Factors influencing the temperature sensitivity of PMMA based optical fiber Bragg gratings

Zhang, W.; Webb, David J.

doi:10.1117/12.2054210

Cited by 13 publications

(19 citation statements)

References 15 publications

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“…Pre-straining the POFBG can get rid of this uncertainty at the cost of reduced responsivity. In contrast, an increased responsivity in temperature sensing can be achieved by using a pre-strained POFBG [16].…”

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confidence: 99%

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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“…This nonlinearity mainly arises from the mechanical responses of PMMA based optical fiber such as swelling and thermal expansion, which is closely related to the polymer fiber drawing process. The larger nonlinearity of response can be observed in un-annealed POFBG [22]. Although a more complicated expression could be obtained by using similar method described in Section III, this drawing process induced nonlinearity may vary with environmental condition, resulting in additional uncertainty.…”

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confidence: 99%

General Expression of Poly(Methyl Methacrylate) Optical Fiber Bragg Grating Sensing Response

Zhang

Webb

2019

IEEE Photon. Technol. Lett.

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Poly(methyl methacrylate) (PMMA) optical fiber inherently responds to the changes of temperature and relative humidity. PMMA optical fiber Bragg grating (POFBG) has been reported with diverse temperature and relative humidity sensitivities. These results cannot present the full performance of POFBG sensor as they are measured at limited environmental conditions. In this work we systematically investigated the POFBG temperature and relative humidity sensing responses. We found that POFBG temperature/relative humidity sensitivity is the function of both temperature and relative humidity. In the experiments POFBG sensing responses vary linearly with temperature/relative humidity at fixed relative humidity/temperature. Based on this linearity a general expression of POFBG sensing response to temperature and relative humidity has been obtained and verified for the first time, to describe the POFBG performance in desired operation range. The anisotropy in POF induced by drawing history could induce uncertainty in POFBG response but pre-straining POFBG overcomes this problem.

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“…4b is only related to the optical absorption in POF at different humidity levels and is not a POFBG humidity sensing response. Indeed the POFBG wavelength actually increases with relative humidity [4,12], as defined by (2).…”

Section: Fig 1 Experimental Arrangement For Investigating Pofbg Wavmentioning

confidence: 97%

“…This corresponds to internal temperature change inside the POF. It performs like a POFBG temperature sensor in which POFBG wavelength varies linearly with temperature in a certain range [12]. However, the wavelength reduction of the POFBG under a certain input power varies nonlinearly with the relative humidity.…”

Section: Fig 1 Experimental Arrangement For Investigating Pofbg Wavmentioning

confidence: 99%

Wavelength Drift of PMMA-Based Optical Fiber Bragg Grating Induced by Optical Absorption

Zhang

Abang

Webb

et al. 2015

IEEE Photon. Technol. Lett.

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The transmission loss in polymer optical fiber is much higher than that in silica fiber. Very strong absorption bands dominate throughout the visible and near infrared. Optical absorption increases the internal temperature of the polymer fiber and reduces the wavelength of any polymer optical fiber Bragg grating inscribed within the fiber. In this work we have investigated the wavelength drift of FBGs inscribed in poly(methyl methacrylate) (PMMA) based fiber under illumination at different wavelengths. The experiments have shown that the characteristic wavelength of such a POFBG starts decreasing after a light source is applied to it. This decrease continues until equilibrium inside the fiber is established, depending on the surrounding humidity, the optical power applied, and operation wavelength.

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Factors influencing the temperature sensitivity of PMMA based optical fiber Bragg gratings

Cited by 13 publications

References 15 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

General Expression of Poly(Methyl Methacrylate) Optical Fiber Bragg Grating Sensing Response

Wavelength Drift of PMMA-Based Optical Fiber Bragg Grating Induced by Optical Absorption

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