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.2009;9(6):4559-71.
doi: 10.3390/s90604559. Epub 2009 Jun 10.

Characterization of Long-period Grating Refractive Index Sensors and Their Applications

Affiliations

Characterization of Long-period Grating Refractive Index Sensors and Their Applications

Hiroshi Tsuda et al. Sensors (Basel).2009.

Abstract

The influence of grating length and bend radius of long-period gratings (LPGs) on refractive index sensing was examined. Sensitivity to refractive indexes smaller than that of silica could be enhanced by bending LPGs. Bent LPGs lost sensitivity to refractive indexes higher than that of silica, whereas a 20-mm-long LPG arranged in a straight line had considerable sensitivity. These experimental results demonstrated that the sensitivity characteristics of LPGs to refractive index could be controlled by grating length and bend radius.

Keywords: long-period grating; refractive index; spectral sensitivity.

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Figures

Figure 1.
Figure 1.
Experimental setup for measuring the transmission spectrum of a straight LPG.
Figure 2.
Figure 2.
Transmission spectra of a 30-mm-long straight LPG surrounded by a medium having a refractive index that is lower than that of silica.
Figure 3.
Figure 3.
Transmission spectra of a 30-mm-long straight LPG surrounded by a medium having a refractive index that is higher than that of silica.
Figure 4.
Figure 4.
Transmission spectra of a 20-mm-long straight LPG surrounded by a medium having a refractive index that is lower than that of silica.
Figure 5.
Figure 5.
Transmission spectra of a 20-mm-long straight LPG surrounded by a medium having a refractive index that is higher than that of silica.
Figure 6.
Figure 6.
Experimental setup for measuring the transmission spectrum of a bent LPG.
Figure 7.
Figure 7.
Transmission spectra of a 20-mm-long bent LPG surrounded by a medium having a refractive index ranging from 1 to 1.5.
Figure 8.
Figure 8.
Discrimination of water from saline water using a 20-mm-long LPG having a bend radius of 43 mm.
Figure 9.
Figure 9.
Schematic diagram of a 20-mm-long LPG having a bend radius of 20 mm.
Figure 10.
Figure 10.
Discrimination of water from saline water with a 20-mm-long LPG having a bend radius of 20 mm.
Figure 11.
Figure 11.
Experimental setup for monitoring epoxy resin cure.
Figure 12.
Figure 12.
Temperature profile in the epoxy resin cure process. The upper right figure is the enlarged temperature profile until 90 minutes after pouring the resin. The blue circles indicate the times at which the transmission spectra were recorded.
Figure 13.
Figure 13.
Change in transmission spectra of an LPG before and after resin infusion.
Figure 14.
Figure 14.
Change in the transmission spectra of an LPG in the resin cure process in which the temperature was saturated. The upper figure is an enlarged view of the transmission spectra in the wavelength range from 1,525 to 1,530 nm.
Figure 15.
Figure 15.
Change in transmission spectra of an LPG in the resin cure process in which temperature decreased gradually. The upper figure is an enlarged view of the transmission spectra in the wavelength range from 1,525 to 1,530 nm.
Figure 16.
Figure 16.
Transmission spectra of an LPG after resin cure.
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References

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