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

Abstract

Recently, single-frequency fiber lasers (SFFLs), which have many advantages of all-fiber compact structure, good beam quality, narrow linewidth, and convenient thermal management, are of great interest for various applications, including optical communication, coherent beam combining, nonlinear frequency conversion, and optical fiber sensing. [1][2][3][4] Among them, as a critical branch of optical fiber sensing, fiber-optic strain sensing is widely used for dynamic deformation measurement, structural health monitoring, and underwater acoustic detection. [5][6][7][8] Particularly, for frontier research areas involving nanotechnology, biophotonics, seismology, and geophysics, [9][10][11][12] a high resolution (typically pε or sub-pε) is demanded of the strain sensor. With the development of photonics technologies and the gradual reduction of other noises, the noise characteristics of the single-frequency laser source have become the key factors limiting the increase of strain sensing resolution, especially for weak strain signals in the low-frequency range. [13][14][15][16] Consequently, the realization of an ultralow-noise singlefrequency laser source, to satisfy the increasing demand for high-resolution fiber-optic dynamic strain sensing, has become a matter of intense interest.The suppression of phase noise, especially in the lowfrequency range, is still technically challenging. As known, Pound-Drever-Hall (PDH) technology provides a reliable solution, and the error signal representing phase fluctuation is usually extracted through the ultrahigh-finesse Fabry-Pérot