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Publication Open Access Highly sensitive optical sensor for hydrogen gas based on a polymer microcylinder ring resonator(Elsevier, 2020) Eryürek, Mustafa; Department of Physics; Department of Chemistry; Department of Electrical and Electronics Engineering; Bavili, Nima; Balkan, Timuçin; Morova, Berna; Uysallı, Yiğit; Kaya, Sarp; Kiraz, Alper; Researcher; Researcher; PhD Student; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; Department of Electrical and Electronics Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; N/A; N/A; N/A; N/A; 116541; 22542A highly sensitive platform is demonstrated for hydrogen gas (H-2) sensing based on a polymer microcylinder ring resonator (PMRR) obtained by an optical fiber coated with an inner nanofilm of amorphous palladium (Pd) and an outer polymer layer of polydimethylsiloxane (PDMS) permeable to H-2. The sensing scheme is based on monitoring the spectral shifts of high-quality optical resonances called whispering gallery modes (WGMs) that propagate in the vicinity of the outer rim of the PDMS layer without being affected by the absorption and scattering losses caused by the Pd nanofilm. WGMs are excited by a single-mode tapered optical fiber evanescently coupled to the PMRR. The observed reversible spectral shifts of the WGMs are induced by changes in the diameter of the PDMS layer caused by expansion or contraction of the Pd nanofilm exposed to varying concentrations of H-2. Maximum spectral shift sensitivity of 140 pm/% H-2, a minimum response time of 95 s, and minimum limit of detection of similar to 60 ppm were measured for sensors prepared with different thicknesses of the amorphous Pd nanofilm and tested in the H-2 concentration range up to 1%, having nitrogen gas (N-2) as a carrier. Experiments were also conducted with Pd nanofilms annealed in air or N-2 atmosphere after the deposition. In both cases, smaller sensitivities were observed due to the formation of larger grains within the film, resulting in slower diffusion and reduced solubility of H in the Pd layer. The impacts of oxygen gas and humidity on sensor performance were also studied.
Publication Metadata only Integrated humidity sensor based on SU-8 polymer microdisk microresonator(Elsevier Science Sa, 2017) Y. Karadag; N. Kilinc; N/A; N/A; Department of Physics; Department of Mechanical Engineering; Department of Physics; Eryürek, Mustafa; Taşdemir, Zuhal; Anand, Suman; Alaca, Burhanettin Erdem; Kiraz, Alper; PhD Student; PhD Student; Researcher; Faculty Member; Faculty Member; Department of Mechanical Engineering; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; College of Sciences; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/A; N/A; 115108; 22542Due to its high interaction with water vapor and photolithographic patterning property, SU-8 is a favorable hygroscopic polymer for developing humidity sensors. In addition, optical resonances of optical microresonators are very sensitive to the dianges in their environment. Here, we present integrated optical humidity sensors based on chips containing SU-8 polymer microdisks and waveguides fabricated by single-step UV photolithography. The performance of these sensors is tested under a wide range of relative humidity (RH) levels (0-50%). A tunable laser light is coupled from an excitation fiber to individual SU-8 waveguides using end-face coupling method. As the laser wavelength is scanned, the whispering gallery modes (WGMs) are revealed as dips in the transmission spectra. Sensing is achieved by recording spectral shifts of the WGMs of the microdisk microresonators. Red shift is observed in the WGMs with increasing RH. Between 0 and 1% RH, an average spectral shift sensitivity of 108 pm/% RH is demonstrated from measurements performed on 4 sensor devices. This sensitivity is comparable to the highest values obtained using microresonators in the literature. Measurements performed with another sensor device revealed a decrease in sensitivity by only around 3 times when RH is increased to 45-50%. Finite element modeling simulations are carried out to determine the dominant effect responsible for the resonance shift. The results show that the refractive index change is more important than the microresonator size change. The standard deviation in wavelength measurement is <3 pm, indicating a limit of detection better than 0.03% RH. These results suggest that optical sensor devices that contain integrated SU-8 microresonators and waveguides can be employed as easy-to-fabricate and sensitive humidity sensors. (C) 2016 Elsevier B.V. All rights reserved.Publication Metadata only Optical sensor for hydrogen gas based on a palladium-coated polymer microresonator(Elsevier, 2015) Karadag, Yasin; Tasaltin, Nevin; Kilinc, Necmettin; N/A; Department of Physics; Eryürek, Mustafa; Kiraz, Alper; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; N/A; 22542We report an integrated optical sensor of hydrogen (H-2) gas employing an SU-8 polymer microdisk resonator coated with a palladium (Pd) layer and coupled to a single-mode optical waveguide. The sensing mechanism relies on the expansion in the Pd lattice due to palladium hydride formation in the presence of H-2. Strain induced in the microresonator then causes a red shift of the spectral positions of the resonator whispering gallery modes (WGMs) which is monitored using a tunable laser coupled to the waveguide. H-2 concentrations below the flammable limit (4%) down to 0.3% could be detected in nitrogen atmosphere at room temperature. For H-2 concentrations between 0.3 and 1%, WGM spectral positions shifted linearly with H-2 concentration at a rate of 32 pm/% H-2. Average response time of the devices was measured to be 50 s for 1% H-2. The proposed device concept can also be used to detect different chemical gases by using appropriate sensing layers. (C) 2015 Elsevier B.V. All rights reserved.Publication Metadata only Use of an elastic buffer layer for improved performance of a polymer microcylinder ring resonator hydrogen sensor(Elsevier Science Sa, 2022) N/A; N/A; Department of Physics; Department of Mechanical Engineering; Department of Physics; Bavili, Nima; Ali, Basit; Morova, Berna; Alaca, Burhanettin Erdem; Kiraz, Alper; PhD Student; PhD Student; Researcher; Faculty Member; Faculty Member; Department of Mechanical Engineering; Department of Physics; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; College of Sciences; N/A; N/A; 152935; 115108; 22542The impact of substrate on Pd nanofilm expansion in a Pd-H-2 system is investigated using polymer microcylinder ring resonator (PMRR) platform. Being a highly sensitive platform for H-2 gas detection, PMRR comprises of an inner sensitive Pd nanofilm and an outer PDMS layer coated on a standard optical fiber. Optical whispering gallery modes (WGMs) are excited in the rim of the outermost PDMS layer through evanescent field of a tapered fiber. H-2 molecules penetrating the H-2-sensitive Pd nanofilm through the PDMS layer cause reversible expansion in the PMRR. This translates into shifts in spectral positions of the WGMs that are observed with tapered fiber transmission spectroscopy. Two types of PMRRs were fabricated. In the first type, Pd nanofilm was directly deposited on the silica surface of an optical fiber. In the other one, a PDMS buffer layer was precoated between Pd nanofilm and the silica surface, with different thicknesses. It is demonstrated that, the use of a PDMS buffer layer yields higher radial expansion of the nanofilm during the interaction with H-2 gas. A 180-nm-thick Pd nanofilm coated on similar to 2.5-mu m-thick PDMS buffer layer showed at least 18% higher radial expansion compared to the case without buffer layer. Identical thickness of Pd nanofilm on a similar to 3.5-mu m-thick PDMS buffer layer showed 30% higher radial expansion. Numerical and analytical calculations were also performed confirming the experimental results. Among mechanical properties of the PDMS buffer layer, Poisson's ratio was found to be the most significant parameter affecting the expansion of the nanofilm.