FSO optical power adaptive compensation based on the position-sensitive detector and variable optical attenuators

In free-space laser communication, the detection power of the beacon light gradually attenuates as the communication distance increases and due to factors such as atmospheric turbulence and aerosols, which subsequently leads to positioning errors in the position-sensitive detector (PSD). In addition, when the communication distance is too short or the background light is excessively strong, the detector may experience power saturation. To address these issues, this paper proposes an adaptive optical power compensation method for PSD based on a variable optical attenuator (VOA). This method first establishes low-speed service communication on the bidirectional beacon link by applying spread-spectrum scrambling modulation to the beacon light. Then, based on real-time power feedback from the beacon link, it drives the VOA to dynamically adjust the beacon transmission power, thereby achieving closed-loop control of the beacon detection energy. Experimental results demonstrate that the input power dynamic range of the detection system is increased by more than 30 dB after introducing the VOA. The overall response delay of the proposed power compensation system is less than 300 µs. For an input sinusoidal power disturbance (amplitude: 3 dB, frequency: 10 Hz), the output power standard deviation (σ) can be reduced to 0.042 dB after suppression.