Fig. 1. (a) Schematic with a superimposed mode at the exit of the optical fiber and the corresponding far-field pattern that can be easily recorded by an imaging device (e.g., CCD) and analyzed by CNN. (b) Mode profiles including the electric intensity profiles and phase profiles of the x-direction field component for the modes of interest in this work.

Fig. 2. Diagram of our proposed CNN architecture to predict the OAM mode purity. The CNN architecture consists of eight layers with three convolutional layers (Conv1, convolutional layer 1; Pool1, pool layer 1; etc.) and five fully connected layers (FC1, fully connected layer 1; etc.).

Fig. 3. (a) Training progress of our proposed CNN-based prediction model. (b) Histogram of AE distribution of 1000 testing samples. Inset: histogram with AE larger than 0.01.

Fig. 4. Predicted OAM mode purities versus the labeled ones for both the training set and the testing set.

Fig. 5. Prediction accuracy as a function of the size of the testing set with the tolerance of 0.02.

Fig. 6. (a) Predicted OAM mode purities versus the labels for both the training set and the testing set when phase differences exist between different modes in the optical fiber. (b) Histogram of AE distribution of 10,000 testing samples. Inset: histogram with AE larger than 0.02.

Fig. 7. Interferograms of the fundamental modes with the high-order modes.

Fig. 8. Predicted OAM mode purities versus the labels for the testing set when no fundamental modes exist in the optical fiber.