ZnO Nanorods Coated Microfiber Loop Resonator For Relative Humidity Sensing

This paper reported a new humidity sensor, employing microfiber loop resonator (MLR) coated with Zinc Oxide (ZnO) as a probe. The MLR was constructed from a silica tapered fiber with a waist diameter of 7 µm, which was prepared using flame brushing technique. The self-touching loop was coated by ZnO using sol–gel method. A significant response to humidity changes from 35%RH to 85%RH was observed due to the changeable refractive index of the ZnO coating material which modified the light propagation at the output of the MLR. The result shows that the sensitivity of the proposed sensor increases by a factor of 2 as compared to the uncoated MLR. The output power of the ZnO coated MLR drops linearly from −29.3 dBm to −43 dBm when relative humidity increases from 35%RH to 85%RH. The linearity and resolution of the ZnO coated MLR also outperformed the uncoated MLR with 99.4% and 0.013%RH respectively

Uric acid sensing using tapered silica optical fiber coated with zinc oxide nanorods

In this paper, fiber-optic sensors by different tapered lengths of silica optical fiber (SOF) coated with zinc oxide (ZnO) nanorods were fabricated and demonstrated to detect different concentrations of uric acid. The SOFs were tapered in the length of 1 cm, 3 cm, 5 cm, and 7 cm using flame brushing technique. ZnO nanorods were coated on the surface of the tapered SOFs for 24 hours using sol-gel immersion method. The sensing experiment was performed by dipping the SOF in the uric acid solution. One end of the SOF was connected to a light source and while the other end to an optical analyzer. The output of the sensor was analyzed for different uric acid concentration from 0 ppm to 500 ppm with the different tapered lengths of SOF sensors. The result shows that the sensor with tapered length of 7 cm had the highest sensitivity response of 0.0006 mV/ppm with linearity of 98.52%. In addition, all tapered size of sensor shows significant improvement of sensing performance with sensitivity consistently improved from 1 cm to 7 cm with good linearity as ZnO nanorods coated the tapered lengths. The detection limit was found to be at 0.2 ppm in the range of uric acid concentration

Optimization of sensing performance factor (γ) based on microfiber-coupled ZnO nanorods humidity scheme

An optimization method of the proposed humidity sensing scheme comprises of silica microfiber laid on a glass surface coated with Zinc Oxide (ZnO) nanorods is reported. The silica microfibers were tapered into several waist diameters of 6 µm, 8 µm, 10 µm and 12 µm using flame brushing technique, while the glass surface was coated with ZnO nanorods using hydrothermal method for 6 h, 9 h, 12 h, 15 h and 18 h of growth time. The samples were exposed to the different humidity level ranging from 35%RH to 85%RH to observe several performance parameters such as scattering coefficient (α), sensing performance factor γ, output light intensity and ultimately the sensitivity. 12-h growth sample exhibited the optimum results in term of α,γ, output light intensity and sensitivity towards the %RH level. The sensitivity improved by a factor of 1.3 as compared to the closest best sample. Besides that, it was found that 6 µm waist diameter microfiber sample produced optimum result in term α, γ and sensitivity towards the %RH level. The sensitivity improved by a factor of 1.1 as compared to the closest best sample. The work provided the best optimization method for microfiber and ZnO nanorods samples for the proposed humidity sensing scheme. It utilized the distinctive features of the scattering and surface absorption capability of the microfiber and ZnO nanomaterials coated glass surface to couple with the surrounding water molecules for humidity sensing. © 2019 Elsevier Inc

Optical characterization of different waist diameter on microfiber loop resonator humidity sensor

In this paper, the effect of different waist diameter on silica microfiber loop resonator (MLR) relative humidity (%RH) sensor is reported. The silica fiber was tapered to vary the waist diameter to 3 μm, 4 μm, 5 μm,7 μm, 8 μm and 10 μm using flame brushing technique. The MLR with a 300 μm diameter loop was formed by manually twisted the tapered fiber under an optical microscope into a self-touching loop. Initially, the effect of whispering gallery modes (WGMs) on the MLR was observed. Transmission mode spectra were observed to determine the number of resonated wavelength and quality factor (Q-factor). The Q-factor is observed to be >105 for all samples and MLR with 3 μm diameter achieve the highest Q-factor value. A significant response to %RH from 35% to 85% was observed due to the change of refractive index between the MLR and the surrounding medium resulting different light attenuation in the microfiber. The sensitivity increased by a factor of 12.2 for the MLR with diameter of 7 μm as compared to the smaller diameter MLRs and a factor of 13.7 as compared to straight microfiber (SmF). As for resolution, the MLR with waist diameter of 7 μm improve by a factor of 5 as compared to the smaller waist diameter and a factor of 6.5 as compared to SmF. The proposed humidity sensor employs the microfiber loop resonator without any sensitive material coated on it which reduced the complexity during the fabrication and manufacturing process. The reported results may contribute to the optimal waist diameter of microfiber loop resonators for humidity sensing application

Characteristic Of Non-Adiabatic Tapered Fiber Towards Humidity

This paper reported the characterization of non-adiabatic tapered fiber using flame brushing technique towards humidity. The tapered fibers were exposed to relative humidity concentrations level ranging from 35%RH to 85%RH to observe the optical characteristic. There are several criterions considered for this study such as scattering coefficient (αmf), transmission loss (TL), output light intensity and enhancement factor (ɣ). The relationship between the waist diameter and the other criterions towards the %RH level has been successfully investigated

Microfiber loop resonator for formaldehyde liquid sensing

This work employed the whispering gallery mode (WGM) of microfiber loop resonator (MLR) for formaldehyde (CH2O) liquid sensing application. A significant sensing response to different concentrations of formaldehyde liquid from 0% to 5% was observed due to the surface absorption and changeable refractive index resulting in different light attenuation in the silica microfiber. As the concentration increases, the output power of the MLR decreased linearly from −18.9 dB m to −36.2.dBm with sensitivity increased by a factor of 2.5 as compared to straight microfiber (SmF). As for resolution, the MLR improved by a factor of 3.28 as compared to SmF. © 2019 Elsevier Gmb