Frequency-stabilized Brillouin random fiber laser enabled by self-inscribed transient population grating.

A frequency-stabilized Brillouin random fiber laser (BRFL) realized by a self-inscribed transient population grating (TPG) is proposed and demonstrated for the first time, to the best of our knowledge. The TPG is formed via the redistribution of the population in erbium-doped fibers (EDFs) by bidirectionally injected phonon-controlled random laser beams. Long-lifetime metastable ion states in EDFs basically prolonged the time dynamics of a stimulated Brillouin scattering (SBS) laser up to milliseconds. Consequently, significant random modes are suppressed with low relative intensity noise, owing to reduced mode hopping in a Stokes random laser, hence one dominating lasing mode at milliseconds of lifetime is established from the competition of numerous random modes, which is proved theoretically and experimentally via TPG.

Underwater acoustic source localization based on phase-sensitive optical time domain reflectometry.

This paper demonstrates an underwater localization system based on an improved phase-sensitive optical time domain reflectometry (φ-OTDR). To localize the underwater acoustic source, 3D-printed materials with relatively high Poisson's ratio and low elastic modulus are wrapped by single-mode optical fibers to serve as an L-shaped planar sensing array, yielding a high-fidelity retrieval of acoustic wave signals. Based on the time difference of arrival (TDOA) algorithm, the time delay of signals detected by multiple sensing elements is used to locate the underwater acoustic source. Consequently, the three-dimensional localization feasibility of the proposed system is experimentally verified, showing a measurement error of about 2% in the localization range. It indicates that the proposed scheme is of great potential for applications in the underwater environment, such as trajectory tracking, oil/gas pipeline security monitoring and coastal defense.