Free-space optical communication (FSOC) offers significant advantages in high bandwidth, low latency, electromagnetic interference resistance, and high confidentiality due to its excellent beam characteristics, making it well-suited for long-distance, large-capacity data transmission. However, optical signal propagation inevitably passes through the Earth’s atmosphere, which significantly influences the signal. In particular, the scintillation caused by atmospheric turbulence results in received power jitter and inter-symbol interference, leading to a degradation of the signal-to-noise ratio (SNR) and an increase in the bit error rate (BER), which limits the transmission efficiency, stability, and reliability of high-speed optical communication systems. Existing compensation methods often require additional communication feedback links, and for atmospheric turbulent channels with rapidly changing fading characteristics, compensation within the turbulence coherence time is challenging. Utilizing the channel reciprocity property to obtain real-time channel state information can substantially reduce delay, but the actual accuracy of turbulence fading compensation is still limited by device noise and nonlinear effects. In this paper, we propose a real-time scintillation suppression system for atmospheric optical transmission based on fuzzy adaptive control, establishing a correlation model between reciprocal channel state information and optical intensity scintillation. A turbulence scintillation adaptive suppression algorithm is proposed and deployed on an field programmable gate array (FPGA) platform to improve the pre-compensation of light intensity scintillation at the transmitter. To demonstrate the effectiveness of our approach, we build an experimental system for atmospheric optical transmission scintillation suppression and show that it suppresses amplitude jitter in received optical signals across various atmospheric turbulence environments. This represents a breakthrough in stable optical signal transmission technology.

A real-time optical intensity scintillation suppression model is established based on the bidirectional reciprocal channel by leveraging the relationship between channel state information and optical intensity scintillation. By adaptively controlling the transmitted optical power, pre-compensation for optical intensity scintillation at the transmitter is achieved. In this scenario, the optical terminals at both ends of the communication, Alice and Bob, interact with each other. The detector at Alice receives a beacon optical signal from Bob, which is affected by atmospheric turbulence. The system extracts transient turbulence decay characteristics from the received signal. Based on this, Alice generates an optical power compensation signal to adaptively adjust the transmit power, compensating for the turbulence fading the signal will experience in the turbulent channel. The accuracy and real-time performance of the compensation signal generation are crucial for effectively compensating turbulence fading. To address the challenges posed by photoelectric conversion device noise, as well as the nonlinear effects of optical power regulation devices such as optical attenuators and erbium-doped optical fiber amplifiers, we propose a transmit power adaptive control algorithm to ensure stable control of the devices during the duration of reciprocity. The algorithm is implemented on an FPGA, which enables powerful parallel data processing. During each operation cycle, the light intensity jitter signal is filtered and extracted. The optical power compensation value required for steady amplitude transmission control is calculated based on the turbulence decay signal and the feedback control signal. The fuzzy PID control algorithm then adjusts the control parameters according to the system state, calculating the optimal compensation signal for the next moment, thus achieving adaptive transmit power control.

To verify the suppression effect of turbulence perturbations, an amplitude jitter suppression experiment based on channel reciprocity is conducted (Fig. 5). The test is set up with bidirectional reciprocity between Alice and Bob, with acquisition cards at both ends sampling at 1 kHz to synchronously capture turbulence fading signals (Fig. 6). By calculating the correlation coefficient, the reciprocity of the communication link is maintained above 0.9. To assess the stability of signal amplitude transmission, the received light intensity before and after transmit power adaptive compensation is compared under conditions of maximum and minimum light intensity scintillation (Fig. 7). The results show that after compensation, the received light intensity stabilizes in a straight line, with only minimal jitter due to measurement equipment noise. The experiment, measuring optical signal amplitude jitter suppression over several hours with varying turbulence intensity from afternoon to night, compares the received signal scintillation index before and after compensation (Fig. 9). The results show that before compensation, the received signal power fluctuates between -22 dBm and -31 dBm. At maximum turbulence intensity during midday, the scintillation index reaches 0.6602, while at lower turbulence intensity during the night, the scintillation index drops to 0.0287. The depth of scintillation index compensation remains consistently above -16 dB, regardless of changes in turbulence intensity.

In this paper, we investigate a real-time method for suppressing free-space optical signal amplitude jitter caused by atmospheric turbulence. Based on bidirectional reciprocity, a real-time optical intensity scintillation suppression model is developed, utilizing the relationship between channel state information and optical intensity jitter. To meet the real-time requirement for turbulence fading compensation, we design a transmit power adaptive control algorithm, which is deployed on the FPGA platform to ensure that signal processing converges faster than the channel coherence time. The proposed transmit power adaptive system is verified through an outfield wireless laser transmission test under varying turbulence intensity. The experimental results demonstrate that the transmit power adaptive compensation significantly reduces the scintillation index of the received optical signal. Specifically, the scintillation index decreases from 0.6602 to 0.0127 under maximum turbulence intensity and from 0.0287 to 0.0002 under minimum turbulence intensity. In addition, the depth of scintillation index compensation remains consistently above -16 dB, effectively mitigating the amplitude jitter caused by turbulence and enabling stable transmission under varying turbulence conditions.