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Optics Express

Optics Express

  • Editor: Michael Duncan
  • Vol. 12, Iss. 15 — Jul. 26, 2004
  • pp: 3515–3520
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Raman amplifier-based long-distance remote, strain and temperature sensing system using an erbium-doped fiber and a fiber Bragg grating

Ju Han Lee, You Min Chang, Young-Geun Han, Haeyang Chung, Sang Hyuck Kim, and Sang Bae Lee  »View Author Affiliations


Optics Express, Vol. 12, Issue 15, pp. 3515-3520 (2004)
http://dx.doi.org/10.1364/OPEX.12.003515


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Abstract

We demonstrate a novel, Raman amplifier-based long-distance sensing system for simultaneous measurement of temperature and strain using a combined sensing probe of an erbium-doped fiber (EDF) and a fiber Bragg grating. By recycling residual Raman pump power for generation of amplified spontaneous emission in the EDF after distributed Raman amplification in the transmission fiber, the overall system configuration was significantly simplified without requiring any additional broadband light source. We obtain a remote sensing operation of simultaneous temperature and strain measurement at a location of 50 km. High quality of sensing signals with a ~11 dB signal-to-noise ratio (SNR) is readily achieved even after the 50 km transmission with distributed Raman amplification.

© 2004 Optical Society of America

1. Introduction

In this paper, we demonstrate a novel and simple, Raman amplifier-based long-distance sensing system for simultaneous measurement of temperature and strain using a combined sensing probe of an erbium doped fiber and a fiber Bragg grating. Our proposed sensing system has only one pump source for distributed Raman amplification in the transmission fiber without any additional broadband light source and the residual pump power after the transmission fiber is recycled for generation of broadband amplified spontaneous emission (ASE) in the erbium-doped fiber. Using the proposed scheme, we obtain a remote sensing operation of simultaneous temperature and strain measurement at a location of 50 km and deliver the sensing signals through the transmission fiber with distributed Raman amplification. High quality of sensing signals with a ~11 dB SNR is readily achieved even after the 50 km transmission. The temperature sensitivity is measured to be 8.19 pm/°C (wavelength variation) and -0.04 dB/°C (optical power variation), and the strain sensitivity is 1.1 pm/µε (wavelength variation) without output signal power variation.

2. Experiment and results

Figure 1 shows the experimental setup for our proposed long-distance remote sensing system. The Raman pump source consists of two laser diodes operating at 1455 and 1465 nm, respectively. By combining the two pump wavelengths with a passive pump combiner a total pump power of up to 600 mW could be launched into a 50 km long standard single mode fiber (SMF) with a ~0.2 dB/km attenuation via a 1550/1460 nm WDM coupler. At first we measured an on-off Raman gain profile of the SMF using a tunable laser source and the measured Raman gain profile is shown in Fig. 2(a). This level of pump was able to provide an on-off gain of ~12 dB at a 1555 nm band within the SMF that was sufficient to compensate for the total cavity loss including background fiber loss. Then, the residual pump power after the SMF which was measured to be ~23 mW, was launched into a 10 m long EDF via two 1550/1460 nm WDM couplers. The residual Raman pump was reused as a pump source for the broadband ASE generation. An isolator was inserted between the two WDM couplers to suppress undesirable lasing within the sensing signal path. The sensing probe consisted of an EDF and a FBG which were connected directly by fusion splicing. The principle of simultaneous measurement of temperature and strain with a cascading EDF and FBG is well known and the full details can be found in Ref. [8

8. J. Jung, H. Nam, J. H. Lee, N. Park, and B. Lee, “Simultaneous measurement of strain and temperature using a single fiber Bragg grating and an erbium-doped fiber amplifier,” Appl. Opt. 38, 2749–2751, (1999). [CrossRef]

]. The peak absorption coefficient of the EDF at 1530 nm was 6 dB/m. We used the UV beam scanning method with a phase mask to fabricate the FBG in a boron (B)-Germanium (Ge) codoped silica based photosensitive fiber. The center wavelengths of the FBG with a 0.2 nm spectral width was 1555.7 and its measured reflectivity was ~99.6 %. Figure 2(b) shows the optical spectrum of the generated ASE in the EDF after passing through the FBG. It is clearly evident that we could obtain sufficient ASE power for required sensing operation with the residual pump power.

Fig. 1. Experimental setup for our Raman amplifier-based long-distance remote sensor system using a sensing probe of an EDF and a FBG.
Fig. 2. (a) Measured Raman gain profile for the 50 km single mode fiber used in this experiment with the two Raman pumps. (b) Measured optical spectrum of the generated ASE in the EDF with the residual pump power after passing through the FBG.

First we performed temperature sensitivity measurement by placing the sensing probe composed of an EDF and a FBG into a temperature-heating oven. Note that the temperature-heating oven used in this experiment has a limited temperature tuning range between 30 °C and 100 °C. We measured center wavelength shift and output peak power variation of the sensing signal while changing the oven temperature in the range from 30 to 100 °C. Figure 3 shows the output optical spectrum of the sensing signal when the temperature was increased. Linear shift of the center wavelength was clearly observed with temperature change while the output peak power also linearly decreased correspondingly. It is clearly evident that high quality of sensing signal with a signal-to-noise ratio (SNR) of ~11 dB was obtained despite such a long distance transmission of 50 km with distributed Raman amplification. The measured data for center wavelength and output peak power as a function of applied temperature are summarized in Figs. 4(a) and (b), respectively. After fitting the measured data with a linear function, the temperature sensitivity in terms of wavelength variation was estimated to be 8.19 pm/°C with an estimated root mean square error (RMSE) of 11.1 pm, and output peak power variation was also estimated to be -0.04 dB/°C with a RMSE of 0.028 dB. The high RMSE value can be attributed to the poor stability of the temperature-heating oven without a proportional, integral, and derivative (PID) controller. The lower temperature sensitivity can be attributed to the B-Ge codoped photosensitive fiber used for our FBG fabrication. It is well known that the opposite temperature dependence between B ions and Ge ions makes B-Ge codoped fiber less sensitive to temperature change than Ge only doped fiber.

Fig. 3. Optical spectrum of the output sensing signal after the 50-km transmission when the temperature was increased
Fig. 4. (a) Laser center wavelength and (b) output peak power as a function of applied temperature.

Fig. 5. (a) Optical spectrum of the output sensing signal after the 50-km transmission when the applied tensile strain was increased. (b) Sensing signal center wavelength as a function of applied tensile strain.

Using the measured temperature and strain sensitivities, a sensitivity matrix for the simultaneous measurement of temperature and strain can be derived as follows.

(ΔTΔε)=(8.19pm°C1.1pmμε0.04dB°C0)1(ΔλΔP)=K1(ΔλΔP)
(1)

where ΔT and Δε are the changes in temperature and strain, respectively. Δλ and ΔP represent the changes in the center wavelength and output peak power, each. By making the inverse sensitivity matrix (K -1) and multiplying it to the vector with the measured Δλ and ΔP of the sensing signal, we can thus achieve the simultaneous measurement of temperature and strain. The measurement resolutions of our system for temperature and strain were estimated to be 0.7 °C and 8.64 µε, respectively using the RMSE values of output peak power and wavelength variation.

3. Discussion and conclusion

We have demonstrated a novel, Raman amplifier-based long-distance sensing system for the simultaneous measurement of temperature and strain using a combined sensing probe of an erbium doped fiber and a fiber Bragg grating [8

8. J. Jung, H. Nam, J. H. Lee, N. Park, and B. Lee, “Simultaneous measurement of strain and temperature using a single fiber Bragg grating and an erbium-doped fiber amplifier,” Appl. Opt. 38, 2749–2751, (1999). [CrossRef]

]. By recycling the residual Raman pump power for generation of ASE in the EDF after distributed Raman amplification in the transmission fiber the overall system configuration was significantly simplified without requiring any additional broadband light source. Using the proposed sensing scheme, we achieved a remote sensing operation of simultaneous temperature and strain measurement at a location of 50 km and delivered the sensing signals through the transmission fiber with distributed Raman amplification. The non-flat gain profile of the Raman amplifier and the EDFA in our system could degrade our sensing signal interrogation sensitivities in some degree. However, the incorporation of a gain-flattening filter would be a solution for the problem. Increase of Raman pump power would lead to further increase of both the sensing signal SNR and the transmission distance.

References and links

1.

A. D. Kersey, M. A. Davis, H. J. Patrick, M. LeBlanc, K. P. Koo, C. G. Askins, M. A. Putnam, and E. J. Friebele, “Fiber grating sensors,” J. Lightwave Technol. 15, 1442–1463 (1997). [CrossRef]

2.

Y. G. Han, S. B. Lee, C. S. Kim, Jin U. Kang, U. C. Paek, and Y. Chung, “Simultaneous measurement of temperature and strain using dual long-period fiber gratings with controlled temperature and strain sensitivity,” Opt. Express 11, 476–481 (2003). http://www.opticsexpress.org/abstract.cfm?URI=OPEX-11-5-476 [CrossRef] [PubMed]

3.

X. Shu, Y. L., D. Zhao, B. Gwandu, F. Floreani, L. Zhang, and Ian Bennion, “Dependence of temperature and strain coefficients on fiber grating type and its application to simultaneous temperature and strain measurement,” Opt. Lett. 27, 701–703 (2002). [CrossRef]

4.

L. Bjerkan, “Application of fiber-optic Bragg grating sensors in monitoring environmental loads of overhead power transmission lines,” App. Opt. 39, 554–560 (2000). [CrossRef]

5.

Y. Nakajima, Y. Shindo, and T. Yoshikawa, “Novel concept as long-distance transmission FBG sensor system using distributed Raman amplification,” in Proc. 16th International Conference on Optical Fiber Sensors (Nara Japan, October2003), Th1–4.

6.

P.-C. Peng, H.-Y Tseng, and Sien Chi, “Long-distance FBG sensor system using a linear-cavity fiber Raman laser scheme,” IEEE Photon. Technol. Lett. 16, 575–577 (2004). [CrossRef]

7.

J. H. Lee, J. Kim, Y. G. Han, S. H. Kim, and S. B. Lee, “Investigation of Raman fiber laser temperature probe incorporating fiber Bragg gratings for long-distance remote sensing Applications,” Opt. Express 12, 1747–1752 (2004). http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-8-1747 [CrossRef] [PubMed]

8.

J. Jung, H. Nam, J. H. Lee, N. Park, and B. Lee, “Simultaneous measurement of strain and temperature using a single fiber Bragg grating and an erbium-doped fiber amplifier,” Appl. Opt. 38, 2749–2751, (1999). [CrossRef]

OCIS Codes
(060.2370) Fiber optics and optical communications : Fiber optics sensors
(060.2410) Fiber optics and optical communications : Fibers, erbium
(190.5650) Nonlinear optics : Raman effect
(230.1480) Optical devices : Bragg reflectors

ToC Category:
Research Papers

History
Original Manuscript: May 27, 2004
Revised Manuscript: July 5, 2004
Published: July 26, 2004

Citation
Ju Han Lee, You Chang, Young-Geun Han, Haeyang Chung, Sang Kim, and Sang Lee, "Raman amplifier-based long-distance remote, strain and temperature sensing system using an erbium-doped fiber and a fiber Bragg grating," Opt. Express 12, 3515-3520 (2004)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-12-15-3515


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References

  1. A. D. Kersey, M. A. Davis, H. J. Patrick, M. LeBlanc, K. P. Koo, C. G. Askins, M. A. Putnam, and E. J. Friebele, �??Fiber grating sensors,�?? J. Lightwave Technol. 15, 1442-1463 (1997). [CrossRef]
  2. Y. G. Han, S. B. Lee, C. S. Kim, Jin U. Kang, U. C. Paek, and Y. Chung, �??Simultaneous measurement of temperature and strain using dual long-period fiber gratings with controlled temperature and strain sensitivity,�?? Opt. Express 11, 476- 481 (2003). <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-11-5-476">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-11-5-476</a>. [CrossRef] [PubMed]
  3. X. Shu, Y. L., D. Zhao, B. Gwandu, F. Floreani, L. Zhang, and Ian Bennion, �??Dependence of temperature and strain coefficients on fiber grating type and its application to simultaneous temperature and strain measurement,�?? Opt. Lett. 27, 701-703 (2002). [CrossRef]
  4. L. Bjerkan, �??Application of fiber-optic Bragg grating sensors in monitoring environmental loads of overhead power transmission lines,�?? App. Opt. 39, 554-560 (2000). [CrossRef]
  5. Y. Nakajima, Y. Shindo, and T. Yoshikawa, �??Novel concept as long-distance transmission FBG sensor system using distributed Raman amplification,�?? in Proc. 16th International Conference on Optical Fiber Sensors (Nara Japan, October 2003), Th1-4.
  6. P.-C. Peng, H.-Y Tseng, and Sien Chi, �??Long-distance FBG sensor system using a linear-cavity fiber Raman laser scheme,�?? IEEE Photon. Technol. Lett. 16, 575-577 (2004). [CrossRef]
  7. . J. H. Lee, J. Kim, Y. G. Han, S. H. Kim, and S. B. Lee, �??Investigation of Raman fiber laser temperature probe incorporating fiber Bragg gratings for long-distance remote sensing Applications,�?? Opt. Express 12, 1747-1752 (2004). <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-8-1747">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-8-1747<a/>. [CrossRef] [PubMed]
  8. J. Jung, H. Nam, J. H. Lee, N. Park, and B. Lee, �??Simultaneous measurement of strain and temperature using a single fiber Bragg grating and an erbium-doped fiber amplifier,�?? Appl. Opt. 38, 2749-2751, (1999). [CrossRef]

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