Fabrication and Qualitative Analysis of an Optical Fibre EFPI-Based Temperature Sensor.

Fintan Mcguinness,Mohamed Oubaha,Aidan Cloonan,Emma Tobin,Gabriel Leen,M Mahmood Ali,Dinesh Babu Duraibabu,Gerald Kilkelly

doi:10.3390/s21134445

Abstract

The following presents a comparison of an extrinsic Fabry–Perot interferometer (EFPI)-based temperature sensor, constructed using a novel diaphragm manufacturing technique, with a reference all-glass EFPI temperature sensor. The novel diaphragm was manufactured using polyvinyl alcohol (PVA). The novel sensor fabrication involved fusing a single-mode fibre (SMF) to a length of fused quartz capillary, which has an inner diameter of 132 μm and a 220 μm outer diameter. The capillary was subsequently polished until the distal face of the capillary extended approximately 60 μm beyond that of the single mode fibre. Upon completion of polishing, the assembly is immersed in a solution of PVA. Controlled extraction resulted in creation of a thin diaphragm while simultaneously applying a protective coating to the fusion point of the SMF and capillary. The EFPI sensor is subsequently sealed in a second fluid-filled capillary, thereby creating a novel temperature sensor structure. Both temperature sensors were placed in a thermogravimetric analyser and heated from an indicated 30 °C to 100 °C to qualitatively compare sensitivities. Initial results indicated that the novel manufacturing technique both expedited production and produces a more sensitive sensor when compared to an all-glass construction.

Highlights

We report on work undertaken on one method to reduce the time required to manufacture an Extrinsic Fabry-Perot Interferometer (EFPI), which may potentially be used in an Ultra-High-Resolution Temperature Sensor (UHRTS) similar to that of Poeggel et al [15], while simultaneously improving its mechanical resistance to failure modes resulting from eternally applied shear stress to the sensor
While the all-glass sensors that are successfully produced give reliable and repeatable results, the authors are of the opinion that the process would benefit from the following changes: (a) mechanical strengthening of the fusion point between the stripped single-mode fibre (SMF) and the capillary; (b) mechanical strengthening of the diaphragm; and (c) removal of the requirement for hydrofluoric acid (HF) in the fabrication process
Initial experiments with an optical fibre re-coater were undertaken to determine whether or not the exposed SMF and capillary fusion point could be accurately re-coated without coating the diaphragm

Summary

Introduction

The use of optical fibre sensors has become increasingly prevalent in the past decade, with significant industry players interfacing with universities to further develop such sensors [1]. Driving factors for this include the small dimensions of optical fibre sensors, their immunity to electromagnetic interference, and general ease of achieving biocompatibility [2,3]. In addition to the aforementioned patient-centric applications, high-resolution temperature sensors may be of benefit in micro-volume calorimetry applications Their small form factor makes them minimally invasive, and the glass-based outer construction is sterilised, which helps minimise the risk of contamination. The temperature resolution of the optical fibre sensors are comparable to that of quartz thermometers (1 × 10−3 –1 × 10−5 K) [13,14]

Methods

Results

Conclusion