Brillouin distributed optical fiber sensing system based on spontaneous Brillouin intensity measurement may measure temperature in the optical fiber, due to the dependence of spontaneous Brillouin scattering intensity on temperature. In this paper, a 4.25km distributed optical fiber temperature sensing experiment system was demonstrated. Using the experiment system, we obtained the traces of spontaneous Brillouin scattering intensity as the sensing fiber was not heated and heated respectively. By normalizing the trace of the fiber being heated to the trace of the fiber not being heated, the intensity change of spontaneous Brillouin scattering corresponding to temperature along the fiber has been obtained. And there was a good
agree between the result and the heated section of the fiber.
Based on the temperature dependence of the intensity of Brillouin scattering in optical fiber, a distributed optical fiber temperature sensing experimental system with Brillouin OTDR configuration was presented. In this system, a narrow line width LD was used as a light source. The output of LD was modulated into light pulses by an AOM. After amplified by an EDFA the light pulses were coupled into the test fiber to generate backscattering signal. A double-pass Mach-Zehnder interferometer was used to separate the spontaneous Brillouin scattering from the Rayleigh scattering. The temperature sensing experiments were carried out on two different length of fibers which were 4.25 km and 22 km long, respectively. The intensity changes in the Brillouin scattering signals due to temperature variation on both of the fibers were measured.
This paper demonstrates the recent achievements in the field of Brillouin based distributed optical fiber temperature sensing. When a dispersion-shifted fiber was subjected to a temperature cycle between 20 and 820 °C, the Brillouin shift exhibited an undesired hysteresis with a maximum frequency discrepancy of larger than 48 MHz between heating and cooling processes. After the fiber was annealed for 9 h at 850 °C, however, the hysteresis almost disappeared for repeated temperature cycles in the ranges of 20-820 °C and of 500-800 °C with deviations of the measurements from the best-fit curve of less than ±12.5MHz. The temperature dependence of Brillouin shift in the range of 20-820 °C in the annealed fiber was well expressed by a second order function of temperature. A sensing scheme that utilizes both output signals of the fiber Mach-Zehnder interferometer used as an optical frequency discriminator has been proposed. The scheme that has the advantages of less system adjustment and fast measurement, combined with a suitably annealed fiber, offers a reliable means for the Brillouin shift-based distributed sensing over the wide temperature range.
A distributed temperature sensing system based on optical fiber Brillouin scattering is presented in this paper. A distributed temperature sensing measurement was achieved with a BOTDR system. The light source was a narrow linewidth LD. The light from the LD was modulated by an AOM and amplified by a high gain EDFA to generate high power light pulses. So a high intensity spontaneous Brillouin scattering can be achieved. A double-pass all-fiber Mach-Zehnder interferometer was designed and used to separate Brillouin scattering from Rayleigh scattering.
The principle of all fiber Mach-Zehnder interferometer as an optical filter was investigated in this paper. All fiber Mach-Zehnder interferometers with single-pass and double-pass configuration were manufactured and used in the measurement of spontaneous Brillouin scattering. The separation of backscattered spontaneous Brillouin from Rayleigh with low losses was achieved effectively. With the Mach-Zehnder interferometer, a direct optical detection method was used in Brillouin OTDR, by which a new detection method for distributed sensing system based on spontaneous Brillouin scattering was proposed.
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.