Accurate and Noise-Robust Mode Decomposition by Analyzing the Intensity Distribution of a Few-Mode Ring Core Fiber

Mode decomposition is a fundamental issue in applications that exploit few-mode fibers. With a prior knowledge of eigenmode field distribution, the amplitudes and phases of each spatial mode can be recovered. In this article, we propose a simple and accurate Fourier-transform-assisted mode decomposition method by only analyzing the intensity distribution of a few-mode fiber output. Numerical demonstration and experimental verification are executed in a few-mode ring core fiber supporting four mode groups. Simulation results of 1000 random samples show the proposed method's superiority in accuracy and noise immunity. The correlation of preset and reconstructed intensity distributions is as high as 0.9999 in the noiseless condition. The amplitudes of fiber modes can still be recovered when the signal-to-noise ratio is as low as 5 dB. In the experiment, the average correlation between the measured and reconstructed intensity distributions for 300 randomly captured pictures is about 0.9906.