Structurally-modified tapered optical fiber sensors for long-term detection of liquids

• Published in: Optical fiber technology 2019-01, Vol.47, p.187-191
• Main Authors: Komanec, Matej, Nemecek, Tomas, Vidner, Premysl Michal, Martan, Tomas, Lahodny, Frantisek, Zvanovec, Stanislav
• Format: Article
• Language: English
• Subjects: Evanescent-wave; Liquid sensing; Long-term effects; Optical fiber taper; Refractometry
• ISSN: 1068-5200; 1095-9912
• DOI: 10.1016/j.yofte.2018.11.010

•Structurally-modified tapered optical fiber sensor for detection of liquids studied.•Described structural modification of the sensor surface for enhanced sensitivity.•Sensors’ response curve can be shifted by structural modification.•Long term tests validated time-stability of structurally-modified sensors. We present an improvement of tapered optical fiber (TOF) sensor’s response for the detection of liquids, which is achieved by TOF surface structural modification. Our TOF sensors utilize the refractometric principle with enhanced evanescent-wave overlap due to the wavelength of 1550 nm and TOF waist diameters of 4–6 μm. The structural modification is achieved by long-term TOF exposition to hygroscopic liquid analytes and ambient atmosphere. To analyze the structural modification process, long-term as well as proof-of-principle tests have been carried out to evaluate TOF sensors stability in terms of sensitivity and resolution. Maximum sensitivity of over 2100 dB/RIU has been reached when TOF is used to detect a liquid analyte with refractive index of 1.415. Increase of more than 1400 dB/RIU is attributed to the enhanced sensitivity. Sample TOF sensors were then linearly calibrated and have been tested in more than one year-long continuous measurement campaign. Resolution better than 7·10-4 for a refractive index range of from 1.405 to 1.425 with working point drift below 2·10-4 over 12 months period has been achieved. Our results and observations are suitable for reliable, low-cost and application-tailored TOF sensor development.