Researcher:
Gökay, Ulaş Sabahattin

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PhD Student

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Ulaş Sabahattin

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Gökay

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Gökay, Ulaş Sabahattin

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2011 - 201813

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Now showing 1 - 10 of 13
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    Mid-infrared elastic scattering from germanium microspheres
    (IEEE, 2016) N/A; N/A; N/A; N/A; Department of Physics; Zakwan, Muhammad; Bayer, Mustafa Mert; Anwar, Muhammad Sohail; Gökay, Ulaş Sabahattin; Serpengüzel, Ali; PhD Student; Master Student; Master Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; N/A; 27855
    Because of their ultrahigh optical nonlinearities and extremely broad transparency window, germanium microsphere resonators offer the potential for optical processing devices, especially in the mid-infrared (mid-IR) wavelengths. As a semiconductor material for microphotonics applications [1], germanium is particularly attractive owing to its large nonlinearity, high optical damage threshold compared with traditional nonlinear glass materials, and above all, its broad transparency window, extending from the near-IR into the mid-IR. Germanium based optical components have found numerous applications in imaging systems operating in the mid-IR wavelengths, where the principal natural greenhouse gases do not exhibit strong absorption. These applications include rapid sensing and diagnosis [2,] [3], industrial process controls, environmental monitors to hazardous chemical detection [4]. Germanium also is a good electromagnetic shielding material, an attribute that has become increasingly important for modern military applications, where other signals (within the millimeter and centimeter wavelength range) can be strong enough to interfere with nearby IR systems. Elastic light scattering from a germanium microsphere has already been observed in the near-IR [5]. Here, elastic light scattering from a germanium microsphere in the mid-IR region is numerically analyzed using generalized Lorenz-Mie theory (GLMT) [6]. Light interaction with microspheres of various materials is of much interest because of their photonic properties [7]. Germanium has a refractive index of 4, which is even higher than the refractive index of silicon (3.5) in the mid-IR region. The higher refractive index results in higher quality factor morphology dependent resonances (MDRs). A higher value of Q indicates a longer lifetime of the photons trapped inside the cavity and a narrower MDR. Here, the MDRs are observed numerically in the transverse magnetically (TM) and transverse electrically (TE) polarized 90° elastic scattering and 0° transmission for a 40 µm radius germanium microsphere in the mid-IR wavelengths ranging from 5.4 µm to 5.6 µm [8]. The mode spacing of approximately 41 nm between the resonances with the same radial mode order and consecutive polar mode number shows good correlation with the optical size of the germanium microsphere. The germanium microsphere with its high quality factor MDRs can be suitable for optical monitoring and sensing applications in the mid-IR, which require a high spectral resolution [9].
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    Silicon microsphere whispering gallery modes excited by femtosecond-laser-inscribed glass waveguides
    (Optical Soc Amer, 2018) Sotillo, Belen; Bharadwaj, Vibhav; Ramponi, Roberta; Eaton, Shane Michael; N/A; N/A; Department of Physics; Çirkinoğlu, Hüseyin Ozan; Bayer, Mustafa Mert; Gökay, Ulaş Sabahattin; Serpengüzel, Ali; Master Student; Master Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; 27855
    We report on the coupling of whispering gallery modes in a 500-mu m-radius silicon microsphere to a femtosecond-laser-inscribed glass optical waveguide. The shallow glass waveguide with a large mode field diameter in the near-infrared is written at a depth of 25 mu m below the glass surface, resulting in a high excitation impact parameter of 525 mu m for the microsphere. The excited whispering gallery modes of the silicon microsphere have quality factors of approximately 10(5) in the 90 degrees elastic scattering and 0 degrees transmission. Integration of such spherical silicon microresonators on femtosecond-laser-inscribed glass waveguides is promising for photonic communication, computation, and sensing applications. (C) 2018 Optical Society of America.
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    Silicon microsphere based filtering application for near-infrared optical fiber based telecommunication
    (IEEE, 2011) Tamer, Mehmet Selman; Gurlu, Oguzhan; N/A; N/A; Department of Physics; Yılmaz, Huzeyfe; Gökay, Ulaş Sabahattin; Serpengüzel, Ali; Master Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 27855
    We demonstrate an optical filter based on the resonances of a silicon microsphere in the near-IR O-Band. The 1300 nm laser light is coupled to the silicon microsphere and optical resonances are observed as dips in the transmission spectrum.
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    Optical fiber excitation of fano resonances in a silicon microsphere
    (Taylor & Francis Inc, 2016) Demir, Abdullah; N/A; N/A; Department of Physics; Gökay, Ulaş Sabahattin; Zakwan, Muhammad; Serpengüzel, Ali; PhD Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 27855
    In this article, Fano lineshape whispering gallery modes were observed in the light scattering spectrum of a silicon microsphere in near-infrared telecommunication wavelengths. A simple model is presented to explain the transition from Lorentzian lineshape to the Fano lineshape resonances with the coupled-mode theory of multiple whispering gallery modes. Polar mode spacing of 0.23 nm is observed in the spectra, which correlates well with the calculated value. The quality factor of the Lorentzian and Fano resonances are on the order of 10(5). By using an appropriate interface design for the microsphere coupling geometries, Fano lineshape optical resonances herald novel device applications for silicon volumetric lightwave circuits.
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    Spherical silicon optical resonators: possible applications to biosensing
    (Springer Heidelberg, 2014) N/A; N/A; Department of Physics; Gökay, Ulaş Sabahattin; Zakwan, Muhammad; Serpengüzel, Ali; PhD Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 27855
    We observed whispering gallery modes in the 90 degrees elastic light scattering and 0 degrees transmission spectra of a 500 mu m silicon microsphere in the near-infrared telecommunication wavelengths. The whispering gallery modes have quality factors on the order of 10(5). An autocorrelation function analysis of the 90 degrees elastic light scattering and 0 degrees transmission spectra is performed. The differential autocorrelation of the 90 degrees elastic light scattering and 0 degrees transmission spectra reveal a spectral mode spacing 0.23nm of the whispering gallery modes, which can be used for spectral calibration as well as the calibration of the microsphere size. The spectral shift of the whispering gallery modes can be measured for biosensing applications. An estimation analysis is performed for the adsorption of 30 DNA base pairs on the microsphere results in a wavelength shift of 0.57 nm, which is approximately 40 times the linewidth of the whispering gallery modes. This high sensitivity heralds silicon microspheres as possible candidates for biosensing applications.
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    Optoelectronic applications of sapphire microspheres
    (Electromagnetics Academy, 2015) N/A; N/A; N/A; N/A; Department of Physics; Zakwan, Muhammad; Anwar, Muhammad Sohail; Bukhari, Syed Sultan Shah; Gökay, Ulaş Sabahattin; Serpengüzel, Ali; PhD Student; Master Student; PhD Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; N/A; 27855
    The sphere with its highly symmetric geometrical shape enhances the efficiency of optical effects with its high quality factor morphology dependent resonances (MDRs). We report here on numerical studies of elastic light scattering in a sapphire microdisk coupled to slab waveguides, i.e., the 2D analog of a microsphere coupled to the 2D analog of an optical waveguide. The numerical electromagnetic simulations for the surface electric field strength are performed at 800 nm. The experimental elastic light scattering measurements are also proposed in the near-infrared from sapphire microspheres. 800 nm operation with sapphire microspheres is suitable for local area networks (LANs) applications such as channel dropping, filtering, switching, modulation, and monitoring.
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    Modification and dynamics inside diamond by femtosecond laser double-pulse irradiation
    (Japan Laser Processing Soc, 2016) Sakakura, Masaaki; Okada, Takuro; Bharadwaj, Vibhav; Sotillo, Belen; Eaton, Shane M.; Ramponi, Roberta; Shimotsuma, Yasuhiko; Miura, Kiyotaka; Department of Physics; N/A; Serpengüzel, Ali; Gökay, Ulaş Sabahattin; Faculty Member; N/A; Department of Physics; College of Sciences; N/A; 27855; N/A
    We investigated modifications and the temporal evolution of the morphology in the photoexcited region inside diamond single crystal after photoexcitation by tightly focused fs laser pulses. We found that double-pulse irradiation with 200-400 fs laser pulses was able to induce a permanent modification in the photoexcited region, while single-pulse irradiation with 100-300 fs laser pulses was not. The modification by double-pulse irradiation became larger for a longer time-difference between the two pulses in the range from 1 ps to 10 ps. The morphology change observed by a pump-probe optical microscope showed that the photoexcited region by double-pulse irradiation was smaller than by single-pulse irradiation, even for the same total pulse energy, with the amplitudes of the laser induced-stress waves being the same. This observation suggests that the photoinduced plasmas by double-pulse irradiation was localized in a smaller region than that by single-pulse irradiation, and the difference in plasma distribution could be the origin of the permanent modification.
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    Far-infrared elastic scattering proposal for the Avogadro Project's silicon spheres
    (Elsevier, 2018) Department of Physics; N/A; N/A; N/A; N/A; N/A; N/A; Serpengüzel, Ali; Humayun, Muhammad Hamza; Khan, Imran; Azeem, Farhan; Chaudhry, Muhammad Rehan; Gökay, Ulaş Sabahattin; Murib, Mohammed Sharif; Faculty Member; Researcher; Master Student; Researcher; Researcher; PhD Student; Researcher; Department of Physics; College of Sciences; College of Sciences; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; Graduate School of Sciences and Engineering; College of Sciences; 27855; N/A; N/A; N/A; N/A; N/A; N/A
    Avogadro constant determines the number of particles in one mole of a substance, thus relating the molar mass of the substance to the mass of this substance. Avogadro constant is related to Systeme Internationale base units by defining the very concept of chemical quantity. Revisions of the base units created a need to redefine the Avogadro constant, where a collaborative work called the Avogadro Project is established to employ optical interferometry to measure the diameter of high quality 100 mm silicon spheres. We propose far-infrared spectroscopy for determining the Avogadro constant by using elastic scattering from the 100 mm Avogadro Project silicon spheres. Similar spectroscopic methods are already in use in the near-infrared, relating whispering gallery modes of the 1 mm silicon spheres to the diameter of the spheres. We present numerical simulations in the far-infrared and the near-infrared, as well as spatially scaled down elastic scattering measurements in the near-infrared. These numerical and experimental results show that, the diameter measurements of 100 mm single crystal silicon spheres with elastic scattering in the far-infrared can be considered as an alternative to optical interferometry.
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    Spatial intensity profiling of elastic and inelastic scattering in isotropic and anisotropic liquids by immersion of a spherical silicon photocell
    (Optical Soc Amer, 2017) Taira, Kenichi; Omura, Etsuji; Nakata, Josuke; N/A; N/A; N/A; N/A; N/A; Department of Physics; Humayun, Muhammad Hamza; Bukhari, Syed Sultan Shah; Zakwan, Muhammad; Bayer, Mustafa Mert; Gökay, Ulaş Sabahattin; Serpengüzel, Ali; Master Student; PhD Student; PhD Student; Master Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; N/A; N/A; 27855
    The transverse spatial intensity distribution of elastic and inelastic light scattering in passive and active as well as weak and strong scattering liquid media has been studied by using Sphelar One p-n junction silicon spherical photocells. We immersed a Sphelar One in these scattering solutions and measured the photoconductive response in reverse biased photodiode (PD) configuration. The passive weak scattering medium was pure ethanol (EtOH), whereas the passive strong scattering medium was 5CB nematic liquid crystal (NLC). Solutions of 0.1 mM Rhodamine 640 perchlorate laser dye in EtOH and in 5CB NLC were used as active scattering media. The response of Sphelar One was strongly enhanced in 5CB NLC compared to EtOH, as well as in active solutions compared to passive solutions. The morphology of the Sphelar One is already advantageous over conventional one-sided planar PDs inside liquid solutions. This omnidirectional response of the Sphelar One can further be enhanced by optimizing the properties of the surrounding passive elastic and active inelastic scatterers.
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    Electromagnetic simulation of coupled silicon and diamond microdisks and slab waveguides in the mid-infrared
    (Electromagnetics Academy, 2015) Uysallı, Yiğit; Kurt, Adnan; N/A; N/A; N/A; Department of Physics; Chaudhry, Muhammad Rehan; Rashid, Muhammed Zeeshan; Gökay, Ulaş Sabahattin; Serpengüzel, Ali; PhD Student; PhD Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; 27855
    Electromagnetic numerical studies of silicon and diamond microdisks coupled with silicon and diamond slab waveguides are performed in the CO2 laser emission region in the mid-infrared. Microdisk is the 2D analog of the microsphere and the slab waveguide is the 2D analog of the rectangular optical waveguide. The evanescent coupling between the waveguide and the microdisk results in efficient pumping of the whispering gallery modes of the microdisk. On-resonant and off-resonant studies are performed by tuning the laser wavelength to the microdisk whispering gallery modes.