Abstract
We demonstrated a biocompatible and highly sensitive temperature sensor using DNA-CTMA (DNA-Cetyl trimethyl ammonium) solid film deposited on micro-tapered fiber. The micro-tapered silica fiber provided a built-in interferometer that was inherently sensitive to the environment variation due to the enhancement of evanescent wave interaction. The tapered region was coated with DNA-CTMA film with a high thermo-optic coefficient enabling a high-temperature sensitivity higher than −0.9 nm/°C in the bio-medically important region from 35 to 80 °C in a water bath. The cross-sensitivity problem between the temperature-sensing and the strain-sensing was successfully resolved since the elastic properties of the DNA-CTMA film on the micro-tapered silica fiber resulted in a very low strain sensitivity of −7 pm/ $\mu \varepsilon $ . Detailed procedures for device fabrication and optical characterization of the proposed device were described.
Highlights
O PTICAL fiber sensors are immune to electromagnetic interference, mechanically flexible, light-weighted, and can be miniaturized with a small footprint
Temperature sensing has been based on key fiber optic technologies including fiber Bragg grating (FBG) [8], photonic crystal fiber (PCF) [9], [10], external Fabry-Perot interferometer on fiber tip (EFPI) [11] and tapered micro/nanofiber [12], which are still being actively pursued in recent years
We proposed and experimentally demonstrated a new type of all-fiber temperature sensor that showed a high-temperature sensitivity exceeding those of prior reports by four folds and a suppressed strain response to achieve a strain insensitive temperature sensor
Summary
O PTICAL fiber sensors are immune to electromagnetic interference, mechanically flexible, light-weighted, and can be miniaturized with a small footprint. The film provided two key roles; 1) a high thermo-optic coefficient (TOC), dn/dT, to modulate RI of the layer sensitive to the temperature variations, 2) an elastic buffer to reduce the straininduced RI change, dn/dε, over the micro-taper. Utilizing these unique features, we achieved a high-temperature sensitivity over −0.9 nm/◦C in the biomedically important region from 35 to 80 ◦C immersed in a water bath whilst successfully suppressing the strain sensitivity to −7 pm/με, for the first time to the best knowledge of the authors. The sensing head had a length of 2.5 mm, which is shorter than prior reports by several folds
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