Seeing the Unseen: A New Way to Steady Laser Links Through Turbulent Skies
Published October 20 2025
By Alex Frost & Aliesha Aden
TN-1 at The University of Western Australia. Photo: Aliesha Aden
Anyone who’s watched a star shimmer in the night sky has seen the atmosphere at work. That twinkle is beautiful to the eye but a constant frustration for astronomers and astrophysicists alike. It’s a reminder that our atmosphere, while vital for life, is a noisy and unpredictable medium for light.
If you’ve ever noticed how objects appear to ripple above a hot road, you’ve seen the same thing on a small scale. Moving air bends and twists light, which is a phenomenon known as atmospheric turbulence. Now imagine trying to send a laser beam through that same shifting air, not to admire the stars, but to send information hundreds of kilometres into space.
That’s the challenge of ground-to-space optical communications. The technology promises ultra-fast, secure data transfer using light instead of radio waves, but it’s continually tested by the restless motion of Earth’s air. Even tiny fluctuations in temperature or wind can bend a laser beam just enough to blur or scatter it, turning what should be a clean signal into something distorted.
Why the uplink is such a challenge
Without turbulence correction, those fluctuations will ruin the signal’s integrity and stop us from achieving the high data rates that optical communications can deliver.
Thankfully, astronomers have been studying and compensating for turbulence for decades.
Their tool of choice is adaptive optics. These are systems that measure how incoming light is distorted and use flexible mirrors to reshape it in real time. This works beautifully for downlink signals, where light travels from a satellite or star down to a telescope. But sending light up is a completely different problem.
Diagram of the intensity fluctuations in atmospheric turbulence for the uplink and downlink paths in communication links. Source: Alex Frost
Because most of the atmosphere’s turbulence sits close to the ground, a laser heading upward hits the roughest air almost immediately, before continuing its long journey through the vacuum of space. That vacuum stretch acts like a magnifying glass, exaggerating the distortions picked up near Earth’s surface. By the time it reaches the satellite, the beam can spread and flicker so much that the receiver barely sees it at all.
For the downlink path, there’s usually plenty of signal to measure and correct once the light arrives. But for the uplink path, those same distortions become too severe to ignore as they spread and as the beam travels. That’s why we need to correct the beam before it leaves the telescope, a process known as uplink pre-compensation.
But even that’s not straightforward. Low-Earth-Orbit (LEO) satellites move so quickly that by the time light from the ground reaches them, they’ve already shifted position. We call this the point-ahead angle. It means the uplink and downlink paths don’t pass through the same pocket of atmosphere, and each experiences different turbulence. What begins as a geometry problem quickly becomes something far more complex, and that’s where my research comes in.
Turning the downlink into a map of the sky
So how do you measure and correct something you can’t directly observe?
The key insight is that while the uplink and downlink beams take different paths, they still share much of the same atmosphere. If we can build a three-dimensional picture of that shared region, we can estimate what the uplink beam will encounter on its way up, even though we never see it.
That’s what LITEUP does. It stands for LEO Interference from Tomographic Estimation for Uplink Pre-Compensation, and while the acronym is a mouthful, the idea is simple: use the light coming down to help correct the light going up.
Every time a satellite sends a laser down to Earth, our adaptive optics system measures how that light is distorted by turbulence. It’s like watching how ripples form on a windy pond. LITEUP takes a series of those “snapshots” of the downlink beam, each showing a slightly different pattern caused by moving air currents. Over time, those changes reveal how the atmosphere is layered and shifting above the telescope.
Schematic of LITEUP. PAA – point-ahead angle. Source: Alex Frost
Here’s where it gets clever! When we track a fast-moving satellite, air at higher altitudes appear to move faster than air close to the ground, like a kind of optical parallax. By analysing that motion, LITEUP can separate the turbulence into distinct layers and reconstructs a 3D map of where distortions are strongest. From that, we can predict how the uplink beam will bend or blur and understand how to correct it.
The beauty of this method lies in its simplicity. It doesn’t need extra lasers, new sensors, or complex additional optics. All the data it relies on already comes from the adaptive optics system we use to stablise the downlink beam. LITEUP simply adds a layer of smart processing, like a filter that uses motion and timing to untangle the atmosphere’s structure in 3D.
To make it work optimally, the uplink beam must be transmitted within the telescope’s main aperture and aligned so it crosses paths with the downlink beam as much as possible. That overlap gives LITEUP enough information to make a reliable estimate of the turbulence both beams share.
Simulation of viewing turbulence through a schlieren imaging system. Source: Alex Frost
What we found
So far, LITEUP has been tested extensively in simulation, modelling how turbulence affects a laser beam under different conditions.
In these tests, the goal was simple: to see how closely LITEUP’s predictions matched the true atmospheric distortion we simulated. Compared to a naive approach that assumes the uplink and downlink are identical, LITEUP consistently performed better, and in some cases, reduced error by up to eight times.
Even when we deliberately introduced uncertainty, the method held strong. That robustness suggests it could perform well under real atmospheric conditions, not just in theory. And notably, it achieves this using only existing adaptive optics hardware, with no additional sensors required
Looking Ahead
Free-space optical communication is one of the most exciting frontiers for connecting Earth and space. But its success depends on sending a beam of light cleanly through air that never stays still.
What excites me about LITEUP is that it doesn't fight the atmosphere but rather learns from it. By using the light already coming down to Earth, we can anticipate how the air above will behave and correct our own signal before it even leaves the telescope.
It’s a small shift in perspective, but an important one. Instead of seeing turbulence as a problem to remove, we’re turning it into information to work with.
Alex Frost’s full research paper, “Uplink pre-compensation for ground-to-space optical communications using downlink tomographic reconstruction,” is published in Optics Express, Vol. 33, No. 21 (2025) Read the paper for the complete methodology and results.