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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6
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Publication Open Access Phase noise in oscillators as differential-algebraic systems with colored noise sources(Society of Photo-optical Instrumentation Engineers (SPIE), 2004) Department of Electrical and Electronics Engineering; Demir, Alper; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 3756Oscillators are key components of many kinds of systems, particularly electronic and opto-electronic systems. Undesired perturbations, i.e. noise, in practical systems adversely affect the spectral and timing properties of the signals generated by oscillators resulting in phase noise and timing jitter, which are key performance limiting factors, being major contributors to bit-error-rate (BER) of RF and possibly optical communication systems, and creating synchronization problems in clocked and sampled-data electronic systems. In this paper. we review our work on the theory and numerical methods for nonlinear perturbation and noise analysis of oscillators described by a system of differential-algebraic equations (DAEs) with white and colored noise sources. The bulk of the work reviewed in this paper first appeared in [1], then in [2] and [3]. Prior to the work mentioned above, we developed a theory and numerical methods for nonlinear perturbation and noise analysis of oscillators described by a system of ordinary differential equations (ODEs) with white noise sources only [4, 5]. In this paper, we also discuss some open problems and issues in the modeling and analysis of phase noise both in free running oscillators and in phase/injection-locked ones.Publication Open Access Microstructured head-up display screen for automotive applications(Society of Photo-optical Instrumentation Engineers (SPIE), 2012) Freeman, Mark O.; Department of Electrical and Electronics Engineering; Hedili, M. Kıvanç; Ürey, Hakan; Master Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 8579A novel see-through screen is developed for automobiles which reduces the size of the head-up display (HUD) unit considerably. The screen is illuminated by a laser scanning pico-projector and a real image is formed on the screen. The screen has thousands of hexagonally packed microlenses that are partially reflective and embedded in an index matched medium which provides very good see-through capability. Light reflected from the microlenses expand and form a hexagon shaped viewing window. This system is called a direct projection HUD system as the pico projector projects directly onto the screen and forms a real image on it. The system is very compact and does not require any space under the dashboard, which saves on space for the car manufacturers, or allows it to be used immediately as an aftermarket HUD installed in any car.Publication Open Access Magnetic actuated FR4 scanners for compact spectrometers - art. no. 699303(Society of Photo-optical Instrumentation Engineers (SPIE), 2008) Department of Electrical and Electronics Engineering; Ataman, Çağlar; Ürey, Hakan; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 8579A novel magnetic actuated polymer optical platform is integrated into a Michelson interferometer type Fourier transform infrared spectrometer. The proposed advantages of the novel platform over existing approaches, such as MEMS spectrometers, or bulky FTIR systems, include millimeter range dimensions providing a large clear aperture and enabling conventional machining for device fabrication, a controllable AC and/or DC motion both in rotational and translational modes, and low frequency operation. It has been demonstrated that the platform is capable of achieving 400 mu m DC deflection in ambient pressure in the translational mode, and a total optical scan angle exceeding 60 degrees in the resonant rotational mode. A Michelson type Fourier transform spectrometer was built using a retro-reflector bearing FR4 platform and a spectral resolution of 25cm(-1) is demonstrated with this setup. In addition, possible use of the same platform in various other spectrometer configurations and methods to improve the motion precision are discussed.Publication Open Access Tunable WGM resonators from optically trapped dye doped liquid crystal emulsion droplets(Society of Photo-optical Instrumentation Engineers (SPIE), 2014) Sery, Mojmir; Pilat, Zdenek; Jezek, Jan; Zemanek, Pavel; Department of Physics; Department of Electrical and Electronics Engineering; Aas, Mehdi; Kiraz, Alper; Faculty Member; Department of Physics; Department of Electrical and Electronics Engineering; College of Sciences; N/A; 22542We have built a complex apparatus for optical trapping, stretching, heating and concurrent whispering gallery mode (WGM) lasing excitation of liquid crystal (LC) emulsion micro-droplets doped with various fluorescent dyes. We have explored the changes of WGM lasing wavelength when the LC droplets were optically stretched or electrically heated beyond the transition to the isotropic phase. We have found that the range of lasing wavelengths was in some cases considerably higher than when we optically stretched ordinary fluorescent oil droplets in our previous experiments.Publication Open Access Spectral self-interference fluorescence microscopy(American Institute of Physics (AIP) Publishing, 2004) Moiseev, L.; Cantor, C. R.; Doğan, M.; Goldberg, B. B.; Swan, A. K.; Ünlü, M. S.; Department of Electrical and Electronics Engineering; Aksun, M. İrşadi; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 28358Spontaneous emission of fluorophores located close to a reflecting surface is modified by the interference between direct and reflected waves. The spectral patterns of fluorescent emission near reflecting surfaces can be precisely described with a classical model that considers the relative intensity and polarization state of direct and reflected waves depending on dipole orientation. An algorithm based on the emission model and polynomial fitting built into a software application can be used for fast and efficient analysis of self-interference spectra, yielding information about the location of the emitters with subnanometer precision. Spectral information was used to study thin films of fluorescent substances on surfaces.Publication Open Access Optical sensors of bulk refractive index using optical fiber resonators(Society of Photo-optical Instrumentation Engineers (SPIE), 2017) Baldini, Francesco; Bavili, N.; Çiçek, K.; Homola, Jiri; Lieberman, Robert A.; Department of Electrical and Electronics Engineering; Department of Physics; Eryürek, Mustafa; Ghafoor, Moeen; Karadağ, Yasin; Kiraz, Alper; PhD Student; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Department of Physics; College of Engineering; College of Sciences; N/A; N/A; N/A; 22542Optical fiber resonator (OFR) sensor is presented for bulk liquid refractive index (RI) sensing. The sensing mechanism relies on the spectral shifts of whispering gallery modes (WGMs) of OFRs which are excited using a tapered fiber. OFR liquid RI sensor is fully characterized using water solutions of ethanol and ethylene glycol (EG). A good agreement is achieved between the analytical calculations and experimental results for both TE and TM polarizations. The detection limit for bulk RI is calculated to be between 2.7 - 4.7 x 10(-5) refractive index unit (RIU). The OFR sensor provides a robust, easy-to-fabricate and sensitive liquid refractive index sensor which can be employed in lab-on-a-chip applications.Publication Open Access Statistical thermodynamics of residue fluctuations in native proteins(American Institute of Physics (AIP) Publishing, 2009) Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; Yoğurtçu, Osman Nuri; Gür, Mert; Erman, Burak; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; College of Engineering; N/A; N/A; 179997Statistical thermodynamics of residue fluctuations of native proteins in a temperature, pressure, and force reservoir is formulated. The general theory is discussed in terms of harmonic and anharmonic fluctuations of residues. The two elastic network models based on the harmonic approximation, the anisotropic network and the Gaussian network models are discussed as the limiting cases of the general theory. The heat capacity and the correlations between the energy fluctuations and residue fluctuations are obtained for the harmonic approximation. The formulation is extended to large fluctuations of residues in order to account for effects of anharmonicity. The fluctuation probability function is constructed for this purpose as a tensorial Hermite series expansion with higher order moments of fluctuations as coefficients. Evaluation of the higher order moments using the proposed statistical thermodynamics model is explained. The formulation is applied to a hexapeptide and the fluctuations of residues obtained by molecular dynamics simulations are characterized in the framework of the model developed. In particular, coupling of two different modes in the nonlinear model is discussed in detail.