New Methods of Enhancing the Thermal Durability of Silica Optical Fibers

Abstract

Microstructured optical fibers can be precisely tailored for many different applications, out of which sensing has been found to be particularly interesting. However, placing silica optical fiber sensors in harsh environments results in their quick destruction as a result of the hydrolysis process. In this paper, the degradation mechanism of bare and metal-coated optical fibers at high temperatures under longitudinal strain has been determined by detailed analysis of the thermal behavior of silica and metals, like copper and nickel. We furthermore propose a novel method of enhancing the lifetime of optical fibers by the deposition of electroless nickel-phosphorous alloy in a low-temperature chemical process. The best results were obtained for a coating comprising an inner layer of copper and outer layer of low phosphorous nickel. Lifetime values obtained during the annealing experiments were extrapolated to other temperatures by a dedicated model elaborated by the authors. The estimated copper-coated optical fiber lifetime under cycled longitudinal strain reached 31 h at 450 °C.

Miniature Uncooled and Unchopped Fiber Optic Infrared Thermometer for Application to Cutting Tool Temperature Measurement

“…The expected temperature range of the machine tool surface was nominally 100 °C when rotating in free air, to approximately 900 °C when cutting [ 1 ]. The temperature expected during cutting necessitated using sapphire fiber optic cable as the embedded sensor, since other fiber optic types would fail at elevated temperatures [ 33 ]. Combining the spectral characteristics of the detector and optical fiber, the instrument was sensitive to wavelengths between 3 μm and 3.5 μm.…”

Electrolytic Joints Between Metal Surfaces and Metal-Coated Fibers for Application in High Temperature Optical Fiber Sensors

“…If the phosphorous addition is higher or lower than 8-10%, the nickel coating is more ductile. What is more, the internal tensions in the nickel layer are lowest for medium (8-10%) phosphorous addition [23]. As the phosphorous content rises, the coating's hardness gradually decreases [24].…”

Stainless steel component with compressed fiber Bragg grating for high temperature sensing applications

“…Additive manufacturing involves building up structures layer by layer and it opens up the prospect of incorporating valuable internal features into parts during their manufacture and one of the possibilities enabled by this technology is the embedment of components during their construction [6]. Recent studies on the temperature characteristics of an embedded FBG in a metallic structure show that due to the mismatch of the coefficient of thermal expansion (CTE) between silica and the host metal, the differential strain at elevated temperatures can lead to delamination and fiber breakage [6][7][8][9][10], thus limiting the application of such direct fiber embedded sensors to ~450°C.…”