We adopt and establish a type of distributed optical fiber sensor (DOFS) system structure with good qualities. Based on the phase-sensitive optical time-domain reflectometry (φ-OTDR) sensing system, we study the aliasing noise in the dual-pulse heterodyne system. Through practical experiment using this setup and parameter setting, we realize a relatively good background noise level as -73.6595 dB at 1 kHz. Through theoretical analysis, we find that the influence of the pulse repetition rate introduces the aliasing noise to the system which follows a linear relation in theory that the phase noise will increase 3 dB when repetition rate goes half. Furthermore, we obtain the experimental result that the changing value is 2.45 dB close to the theoretical value which can verify the reliability of the conclusion about the aliasing noise in the dual-pulse phase-sensitive φ-OTDR system.
Phase noise is an important parameter of the phase-sensitive optical time-domain reflectometry (φ-OTDR) which determines the minimum detectable signal. In this paper, we study the effect of MI on the phase noise in the long-haul φ-OTDR system. The results show that the phase noise increases dramatically with the occurrence of MI, especially at the far end of the sensing fiber. The distribution of the phase noise in the fiber is related to the Fermi-Pasta-Ulam recurrence.
A numerical simulation model for investigating modulation instability in a Raman-assisted fiber-optics system is presented and used. The modulation instability (MI) spectrum and its threshold are numerically analyzed based on this theoretical model. The different MI behaviors between forward and backward Raman pumping are studied in detail, respectively. The MI threshold in the case of forward Raman pumping is lower than that in the case of backward Raman pumping. Experiments are conducted based on the theoretical analysis, and the results agree well with the numerical calculations.
KEYWORDS: Sensing systems, Control systems, Electrooptic modulators, Signal to noise ratio, Modulation, Signal detection, Modulators, Signal processing, Continuous wave operation
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.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.