Brillouin Fiber Laser Sensors

A single longitudinal mode (SLM) Brillouin fiber laser (BFL) with cascaded ring (CR) Fabry–Pérot resonator, a SLM triple ring (TR) BFL with a saturable absorber ring (SAR) resonator and a stable multiwavelength (MW) SLM dual ring BFL (MW-SLM-DRBFL) are proposed and demonstrated. By optimizing the CR length of the single-mode fiber cavity at 100 m (or 50 m) and 10 m, stable SLM operation is obtained with 0.41 kHz (or 3.23 kHz). TR-BFL with approximately 65-Hz linewidth and 185 linewidth-reduction ratio is composed of a 1-km-long single-mode fiber (SMF) ring, a 100-m-long SMF ring, and an SAR with 8-m-long unpumped Erbium-doped fiber (UP-EDF), respectively. 7 stable SLM lasing wavelengths with DR configuration of 100 and 10 m length SMF are obtained with 0.084 nm wavelength spacing and 15 dB average optical signal-to-noise ratio (OSNR) through the cascaded stimulated Brillouin scattering (cSBS) and four-wave mixing (FWM). A MW SLM Brillouin–Erbium fiber laser (BEFL) sensor with ultrahigh resolution is proposed and demonstrated and Iezzi et al. proposed and investigated experimentally a distributed higher order Stokes SBS temperature fiber sensor. The one short common cavity of MW-SLM-BEFL with 50 m of SMF as the fiber under test (FUT) and 100 m of SMF as the reference realize 3.104 MHz/°C sensitivity and approximately 10⁻⁶ °C ultrahigh resolution in the short term of the third-order Stokes wavelength. While maintaining a fairly normal spatial resolution over a few kilometers of sensing length using time gating technology, sensitivity is increased by several folds to over 4 MHz/°C.