Investigation Into Time Response of Polymer Fiber Bragg Grating Based Humidity Sensors

Zhang, W.; Webb, David J.; Peng, Gang-Ding

doi:10.1109/jlt.2011.2169941

Cited by 156 publications

(84 citation statements)

References 24 publications

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“…For a given type of POF, the response time of a POFBG depends on the diameter of the fiber [17]. Figure 4(a) shows the normalized wavelength changes of the POFBG (with a fiber diameter of 200 μm) over a 10% step humidity change at 35°C.…”

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Humidity responsivity of poly(methyl methacrylate)-based optical fiber Bragg grating sensors

2014

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The humidity response of poly(methyl methacrylate) (PMMA)-based optical fiber Bragg gratings (POFBGs) has been studied. The characteristic wavelength of the grating is modulated by water absorption-induced swelling and refractive index change in the fiber. This work indicates that anisotropic expansion may exist in PMMA optical fiber, reducing the humidity responsivity of the grating and introducing uncertainty in the responsivity from fiber to fiber. By pre-straining a grating, one can get rid of this uncertainty and simultaneously improve the POFBG response time. and affinity for water that leads to a swelling of the fiber and an increase of RI. The former feature offers a wellconditioned performance for overcoming the cross sensitivity issues existing in silica fiber [1], while the latter feature leads to an increase with humidity of the Bragg wavelength of a Bragg grating written in the fiber [2]. This is a potentially very useful property that has possible applications in the chemical processing, agricultural, food storage, paper manufacturing, semiconductor, and pharmaceutical industries, where humidity is monitored and controlled to ensure product quality. This property has also been exploited for the detection of saline concentration [3] and water in fuel [4]. There have been many reports on the use of PMMAbased fiber gratings for humidity sensing. However, the reported humidity responsivities show considerable variation (see, e.g., [1,2,5]). This variation has not been satisfactorily explained and causes great uncertainty concerning the POFBG's performance and applicability.The Bragg wavelength of a fiber grating depends on the effective core RI and the grating pitch, both of which depend on the temperature and the water content in the case of a PMMA-based POFBG. For constant temperature, the Bragg wavelength change of a POFBG against humidity can be expressed aswhere λ B is the initial Bragg wavelength, η is the normalized RI change with humidity %RH −1 , and β the swelling coefficient related to humidity induced volumetric change %RH −1 . The wavelength change in POFBG sensors varies linearly with humidity, if η and β are constant; however both η and β can be temperature or humidity dependent [6,7]. It should be pointed out that not every polymer shows this water affinity: Bragg gratings made in TOPAS polymer are insensitive to humidity [8] and are therefore suitable in applications where cross sensitivity to humidity needs to be avoided. Bragg gratings can be written into pure PMMA optical fibers by using UV illumination to induce polymerization of unreacted monomers that contribute to an increase in RI. Better performance has been achieved using dopedcore PMMA-based optical fibers [9]. Since additional dopants or copolymers are required to control the core index of step index fibers, the performance of PMMAbased fiber gratings may vary with the type of fiber used. The detailed composition of dopant and copolymer used in a specific PMMA-based optical fiber is often not known and neither are their dep...

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Humidity responsivity of poly(methyl methacrylate)-based optical fiber Bragg grating sensors

2014

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“…Particularly, trace water vapor qualification analysis is indispensable in a wide of applications, ranging from polymer fabrication [1], environment analysis [2] to chemical production [3]. Because of remote detection capability, safety in hazardous environments, and immunity to electromagnetic radiation, the distributed feedback diode laser (DFB-DL) based hygrometer attracted the widest applications.…”

Section: Introductionmentioning

confidence: 99%

Study of a distributed feedback diode laser based hygrometer combined Herriot-gas cell and waterless optical components

et al. 2016

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Abstract:A distributed feedback diode laser (DFB-DL) based hygrometer combined with a long-path-length Herriot gas cell and waterless optical components was proposed and investigated. The main function of this sensor was to simultaneously improve the measurement reliability and resolution. A comparison test between a 10-cm normal transmission-type gas cell and a 3-m Herriot gas cell was carried out to demonstrate the improvement. Reliability improvement was achieved by influence suppression of water vapor inside optical components (WVOC) through combined action of the Herriot gas cell and waterless optical components. The influence of WVOC was suppressed from 726 ppmv to 25 ppmv using the Herriot gas cell. Moreover, combined with waterless optical components, the influence of WVOC was further suppressed to no more than 4 ppmv. Resolution improvement from 11.7 ppmv to 0.32 ppmv was achieved mainly due to the application of the long-path-length Herriot gas cell. The results show that the proposed sensor has a good performance and considerable potential application in gas sensing, especially when probed gas possibly permeates into optical components.

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“…PMMA-based optical fiber Bragg gratings (POFBGs) were found to be sensitive to relative humidity, temperature, strain and pressure with high sensitivity [8][9][10][11]. The sensing response time of POFBGs can be significantly improved either by reducing the fiber diameter with chemical etching [9] or by spatial modification of fiber geometry using laser micromachining [12]. There has been a report recently that the sensitivity of chemically etched POFBG over strain, temperature, and pressure can be improved [a1].…”

Section: Introductionmentioning

confidence: 99%

Characterization of Polymer Fiber Bragg Grating With Ultrafast Laser Micromachining

Liu

Cardoso²,

Zhang

et al. 2016

IEEE Photon. Technol. Lett.

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Abstract-We report that the main photosensitive mechanism of poly(methyl methacrylate)-based optical fiber Bragg grating (POFBG) under ultraviolet laser micromachining is a complex process of both photodegradation and negative thermo-optic effect. We found experimentally the unique characteristics of Bragg resonances splitting and reunion during laser micromachining process providing evidence of photodegradation while the mean refractive index change of POFBG was measured to be negative confirming further photodegradation of polymer fiber. The thermal-induced refractive index change of POFBG was also observed by recording the Bragg wavelength shift. Furthermore the dynamic thermal response of the micromachined-POFBG was demonstrated under constant humidity, showing a linear and negative response of around -47.1 pm/°C.

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Investigation Into Time Response of Polymer Fiber Bragg Grating Based Humidity Sensors

Cited by 156 publications

References 24 publications

Humidity responsivity of poly(methyl methacrylate)-based optical fiber Bragg grating sensors

Humidity responsivity of poly(methyl methacrylate)-based optical fiber Bragg grating sensors

Study of a distributed feedback diode laser based hygrometer combined Herriot-gas cell and waterless optical components

Characterization of Polymer Fiber Bragg Grating With Ultrafast Laser Micromachining

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