A method for measuring laser focal spot distribution based on AFC scanning and a single PD

Accurate measurement of laser focal spots holds significant importance in fields such as laser communication, beam control, and target alignment. Traditional spot measurement methods often rely on CCD or CMOS image sensors to capture two-dimensional light intensity distributions. However, such systems typically require complex beam-splitting and imaging lens assemblies, which not only increase optical complexity but also limit real-time performance and environmental adaptability. To address these limitations, this paper proposes a method for measuring laser focal spot distributions based on an adaptive fiber coupler (AFC) for scanning and a single photodetector (PD) for detection. This approach utilizes electrically controlled AFC to achieve precise two-dimensional deflection of the laser focus in space, enabling point-by-point sampling of the target area. The light intensity signals from each sampling point are captured by a highly sensitive PD, ultimately reconstructing a two-dimensional light intensity distribution image of the spot. The experimental system was constructed using a laser source with a wavelength of 1550 nm, with adjustable scanning step size and resolution. During experiments, the PD demonstrated excellent signal-to-noise ratio even under weak signal conditions, ensuring high-quality spot image measurement. Key parameters such as the centroid position and diameter of the spot were further extracted from the reconstructed images. Experimental results indicate that this method not only offers advantages such as simple structure, high sensitivity, and ease of integration but also significantly reduces system complexity and cost. This technology provides effective support for the integrated and miniaturized design of laser systems and lays the foundation for subsequent spatial light field reconstruction in multi-aperture phased array systems, demonstrating promising application prospects.