Xiaoyang Hu

Performance analysis of slope-assisted dynamic BOTDA based on Brillouin gain or phase-shift in optical fibers

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.

Experimental observation of the competition between stimulated Brillouin scattering, modulation instability and stimulated Raman scattering in long single mode fiber

The complicated competition relationships between stimulated Brillouin scattering (SBS), modulation instability (MI) and stimulated Raman scattering (SRS) are observed, by injecting rectangular optical pulses with duration of 200 ns into 50 km single mode fiber. Under certain conditions, SBS suppresses MI by converting the transmission power to the backscattering power. MI also can suppress SBS by broadening the spectrum of the transmission light and decreasing the Brillouin gain. When SRS occurs, MI and SBS are suppressed simultaneously because a large amount of transmission power is consumed by converting to the Raman Stokes light.

Impact of dither-based Electro-Optic Modulator bias control on distributed Brillouin sensing system

In most distributed Brillouin sensing systems, it is crucial to keep the long-term stability of the electro-optic modulator (EOM) operating point. The dither-tone based bias control methods are widely adopted in this kind of systems for its robustness and reliability, but the low frequency dither tone (a few kilohertz) added into the dc bias port of the EOM may have a detrimental impact on the sensing performance of the Brillouin sensing system. Experimental results show that the dither frequency should not be set around quarter of the pulse repetition rate or its multiples, and the employed dither amplitude should be in the range of 0.003Vπ to 0.015Vπ (Vπ is the RF half-wave voltage of the EOM), in order to overcome the limitation of dither tone based bias control techniques in BOTDA systems. These results will provide guidelines to improve the performance of the Brillouin sensing systems using dither-based EOM bias control method.

The effect of modulation instability on the interferometric fiber sensing systems

An experiment is presented to study the effect of modulation instability (MI) on the interferometric fiber sensing system. It is found that MI induces serious phase noise in the system. The MI suppression methods in the interferometric fiber sensing systems are discussed in the paper.

Competition between modulation instability and four-wave mixing in the dispersion-shifted fiber

We demonstrate the modulation instability (MI) and four-wave mixing (FWM) spectra at the input of a pump accompanied with a seed in the dispersion-shifted fiber. By numerically solving the nonlinear Schrodinger equation, it is confirmed that there are two regions as the absolute value of the second-order fiber dispersion decreases, where MI and FWM dominates, respectively. We attribute this phenomenon to the competition between MI and FWM. Furthermore, for the FWM-dominating region, it can be divided into two subregions according to the different power levels of MI, which mainly results from the power transfer between MI and dispersive wave. Our results may lead to a further understanding of nonlinear interactions in optical fiber.

Theoretical and experimental study of suppressing stimulated Brillouin scattering and phase noise in interferometric fiber sensing systems with phase modulation

The effect of phase modulation on the phase noise in remote interferometric fiber sensing systems is analyzed in both theory and experiment. A matching condition between the modulation frequency and optical delay difference is derived to choose the matching modulation frequency. The matching modulation frequency for an interferometer with 5 m optical-path difference is 60 MHz and its integer harmonic frequencies. By matching the condition, the phase modulation method can suppress the stimulated Brillouin scattering in an interferometric fiber sensing system effectively without bringing excess phase noise, which is verified by the experiment. The results indicate that the maximum input power of the system can be increased effectively, which has great potential in the design of remote interferometric fiber-sensing systems.