Phlux APDs to boost ESA satcomms

Funded by the European Space Agency (ESA), the project’s medium-term goal is to achieve reliable 2.5 Gbps communications with Low Earth Orbit (LEO) satellites at 1550 nm wavelength. These satellites orbit the earth at heights of up to 2000 km (1,200 miles). A longer-term aim is to produce links that will operate at 10 Gbps.

“This project is an endorsement of the value of our patented APD technology developed at The University of Sheffield,” says Phlux CEO Ben White (pictured), “with more than an order-of-magnitude improvement in sensitivity over traditional devices, we offer the enabling component that makes other technology breakthroughs possible. Higher performance FSOC links are a perfect example and it’s exciting to be working with such prestigious organisations as ESA and Airbus Defence and Space.”

Phlux Noiseless InGaAs avalanche photodiodes (APDs) are at the heart of the project. They are used as infrared sensors in FSOC receivers and are expected to deliver 6 dBm more sensitive than traditional InGaAs APDs operating at 1550 nm.

This means that they can detect much lower signal levels, enabling faster and higher bandwidth links with low latency to be developed. It also means that adequate performance can be maintained for longer periods because link integrity is maintained over a wider angle as the satellite passes overhead.

One of the key technical challenges with realising FSOC is that the infrared signals used to transmit data are diffracted as they pass through the troposphere, the atmospheric layer closest to Earth.

Variations in our atmosphere’s air temperature, humidity and turbulence cause fluctuations in the intensity and angle of incidence of the infrared signal. This makes the beam wander over the signal detector area, limiting performance.

This issue is being addressed by developing a large area, high sensitivity APD to produce a wider receptor. A radiation-hard detector module being developed in this project has other potential applications including space debris monitoring, greenhouse gas detection, and space navigation.

“This will be an enabler for the rapid development of optical communication in satellites for direct-to-earth applications and inter-satellite links with data rates below 10Gbps,” says Ludovic Blarre of Airbus Space Systems.

The first phase of the project runs until the end of September 2025.