High Sensitivity Ammonia Gas Sensor Based on a Silica-Gel-Coated Microfiber Coupler

Abstract

(2017) High sensitivity ammonia gas sensor based on a silica gel coated microfiber coupler. Journal of Lightwave Technology, 35 (14 Northumbria University has developed Northumbria Research Link (NRL) to enable users to access the University's research output. Copyright © and moral rights for items on NRL are retained by the individual author(s) and/or other copyright owners. Single copies of full items can be reproduced, displayed or performed, and given to third parties in any format or medium for personal research or study, educational, or not-for-profit purposes without prior permission or charge, provided the authors, title and full bibliographic details are given, as well as a hyperlink and/or URL to the original metadata page. The content must not be changed in any way. Full items must not be sold commercially in any format or medium without formal permission of the copyright holder. The full policy is available online: http://nrl.northumbria.ac.uk/policies.html This document may differ from the final, published version of the research and has been made available online in accordance with publisher policies. To read and/or cite from the published version of the research, please visit the publisher's website (a subscription may be required.) > REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 1 Abstract-In this paper, a high sensitivity ammonia gas sensor is proposed based on a silica gel coated microfiber coupler (MFC). The MFC structure is formed by the two tapered fibers with 3 μm waist diameter each, which were fabricated by using a customized microheater brushing technique. Silica gel coating was prepared by a sol-gel technique and applied on the surface of the MFC as a thin layer. The spectral characteristics of the proposed sensor were studied under various ammonia gas concentrations. The experimental results show that the coating thickness strongly affected the sensitivity of the MFC-based sensor to ammonia gas concentration. For the sensor with a 90 nm silica gel coating thickness, the highest measurement sensitivity is 2.23 nm/ppm for ammonia gas concentration, and the resolution is as good as 5 ppb, while the measured response and recovery times are about 50 and 35 seconds, respectively. Finally, it is demonstrated that the proposed sensor offers good repeatability and selectivity to ammonia.Index Terms-optical fiber sensors, microfiber coupler, ammonia gas sensor.

Silica Gel Coated Spherical Micro resonator for Ultra-High Sensitivity Detection of Ammonia Gas Concentration in Air

“… Optical technique Range (ppm) Response/recovery times (sec) Detection Limit (ppb) Ref. Bromocresol purple coated U-shaped plastic fiber 145–3518 10 10,000 7 Silica gel coated micro fiber coupler 0.25–10.4 50/35 5 23 Surface plasmon resonance, Ag/Sn O 2 10–100 n/a 154 24 Nanostructured dye-doped 12–216 50 5,000 25 Mach-Zehnder interferometer using graphene 0–360 0.5 300 26 Graphene-coated microfiber Bragg grating 0–100 n/a 200 27 Silica gel coated microsphere (this work) 0.0025–0.0123 1.5/3.6 0.16 …”

Temperature Self-Compensated Refractive Index Sensor Based on Fiber Bragg Grating and the Ellipsoid Structure

“…The refractive index sensor has many important applications, such as the quality control of chemical industries, monitoring biochemical reactions, the prevention of global warming, etc. [1,2,3,4,5,6,7]. The most famous refractive index sensor is the Abbe refractometer, which measures the surrounding refractive index (SRI) according to the total internal reflection [8].…”

Study of the influence of the sol-gel silica layer thickness on sensitivity of the coated silica microsphere resonator to ammonia in air

“…As can be seen from the graph, for the sample with the thickest coating (L7, ~359 nm), the WGM resonance disappears from the transmission spectrum of the tapered fiber, indicating that no optical coupling to the microsphere occurs between 40 s to 110 s. The phenomenon could be explained as follows. Since the mechanism of interaction is based on adsoption of ammonia at the coating surface [11], for a thicker porous silica coating a greater surface area is availabe to be occupied by the NH3 molecules and thus there is a higher RI change within the coating [12]. When the RI of the coating layer exceeds some critical value, coupling losses increase resulting in that light coupling no longer takes place between the microsphere and fiber taper.…”