so severely that stable data transmission would barely be possible without corrective measures.

Not a home router, but a backbone node

The system assembled by the researchers is clearly not intended for consumer customers. With its 1.8-metre mirror and complex optical equipment, it is better understood as a prototype for future network nodes:

• large ground stations connecting satellites at high data rates
• backbone links between continents
• data hubs for Earth observation, military use or research

One conceivable arrangement would see a single geostationary laser satellite sending huge quantities of data to a small number of highly equipped ground stations. From there, the information could continue via fibre-optic links into regional networks or directly to data centres.

What this could mean for internet from space

The test does not represent an immediate “death blow” for radio networks in space, but it does bring an alternative into sharper focus. Optical links offer several practical benefits:

Aspect	Radio	Laser/optics
Bandwidth	limited by spectrum	very high, many Tbit/s conceivable
Beam focus	relatively broad	extremely narrow and precise
Resistance to interception	emissions can be detected across a wide area	harder to detect, strongly directional
Sensitivity to weather	rain and clouds are often tolerable	fog, clouds and heavy rain are critical

Laser links are therefore particularly suitable for a small number of high-capacity nodes where the technical expense is worthwhile. Conventional radio networks could continue operating alongside them, providing the core service in areas with frequent poor weather or for mobile users.

How reliable is the technology in everyday use?

One question remains: what happens during dense cloud cover, smog or heavy rain? Optical links are highly sensitive to scattering and absorption. In real-world networks, operators would need to use alternative routes, for example:

• several ground stations spread across different locations, ensuring that some remain cloud-free
• hybrid operation, with radio and laser links running in parallel
• intelligent routing that redistributes traffic according to weather conditions

There is also considerable technical complexity. The precision micro-mirrors, alignment with a tiny point in the sky and exact synchronisation with the satellite all demand highly specialised equipment and maintenance. At present, that makes the system too expensive for a mass-market consumer product.

Terms worth knowing

Geostationary orbit (GEO): A circular orbit above the Equator in which a satellite travels around Earth at exactly the same rate as Earth rotates. It appears to “stand still” in the sky.

Adaptive optics: A technology in which movable mirrors or optical elements correct, in real time, light waves distorted by the atmosphere.

Mode diversity reception: A method in which scattered light is divided into multiple channels before the best components are recombined.

AO-MDR synergy: The combination of adaptive optics and multi-channel reception used in the Lijiang experiment to greatly improve signal quality.

What could come next

If comparable systems become smaller and less expensive in future, new applications could emerge. Possible examples include laser relay stations on large ships, remote islands or desert regions where fibre-optic infrastructure is not an option.

Military and security-critical communications are also likely to take an interest in these developments. A tightly focused laser beam is significantly more difficult to intercept unnoticed than a broadly dispersed radio signal. At the same time, geostationary platforms provide a stable line of sight across entire continents.

One thing is certain: with its 2-watt laser from 36,000 kilometres above Earth, China has shown that the limit for satellite internet is far from being reached. Those planning global data networks in future will no longer see optics and radio as opposites, but as building blocks in a shared and far more powerful system.