Abstract
In this work, fibre Bragg gratings (FBGs) were inscribed in two different undoped poly- (methyl methacrylate) (PMMA) polymer optical fibres (POFs) using different types of UV lasers and their inscription times, temperature and strain sensitivities are investigated. The POF Bragg gratings (POFBGs) were inscribed using two UV lasers: a continuous UV HeCd @325 nm laser and a pulsed UV KrF @248 nm laser. Two PMMA POFs are used in which the primary and secondary preforms (during the two-step drawing process) have a different thermal treatment. The PMMA POFs drawn in which the primary or secondary preform is not specifically pre-treated need longer inscription time than the fibres drawn where both preforms have been pre-annealed at 80 °C for 2 weeks. Using both UV lasers, for the latter fibre much less inscription time is needed compared to another homemade POF. The properties of a POF fabricated with both preforms thermally well annealed are different from those in which just one preform step process is thermally treated, with the first POFs being much less sensitive to thermal treatment. The influence of annealing on the strain and temperature sensitivities of the fibres prior to FBG inscription is also discussed, where it is observed that the fibre produced from a two-step drawing process with well-defined pre-annealing of both preforms did not produce any significant difference in sensitivity. The results indicate the impact of preform thermal pre-treatment before the PMMA POFs drawing, which can be an essential characteristic in the view of developing POF sensors technology.
Highlights
polymer optical fibres (POFs) can be considered as a strong alternative to silica fibres, in applications such as short distance optical links, Terahertz waveguides and filters, and mainly in sensing applications [1,2,3,4] due Sensors 2017, 17, 891; doi:10.3390/s17040891 www.mdpi.com/journal/sensorsSensors 2017, 17, 891 to their flexibility, high failure strain, large cores and great elasticity
The results presented here indicate the impact of thermal pre-treatment in both preforms processes before the poly-methyl methacrylate (PMMA) POFs drawing on the fast inscription of Polymer optical fibre Bragg gratings (POFBGs), which is an essential characteristic in the view of developing stable POFBG based thermo-mechanical sensors
Improvements were reported in the photosensitivity of undoped POFs, where there was a well-defined pre-annealing of both the preforms fabricated in two-step process
Summary
POFs can be considered as a strong alternative to silica fibres, in applications such as short distance optical links, Terahertz waveguides and filters, and mainly in sensing applications [1,2,3,4] due Sensors 2017, 17, 891; doi:10.3390/s17040891 www.mdpi.com/journal/sensors. The mechanical properties provide enhanced sensitivity or longer operational range to intrinsic polymer fibre sensors when they are used for strain, stress, pressure, temperature and humidity monitoring, as well as for transverse force sensing [5,6,7,8,9,10,11,12] Many of these sensors are based on FBGs, which have been written in different spectral regions in doped and undoped step-index POFs [13], microstructured POF (mPOF) (including PMMA and TOPAS materials) [13,14,15], as well as low loss cyclic optical polymer (CYTOP)-perfluorinated. The drawing process can be done in two-step process where first we draw a cane, sleeve it, and we draw the secondary preform Both fibres were drawn in this way.
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