Browsing by Author "Mutlu, Mehmet"

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Open Access
Chiral metamaterial and high-contrast grating based polarization selective devices
(2013) Mutlu, Mehmet
The utilization of purposely designed artificial media with engineered electromagnetic responses enables the obtaining of intriguing features that are either impossible or difficult to realize using readily available natural materials. Here, we focus on two classes of artificial media: metamaterials and high-contrast gratings. Metamaterials and high-contrast gratings are designed within the subwavelength periodicity range and therefore, they are non-diffractive. We exploit the magnetoelectric coupling effect in chiral metamaterials to design several structures. Firstly, we design a linear to circular polarization convertor that operates for x-polarized normally incident plane waves. Then, we combine the chirality feature and the electromagnetic tunneling phenomenon to design a polarization insensitive 90◦ polarization rotator that exhibits unity transmission and crosspolarization conversion efficiencies. Subsequently, we combine this polarization rotator with a symmetric metallic grating with a subwavelength slit for the purpose of enabling the one-way excitation of spoof surface plasmons and achieving a reversible diodelike beaming regime. Then, we exploit the asymmetric transmission property of chiral metamaterials and show that a polarization angle dependent polarization rotation and a strongly asymmetric diodelike transmission is realizable. Afterwards, a brief waveguide theory is provided and eventually, the dispersion relations for a periodic dielectric waveguide geometry are derived. Then, using these relations and considering the finiteness of the waveguide length, we show the theoretical description of high-contrast gratings. Finally, we theoretically and experimentally show that the achievement of a broadband quarter-wave plate regime is possible by using carefully designed high-contrast gratings.
Open Access
Chiral metamaterials: From negative index to asymmetric transmission
(IEEE, 2013) Mutlu, Mehmet; Li, Zhaofeng; Özbay, Ekmel
Chiral metamaterials are attractive for their intriguing properties such as negative refractive index, optical activity and circular dichroism, and asymmetric transmission. In this paper, we review the research we have conducted for the purpose of investigating these exciting properties. © 2013 EurAAP.
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
Photonic crystal based multi-mode high-qcavity
(IEEE, 2011) Akosman, Ahmet Emin; Mutlu, Mehmet; Kurt H.; Özbay, Ekmel
An optical race-track has been investigated in order to obtain a multi resonant structure with high-Q factors. Photonic crystal based structure provides strong field confinement and scalability in the dimensions of the structure. The average value of the quality factors at the resonances have been calculated to be on the order of ∼105. © 2011 IEEE.
Open Access
Tight-binding mechanism in slow light regime
(IEEE, 2011) Akosman, Ahmet Emin; Mutlu, Mehmet; Kurt, Hamza; Özbay, Ekmel
In this study, tight-binding formalism is applied to a photonic crystal coupled cavity structure in order to investigate the characteristics of ultra slow light modes. Eigen-mode splitting is observed and resulting group indices obtained from the tight-binding formalism and numerical results are compared. © 2011 IEEE.