Abstract

A long-period fiber grating (LPFG) humidity sensor is reported utilizing poly(ethylene oxide)∕cobalt chloride (PEO/CoCl2) as a hybrid hygrosensitive cladding coating. A thin overlay of the material is deposited on the LPFG and with exposure to different ambient humidity levels, its spectral properties are modified. The material parameters associated with the sensing mechanism may include those of refractive index, absorption, and morphological alterations of the overlaid material. Relative humidity variations in the range from 50% to 95% have been detected with a resolution better than 0.2%. The response time constant of the fiber sensor is of the order of a few hundred milliseconds.

© 2006 Optical Society of America

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  1. C. Bariain, I. R. Matias, F. J. Arregui, and M. Lopez-Amo, "Optical fiber humidity sensor based on a tapered fiber coated with agarose gel," Sens. Actuators B 69, 127-131 (2000).
    [CrossRef]
  2. L. Xu, J. C. Fanguy, K. Soni, and S. Tao, "Optical fiber humidity sensor based on evanescent-wave scattering," Opt. Lett. 29, 1191-1193 (2004).
    [CrossRef] [PubMed]
  3. A. Gaston, F. Perez, and J. Sevilla, "Optical fiber relative-humidity sensor with polyvinyl alcohol film," Appl. Opt. 43, 4127-4132 (2004).
    [CrossRef] [PubMed]
  4. S. K. Shukla, G. K. Parashar, A. P. Mishra, P. Misra, B. C. Yadav, R. K. Shukla, L. M. Bali, and G. C. Dubey, "Nano-like magnesium oxide films and its significance in optical fiber humidity sensors," Sens. Actuators B 98, 5-11 (2004).
    [CrossRef]
  5. S. W. James and R. P. Tatam, "Optical fibre long-period grating sensors: characteristics and applications," Meas. Sci. Technol. 14, R49-R61 (2003).
    [CrossRef]
  6. R. Falciai, A. G. Mignani, and A. Vannini, "Long period gratings as solution concentration sensors," Sens. Actuators B 74, 74-77 (2001).
    [CrossRef]
  7. A. Kharaz and B. E. Jones, "A distributed optical-fibre sensing system for multi-point humidity measurement," Sens. Actuators A 47, 491-493 (1995).
    [CrossRef]
  8. C. M. Tay, K. M. Tan, S. C. Tjin, C. C. Chan, and H. Rahardjo, "Humidity sensing using plastic optical fibers," Microwave Opt. Technol. Lett. 43, 387-390 (2004).
    [CrossRef]
  9. A. P. Russell and K. S. Fletcher, "Optical sensor for the determination of moisture," Anal. Chem. Acta , 170, 209-216 (1985).
    [CrossRef]
  10. G. Manasis, A. Tsigara, A. Giannoudakos, G. Anyfantis, K. Gatsouli, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Cobalt chloride based nanocomposite humidity sensors," Glass Technol. 46, 171-174 (2005).
  11. A. Tsigara, G. Mountrihas, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Photonic humidity integrated sensor based on hybrid polymer/cobalt chloride systems," presented at the CLEO/Europe 2005, CH-11-TUE, Munich, Germany, 12-16 June 2005.
  12. A. M. Vengsarkar, P. J. Lemaire, J. B. Judkins, V. Bhatia, T. Erdogan and J. E. Sipe, "Long-period fiber gratings as band rejection filters," J. Lightwave Technol. 14, 58-65 (1996).
    [CrossRef]
  13. H.M.Smith, ed., Holographic Recording Materials(Springer-Verlag, 1977).
  14. X. Daxhelet and M. Kulishov, "Theory and practice of long-period gratings: when a loss becomes a gain," Opt. Lett. 28, 686-688 (2003).
    [CrossRef] [PubMed]

2005

G. Manasis, A. Tsigara, A. Giannoudakos, G. Anyfantis, K. Gatsouli, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Cobalt chloride based nanocomposite humidity sensors," Glass Technol. 46, 171-174 (2005).

A. Tsigara, G. Mountrihas, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Photonic humidity integrated sensor based on hybrid polymer/cobalt chloride systems," presented at the CLEO/Europe 2005, CH-11-TUE, Munich, Germany, 12-16 June 2005.

2004

C. M. Tay, K. M. Tan, S. C. Tjin, C. C. Chan, and H. Rahardjo, "Humidity sensing using plastic optical fibers," Microwave Opt. Technol. Lett. 43, 387-390 (2004).
[CrossRef]

S. K. Shukla, G. K. Parashar, A. P. Mishra, P. Misra, B. C. Yadav, R. K. Shukla, L. M. Bali, and G. C. Dubey, "Nano-like magnesium oxide films and its significance in optical fiber humidity sensors," Sens. Actuators B 98, 5-11 (2004).
[CrossRef]

L. Xu, J. C. Fanguy, K. Soni, and S. Tao, "Optical fiber humidity sensor based on evanescent-wave scattering," Opt. Lett. 29, 1191-1193 (2004).
[CrossRef] [PubMed]

A. Gaston, F. Perez, and J. Sevilla, "Optical fiber relative-humidity sensor with polyvinyl alcohol film," Appl. Opt. 43, 4127-4132 (2004).
[CrossRef] [PubMed]

2003

X. Daxhelet and M. Kulishov, "Theory and practice of long-period gratings: when a loss becomes a gain," Opt. Lett. 28, 686-688 (2003).
[CrossRef] [PubMed]

S. W. James and R. P. Tatam, "Optical fibre long-period grating sensors: characteristics and applications," Meas. Sci. Technol. 14, R49-R61 (2003).
[CrossRef]

2001

R. Falciai, A. G. Mignani, and A. Vannini, "Long period gratings as solution concentration sensors," Sens. Actuators B 74, 74-77 (2001).
[CrossRef]

2000

C. Bariain, I. R. Matias, F. J. Arregui, and M. Lopez-Amo, "Optical fiber humidity sensor based on a tapered fiber coated with agarose gel," Sens. Actuators B 69, 127-131 (2000).
[CrossRef]

1996

A. M. Vengsarkar, P. J. Lemaire, J. B. Judkins, V. Bhatia, T. Erdogan and J. E. Sipe, "Long-period fiber gratings as band rejection filters," J. Lightwave Technol. 14, 58-65 (1996).
[CrossRef]

1995

A. Kharaz and B. E. Jones, "A distributed optical-fibre sensing system for multi-point humidity measurement," Sens. Actuators A 47, 491-493 (1995).
[CrossRef]

1985

A. P. Russell and K. S. Fletcher, "Optical sensor for the determination of moisture," Anal. Chem. Acta , 170, 209-216 (1985).
[CrossRef]

Anyfantis, G.

G. Manasis, A. Tsigara, A. Giannoudakos, G. Anyfantis, K. Gatsouli, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Cobalt chloride based nanocomposite humidity sensors," Glass Technol. 46, 171-174 (2005).

Arregui, F. J.

C. Bariain, I. R. Matias, F. J. Arregui, and M. Lopez-Amo, "Optical fiber humidity sensor based on a tapered fiber coated with agarose gel," Sens. Actuators B 69, 127-131 (2000).
[CrossRef]

Bali, L. M.

S. K. Shukla, G. K. Parashar, A. P. Mishra, P. Misra, B. C. Yadav, R. K. Shukla, L. M. Bali, and G. C. Dubey, "Nano-like magnesium oxide films and its significance in optical fiber humidity sensors," Sens. Actuators B 98, 5-11 (2004).
[CrossRef]

Bariain, C.

C. Bariain, I. R. Matias, F. J. Arregui, and M. Lopez-Amo, "Optical fiber humidity sensor based on a tapered fiber coated with agarose gel," Sens. Actuators B 69, 127-131 (2000).
[CrossRef]

Bhatia, V.

A. M. Vengsarkar, P. J. Lemaire, J. B. Judkins, V. Bhatia, T. Erdogan and J. E. Sipe, "Long-period fiber gratings as band rejection filters," J. Lightwave Technol. 14, 58-65 (1996).
[CrossRef]

Chan, C. C.

C. M. Tay, K. M. Tan, S. C. Tjin, C. C. Chan, and H. Rahardjo, "Humidity sensing using plastic optical fibers," Microwave Opt. Technol. Lett. 43, 387-390 (2004).
[CrossRef]

Daxhelet, X.

Dubey, G. C.

S. K. Shukla, G. K. Parashar, A. P. Mishra, P. Misra, B. C. Yadav, R. K. Shukla, L. M. Bali, and G. C. Dubey, "Nano-like magnesium oxide films and its significance in optical fiber humidity sensors," Sens. Actuators B 98, 5-11 (2004).
[CrossRef]

Erdogan, T.

A. M. Vengsarkar, P. J. Lemaire, J. B. Judkins, V. Bhatia, T. Erdogan and J. E. Sipe, "Long-period fiber gratings as band rejection filters," J. Lightwave Technol. 14, 58-65 (1996).
[CrossRef]

Falciai, R.

R. Falciai, A. G. Mignani, and A. Vannini, "Long period gratings as solution concentration sensors," Sens. Actuators B 74, 74-77 (2001).
[CrossRef]

Fanguy, J. C.

L. Xu, J. C. Fanguy, K. Soni, and S. Tao, "Optical fiber humidity sensor based on evanescent-wave scattering," Opt. Lett. 29, 1191-1193 (2004).
[CrossRef] [PubMed]

Fletcher, K. S.

A. P. Russell and K. S. Fletcher, "Optical sensor for the determination of moisture," Anal. Chem. Acta , 170, 209-216 (1985).
[CrossRef]

Gaston, A.

Gatsouli, K.

G. Manasis, A. Tsigara, A. Giannoudakos, G. Anyfantis, K. Gatsouli, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Cobalt chloride based nanocomposite humidity sensors," Glass Technol. 46, 171-174 (2005).

Giannoudakos, A.

G. Manasis, A. Tsigara, A. Giannoudakos, G. Anyfantis, K. Gatsouli, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Cobalt chloride based nanocomposite humidity sensors," Glass Technol. 46, 171-174 (2005).

James, S. W.

S. W. James and R. P. Tatam, "Optical fibre long-period grating sensors: characteristics and applications," Meas. Sci. Technol. 14, R49-R61 (2003).
[CrossRef]

Jones, B. E.

A. Kharaz and B. E. Jones, "A distributed optical-fibre sensing system for multi-point humidity measurement," Sens. Actuators A 47, 491-493 (1995).
[CrossRef]

Judkins, J. B.

A. M. Vengsarkar, P. J. Lemaire, J. B. Judkins, V. Bhatia, T. Erdogan and J. E. Sipe, "Long-period fiber gratings as band rejection filters," J. Lightwave Technol. 14, 58-65 (1996).
[CrossRef]

Kharaz, A.

A. Kharaz and B. E. Jones, "A distributed optical-fibre sensing system for multi-point humidity measurement," Sens. Actuators A 47, 491-493 (1995).
[CrossRef]

Kulishov, M.

Lemaire, P. J.

A. M. Vengsarkar, P. J. Lemaire, J. B. Judkins, V. Bhatia, T. Erdogan and J. E. Sipe, "Long-period fiber gratings as band rejection filters," J. Lightwave Technol. 14, 58-65 (1996).
[CrossRef]

Lopez-Amo, M.

C. Bariain, I. R. Matias, F. J. Arregui, and M. Lopez-Amo, "Optical fiber humidity sensor based on a tapered fiber coated with agarose gel," Sens. Actuators B 69, 127-131 (2000).
[CrossRef]

Madamopoulos, N.

G. Manasis, A. Tsigara, A. Giannoudakos, G. Anyfantis, K. Gatsouli, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Cobalt chloride based nanocomposite humidity sensors," Glass Technol. 46, 171-174 (2005).

A. Tsigara, G. Mountrihas, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Photonic humidity integrated sensor based on hybrid polymer/cobalt chloride systems," presented at the CLEO/Europe 2005, CH-11-TUE, Munich, Germany, 12-16 June 2005.

Manasis, G.

G. Manasis, A. Tsigara, A. Giannoudakos, G. Anyfantis, K. Gatsouli, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Cobalt chloride based nanocomposite humidity sensors," Glass Technol. 46, 171-174 (2005).

Matias, I. R.

C. Bariain, I. R. Matias, F. J. Arregui, and M. Lopez-Amo, "Optical fiber humidity sensor based on a tapered fiber coated with agarose gel," Sens. Actuators B 69, 127-131 (2000).
[CrossRef]

Mignani, A. G.

R. Falciai, A. G. Mignani, and A. Vannini, "Long period gratings as solution concentration sensors," Sens. Actuators B 74, 74-77 (2001).
[CrossRef]

Mishra, A. P.

S. K. Shukla, G. K. Parashar, A. P. Mishra, P. Misra, B. C. Yadav, R. K. Shukla, L. M. Bali, and G. C. Dubey, "Nano-like magnesium oxide films and its significance in optical fiber humidity sensors," Sens. Actuators B 98, 5-11 (2004).
[CrossRef]

Misra, P.

S. K. Shukla, G. K. Parashar, A. P. Mishra, P. Misra, B. C. Yadav, R. K. Shukla, L. M. Bali, and G. C. Dubey, "Nano-like magnesium oxide films and its significance in optical fiber humidity sensors," Sens. Actuators B 98, 5-11 (2004).
[CrossRef]

Mountrihas, G.

A. Tsigara, G. Mountrihas, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Photonic humidity integrated sensor based on hybrid polymer/cobalt chloride systems," presented at the CLEO/Europe 2005, CH-11-TUE, Munich, Germany, 12-16 June 2005.

Mousdis, G.

A. Tsigara, G. Mountrihas, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Photonic humidity integrated sensor based on hybrid polymer/cobalt chloride systems," presented at the CLEO/Europe 2005, CH-11-TUE, Munich, Germany, 12-16 June 2005.

G. Manasis, A. Tsigara, A. Giannoudakos, G. Anyfantis, K. Gatsouli, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Cobalt chloride based nanocomposite humidity sensors," Glass Technol. 46, 171-174 (2005).

Parashar, G. K.

S. K. Shukla, G. K. Parashar, A. P. Mishra, P. Misra, B. C. Yadav, R. K. Shukla, L. M. Bali, and G. C. Dubey, "Nano-like magnesium oxide films and its significance in optical fiber humidity sensors," Sens. Actuators B 98, 5-11 (2004).
[CrossRef]

Perez, F.

Pispas, S.

G. Manasis, A. Tsigara, A. Giannoudakos, G. Anyfantis, K. Gatsouli, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Cobalt chloride based nanocomposite humidity sensors," Glass Technol. 46, 171-174 (2005).

A. Tsigara, G. Mountrihas, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Photonic humidity integrated sensor based on hybrid polymer/cobalt chloride systems," presented at the CLEO/Europe 2005, CH-11-TUE, Munich, Germany, 12-16 June 2005.

Rahardjo, H.

C. M. Tay, K. M. Tan, S. C. Tjin, C. C. Chan, and H. Rahardjo, "Humidity sensing using plastic optical fibers," Microwave Opt. Technol. Lett. 43, 387-390 (2004).
[CrossRef]

Russell, A. P.

A. P. Russell and K. S. Fletcher, "Optical sensor for the determination of moisture," Anal. Chem. Acta , 170, 209-216 (1985).
[CrossRef]

Sevilla, J.

Shukla, R. K.

S. K. Shukla, G. K. Parashar, A. P. Mishra, P. Misra, B. C. Yadav, R. K. Shukla, L. M. Bali, and G. C. Dubey, "Nano-like magnesium oxide films and its significance in optical fiber humidity sensors," Sens. Actuators B 98, 5-11 (2004).
[CrossRef]

Shukla, S. K.

S. K. Shukla, G. K. Parashar, A. P. Mishra, P. Misra, B. C. Yadav, R. K. Shukla, L. M. Bali, and G. C. Dubey, "Nano-like magnesium oxide films and its significance in optical fiber humidity sensors," Sens. Actuators B 98, 5-11 (2004).
[CrossRef]

Sipe, J. E.

A. M. Vengsarkar, P. J. Lemaire, J. B. Judkins, V. Bhatia, T. Erdogan and J. E. Sipe, "Long-period fiber gratings as band rejection filters," J. Lightwave Technol. 14, 58-65 (1996).
[CrossRef]

Soni, K.

L. Xu, J. C. Fanguy, K. Soni, and S. Tao, "Optical fiber humidity sensor based on evanescent-wave scattering," Opt. Lett. 29, 1191-1193 (2004).
[CrossRef] [PubMed]

Tan, K. M.

C. M. Tay, K. M. Tan, S. C. Tjin, C. C. Chan, and H. Rahardjo, "Humidity sensing using plastic optical fibers," Microwave Opt. Technol. Lett. 43, 387-390 (2004).
[CrossRef]

Tao, S.

L. Xu, J. C. Fanguy, K. Soni, and S. Tao, "Optical fiber humidity sensor based on evanescent-wave scattering," Opt. Lett. 29, 1191-1193 (2004).
[CrossRef] [PubMed]

Tatam, R. P.

S. W. James and R. P. Tatam, "Optical fibre long-period grating sensors: characteristics and applications," Meas. Sci. Technol. 14, R49-R61 (2003).
[CrossRef]

Tay, C. M.

C. M. Tay, K. M. Tan, S. C. Tjin, C. C. Chan, and H. Rahardjo, "Humidity sensing using plastic optical fibers," Microwave Opt. Technol. Lett. 43, 387-390 (2004).
[CrossRef]

Tjin, S. C.

C. M. Tay, K. M. Tan, S. C. Tjin, C. C. Chan, and H. Rahardjo, "Humidity sensing using plastic optical fibers," Microwave Opt. Technol. Lett. 43, 387-390 (2004).
[CrossRef]

Tsigara, A.

A. Tsigara, G. Mountrihas, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Photonic humidity integrated sensor based on hybrid polymer/cobalt chloride systems," presented at the CLEO/Europe 2005, CH-11-TUE, Munich, Germany, 12-16 June 2005.

G. Manasis, A. Tsigara, A. Giannoudakos, G. Anyfantis, K. Gatsouli, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Cobalt chloride based nanocomposite humidity sensors," Glass Technol. 46, 171-174 (2005).

Vainos, N.

G. Manasis, A. Tsigara, A. Giannoudakos, G. Anyfantis, K. Gatsouli, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Cobalt chloride based nanocomposite humidity sensors," Glass Technol. 46, 171-174 (2005).

A. Tsigara, G. Mountrihas, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Photonic humidity integrated sensor based on hybrid polymer/cobalt chloride systems," presented at the CLEO/Europe 2005, CH-11-TUE, Munich, Germany, 12-16 June 2005.

Vannini, A.

R. Falciai, A. G. Mignani, and A. Vannini, "Long period gratings as solution concentration sensors," Sens. Actuators B 74, 74-77 (2001).
[CrossRef]

Vengsarkar, A. M.

A. M. Vengsarkar, P. J. Lemaire, J. B. Judkins, V. Bhatia, T. Erdogan and J. E. Sipe, "Long-period fiber gratings as band rejection filters," J. Lightwave Technol. 14, 58-65 (1996).
[CrossRef]

Xu, L.

L. Xu, J. C. Fanguy, K. Soni, and S. Tao, "Optical fiber humidity sensor based on evanescent-wave scattering," Opt. Lett. 29, 1191-1193 (2004).
[CrossRef] [PubMed]

Yadav, B. C.

S. K. Shukla, G. K. Parashar, A. P. Mishra, P. Misra, B. C. Yadav, R. K. Shukla, L. M. Bali, and G. C. Dubey, "Nano-like magnesium oxide films and its significance in optical fiber humidity sensors," Sens. Actuators B 98, 5-11 (2004).
[CrossRef]

Anal. Chem. Acta

A. P. Russell and K. S. Fletcher, "Optical sensor for the determination of moisture," Anal. Chem. Acta , 170, 209-216 (1985).
[CrossRef]

Appl. Opt.

Glass Technol.

G. Manasis, A. Tsigara, A. Giannoudakos, G. Anyfantis, K. Gatsouli, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Cobalt chloride based nanocomposite humidity sensors," Glass Technol. 46, 171-174 (2005).

J. Lightwave Technol.

A. M. Vengsarkar, P. J. Lemaire, J. B. Judkins, V. Bhatia, T. Erdogan and J. E. Sipe, "Long-period fiber gratings as band rejection filters," J. Lightwave Technol. 14, 58-65 (1996).
[CrossRef]

Meas. Sci. Technol.

S. W. James and R. P. Tatam, "Optical fibre long-period grating sensors: characteristics and applications," Meas. Sci. Technol. 14, R49-R61 (2003).
[CrossRef]

Microwave Opt. Technol. Lett.

C. M. Tay, K. M. Tan, S. C. Tjin, C. C. Chan, and H. Rahardjo, "Humidity sensing using plastic optical fibers," Microwave Opt. Technol. Lett. 43, 387-390 (2004).
[CrossRef]

Opt. Lett.

L. Xu, J. C. Fanguy, K. Soni, and S. Tao, "Optical fiber humidity sensor based on evanescent-wave scattering," Opt. Lett. 29, 1191-1193 (2004).
[CrossRef] [PubMed]

Opt. Lett.

Sens. Actuators A

A. Kharaz and B. E. Jones, "A distributed optical-fibre sensing system for multi-point humidity measurement," Sens. Actuators A 47, 491-493 (1995).
[CrossRef]

Sens. Actuators B

C. Bariain, I. R. Matias, F. J. Arregui, and M. Lopez-Amo, "Optical fiber humidity sensor based on a tapered fiber coated with agarose gel," Sens. Actuators B 69, 127-131 (2000).
[CrossRef]

Sens. Actuators B

R. Falciai, A. G. Mignani, and A. Vannini, "Long period gratings as solution concentration sensors," Sens. Actuators B 74, 74-77 (2001).
[CrossRef]

Sens. Actuators B

S. K. Shukla, G. K. Parashar, A. P. Mishra, P. Misra, B. C. Yadav, R. K. Shukla, L. M. Bali, and G. C. Dubey, "Nano-like magnesium oxide films and its significance in optical fiber humidity sensors," Sens. Actuators B 98, 5-11 (2004).
[CrossRef]

Other

H.M.Smith, ed., Holographic Recording Materials(Springer-Verlag, 1977).

A. Tsigara, G. Mountrihas, G. Mousdis, S. Pispas, N. Madamopoulos, and N. Vainos, "Photonic humidity integrated sensor based on hybrid polymer/cobalt chloride systems," presented at the CLEO/Europe 2005, CH-11-TUE, Munich, Germany, 12-16 June 2005.

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Figures (5)

Fig. 1
Fig. 1

Modification of the LPFG spectrum for increasing humidity. For clarity, only three characteristic spectra are shown for 52% (solid line), 77% (dashed line), and 95% (dotted line) RH. The sharp noise peaks observed in the above spectra are attributed to artifacts of the spectral source and are not correlated with the sensing mechanism.

Fig. 2
Fig. 2

Evolution of the wavelength (open squares; left y axis) and the minimum transmission (full circles; right y axis) of the LPFG notch under increasing humidity.

Fig. 3
Fig. 3

Real-time response of the humidity sensor. Change in RH (%) (top graph) and corresponding change in LPFG wavelength (middle graph) and minimum transmission (bottom graph). Overlayer thickness, 10 μm.

Fig. 4
Fig. 4

Effect of overlayer thickness on the time response of the sensor. Upper graph (straight line): change in RH; lower graph: response of the 10 μm overlayer (open circles) and the 30 μm overlayer (filled squares).

Fig. 5
Fig. 5

Equivalent refractive-index change of PEO∕CoCl2 for different values of humidity determined by diffraction efficiency measurements.

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