Browsing by Author "Akosman, A. E."
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Item Open Access Asymmetric chiral metamaterial circular polarizer based on four U-shaped split ring resonators(Optical Society of America, 2011-04-28) Mutlu, M.; Akosman, A. E.; Serebryannikov, A. E.; Özbay, EkmelAn asymmetric chiral metamaterial structure is constructed by using four double-layered U-shaped split ring resonators, which are each rotated by 90° with respect to their neighbors. The peculiarity of the suggested design is that the sizes of the electrically and magnetically excited rings are different, which allows for equalizing the orthogonal components of the electric field at the output interface with a 90° phase difference when the periodic structure is illuminated by an x-polarized wave. As a result, left-hand circular polarization and right-hand circular polarization are obtained in transmission at 5:1 GHz and 6:4 GHz, respectively. The experiment results are in good agreement with the numerical results.Item Open Access Asymmetric transmission of linearly polarized waves and polarization angle dependent wave rotation using a chiral metamaterial(Optical Society of America, 2011-07-18) Mutlu, M.; Akosman, A. E.; Serebryannikov, A. E.; Özbay, EkmelAn electrically thin chiral metamaterial structure composed of four U-shaped split ring resonator pairs is utilized in order to realize polarization rotation that is dependent on the polarization of the incident wave at 6.2 GHz. The structure is optimized such that a plane wave that is linearly polarized at an arbitrary angle is an eigenwave of the system at this frequency. The analytical relation between the incident polarization and the polarization rotation is derived using transmission matrices. Furthermore, the proposed structure exhibits an asymmetric transmission of linearly polarized waves at 6.2 GHz. Plane waves traveling in opposite but perpendicular directions to the material plane are rotated by different angles. On the other hand, four incident polarization angles have been found for the same structure, at which the transmission is symmetric. The experiment results are in good agreement with the numerical results. (C)2011 Optical Society of AmericaItem Open Access Broadband circular polarizer based on high-contrast gratings(Optical Society of America, 2012-05-30) Mutlu, M.; Akosman, A. E.; Özbay, EkmelA circular polarizer, which is composed of periodic and two-dimensional dielectric high-contrast gratings, is designed theoretically such that a unity conversion efficiency is achieved at λ0 = 1.55 μm. The operation is obtained by the achievement of the simultaneous unity transmission of transverse magnetic and transverse electric waves with a phase difference of π/2, meaning that an optimized geometrical anisotropy is accomplished. By the utilization of the rigorous coupled-wave analysis and finite-difference time-domain methods, it is shown that a percent bandwidth of ∼50% can be achieved when the operation bandwidth is defined as the wavelengths for which the conversion efficiency exceeds 0.9.Item Open Access Diodelike asymmetric transmission of linearly polarized waves using magnetoelectric coupling and electromagnetic wave tunneling(American Physical Society, 2012-05-24) Mutlu, M.; Akosman, A. E.; Serebryannikov, A. E.; Özbay, EkmelAn asymmetric, reciprocal, diffraction-free transmission of linearly polarized waves in a new diodelike, three-layer, ultrathin, chiral structure is studied theoretically and experimentally. The exploited physical mechanism is based on the maximization of the cross-polarized transmission in one direction due to the polarization selectivity dictated by the peculiar eigenstate combination, which is efficiently controlled by the electromagnetic tunneling through the metallic subwavelength mesh sandwiched between these layers. Simulation and microwave experiment results demonstrate a nearly total intensity transmission at normal incidence in one direction and a small intensity transmission in the opposite direction.Item Open Access Efect of thermal annealing on mid infrared transmission in semiconductor alloy core glass cladded fibers(Springer, 2020) Ordu, Mustafa; Guo, J.; Akosman, A. E.; Erramilli, S.; Ramachandran, S.; Basu, S. N.We report a study investigating the effects of thermal annealing on the optical properties of Si-Ge alloy-core silica-cladded fibers. Low temperature fiber draw was performed with a laboratory-made draw tower at 1760 °C that minimizes impurity diffusion from cladding to the core. As a post-drawing process, Si–Ge core fibers were annealed in a box furnace to alter the core structure. Microstructural and optical properties of fibers were investigated, and transmission losses were measured as 28 dB/cm at 6.1 µm. Numerical studies were performed to analyze the experimental results and to find the optimum structure for low loss semiconductor-core glass-cladded fibers.Item Embargo Enhancing polarization maintenance and spectral filtering in negative curvature hollow-core fibers(Elsevier BV, 2023-12-09) Siddiqui, Muhammad Zain; Akosman, A. E.; Ordu, MustafaA new design of polarization-maintaining and spectral filtering negative curvature hollow-core fiber tailored for the telecommunication bands in the near-infrared region is presented. The optical fiber, consisting of a six-tube silica structure, incorporates vertically nested tubes anchored radially by a pole structure. By contrast, standard nested tubes in the horizontal direction form the asymmetric fiber structure, which encounters birefringence. This unique fiber design not only preserves the polarization states of light but also exhibits frequency selective transmission exclusively in the vertical direction due to the pole structure. Through fiber design optimization, a transmission loss below 0.1 dB/km for spectrally filtered wavelengths is achieved, with birefringence on the order of 10−5 within the wavelength range of 1.45 µm to 1.60 µm. These results demonstrate significant improvements in terms of birefringence, distinct loss separation between horizontally and vertically polarized states, and a reduced number of spectrally filtered wavelengths compared to previously reported findings. The proposed fiber design holds untapped potential for applications requiring selective transmissions with specific polarization.Item Open Access Experimental realization of a high-contrast grating based broadband quarter-wave plate(Optical Society of America, 2012-12-03) Mutlu, M.; Akosman, A. E.; Kurt, G.; Gokkavas, M.; Özbay, EkmelFabrication and experimental characterization of a broadband quarter-wave plate, which is based on two-dimensional and binary silicon high-contrast gratings, are reported. The quarter-wave plate feature is achieved by the utilization of a regime, in which the proposed grating structure exhibits nearly total and approximately equal transmission of transverse electric and transverse magnetic waves with a phase difference of approximately pi/2. The numerical and experimental results suggest a percent bandwidth of 42% and 33%, respectively, if the operation regime is defined as the range for which the conversion efficiency is higher than 0.9. A compact circular polarizer can be implemented by combining the grating with a linear polarizer. (C) 2012 Optical Society of AmericaItem Open Access Low-loss nested-compound negative curvature hollow-core fiber for Mid-IR transmission(Optica Publishing Group, 2021) Akosman, A. E.; Ordu, MustafaA new negative curvature hollow-core fiber with a compound cladding structure is proposed. Compared to conventional nested structures, the proposed design features one order of magnitude improvement in confinement losses as low as 0.03 dB/kmItem Open Access Nested compound negative curvature hollow-core fiber for single-mode operation in the infrared region(Elsevier, 2021-06-10) Akosman, A. E.; Ordu, MustafaIn this study, a novel tubular hollow-core fiber design with extended cladding structures aiming low transmission losses and dominant single-mode guidance in the infrared region is proposed. The fiber parameters are optimized to achieve low-loss operation at the target wavelength of , at which the emission spectrum of thulium-doped fiber lasers are centered. The confinement loss of the fundamental mode is found to be less than 0.02 dB/km in the near- and mid-infrared region, which makes the proposed design a strong alternative for conventional step-index silica optical fibers. Strong suppression of the higher order modes, and low bending sensitivity are also observed in the proposed design. The proposed fiber shows promising results to achieve low-loss transmission in the infrared spectrum.Item Open Access Passive polarization filtering in negative curvature hollow-core fibers(SPIE - International Society for Optical Engineering, 2023-10-05) Siddiqui, Muhammad Zain; Akosman, A. E.; Ordu, Mustafa; Yin, Shizhuo; Guo, RuyonA novel negative curvature hollow-core fiber (NCF) design is proposed capable of spectral and polarization filtering in the near-infrared region. The designed six-tube silica-based NCF contains nest elements in the form of suspended tubes radially anchored with a pole to the outer cladding in the vertical direction. In contrast, standard nested cladding elements without any suspension are used through the horizontal axis. This fiber configuration introduces an asymmetry in the core, which helps maintain the orthogonal X and Y polarization states in the fiber core. Pole anchors in vertically positioned tubes only give rise to the spectral filtering confinement loss profile for a vertically polarized state. Based on the geometrical optimization of the fiber, we achieved an improved birefringence on the order of 10-5 with filtered wavelength losses below 0.01 dB/km in the wavelength range of 1.4 µm to 1.7 µm. The operational bandwidth, polarization extinction ratio, filtered wavelengths, birefringence, and modulation depth loss can be tuned by optimizing the fiber parameters, including outer tube thickness, nest tube diameter, and pole dimensions. This proposed fiber design with selective transmission spectrums has untapped potential sensing capabilities in hollow-core negative curvature fibers. © 2023 SPIE. All rights reserved.