Reference-free mode decomposition of few-mode fibers via coherent modulation imaging

A comprehensive understanding of fiber modes is critical for the practical application of few-mode fibers (FMFs) in areas such as telecommunications, high-power lasers, and optical imaging. This paper introduces a single-exposure, reference-free method for mode decomposition (MD) of FMFs using coherent modulation imaging (CMI). A key advantage of the proposed method is that it requires only one experimentally captured diffraction pattern to reconstruct the complex amplitude of the optical field and perform MD, thereby eliminating the need for multiple measurements, reference beams, or complex preprocessing. To ensure accurate coordinate alignment, the method employs a simulated annealing mode projection (SAMP) algorithm. The approach achieves robust and complete MD with high precision and computational efficiency, requiring less than 2 s per mode projection analysis. Experimental results demonstrate excellent agreement between the retrieved and synthesized optical fields, with intensity correlation coefficients exceeding 0.985 across various mode distributions. This novel technique, to the best of our knowledge, simplifies experimental setups while maintaining exceptional reliability, offering significant potential for industrial and practical applications of FMFs.