Abstract
We experimentally demonstrate an all-silica first-order fiber Bragg grating (FBG) for high temperature sensing by focused ion beam (FIB) machining in a fiber probe tapered to a point. This 61-period FBG is compact (~36.6 μm long and ~6.5 μm in diameter) with 200-nm-deep shallow grooves. We have tested the sensor from room temperature to around 500 °C and it shows a temperature sensitivity of nearly 20 pm/°C near the resonant wavelength of 1550 nm. This kind of sensor takes up little space because of its unique geometry and small size and may be integrated in devices that work in harsh environment or for detecting small objects.
Highlights
Over the last two decades, optical sensors based on fiber gratings, including fiber Bragg gratings (FBGs) and long-period gratings (LPGs), have attracted much attention due to their widespread applications in various physical or chemical parameter measurements such as refractive index, strain and temperature
These gratings fabricated in thick fibers have weak index modulation and the grating lengths are at least several millimeters, which greatly limit the size of sensor heads
We experimentally demonstrate a compact all-silica deeply-corrugated first-order-FBG for high-temperature sensing by focused ion beam (FIB) machining in a tapered non-photosensitive single-mode-fiber probe with a sharp profile
Summary
Over the last two decades, optical sensors based on fiber gratings, including fiber Bragg gratings (FBGs) and long-period gratings (LPGs), have attracted much attention due to their widespread applications in various physical or chemical parameter measurements such as refractive index, strain and temperature. Standard fiber gratings fabricated by exposing photosensitive fibers to an intense ultraviolet interference pattern can be normally used for measuring relatively low temperature below 200 °C Various fabrication methods such as CO2 laser irradiation [1,2], femtosecond laser exposure [3,4] and etched corrugations [5,6], have been demonstrated to write gratings for high temperature sensing in different types of optical fibers [7]. Several kinds of techniques on fabrication microfiber gratings have been proposed, for example, wrapping a microfiber on a microstructured rod [8,9], using CO2 lasers [10] and femtosecond lasers [11,12] The former can be used to realize compact FBG but it needs extra polymer coating which is not suitable for high temperature sensing. All fiber connection, high sensitivity and especially unique structure offer possible potentials for fast-response high temperature sensing, in small object, e.g. bubbles
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