Browsing by Author "Akosman, Ahmet E."

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Open Access
Dual-frequency division de-multiplexer based on cascaded photonic crystal waveguides
(Elsevier, 2012-02-28) Akosman, Ahmet E.; Mutlu, Mehmet; Kurt, H.; Özbay, Ekmel
A 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.
Open Access
Frequency selective low-loss transmission in negative curvature hollow-core fibers
(Institute of Physics Publishing Ltd., 2024-04-12) Gamble, Jacob; Ordu, Mustafa; Akosman, Ahmet E.
A new low-loss negative curvature fiber design, named as the pole-anchored nested tubular negative curvature fiber, which exhibits frequency selective capabilities in the near-infrared region is proposed. This unique approach involves the addition of nested tubular elements anchored by vertical poles, which serve as an in-fiber resonator. The resulting frequency selective resonant loss dips exhibit high finesse and relative loss modulation depth. The concept of frequency selectivity in negative curvature fibers introduces unique possibilities for future applications of hollow-core structures.
Open Access
Higher order mode analysis in frequency selective negative curvature fibers
(Optica Publishing Group, 2024-08-01) Siddiqui, Muhammad Zain; Akosman, Ahmet E.; Ordu, Mustafa
A novel negative curvature hollow-core fiber is numerically designed capable of filtering specific frequencies. The six-tube silica fiber strongly favors fundamental mode transmission over higher order modes despite uneven positioning of cladding elements.
Open Access
Numerical investigation of confinement losses in semiconductor-core optical fibers
(IEEE, 2021-08-27) Syed, Mustafa W.; Akosman, Ahmet E.; Ordu, Mustafa
The 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.
Open Access
Re-thinking the design of low-loss hollow-core fibers via optimal positioning of the nested elements
(Optica, 2022) Ordu, Mustafa; Akosman, Ahmet E.
Nested 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.
Open Access
Step-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.
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.