MI-SI Based Distributed Optical Fiber Sensor for No-Blind Zone Location and Pattern Recognition

We designed a distributed fiber optic sensor based on a hybrid Michelson-Sagnac interferometer to overcome the defect that the conventional hybrid structure cannot locate when the disturbance position is close to the midpoint of the Sagnac ring. The sensor has excellent and flat frequency response for no-blind zone location. With the demodulation algorithm based on 3 × 3 optical coupler and simple mathematical operations, we can get two phase signals with time difference for location and pattern recognition. The phase signals were converted to two-dimensional images by Gramian Angular Field. Tagging images to create a dataset and feeding dataset into a convolutional neural network to achieve pattern recognition. After experiments, the frequency response capability of the structure was verified, and it was able to achieve location within 0-20 km with location errors of $ \pm $ 42 m. In a six-category pattern recognition, the testing set accuracy was 97.83%.