PubMed İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/397
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Article Citation - WoS: 1Citation - Scopus: 1RF Injection Locked 18 GhZ Regeneratively Mode-Locked Semiconductor Laser(Optical Soc Amer, 2018-01-04) Oran, Abdullah; Ozharar, Sarper; Can, Gokhan; Olcer, Ibrahim; Ozdur, IbrahimIn this manuscript, a semiconductor based fiber ring cavity mode-locked laser regeneratively driven at 18 GHz is presented. The optical spectrum of the laser is centered at 1578 nm. The laser is RF injection locked via an external source at 18 GHz. The phase noise of the mode-locked laser is measured and the integrated timing jitter was found to be 10.8 fs (from 100 Hz to 20 MHz) and 13.3 fs (from 100 Hz to Nyquist frequency). The integrated amplitude fluctuation (from 100 Hz to 20 MHz) was less than 0.02%. The laser phase and amplitude noise responses to various injected RF power levels were also investigated. The injection RF power has significant effect on the phase noise and the best jitter value is around 40 dB lower than the cavity regenerated RF power. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing AgreementArticle Citation - WoS: 21Citation - Scopus: 23Photonic-Lantern Coherent LIDAR System(Optical Soc Amer, 2015-02-20) Ozdur, Ibrahim; Toliver, Paul; Woodward, T. K.In this work, a photonic-lantern-based coherent LIDAR system is experimentally demonstrated and the voltage signal-to-noise ratio improvement is analyzed. A voltage signal-to-noise ratio (SNRV) improvement of 2.8 is demonstrated experimentally for photonic-lantern-based coherent receivers relative to single-mode coherent receivers. The voltage signal-to-noise ratio improvement is obtained when other parameters are kept constant. We have also analyzed the effect of random optical power distribution among the single-mode fibers. We found that the distribution does not significantly impact the SNRV improvement. The mean value of voltage signal-to-noise ratio improvement is found to be similar to 2.4. (C) 2015 Optical Society of AmericaArticle Citation - WoS: 29Citation - Scopus: 30Nanosecond Colloidal Quantum Dot Lasers for Sensing(Optical Soc Amer, 2014-03-21) Guilhabert, B.; Foucher, C.; Haughey, A-M.; Mutlugun, E.; Gao, Y.; Herrnsdorf, J.; Laurand, N.Low-threshold, gain switched colloidal quantum dot (CQD) distributed-feedback lasers operating in the nanosecond regime are reported and proposed for sensing applications for the first time to the authors' knowledge. The lasers are based on a mechanically-flexible polymeric, second order grating structure overcoated with a thin-film of CQD/PMMA composite. The threshold fluence of the resulting lasers is as low as 0.5 mJ/cm(2) for a 610 nm emission and the typical linewidth is below 0.3 nm. The emission wavelength of the lasers can be set at the design stage and laser operation between 605 nm and 616 nm, while using the exact same CQD gain material, is shown. In addition, the potential of such CQD lasers for refractive index sensing in solution is demonstrated by immersion in water. (C) 2014 Optical Society of AmericaArticle Citation - WoS: 4Citation - Scopus: 5Multiple Slow Waves and Relevant Transverse Transmission and Confinement in Chirped Photonic Crystals(Optical Soc Amer, 2014-09-02) Serebryannikov, Andriy E.; Cakmak, A. Ozgur; Colak, Evrim; Caglayan, Humeyra; Kurt, Hamza; Ozbay, EkmelThe dispersion properties of rod-type chirped photonic crystals (PhCs) and non-channeled transmission in the direction of the variation of structural parameters from one cell of such a PhC to another are studied. Two types of configurations that enable multiple slow waves but differ in the utilized chirping scheme are compared. It is demonstrated that the multiple, nearly flat bands with a group index of refraction exceeding 180 can be obtained. For these bands, transmission is characterized by multiple narrow peaks of perfect transmission, strong field enhancement inside the slab, and large values of the Q-factor. Among the bands, there are some that show negative phase velocity. Symmetry with respect to the slab mid-plane must be kept in order to obtain constructive interferences that are necessary for reflection-free transmission. It is shown that 15 and more slow wave bands can be obtained in one configuration. The corresponding transmission peaks are well separated from each other, being the only significant feature of the transmission spectrum, while the Q-factor can exceed 10(5). The observed features are preserved in a wide range of the incidence angle variation. They can be used for tuning the locations and spectral widths of the transmission peaks. Some comparisons with the chirped multilayer structures have been carried out. (C) 2014 Optical Society of AmericaArticle Citation - WoS: 5Citation - Scopus: 5Linear Variable Optical Attenuators With Shaped-Finger Comb-Drive Actuators(Optical Soc Amer, 2020-01-06) Hah, DooyoungA design method is proposed for variable optical attenuators (VOAs), aiming at linear attenuation-voltage characteristics, and verified by finite element analysis. Devices of interest are planar VOAs based on microelectromechanical systems technology, with either a knife-edge shutter or a reflector. The proposed method calculates the shape of the fingers of the comb-drive actuators that are used to move the optical component (shutter or reflector) to change the attenuation level. The calculation is, in effect, tantamount to solving a differential equation that encompasses the optical model of the device, electromechanical behavior of the actuators, and the objective of the design, i.e., linear attenuation-voltage characteristics. The design method is almost all-analytical with minimum usage of numerical analysis. The obtained designs are further examined by three-dimensional finite element analysis to understand their effectiveness and to probe the validity of the approximations used. The best linearity factor (defined as % deviation from the ideal case) obtained is 1.34% for both shutter- and reflection-type devices when the conditions are set as 1-dB insertion loss and 50-dB maximum attenuation. (C) 2020 Optical Society of AmericaArticle Citation - WoS: 7Citation - Scopus: 6Absorption Enhancement by Semi-Cylindrical Structures for an Organic Solar Cell Application(Optical Soc Amer, 2020-09-25) Hah, DooyoungOrganic solar cells are attractive for various applications with their flexibility and low-cost manufacturability. In order to increase their attractiveness in practice, it is essential to improve their energy conversion efficiency. In this work, semi-cylindrical-shell-shaped structures are proposed as one of the approaches, aiming at absorption enhancement in an organic solar cell. Poly(3-hexylthiophene-2,5-diyl) blended with indene-C60 bisadduct (P3HT:ICBA) is considered as the active layer. Light coupling to the guided modes and a geometrical advantage are attributed to this absorption enhancement. Finite-difference time-domain methods and finite element analysis are used to examine the absorption spectra for two types of devices, i.e., a debossed type and an embossed type. It is shown that absorption enhancement increases as the radius of the cylinder increases, but reaches a saturation at about 4-mu m radius. The average absorption enhancement with an active layer thickness of 200 nm and radius of 4 mu m, and for incidence angles between 0 degrees and 70 degrees, is found as 51%-52% for TE-polarized input and as 30%-33% for TM-polarized input when compared to a flat structure. Another merit of the proposed structures is that the range of incidence angles where the integrated absorption is at the level of the normal incidence is significantly broadened, reaching 70 degrees-80 degrees. This feature can be highly useful especially when organic solar cells are to be placed around a round object. The study results also exhibit that the proposed devices bear broadband absorption characteristics. (C) 2020 Optical Society of America