Browsing by Author "Akosman, Ahmet E."
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Item Open AccessDual-frequency division de-multiplexer based on cascaded photonic crystal waveguides(Elsevier, 2012-02-28) Akosman, Ahmet E.; Mutlu, Mehmet; Kurt, H.; Özbay, EkmelA dual-frequency division de-multiplexing mechanism is demonstrated using cascaded photonic crystal waveguides with unequal waveguide widths. The de-multiplexing mechanism is based on the frequency shift of the waveguide bands for the unequal widths of the photonic crystal waveguides. The modulation in the waveguide bands is used for providing frequency selectivity to the system. The slow light regime of the waveguide bands is utilized for extracting the desired frequency bands from a wider photonic crystal waveguide that has a relatively larger group velocity than the main waveguide for the de-multiplexed frequencies. In other words, the wider spatial distribution of the electric fields in the transverse direction of the waveguide for slow light modes is utilized in order to achieve the dropping of the modes to the output channels. The spectral and spatial de-multiplexing features are numerically verified. It can be stated that the presented mechanism can be used to de-multiplex more than two frequency intervals by cascading new photonic crystal waveguides with properly selected widths. Item Open AccessNumerical investigation of confinement losses in semiconductor-core optical fibers(IEEE, 2021-08-27) Syed, Mustafa W.; Akosman, Ahmet E.; Ordu, Mustafa; Syed, Mustafa W.; Ordu, MustafaThe sources of the confinement losses in semiconductor-core optical fibers are numerically investigated by introducing fabrication-inspired imperfections such as micro-cracks and core ellipticity. The imperfections increase the losses up to 200 dB/m at the targeted spectrum that is comparable to experimental findings. Item Open AccessRe-thinking the design of low-loss hollow-core fibers via optimal positioning of the nested elements(Optica, 2022) Ordu, Mustafa; Akosman, Ahmet E.; Ordu, MustafaNested negative curvature hollow-core fibers (NCFs) represent state-of-art optical guidance in the near-infrared (near-IR) region. In this Letter, we propose a unique design approach for these types of fibers in order to further improve optical transmission via the optimal positioning of the nested elements. The nested elements in the proposed design are located at the center of the cladding tubes and are supported by bar-type structures. The topological optimization for the nested elements results in improved light guidance by two orders of magnitude with confinement losses as low as 0.003 dB/km within the targeted wavelength range of 1450 nm to 1600 nm. This bar-supported design features strong single-mode operation and low bending sensitivity in a wide range of bending radii. Item Open AccessStep-index Si-Ge-core silica-cladded optical fibers(IEEE, 2020-09) Ordu, Mustafa; Akosman, Ahmet E.; Guo, J.; Erramilli, S.; Ramachandran, S.; N. Basu, S.; Ordu, Mustafa; Akosman, Ahmet E.Si-Ge alloy-core silica-cladded fibers were drawn at a low temperature to minimize impurity diffusion. The elemental segregation in the as-drawn fibers was overcome by a thermal treatment. The transmission losses of the fibers were calculated as 28 dB/cm at 6.1 μm wavelength.