Temperature insensitive hysteresis free highly sensitive polymer optical fiber Bragg grating humidity sensor

Abstract

The effect of humidity on annealing of poly (methyl methacrylate) (PMMA) based microstructured polymer optical fiber Bragg gratings (mPOFBGs) and the resulting humidity responsivity are investigated. Typically annealing of PMMA POFs is done in an oven without humidity control around 80°C and therefore at low humidity. We demonstrate that annealing at high humidity and high temperature improves the performances of mPOFBGs in terms of stability and sensitivity to humidity. PMMA POFBGs that are not annealed or annealed at low humidity level will have a low and highly temperature dependent sensitivity and a high hysteresis in the humidity response, in particular when operated at high temperature. PMMA mPOFBGs annealed at high humidity show higher and more linear humidity sensitivity with negligible hysteresis. We also report how annealing at high humidity can blue-shift the FBG wavelength more than 230 nm without loss in the grating strength.

Fast and stable gratings inscription in POFs made of different materials with pulsed 248 nm KrF laser

“…The annealing can be made before the grating inscription (preannealing) or after the inscription (post-annealing). If it is made after the grating inscription, the annealing can lead to a blue-shift of the Bragg wavelength [9]. All fibers except of PC were pre-annealed.…”

“…In addition, the biocompatibility and non-brittle nature of POFs means that they are clinically acceptable and can be employed in in-vivo applications [6]. Such advantages of POF sensors enable their application to measure parameters like temperature [7], strain [8], humidity [9], curvature [10], acceleration [11], and liquid level [12]. Furthermore, POF sensors are employed in biomedical applications such as antibody [13,14] and glucose sensors [15].…”

Simultaneous measurement of temperature and humidity with microstructured polymer optical fiber Bragg gratings

“…The grating inscription technique and the configuration setup used in this work were described in reference 25. The two FBGs then annealed together in an environmental climate chamber (CLIMACELL, MMM group) for 24 hours at 85 ºC and 90 % RH for a stable operation of the sensor 15 . The new Bragg wavelengths for FBG1 and FBG2 after annealing were found to be 841.21 nm and 855.32 nm, respectively.…”

“…Some polymers, such as PMMA, are humidity sensitive and strongly absorb water 9 , while other polymers, for instance TOPAS and Zeonex, are insensitive to humidity [10][11][12] . Exploiting such unique and intrinsic properties of POFs, researchers in this area have developed different single parameter POFBG sensors such as strain, temperature, humidity, pressure and soon [13][14][15][16][17] . Only little work has been done in the development of multi-parameter POFBG sensors.…”

Effects of pre-strain on the intrinsic pressure sensitivity of polymer optical fiber Bragg gratings

“…Previous research includes POFBGs for strain 1,2 , temperature 3,4 and humidity 5,6 sensing, but also investigations towards measuring hydrostatic pressure have been carried out [7][8][9] . These investigations show that, contrary to FBGs in silica fibers, the pressure response in POFBGs is positive, i.e.…”