The research team, led by Hoa T. Le of the University of Transport and Communications in Vietnam together with collaborators including Peter LoPresti of the University of Tulsa, built a complete FSO-SLIPT testbed in which atmospheric turbulence was deliberately generated, measured, and varied as an experimental parameter. This distinguishes the work from earlier laboratory demonstrations of optical data-and-power transfer, which typically ran over short, still-air paths where turbulence was never controlled or characterized. In those prior experiments, such as demonstrations of gigabit-per-second data-and-power links using gallium arsenide photovoltaic cells, the focus fell on receiver electronics and modulation formats rather than on the physics of a fluctuating channel. The new study instead treats turbulence as the primary variable, bringing experimental practice into line with the statistical channel models that theorists have relied on for years.

The underlying system architecture is elegant in its simplicity. At the transmitter, an on-off keying generator produces an alternating-current signal carrying the information, while a separate fiber-coupled laser at 1550 nanometers supplies a direct-current bias that represents pure optical energy. A wideband coupler merges the two into a single composite beam, so the light leaving the transmitter is simultaneously a data stream and a power beam. At the receiver, an indium gallium arsenide photodetector converts the incoming light back into an electrical signal, which is then fed into an AC-DC separator circuit. A high-pass branch, built from a 0.47-microfarad capacitor and a 560-ohm resistor, routes the rapidly varying data component to the decoder. A low-pass branch, using a 10-picofarad capacitor and a 120-kilo-ohm resistor, extracts the slow direct-current component that charges the energy-harvesting circuit. This AC/DC separation scheme is the simplest of the three main SLIPT receiver architectures, which also include time-splitting and power-splitting designs, and it allowed the team to measure both communication quality and harvested power from the same received signal.

The turbulence itself was created inside a customized chamber 77 centimeters long, fitted with two heaters along its base and two fans on its sides. By heating the air and stirring it with fans, the researchers produced convective pockets of air with different temperatures and densities, mimicking the refractive-index fluctuations that plague real outdoor and airborne optical links. Two scenarios were tested. Weak turbulence was generated with the chamber at 22 degrees Celsius and fans at maximum speed, yielding a scintillation index of 0.007 and a refractive-index structure constant of 5.41 times ten to the minus eleven. Moderate turbulence, produced at 100 degrees Celsius with heaters and fans both at full power, raised the scintillation index to 0.096 and the structure constant to 7.32 times ten to the minus ten. Both values fall in the weak-to-moderate regime, where the received intensity is well described by a log-normal statistical distribution, a fact the team confirmed by fitting the measured voltage histograms with log-normal probability density functions that achieved root-mean-square errors of just 0.016 and 0.013 respectively.

On the communication side, the results followed the expected and sobering pattern. The team transmitted on-off-keyed data at bit rates from 0.5 to 4 megabits per second and estimated the bit-error rate from the Q-factor, a standard quality metric derived from the mean and standard deviation of the voltages representing digital ones and zeros. At every bit rate, moderate turbulence produced a consistently higher bit-error rate than weak turbulence. The mechanism is visible in the voltage statistics: under weak turbulence the probability distributions for ones and zeros remain narrow and well separated, preserving a wide decision margin at the receiver. Under moderate turbulence, scintillation broadens both distributions and pulls them into overlap, shrinking the margin between the decision thresholds and driving errors upward. Theoretical BER curves computed from the measured voltage statistics tracked the experimental curves closely, with the small residual gap attributed to circuit noise and non-idealities in the AC-DC separator that the simplified linear model does not capture.

The energy results told a very different story. Average harvested power, calculated from the root-mean-square voltage on the DC branch across a one-megaohm load, showed no clear dependence on bit rate, fluctuating in both turbulence scenarios. But when the researchers compared turbulence strengths, the moderate-turbulence case consistently delivered more harvested power than the weak-turbulence case. Far from being a measurement artifact, this counterintuitive outcome follows directly from the mathematics of fluctuating signals. The harvested-power estimate depends on the second moment of the received intensity, and the scintillation index is defined as the normalized second moment. For a fixed mean received power, increasing the scintillation index mathematically increases the second moment, raising the RMS voltage and therefore the estimated harvested power. The effect requires no exotic nonlinear harvesting circuitry; it emerges purely from second-order signal statistics.

The voltage distributions on the DC branch make the physics tangible. Under weak turbulence, the DC voltage forms a sharp, narrow peak, indicating a steady and predictable power level. Under moderate turbulence, the distribution spreads dramatically, and occasional voltage samples climb to notably higher values. Those intermittent bursts of strong received intensity inflate the average harvested power, even though they also make the instantaneous power less reliable, as reflected in the higher power variance measured in the moderate case, 9.998 times ten to the minus eleven compared with 8.371 times ten to the minus eleven under weak turbulence. In other words, turbulence trades stability for intensity: the receiver sees a rockier energy supply, but on average a richer one.

The experimental protocol was designed for statistical rigor despite the modest scale of the benchtop link. Data were recorded at 10 million samples per second across 200 trials per measurement, totaling one second of capture, which corresponds to roughly one million bits at the 1-megabit-per-second setting and scales proportionally at higher rates. All measurements were conducted in total darkness to eliminate ambient light, and the scintillation metrics were computed from signals measured after the photodetector but before the separation circuit, with noise removed. The authors are candid about one methodological limitation: the Q-factor approach to BER estimation assumes approximately Gaussian decision statistics, whereas log-normal intensity fluctuations make the AC voltage slightly non-Gaussian. They argue that the method remains a widely accepted practical estimator when large sample counts are available, and the close agreement between experimental and theoretical BER trends supports that claim, while direct bit-by-bit error counting is deferred to future work.

The broader significance of the study lies in what it implies for the design of future optical wireless networks. Sixth-generation systems envision connectivity not only across massive terrestrial and underwater sensor fleets but also for unmanned aerial vehicles, high-altitude platforms, and satellites, all competing for scarce radio-frequency spectrum. Free-space optics offers fiber-like data rates and immunity to RF interference, and SLIPT extends it into a genuine data-plus-power delivery system for energy-constrained nodes. Until now, engineers designing such systems had only simulation results to guide them, and those simulations uniformly treated turbulence as a pure impairment. The new experimental evidence shows that this framing is incomplete. A system optimized purely for communication reliability would suppress turbulence effects wherever possible, yet the same fluctuations that corrupt the data can be exploited to boost energy delivery. The authors conclude that SLIPT-enabled FSO systems demand joint optimization of communication and energy objectives rather than conventional communication-centric design, and they point toward adaptive transmission strategies that dynamically balance reliability against harvested power as channel conditions change. While the 77-centimeter laboratory path is far shorter than any real deployment, the team notes that scintillation statistics over longer links obey the same underlying physics, so the observed trade-off is expected to persist. If the finding holds at scale, the turbulent air that once seemed destined to ruin laser links may instead become a resource to be managed, turning an old adversary of free-space optics into an unexpected ally for the power-hungry devices of the 6G era.

Subject of Research: Experimental evaluation of simultaneous lightwave information and power transfer over turbulent free-space optical links

Article Title: Laboratory evaluation of simultaneous lightwave information and power transfer in turbulent FSO environments

Article References: Le, H. T., Seifi, E., Nguyen, T. V., Pham, H. T., Dang, N. T., & LoPresti, P. (2026). Laboratory evaluation of simultaneous lightwave information and power transfer in turbulent FSO environments. Results in Optics, Article 101182. https://doi.org/10.1016/j.rio.2026.101182

Image Credits: AI Generated

DOI: 10.1016/j.rio.2026.101182

Keywords: free-space optics, SLIPT, atmospheric turbulence, wireless power transfer, 6G networks, bit-error rate, scintillation, energy harvesting, optical communications, log-normal fading, photodetector, laboratory experiment