This paper reports a vector Brillouin optical time-domain analyzer based on heterodyne detection and IQ demodulation algorithm. This approach employs an acoustooptic frequency shifter to generate a single-frequency reference, which simplifies the probe spectrum and directly features the Brillouin gain and phase shift compared with the phase modulation. In addition, the proposed IQ demodulation algorithm makes signal processing easy to implement and allows fast and real-time demodulation. A proof-of-concept experiment is carried out in an $1.6-km standard single-mode fiber consisting of two different sections of fibers. Both the Brillouin gain and phase-shift spectrograms are successfully measured with an $2-m spatial resolution. The temperature dependence values of the Brillouin gain and phase-shift spectra are also measured, and the temperature dependence values of the Brillouin frequency shift show excellent linearity larger than 0.999 and almost identical slopes of 1.166 and 1.159 MHz/ C, respectively.

This paper analyzes the performance of the slope-assisted dynamic BOTDA based on Brillouin gain or phase-shift in an experiment. Dynamic strains with frequency of 60 Hz are successfully measured with an effective sensing rate of 1 kHz over a 46 m sensing fiber in both schemes. The dynamic ranges of these two schemes are measured to be about 47 MHz (940 ), through dynamic strain measurements while linearly sweeping the work point. The optimum work point for Brillouin gain is theoretically and experimentally proved to be , not as commonly known, where corresponds to the Brillouin frequency shift and is the Brillouin linewidth. The distortion factors are also measured to stay in a quite low level in the dynamic range. These results will provide guidelines for practical dynamic strain measurements and to further improve the performance of the slope-assisted BOTDA systems.

We demonstrate a low-noise Brillouin/erbium fiber laser (BEFL), which uses only 1.5 m polarization-maintaining erbium-doped fiber as both the Brillouin and erbium gain media. This BEFL presents a phase noise of -125 dB/Hz(1/2) at 1 kHz frequency, at 2 mW Brillouin pump (~3 MHz linewidth) power and 200 mW 980 nm pump power. The polarization extinction ratio of the laser output light is 31 dB. Stable (~2 h) single-mode operation is observed. This BEFL presents potential applications in distributed Brillouin fiber sensors, inteferometric fiber sensors, and optical communications.

A fast-tuning Brillouin/erbium fiber laser (BEFL) is investigated on its mechanism and characteristics in detail, in which a 4 m erbium-doped fiber (EDF) as both the Brillouin gain and linear gain media is coiled on a piezoelectric transducer (PZT) for laser frequency modulations. We demonstrate the fast-tuning mechanism theoretically and experimentally that only the lasing cavity mode is modulated, instead of the previous presumption that the Brillouin frequency shift of the EDF is modulated synchronously with the lasing mode. And the maximum tuning range (~60 MHz) is limited by the bandwidth of the Brillouin gain spectrum. The frequency tuning amplitude is direct proportional to the voltage on the PZT. The tuning rates reach up to 48 kHz. The BEFL keeps high-coherence property under fast frequency modulation. Its phase noise remains about -124 dB/Hz1/2 (normalized to 1 m optical path difference) at 1 kHz under 32 kHz modulations. This fast-tuning BEFL presents a wide range of applications in fiber sensors, optical fiber communications, and so forth.

We propose and demonstrate a long-range Brillouin optical time-domain analysis (BOTDA) sensor based on the pre-pumped Simplex coding technique. This approach combines Simplex coding with the pulse pre-pump technique, which takes full advantage of the signal-to-noise ratio enhancement provided by optical pulse coding and achieves meter-scale spatial resolution with an unbroadened Brillouin gain spectrum by the use of pre-pumped short pump pulse. Compared to the widely used differential pulse-width pair technique, a comparable performance can be realized while the measurement time is reduced by half. The theoretical analysis of pre-pumped Simplex coding applied to BOTDA systems is presented and a proof-of-concept experiment is carried out along a ∼51 km single-mode fiber composed of two fiber segments with slightly different Brillouin frequency shift values. With the proposed technique, Brillouin frequency shifts of the two different fiber sections at the end of the sensing fiber are clearly distinguished, and the obtained spatial resolution and temperature/strain accuracy along the sensing fiber are respectively 1 m and . According to the experimental results, we believe that the BOTDA employing pre-pumped Simplex coding is able to realize extra-long distance sensing without Raman amplification, while keeping a high spatial resolution and measurement accuracy.