Optical communication using laser beams is increasingly favored over radio waves for space applications, as it suffers from less signal loss over vast distances. However, even light-based signals diminish in strength over the journey, requiring highly sensitive receivers on Earth to detect these weakened signals. The new system by Chalmers researchers seeks to meet this need by providing a pathway for higher-speed, error-free transmissions over distances such as those from the Moon or Mars to Earth.

"We can demonstrate a new system for optical communication with a receiver that is more sensitive than has been demonstrated previously at high data rates. This means that you can get a faster and more error-free transfer of information over very long distances, for example when you want to send high-resolution images or videos from the Moon or Mars to Earth," said Peter Andrekson, Professor of Photonics at Chalmers and one of the lead authors of the study, which was recently published in the scientific journal 'Optica'.

Silent Amplifier and Simplified Transmitter
At the heart of the system is an optical amplifier designed to enhance the signal with minimal noise, making data transmission more reliable. As light spreads and weakens with distance - similar to a flashlight beam - signals sent from space are often too faint upon reaching Earth to overcome the electronic noise in receivers. The Chalmers team previously developed a noise-free optical amplifier, but its practical implementation had been hindered by the demanding requirements it placed on both transmitter and receiver.

The current design simplifies these demands, with the receiver on Earth generating two of the three light frequencies necessary for noise-free amplification, allowing the transmitter to produce only a single frequency. This adjustment means the noise-free amplifier can now be utilized with a standard laser transmitter, potentially allowing existing optical transmitters on space probes to function seamlessly with the new system on Earth.

"This phase-sensitive optical amplifier does not, in principle, generate any extra noise, which contributes to a more sensitive receiver and that error-free data transmission is achieved even when the power of the signal is lower. By generating two extra waves of different frequencies in the receiver, rather than as previously done in the transmitter, a conventional laser transmitter with one wave can now be used to implement the amplifier. Our simplification of the transmitter means that already existing optical transmitters on board satellites and probes could be used together with the noise-free amplifier in a receiver on Earth," explained Rasmus Larsson, Postdoctoral Researcher in Photonics at Chalmers and a lead author of the study.

Addressing Communication Bottlenecks
This progress brings Chalmers' silent amplifier closer to practical use in space-Earth communication links, which could alleviate a bottleneck currently facing space agencies, referred to as "the science return bottleneck." This bottleneck arises from the challenges in rapidly transmitting scientific data from space back to Earth.

NASA has highlighted this bottleneck as a critical issue in the data transmission chain. "We believe that our system is an important step forward towards a practical solution that can resolve this bottleneck," said Andrekson.

The Chalmers team plans to advance this technology by testing the optical communication system in field conditions on Earth, followed by trials in satellite-to-Earth communication links.

Research Report:Ultralow-noise preamplified optical receiver using conventional single-wavelength transmission

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