Electrical - Electronic Engineering / Elektrik - Elektronik Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/11
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Article Enhancing Thickness Determination of Nanoscale Dielectric Films in Phase Diffraction-Based Optical Characterization Systems With Radial Basis Function Neural Networks(IOP Publishing, 2023) Ataç, Enes; Karatay, Anıl; Dinleyici, Mehmet SalihAccurate determination of the optical properties of ultra-thin dielectric films is an essential and challenging task in optical fiber sensor systems. However, nanoscale thickness identification of these films may be laborious due to insufficient and protracted classical curve matching algorithms. Therefore, this experimental study presents an application of a radial basis function neural network in phase diffraction-based optical characterization systems to determine the thickness of nanoscale polymer films. The non-stationary measurement data with environmental and detector noise were subjected to a detailed analysis. The outcomes of this investigation are benchmarked against the linear discriminant analysis method and further verified by means of scanning electron microscopy. The results show that the neural network has reached a remarkable accuracy of 98% and 82.5%, respectively, in tests with simulation and experimental data. In this way, rapid and precise thickness estimation may be realized within the tolerance range of 25 nm, offering a significant improvement over conventional measurement techniques.Article Citation - WoS: 2Citation - Scopus: 2Subwavelength Thickness Characterization of Curved Dielectric Films Exploiting Spatially Structured Entangled Photons(Optica Publishing Group, 2023) Ataç, Enes; Dinleyici, Mehmet SalihPrecise determination of thin dielectric film optical properties is a critical issue for fiber optic sensor technologies. However, conventional methods for the optical characterization of these films not only are generally complex and tedious processes on curved surfaces but also require well-calibrated and overly sophisticated devices. We, on the other hand, propose a novel and practical quantum-based phase diffraction scheme to characterize the thickness of ultra-thin transparent dielectric films coated on an optical fiber beyond the classical diffraction limits in this paper. The approach is implemented by evaluating the effect of thickness variations on the highly visible two-photon diffraction pattern's zero crossings and amplitudes. The mathematical model and numerical simulations con-tribute to a better understanding of how the spatially structured entangled photons improve thickness precision with the help of intensity correlations and a confocal aperture. To prove the impact of the proposed system, it is compared with the classical phase diffraction method in the literature via simulations. According to the results, the thickness of the transparent dielectric films can be accurately estimated below one-twentieth of the wavelength of interest. & COPY; 2023 Optica Publishing GroupArticle Citation - WoS: 5Citation - Scopus: 5Nanoscale Curved Dielectric Film Characterization Beyond Diffraction Limits Using Spatially Structured Illumination(Academic Press, 2020) Ataç, Enes; Dinleyici, Mehmet SalihOptical fiber based sensor systems often utilize thin dielectric films coated on non-planar surfaces are needed to be inspected for quality assurance. However, non-destructive optical characterization of these films is not a simple method especially on curved large surfaces. In this study, we propose a real time procedure to estimate the optical properties of sub-wavelength transparent dielectric films coated on optical fibers. The paper includes developing a mathematical model and its experimental verification. The near field phase diffraction method is combined with the structured light illumination that is spatial modes of optical fibers to estimate the thickness of the phase object beyond the classical diffraction limits. Numerical simulations and experimental results show that the film thickness can safely be characterized up to one tenth of wavelength of interest via selective spatial field distribution determined according to the morphology of the thin film. The outcomes have good agreements with destructive Scanning Electron Microscope (SEM) measurements. © 2020 Elsevier Inc.Article Citation - WoS: 2Citation - Scopus: 2Investigating the Experimental Limits of the Brewster’s Angle Method(Türkiye Klinikleri Journal of Medical Sciences, 2018) Sümer, Can; Kuştepeli, Alp; Dinleyici, Mehmet SalihWe present the method, analysis, and experimental results of the Brewster’s angle method commonly used for determining the refractive indices of optical films. We show the significance of the intersection of reflectance curves, in that the necessity for substrate refractive index and film layer thickness knowledge are both eliminated. We present the conditions for the existence of the second intersection of reflectance curves and introduce a method for determining the refractive index of the substrate layer by using the angular information alone. Analytical results reveal impressive practical sensitivity and accuracy limits for the method, where the experimental results also support the theoretical analysis.Article Citation - WoS: 5Citation - Scopus: 7A Practical Approach for Optical Characterization of a Film Coated on the Optical Fiber(Academic Press Inc., 2017) Ekici, Çağın; Dinleyici, Mehmet SalihPhase Diffraction (PD) Phase Diffraction. which is a result of the interaction of light waves with a transparent object, is exploited to characterize precisely optical properties of dielectric films coated on the optical fiber without harming any feature of the sample. Typical fiber sensor applications require films coated on the side surface of the optical fiber and optical properties of that curved films are crucial for design purposes. In this study, three Polyvinyl Alcohol (PVA) films are prepared, their thicknesses are estimated based on the phase diffraction method by fitting experimental results with a mathematical model within 2.3% error. The outcomes of this practical method show good agreement with findings of the destructive Scanning Electron Microscopy (SEM) measurements. The method has the potential to allow real time monitoring abrupt changes of surrounding medium's properties and to examine coating quality (i.e. thickness uniformity) of the film.Article A Fiber-Integrated Optical Component Fabricated Via Photopolymerization: Mode-Selective Grating Coupler(Elsevier Ltd., 2013) Sümer, Can; Dinleyici, Mehmet SalihWe demonstrate a mode-selective directional coupler based on a grating structure, which is fabricated by laser direct-writing on a photopolymer thin film. The device is implemented on the flat planar surface of the D-Fiber, enabling fiber integration, where an Acrylamide/Polyvinyl Alcohol based photopolymer material is used in the fabrication of the device. While the refractive index modulation properties of the polymer material are well known, surface relief and corrugation properties due to photopolymerization are investigated in this study. Theoretical model of the device is presented together with the optimization and simulation results of the final device; experimental results have been found to be in good agreement with simulations.Article Citation - WoS: 1Citation - Scopus: 1Interference Grating Structures in Photonic Crystal Circuits(Springer Verlag, 2011) Karakılınç, Özgür Önder; Dinleyici, Mehmet SalihPhotonic Crystal Circuits have been widely investigated for various optoelectronics device applications. And the gratings in photonics devices are indispensable tool, which is very common for light manipulation. In this study, an interference grating structure formed by Gaussian beam interferences in photonic crystal waveguide such that having Kerr type nonlinearity is proposed and its transmission characteristics are investigated. Finite-Difference Time-Domain method is used to analyze the device characteristics. According to simulation results, the interference grating has shown special transmission characteristics that can bring tunability for photonic crystal devices. This can be an effective method for controlling optical signals in the photonic crystal for all optical switching/routing applications as a part of add/drop multiplexing.Article Citation - WoS: 8Citation - Scopus: 8Characterization and Estimation of Refractive Index Profile of Laser-Written Photopolymer Optical Waveguides(Elsevier Ltd., 2011) Dinleyici, Mehmet Salih; Sümer, CanIn this study, channel waveguides fabricated in photopolymer films by direct-writing using a low-power CW laser, are used as phase objects in a simple plane-wave diffraction setup, and the refractive index modulation profiles of the waveguides are characterized using the recorded diffraction patterns. Index profiles are modeled by piece-wisely combining two Gaussian functions representing the central and the tail regions. Measured diffraction patterns are matched with patterns generated using the model. This simple model makes it possible to design various channel waveguides embedded into polymer substrates. The proposed model is tested on three distinctive waveguide profiles written on the same Acrylamide/Polyvinyl Alcohol based photopolymer with different exposures.Article A Novel All-Optical Routing Architecture for Optical Packet Switched Networks(Springer Verlag, 2006) Mocan, Bora; Dinleyici, Mehmet SalihIncreasing bandwidth demand, mostly driven by the Internet Protocol (IP), has made researchers consider to deploy all-optical devices into packet switched networks. Despite huge bandwidth of the optical communication links (optical fiber) the usable capacity is limited due to bottlenecks (congestions) at the switching nodes. In this paper, a novel all-optical routing architecture is proposed for optical packet switched networks. In the design, practical optical devices (gratings, threshold elements, optical delays, and couplers) have been improved and exploited in order to integrate into an all-optical routing device. The system has been implemented and simulated by using an photonics simulation package (VPI-Virtual Photonics). The packets conveying a three-bit routing information tag at the bit rate of 10 Gbps have been successfully routed between two links. Some of the components are standard tools of the simulation package and some needed to be designed using the transfer function or theory developed in the literature. Noise and losses associated to the nonideal nature of the components are considered in the simulation as well.Article Citation - WoS: 5Citation - Scopus: 7An Experimental Work on Optical Component Based on D-fiber/Slab Evanescent Coupling Structure(Springer Verlag, 2003) Dinleyici, Mehmet SalihFiber/slab coupler structure has been exploited as a passive in-line optical fiber component for functions of filtering, intensity modulating and switching by many researchers. In this work a device based on the elliptic core D-fiber and polymer slab waveguide is proposed and its fabrication is experimentally investigated. The device is constructed by placing the polymer slab on the top of the flat side of the D-fiber, and then they are tested for transmission characteristics and polarization preserving properties for various configurations. The geometrical uniformity of the device is examined under Scanning Electron Microscope for the purpose of device performance evaluation. Potential usage of this device as an all-optical switch is also discussed at the end.