Polymer PCF Bragg grating sensors based on poly(methyl methacrylate) and TOPAS cyclic olefin copolymer

Abstract

Fibre Bragg grating (FBG) sensors have been fabricated in polymer photonic crystal fibre (PCF). Results are presented using two different types of polymer optical fibre (POF); first multimode PCF with a core diameter of 50μm based on poly(methyl methacrylate) (PMMA) and second, endlessly single mode PCF with a core diameter of 6μm based on TOPAS cyclic olefin copolymer. Bragg grating inscription was achieved using a 30mW continuous wave 325nm helium cadmium laser. Both TOPAS and PMMA fibre have a large attenuation of around 1dB/cm in the 1550nm spectral region, limiting fibre lengths to no longer than 10cm. However, both have improved attenuation of under 10dB/m in the 800nm spectral region, thus allowing for fibre lengths to be much longer. The focus of current research is to utilise the increased fibre length, widening the range of sensor applications. The Bragg wavelength shift of a grating fabricated in PMMA fibre at 827nm has been monitored whilst the POF is thermally annealed at 80 ˚C for 7 hours. The large length of POF enables real time monitoring of the grating, which demonstrates a permanent negative Bragg wavelength shift of 24nm during the 7 hours. This creates the possibility to manufacture multiplexed Bragg sensors in POF using a single phase mask in the UV inscription manufacturing. TOPAS holds certain advantages over PMMA including a much lower affinity for water, this should allow for the elimination of cross-sensitivity to humidity when monitoring temperature changes or axial strain, which is a significant concern when using PMMA fibre.

Fiber optic liquid level monitoring system using microstructured polymer fiber Bragg grating array sensors: performance analysis

“…To obtain five gratings with different wavelengths, we used two different phase masks (pitches of 557.5 and 580 nm) and made use of the thermal annealing process to mPOF-1. change their wavelengths [10]. Following grating inscription, the 75 cm long mPOF containing FBGs was UV-glued (Norland 78) to one 8° angled silica fiber pigtail.…”

Fabrication of Polymer Optical Fibre (POF) Gratings

“…[83] though there have been many reports regarding MM POF gratings [22,64,65,66,76,84,85,86,87,88,89,90,91,92]. For SM transmission of step index (SI) POF, the normalized frequency should obey the following equation [93]: $V=\frac{2\pi }{\lambda }\cdot a\sqrt{n_{\mathrm{co}}^2-n_{\mathrm{cl}}^2}<2.4$ where 2 a and λ are the diameter of fibre core and the operating wavelength, respectively.…”

Aviation Fuel Gauging Sensor Utilizing Multiple Diaphragm Sensors Incorporating Polymer Optical Fiber Bragg Gratings

“…The inscription process was monitored using a continuous wave, super-luminescent diode from Superlum centered at 835 nm (with a power output of 1.25 mW over a spectrum width of 50 nm) with FC/APC terminated pigtail and an optical spectrum analyzer (OSA) connected to an 850 nm single-mode silica fiber coupler. To obtain five gratings with different wavelengths, two different phase masks were used with pitches of 557.5 and 580 nm and thermal annealing of the inscribed fiber was used to change the Bragg wavelengths [15]. The reflection and transmission spectra of the sensors are shown in Figs.…”