Researcher: Anand, Suman
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Anand, Suman
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Publication Metadata only Optical sensor for humidity and hydrogen gas based on polymer microresonators(IEEE, 2016) Karadağ, Y.; Kılınç, N.; Department of Physics; N/A; N/A; Department of Physics; Department of Mechanical Engineering; Department of Physics; Department of Mechanical Engineering; Kiraz, Alper; Eryürek, Mustafa; Taşdemir, Zuhal; Anand, Suman; Alaca, Burhanettin Erdem; Faculty Member; PhD Student; PhD Student; Researcher; Faculty Member; College of Sciences; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Science; College of Engineering; 22542; N/A; N/A; N/A; 115108Summary form only given. We report humidity and hydrogen sensors employing elastic polymer (SU-8) optical microresonators fabricated with photolithography. The sensing mechanism relies on monitoring the spectral shifts of the optical whispering gallery modes (WGMs) in the transmission spectra recorded from the microresonators. WGMs are excited through SU-8 waveguides in which a tunable laser light is coupled from an optical fiber.Publication Metadata only Efficient optical fiber coupling to whispering gallery modes of optically manipulated emulsion microdroplets(Electromagnetics Academy, 2015) Karadag, Y.; Department of Physics; N/A; Department of Physics; Department of Physics; Department of Physics; Anand, Suman; Eryürek, Mustafa; Serpengüzel, Ali; Kiraz, Alper; Researcher; PhD Student; Faculty Member; Faculty Member; College of Sciences; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; 27855; 22542We demonstrate efficient coupling to the optical whispering gallery modes of a spherical resonator consisting of a liquid droplet embedded in another liquid medium. Whispering gallery mode particle sensing experiment is commonly performed with solid resonators, whereby the sensing volume is limited to the weak evanescent tail of the mode near the resonator surface. In this work, we demonstrate efficient coupling to the optical whispering gallery modes by introducing a portable, all liquid emulsion microdroplet resonator held in a single beam optical trap. We have observed coupling to the fundamental whispering gallery modes of 10 to 60 nm diameter emulsion droplets at 1550 nm. The experimental challenges towards making, stabilizing and coupling to the droplet resonators are also addressed in this paper.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; 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; 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 Biological lasing in liquid microdroplets deposited on a superhydrophobic surface(IEEE, 2014) Jonas, A.; McGloin, D.; N/A; N/A; Department of Chemistry; Department of Physics; Department of Physics; Department of Chemistry; Department of Physics; Aas, Mehdi; Karadağ, Yasin; Bayraktar, Halil; Anand, Suman; Kiraz, Alper; PhD Student; PhD Student; Faculty Member; Researcher; Faculty Member; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; College of Sciences; N/A; N/A; 201764; N/A; 22542Publication Metadata only Observation of whispering gallery modes in elastic light scattering from microdroplets optically trapped in a microfluidic channel(Optical Soc Amer, 2016) Karadağ, Yasin; Jonas, Alexandr; Department of Physics; N/A; Department of Physics; Department of Physics; Department of Physics; Department of Physics; Anand, Suman; Eryürek, Mustafa; Erten, Ahmet Can; Serpengüzel, Ali; Kiraz, Alper; Researcher; PhD Student; Teaching Faculty; Faculty Member; Faculty Member; College of Sciences; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; College of Sciences; N/A; N/A; 233923; 27855; 22542Optical whispering gallery modes (WGMs) were observed in elastic scattering spectra recorded from oil-in-water emulsion droplets in a microfluidic channel. Droplets with diameters ranging between 15 and 50 mu m were trapped by optical tweezers near the tip of a single mode fiber that enabled the excitation of the WGMs using a tunable laser. Quality factors of the WGMs were observed to increase with droplet size. WGMs with quality factors of more than 10(4) were observed for droplets with diameters around 45 mu m. In some cases, recorded WGMs drifted monotonically to the blue end of the spectrum due to droplet dissolution in the host liquid. Fluctuating spectral shifts to both blue and red ends of the spectrum were also observed. These were attributed to the presence of randomly diffusing particulate contaminants in the droplet liquid, indicating the potential of optically trapped droplet resonators for optical sensing applications. (C) 2016 Optical Society of AmericaPublication Metadata only Hydrogen and humidity sensing based on WGMs of elastic polymer optical microresonators(Electromagnetics Academy, 2015) N/A; Department of Physics; Department of Physics; Department of Physics; Eryürek, Mustafa; Anand, Suman; Kiraz, Alper; PhD Student; Researcher; Faculty Member; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; 22542We report hydrogen and humidity sensor employing elastic polymer (SU-8) optical microresonators. The sensing mechanism relies on the optical whispering gallery mode (WGM) resonance shifts in the transmission spectra of these microresonators. WGMs are excited through SU-8 waveguides in which a tunable laser light is coupled from an optical fiber. Relative humidity between 0 and 65% is detected at room temperature. For hydrogen sensing, the microresonators are coated with a thin layer of palladium (Pd) metal layer to increase the sensing performance. Hydrogen gas is detected reversibly between 0.3 and 1.5%. Hydrogen gas concentrations higher than 1.5% result irreversible degradation of the devices because of a phase transition occurring in the Pd layer.