Source: http://aoot.osa.org/oe/abstract.cfm?uri=oe-27-6-9232
Timestamp: 2019-04-24 08:04:17+00:00

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In this paper, a splitting ratio-adjustable Mach-Zehnder interferometer (MZI) for the measurement of relative humidity (RH) is proposed and experimentally demonstrated. The sensing head contains three sections of single mode fiber (SMF) and two sections of multimode fiber (MMF), in which the two MMFs are spliced among the three SMFs. The MMFs are corroded with hydrofluoric acid and act as mode couplers to split and recombine light owing to the core diameter mismatch with the SMF. A layer of graphene oxide (GO) is coated on the MMFs by dip-coating and natural evaporation. The effective refractive index of the GO will vary when it absorbs the water molecules. As a result, the intensity of the transmission light in the core and cladding of the single mode fiber can be adjusted. Thus, the intensity of the resonant dip will vary when the relative humidity changes. The experimental results show that a humidity sensitivity of 0.263 dB/RH% with a linear correlation coefficient of 99% can be achieved in a relative humidity range of 35% to 85%.
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Tong Sun, K. T. V.
Fig. 1 Structure of sensing head.
Fig. 2 Schematic diagram of etching device.
Fig. 3 (a) Relation between etch time and waist diameter. (b) Transmission spectrum of 19th minute of corrosion.
Fig. 4 (a) Multimode fiber coated with graphene oxide at magnification of 82. (b) Detailed drawing of part coated with graphene at magnification of 20K. (c) Enlarged drawing of cross section at multimode fiber at magnification of 30K under scanning electron microscope (SEM).
Fig. 5 Transmission spectrogram before and after coating of graphene oxide.
Fig. 6 Schematic diagram of experimental device.
Fig. 7 (a) Change in transmission spectrum with change in HR from 35% to 85%. (b) Relation between relative humidity and transmission peak at dip of A.
Fig. 8 Relation between RH and transmission peaks at dips of A, B, and C.
Fig. 9 (a) The spatial frequency spectrum of the transmission spectrum at different RH values. (b) Spatial spectrum in the range of spatial frequencies from 0 to 0.002. (c) Spatial spectrum in the range of spatial frequencies from 0.05 to 0.17.
Fig. 10 Stability test results of three different transmission peaks under fixed relative humidity.

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