Abstract
Xenon plasma-FIB micromachining has been used for relatively rapid (10-20 minutes) production of intrinsic Fabry-Perot cavities in fused silica single and multimode fibers without any post-processing. Infiltration of organic solvents into the cavity produced in the proximity of cleaved-end of a single mode fiber has enabled refractive index sensing with a sensitivity of ∼-65 dB/riu in the range 1.31-1.37. The influence of cavity wall-angle and cleave imperfections on the performance of the sensor have been discussed. Theoretical interpretation shows that the index sensitivity and measurement range can be tailored via the length of the cavity and its distance from the cleaved-end. The same sensor when heated up to 900 °C has shown a wavelength-temperature sensitivity of 8.1 pm/°C and 8.7 pm/°C during the first and second heating cycles respectively owing to the irreversible effects of dopant-diffusion. Multimode fiber cavity has enabled chemical sensing via NIR-absorption spectroscopy of an epoxy resin, amine-based hardener and its affinity for atmospheric moisture, offering scope for remote chemical process monitoring of engineering materials and structures.
Highlights
Intrinsic fiber Fabry-Perot sensors based on air cavities are fabricated largely by means of 157 nmexcimer [1,2] and femto-second laser micromachining [3,4]; chemical etching of cleaved fibers [5,6,7]; and focussed ion beam (FIB) milling [8,9]
Infiltration of organic solvents into the cavity produced in the proximity of cleaved-end of a single mode fiber has enabled refractive index sensing with a sensitivity of ∼-65 dB/riu in the range 1.31-1.37
The magnitudes of FFT peaks corresponding to the superposition of 3-normal Fresnel reflections produced from a Fabry-Perot cavity micromachined in the proximity of the cleaved-end of a fiber show different sensitivities to refractive index of infiltrated liquid
Summary
Intrinsic fiber Fabry-Perot sensors based on air cavities are fabricated largely by means of 157 nmexcimer [1,2] and femto-second laser micromachining [3,4]; chemical etching of cleaved fibers [5,6,7]; and focussed ion beam (FIB) milling [8,9]. As governed by the pulsed laser-material interactions, the topography of high-aspect ratio microcavities in fused silica is often accompanied by one or more of the unwanted effects to a varying degree in the form of surface swelling and rugged topography, ablation debris, microcracking and cavity wall-tapering [11,12]. These collateral effects can be detrimental to the optical performance and the mechanical integrity of the fiber sensor. Bellouard [15] used HF-etching to reduce the ultrafast laser-induced density of topographical surface peaks that act as stress concentrators after the production of micro-flexures in fused silica
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