Research on testing the characteristics of hydrogel film by using a long-period fiber grating

Abstract

A method for testing the physical and optical properties of hydrogel thin films is reported based on using long-period fiber gratings. For humidity levels from 50% to 70% RH, a wavelength decrease of 11:0 nm is observed, with a sensitivity of 0:6 nm=%RH. For humidity levels from 70% to 98% RH, a wavelength increase of 6:3 nm is seen, with a sensitivity of 0:2 nm=%RH. For humidity levels greater than 60% RH, the transmission loss at resonance increases rapidly, showing a high degree of sensitivity of 0:5 dB=%RH. The blueshift of the wavelength was seen to be due to a thickening of the overlay, while the redshift of wavelength is due to the contribution of the drop in refractive index of the overlay. The results match well with what is expected theoretically.

photonic sensors review progress of optical fiber sensors and its application in harsh environment

“…The transmission spectrum of cascaded LFPGs shown in Fig. 3 contains several sinusoidal interference fringes exhibiting an envelope corresponding to the attenuation bands normally presented for single LFPG [2][3]. When being coated with hydrogel or palladium silver (Pd-Ag) film, the cascaded LFPGs can be used as relative humidity (RH) sensors or hydrogen (H 2 ) sensors respectively, which is useful for strategic weapon storage where the space is airtight and cramped, and conventional electrical humidity sensors cannot be used.…”