Abstract

A network for multiplexing fiber Bragg gratings (FBGs) and intensity-modulated fiber-optic sensors with no need to distinguish between the two kinds of sensor is proposed and experimentally demonstrated. Two FBG sensors and two intensity-modulated sensors are wavelength-division multiplexed; the electrical phase of the output signal is measured as a common parameter for both types of sensor. Furthermore, the intensity sensors become power referenced, and the FBG sensors are interrogated by a low-cost technique. Low cross talk is achieved by use of a tunable optical filter at the detector.

© 2003 Optical Society of America

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  1. A. Cobo García, J. Echevarría Cuenca, “Transduction techniques based on intensity modulation of light,” in Handbook of Fibre Optic Sensing Technology, J. M. López-Higuera, ed. (Wiley, New York, 2002), pp. 209–226.
  2. G. Murtaza, J. M. Senior, “Dual wavelength referencing of optical fiber sensors,” Opt. Commun. 120, 348–357 (1995).
    [CrossRef]
  3. R. I. MacDonald, R. Nychka, “A differential measurement technique for optical fibre sensors,” Electron. Lett. 27, 2194–2196 (1991).
    [CrossRef]
  4. S. T. Vohra, M. D. Todd, G. A. Johnson, C. C. Chang, B. A. Danver, “Fiber Bragg grating sensor system for civil structure monitoring applications and field tests,” in 13th International Conference on Optical Fiber Sensors, K. Hotate, B. Kim, eds., Proc. SPIE3746, 32–37 (1999).
  5. A. D. Kersey, “Optical fiber sensors for downwell monitoring applications in the oil & gas industry,” in 13th International Conference on Optical Fiber Sensors, K. Hotate, B. Kim, eds., Proc. SPIE3746, 326–331 (1999).
  6. L. A. Ferreira, P. Cavaleiro Dias, J. L. Santos, “Demodulation of two time-multiplexed fiber Bragg sensors using source spectral characteristics,” Pure Appl. Opt. 6, 717–726 (1997).
    [CrossRef]
  7. J. Jung, Y. W. Lee, B. Lee, “High-resolution interrogation technique for fiber Bragg grating strain sensor using long period grating pair and EDF,” in 14th International Conference on Optical Fiber Sensors, A. G. Mignani, ed., Proc. SPIE4185, 114–117 (2000).
  8. S. Abad, M. López-Amo, F. M. Araújo, L. A. Ferreira, J. L. Santos, “Fiber Bragg grating-based self-referencing technique for wavelength-multiplexed intensity sensors,” Opt. Lett. 27, 222–224 (2002).
    [CrossRef]
  9. S. Abad, F. M. Araújo, L. A. Ferreira, J. L. Santos, M. López-Amo, “Bragg-grating interrogation scheme using spectral filtering and amplitude-to-phase optical conversion,” in Proceedings of the 15th International Conference on Optical Fiber Sensors (Institute of Electrical and Electronics Engineers, Piscataway, N. J., 2002), pp. 103–106.
  10. S. Abad, F. M. Araújo, L. A. Ferreira, J. L. Santos, M. López-Amo, “Interrogation of wavelength multiplexed fiber Bragg gratings using spectral filtering and amplitude-tophase optical conversion,” J. Lightwave Technol. 21, 127–131 (2003).
    [CrossRef]
  11. Y. J. Rao, P. J. Henderson, D. A. Jackson, L. Zhang, I. Bennion, “Simultaneous strain, temperature and vibration measurements using a multiplexed in-fibre-Bragg-grating/fibre Fabry-Perot sensor system,” Electron. Lett. 33, 2063–2064 (1997).
    [CrossRef]
  12. X. Zeng, Y. Rao, Y. Wang, Z. Ran, T. Zhu, “Transverse load, static strain, temperature and vibration measurement using a cascaded FBG/EFPI/LPFG sensor system,” in Proceedings of the 15th International Conference on Optical Fiber Sensors (Institute of Electrical and Electronics Engineers, Piscataway, N. J., 2002), pp. 199–202.
  13. Y. J. Rao, D. A. Jackson, “Universal fiber-optic point sensor system for quasi-static absolute measurements of multiparameters exploiting low coherence interrogation,” J. Lightwave Technol. 14, 592–600 (1996).
    [CrossRef]
  14. F. J. Arregui, I. R. Matías, C. Bariain, M. López-Amo, “Experimental design rules for implementing biconically tapered single mode optical fiber displacement sensors,” in European Workshop on Optical Fiber Sensors, B. Culshaw, J. D. C. Jones, eds., Proc. SPIE3483, 164–168 (1998).
    [CrossRef]

2003 (1)

2002 (1)

1997 (2)

L. A. Ferreira, P. Cavaleiro Dias, J. L. Santos, “Demodulation of two time-multiplexed fiber Bragg sensors using source spectral characteristics,” Pure Appl. Opt. 6, 717–726 (1997).
[CrossRef]

Y. J. Rao, P. J. Henderson, D. A. Jackson, L. Zhang, I. Bennion, “Simultaneous strain, temperature and vibration measurements using a multiplexed in-fibre-Bragg-grating/fibre Fabry-Perot sensor system,” Electron. Lett. 33, 2063–2064 (1997).
[CrossRef]

1996 (1)

Y. J. Rao, D. A. Jackson, “Universal fiber-optic point sensor system for quasi-static absolute measurements of multiparameters exploiting low coherence interrogation,” J. Lightwave Technol. 14, 592–600 (1996).
[CrossRef]

1995 (1)

G. Murtaza, J. M. Senior, “Dual wavelength referencing of optical fiber sensors,” Opt. Commun. 120, 348–357 (1995).
[CrossRef]

1991 (1)

R. I. MacDonald, R. Nychka, “A differential measurement technique for optical fibre sensors,” Electron. Lett. 27, 2194–2196 (1991).
[CrossRef]

Abad, S.

S. Abad, F. M. Araújo, L. A. Ferreira, J. L. Santos, M. López-Amo, “Interrogation of wavelength multiplexed fiber Bragg gratings using spectral filtering and amplitude-tophase optical conversion,” J. Lightwave Technol. 21, 127–131 (2003).
[CrossRef]

S. Abad, M. López-Amo, F. M. Araújo, L. A. Ferreira, J. L. Santos, “Fiber Bragg grating-based self-referencing technique for wavelength-multiplexed intensity sensors,” Opt. Lett. 27, 222–224 (2002).
[CrossRef]

S. Abad, F. M. Araújo, L. A. Ferreira, J. L. Santos, M. López-Amo, “Bragg-grating interrogation scheme using spectral filtering and amplitude-to-phase optical conversion,” in Proceedings of the 15th International Conference on Optical Fiber Sensors (Institute of Electrical and Electronics Engineers, Piscataway, N. J., 2002), pp. 103–106.

Araújo, F. M.

S. Abad, F. M. Araújo, L. A. Ferreira, J. L. Santos, M. López-Amo, “Interrogation of wavelength multiplexed fiber Bragg gratings using spectral filtering and amplitude-tophase optical conversion,” J. Lightwave Technol. 21, 127–131 (2003).
[CrossRef]

S. Abad, M. López-Amo, F. M. Araújo, L. A. Ferreira, J. L. Santos, “Fiber Bragg grating-based self-referencing technique for wavelength-multiplexed intensity sensors,” Opt. Lett. 27, 222–224 (2002).
[CrossRef]

S. Abad, F. M. Araújo, L. A. Ferreira, J. L. Santos, M. López-Amo, “Bragg-grating interrogation scheme using spectral filtering and amplitude-to-phase optical conversion,” in Proceedings of the 15th International Conference on Optical Fiber Sensors (Institute of Electrical and Electronics Engineers, Piscataway, N. J., 2002), pp. 103–106.

Arregui, F. J.

F. J. Arregui, I. R. Matías, C. Bariain, M. López-Amo, “Experimental design rules for implementing biconically tapered single mode optical fiber displacement sensors,” in European Workshop on Optical Fiber Sensors, B. Culshaw, J. D. C. Jones, eds., Proc. SPIE3483, 164–168 (1998).
[CrossRef]

Bariain, C.

F. J. Arregui, I. R. Matías, C. Bariain, M. López-Amo, “Experimental design rules for implementing biconically tapered single mode optical fiber displacement sensors,” in European Workshop on Optical Fiber Sensors, B. Culshaw, J. D. C. Jones, eds., Proc. SPIE3483, 164–168 (1998).
[CrossRef]

Bennion, I.

Y. J. Rao, P. J. Henderson, D. A. Jackson, L. Zhang, I. Bennion, “Simultaneous strain, temperature and vibration measurements using a multiplexed in-fibre-Bragg-grating/fibre Fabry-Perot sensor system,” Electron. Lett. 33, 2063–2064 (1997).
[CrossRef]

Cavaleiro Dias, P.

L. A. Ferreira, P. Cavaleiro Dias, J. L. Santos, “Demodulation of two time-multiplexed fiber Bragg sensors using source spectral characteristics,” Pure Appl. Opt. 6, 717–726 (1997).
[CrossRef]

Chang, C. C.

S. T. Vohra, M. D. Todd, G. A. Johnson, C. C. Chang, B. A. Danver, “Fiber Bragg grating sensor system for civil structure monitoring applications and field tests,” in 13th International Conference on Optical Fiber Sensors, K. Hotate, B. Kim, eds., Proc. SPIE3746, 32–37 (1999).

Cobo García, A.

A. Cobo García, J. Echevarría Cuenca, “Transduction techniques based on intensity modulation of light,” in Handbook of Fibre Optic Sensing Technology, J. M. López-Higuera, ed. (Wiley, New York, 2002), pp. 209–226.

Danver, B. A.

S. T. Vohra, M. D. Todd, G. A. Johnson, C. C. Chang, B. A. Danver, “Fiber Bragg grating sensor system for civil structure monitoring applications and field tests,” in 13th International Conference on Optical Fiber Sensors, K. Hotate, B. Kim, eds., Proc. SPIE3746, 32–37 (1999).

Echevarría Cuenca, J.

A. Cobo García, J. Echevarría Cuenca, “Transduction techniques based on intensity modulation of light,” in Handbook of Fibre Optic Sensing Technology, J. M. López-Higuera, ed. (Wiley, New York, 2002), pp. 209–226.

Ferreira, L. A.

S. Abad, F. M. Araújo, L. A. Ferreira, J. L. Santos, M. López-Amo, “Interrogation of wavelength multiplexed fiber Bragg gratings using spectral filtering and amplitude-tophase optical conversion,” J. Lightwave Technol. 21, 127–131 (2003).
[CrossRef]

S. Abad, M. López-Amo, F. M. Araújo, L. A. Ferreira, J. L. Santos, “Fiber Bragg grating-based self-referencing technique for wavelength-multiplexed intensity sensors,” Opt. Lett. 27, 222–224 (2002).
[CrossRef]

L. A. Ferreira, P. Cavaleiro Dias, J. L. Santos, “Demodulation of two time-multiplexed fiber Bragg sensors using source spectral characteristics,” Pure Appl. Opt. 6, 717–726 (1997).
[CrossRef]

S. Abad, F. M. Araújo, L. A. Ferreira, J. L. Santos, M. López-Amo, “Bragg-grating interrogation scheme using spectral filtering and amplitude-to-phase optical conversion,” in Proceedings of the 15th International Conference on Optical Fiber Sensors (Institute of Electrical and Electronics Engineers, Piscataway, N. J., 2002), pp. 103–106.

Henderson, P. J.

Y. J. Rao, P. J. Henderson, D. A. Jackson, L. Zhang, I. Bennion, “Simultaneous strain, temperature and vibration measurements using a multiplexed in-fibre-Bragg-grating/fibre Fabry-Perot sensor system,” Electron. Lett. 33, 2063–2064 (1997).
[CrossRef]

Jackson, D. A.

Y. J. Rao, P. J. Henderson, D. A. Jackson, L. Zhang, I. Bennion, “Simultaneous strain, temperature and vibration measurements using a multiplexed in-fibre-Bragg-grating/fibre Fabry-Perot sensor system,” Electron. Lett. 33, 2063–2064 (1997).
[CrossRef]

Y. J. Rao, D. A. Jackson, “Universal fiber-optic point sensor system for quasi-static absolute measurements of multiparameters exploiting low coherence interrogation,” J. Lightwave Technol. 14, 592–600 (1996).
[CrossRef]

Johnson, G. A.

S. T. Vohra, M. D. Todd, G. A. Johnson, C. C. Chang, B. A. Danver, “Fiber Bragg grating sensor system for civil structure monitoring applications and field tests,” in 13th International Conference on Optical Fiber Sensors, K. Hotate, B. Kim, eds., Proc. SPIE3746, 32–37 (1999).

Jung, J.

J. Jung, Y. W. Lee, B. Lee, “High-resolution interrogation technique for fiber Bragg grating strain sensor using long period grating pair and EDF,” in 14th International Conference on Optical Fiber Sensors, A. G. Mignani, ed., Proc. SPIE4185, 114–117 (2000).

Kersey, A. D.

A. D. Kersey, “Optical fiber sensors for downwell monitoring applications in the oil & gas industry,” in 13th International Conference on Optical Fiber Sensors, K. Hotate, B. Kim, eds., Proc. SPIE3746, 326–331 (1999).

Lee, B.

J. Jung, Y. W. Lee, B. Lee, “High-resolution interrogation technique for fiber Bragg grating strain sensor using long period grating pair and EDF,” in 14th International Conference on Optical Fiber Sensors, A. G. Mignani, ed., Proc. SPIE4185, 114–117 (2000).

Lee, Y. W.

J. Jung, Y. W. Lee, B. Lee, “High-resolution interrogation technique for fiber Bragg grating strain sensor using long period grating pair and EDF,” in 14th International Conference on Optical Fiber Sensors, A. G. Mignani, ed., Proc. SPIE4185, 114–117 (2000).

López-Amo, M.

S. Abad, F. M. Araújo, L. A. Ferreira, J. L. Santos, M. López-Amo, “Interrogation of wavelength multiplexed fiber Bragg gratings using spectral filtering and amplitude-tophase optical conversion,” J. Lightwave Technol. 21, 127–131 (2003).
[CrossRef]

S. Abad, M. López-Amo, F. M. Araújo, L. A. Ferreira, J. L. Santos, “Fiber Bragg grating-based self-referencing technique for wavelength-multiplexed intensity sensors,” Opt. Lett. 27, 222–224 (2002).
[CrossRef]

S. Abad, F. M. Araújo, L. A. Ferreira, J. L. Santos, M. López-Amo, “Bragg-grating interrogation scheme using spectral filtering and amplitude-to-phase optical conversion,” in Proceedings of the 15th International Conference on Optical Fiber Sensors (Institute of Electrical and Electronics Engineers, Piscataway, N. J., 2002), pp. 103–106.

F. J. Arregui, I. R. Matías, C. Bariain, M. López-Amo, “Experimental design rules for implementing biconically tapered single mode optical fiber displacement sensors,” in European Workshop on Optical Fiber Sensors, B. Culshaw, J. D. C. Jones, eds., Proc. SPIE3483, 164–168 (1998).
[CrossRef]

MacDonald, R. I.

R. I. MacDonald, R. Nychka, “A differential measurement technique for optical fibre sensors,” Electron. Lett. 27, 2194–2196 (1991).
[CrossRef]

Matías, I. R.

F. J. Arregui, I. R. Matías, C. Bariain, M. López-Amo, “Experimental design rules for implementing biconically tapered single mode optical fiber displacement sensors,” in European Workshop on Optical Fiber Sensors, B. Culshaw, J. D. C. Jones, eds., Proc. SPIE3483, 164–168 (1998).
[CrossRef]

Murtaza, G.

G. Murtaza, J. M. Senior, “Dual wavelength referencing of optical fiber sensors,” Opt. Commun. 120, 348–357 (1995).
[CrossRef]

Nychka, R.

R. I. MacDonald, R. Nychka, “A differential measurement technique for optical fibre sensors,” Electron. Lett. 27, 2194–2196 (1991).
[CrossRef]

Ran, Z.

X. Zeng, Y. Rao, Y. Wang, Z. Ran, T. Zhu, “Transverse load, static strain, temperature and vibration measurement using a cascaded FBG/EFPI/LPFG sensor system,” in Proceedings of the 15th International Conference on Optical Fiber Sensors (Institute of Electrical and Electronics Engineers, Piscataway, N. J., 2002), pp. 199–202.

Rao, Y.

X. Zeng, Y. Rao, Y. Wang, Z. Ran, T. Zhu, “Transverse load, static strain, temperature and vibration measurement using a cascaded FBG/EFPI/LPFG sensor system,” in Proceedings of the 15th International Conference on Optical Fiber Sensors (Institute of Electrical and Electronics Engineers, Piscataway, N. J., 2002), pp. 199–202.

Rao, Y. J.

Y. J. Rao, P. J. Henderson, D. A. Jackson, L. Zhang, I. Bennion, “Simultaneous strain, temperature and vibration measurements using a multiplexed in-fibre-Bragg-grating/fibre Fabry-Perot sensor system,” Electron. Lett. 33, 2063–2064 (1997).
[CrossRef]

Y. J. Rao, D. A. Jackson, “Universal fiber-optic point sensor system for quasi-static absolute measurements of multiparameters exploiting low coherence interrogation,” J. Lightwave Technol. 14, 592–600 (1996).
[CrossRef]

Santos, J. L.

S. Abad, F. M. Araújo, L. A. Ferreira, J. L. Santos, M. López-Amo, “Interrogation of wavelength multiplexed fiber Bragg gratings using spectral filtering and amplitude-tophase optical conversion,” J. Lightwave Technol. 21, 127–131 (2003).
[CrossRef]

S. Abad, M. López-Amo, F. M. Araújo, L. A. Ferreira, J. L. Santos, “Fiber Bragg grating-based self-referencing technique for wavelength-multiplexed intensity sensors,” Opt. Lett. 27, 222–224 (2002).
[CrossRef]

L. A. Ferreira, P. Cavaleiro Dias, J. L. Santos, “Demodulation of two time-multiplexed fiber Bragg sensors using source spectral characteristics,” Pure Appl. Opt. 6, 717–726 (1997).
[CrossRef]

S. Abad, F. M. Araújo, L. A. Ferreira, J. L. Santos, M. López-Amo, “Bragg-grating interrogation scheme using spectral filtering and amplitude-to-phase optical conversion,” in Proceedings of the 15th International Conference on Optical Fiber Sensors (Institute of Electrical and Electronics Engineers, Piscataway, N. J., 2002), pp. 103–106.

Senior, J. M.

G. Murtaza, J. M. Senior, “Dual wavelength referencing of optical fiber sensors,” Opt. Commun. 120, 348–357 (1995).
[CrossRef]

Todd, M. D.

S. T. Vohra, M. D. Todd, G. A. Johnson, C. C. Chang, B. A. Danver, “Fiber Bragg grating sensor system for civil structure monitoring applications and field tests,” in 13th International Conference on Optical Fiber Sensors, K. Hotate, B. Kim, eds., Proc. SPIE3746, 32–37 (1999).

Vohra, S. T.

S. T. Vohra, M. D. Todd, G. A. Johnson, C. C. Chang, B. A. Danver, “Fiber Bragg grating sensor system for civil structure monitoring applications and field tests,” in 13th International Conference on Optical Fiber Sensors, K. Hotate, B. Kim, eds., Proc. SPIE3746, 32–37 (1999).

Wang, Y.

X. Zeng, Y. Rao, Y. Wang, Z. Ran, T. Zhu, “Transverse load, static strain, temperature and vibration measurement using a cascaded FBG/EFPI/LPFG sensor system,” in Proceedings of the 15th International Conference on Optical Fiber Sensors (Institute of Electrical and Electronics Engineers, Piscataway, N. J., 2002), pp. 199–202.

Zeng, X.

X. Zeng, Y. Rao, Y. Wang, Z. Ran, T. Zhu, “Transverse load, static strain, temperature and vibration measurement using a cascaded FBG/EFPI/LPFG sensor system,” in Proceedings of the 15th International Conference on Optical Fiber Sensors (Institute of Electrical and Electronics Engineers, Piscataway, N. J., 2002), pp. 199–202.

Zhang, L.

Y. J. Rao, P. J. Henderson, D. A. Jackson, L. Zhang, I. Bennion, “Simultaneous strain, temperature and vibration measurements using a multiplexed in-fibre-Bragg-grating/fibre Fabry-Perot sensor system,” Electron. Lett. 33, 2063–2064 (1997).
[CrossRef]

Zhu, T.

X. Zeng, Y. Rao, Y. Wang, Z. Ran, T. Zhu, “Transverse load, static strain, temperature and vibration measurement using a cascaded FBG/EFPI/LPFG sensor system,” in Proceedings of the 15th International Conference on Optical Fiber Sensors (Institute of Electrical and Electronics Engineers, Piscataway, N. J., 2002), pp. 199–202.

Electron. Lett. (2)

R. I. MacDonald, R. Nychka, “A differential measurement technique for optical fibre sensors,” Electron. Lett. 27, 2194–2196 (1991).
[CrossRef]

Y. J. Rao, P. J. Henderson, D. A. Jackson, L. Zhang, I. Bennion, “Simultaneous strain, temperature and vibration measurements using a multiplexed in-fibre-Bragg-grating/fibre Fabry-Perot sensor system,” Electron. Lett. 33, 2063–2064 (1997).
[CrossRef]

J. Lightwave Technol. (2)

Y. J. Rao, D. A. Jackson, “Universal fiber-optic point sensor system for quasi-static absolute measurements of multiparameters exploiting low coherence interrogation,” J. Lightwave Technol. 14, 592–600 (1996).
[CrossRef]

S. Abad, F. M. Araújo, L. A. Ferreira, J. L. Santos, M. López-Amo, “Interrogation of wavelength multiplexed fiber Bragg gratings using spectral filtering and amplitude-tophase optical conversion,” J. Lightwave Technol. 21, 127–131 (2003).
[CrossRef]

Opt. Commun. (1)

G. Murtaza, J. M. Senior, “Dual wavelength referencing of optical fiber sensors,” Opt. Commun. 120, 348–357 (1995).
[CrossRef]

Opt. Lett. (1)

Pure Appl. Opt. (1)

L. A. Ferreira, P. Cavaleiro Dias, J. L. Santos, “Demodulation of two time-multiplexed fiber Bragg sensors using source spectral characteristics,” Pure Appl. Opt. 6, 717–726 (1997).
[CrossRef]

Other (7)

J. Jung, Y. W. Lee, B. Lee, “High-resolution interrogation technique for fiber Bragg grating strain sensor using long period grating pair and EDF,” in 14th International Conference on Optical Fiber Sensors, A. G. Mignani, ed., Proc. SPIE4185, 114–117 (2000).

S. Abad, F. M. Araújo, L. A. Ferreira, J. L. Santos, M. López-Amo, “Bragg-grating interrogation scheme using spectral filtering and amplitude-to-phase optical conversion,” in Proceedings of the 15th International Conference on Optical Fiber Sensors (Institute of Electrical and Electronics Engineers, Piscataway, N. J., 2002), pp. 103–106.

A. Cobo García, J. Echevarría Cuenca, “Transduction techniques based on intensity modulation of light,” in Handbook of Fibre Optic Sensing Technology, J. M. López-Higuera, ed. (Wiley, New York, 2002), pp. 209–226.

S. T. Vohra, M. D. Todd, G. A. Johnson, C. C. Chang, B. A. Danver, “Fiber Bragg grating sensor system for civil structure monitoring applications and field tests,” in 13th International Conference on Optical Fiber Sensors, K. Hotate, B. Kim, eds., Proc. SPIE3746, 32–37 (1999).

A. D. Kersey, “Optical fiber sensors for downwell monitoring applications in the oil & gas industry,” in 13th International Conference on Optical Fiber Sensors, K. Hotate, B. Kim, eds., Proc. SPIE3746, 326–331 (1999).

F. J. Arregui, I. R. Matías, C. Bariain, M. López-Amo, “Experimental design rules for implementing biconically tapered single mode optical fiber displacement sensors,” in European Workshop on Optical Fiber Sensors, B. Culshaw, J. D. C. Jones, eds., Proc. SPIE3483, 164–168 (1998).
[CrossRef]

X. Zeng, Y. Rao, Y. Wang, Z. Ran, T. Zhu, “Transverse load, static strain, temperature and vibration measurement using a cascaded FBG/EFPI/LPFG sensor system,” in Proceedings of the 15th International Conference on Optical Fiber Sensors (Institute of Electrical and Electronics Engineers, Piscataway, N. J., 2002), pp. 199–202.

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Figures (7)

Fig. 1
Fig. 1

Hybrid sensor multiplexing setup: FBG1, FBG2, FBG sensors; SI, SII, intensity-modulated sensor heads; D, photodetector; C1, C2, 3-dB couplers; EOM, electro-optic modulator; L d FBG (=2.3 km), L d I (=600 m), L d II (=920 m), delay coils; f (=32.5 kHz), modulation frequency.

Fig. 2
Fig. 2

Spectra from the sensors superimposed upon the detection-block WDM and the tunable filter (tuned to sensor SII) transfer functions. The two FBG sensors are placed on the 3-dB points of the WDM, whereas the reflectors that form the intensity heads are placed around the WDM peak wavelengths.

Fig. 3
Fig. 3

Output phase variation for the four multiplexed sensors. The two intensity sensors have a 6.5-dB operation range, and the FBG sensors operate in a 2-nm range. Increasing and decreasing measurement cycles show no hysteresis.

Fig. 4
Fig. 4

Response of sensor SI to three power losses induced in the network. The system is unaffected by power losses as high as 6 dB.

Fig. 5
Fig. 5

Output optical spectrum with the detection tunable filter tuned to SI, showing optical cross talk below 22 dB.

Fig. 6
Fig. 6

Cross-talk effects on sensor SI weighted against the total sensor output range. The sensor was placed in the middle of its operation range, and the rest of the sensors were swept over their entire range. Cross-talk effects were kept below 0.5% of the total output range.

Fig. 7
Fig. 7

Variation in intensity-sensor response for a 50 °C temperature change induced in the intensity sensor FBG reflectors. The temperature-induced wavelength shift causes the sensor to deviate from the WDM peak, varying the power ratio and therefore the output phase. The measured variation is less than 5% of the total output range.

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