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Ultralow‐Noise Single‐Frequency Fiber Laser and Application in High‐Resolution Fiber‐Optic Dynamic Strain Sensing

A 1.5 μm ultralow‐noise single‐frequency fiber laser (SFFL) is realized based on a delay fiber phase‐locked method and the nonlinear amplification effect of a semiconductor optical amplifier (SOA). Via feedback locking of the phase jitter signal, the phase noise achieves the minimum value of −160 dB rad Hz−1/2 m−1 with a maximum reduction of 50 dB. Meanwhile, SOA reduces the intensity noise by a maximum of 65 dB, making it near the shot‐noise limit for frequencies above 40 kHz. To demonstrate this state‐of‐art SFFL with ultralow‐noise property, a high‐resolution fiber‐optic dynamic strain sensing based on a fiber‐based Michelson interferometer (FMI) is performed. As a result, the strain resolution reaches 26 fε Hz−1/2 in the 30–200 Hz band, which is improved by almost three orders of magnitude than that realized by a free‐running SFFL. To the best of the knowledge, this is the first time to achieve such a high‐resolution fiber‐optic dynamic strain sensor in the low‐frequency range utilizing the FMI system. This high‐resolution fiber‐optic strain sensing has promising applications in geophysics and biophotonics. Moreover, this ultralow‐noise SFFL is competitive for sophisticated applications, such as precise absolute distance measurement, quantum key distribution, and generating squeezed light.