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Enhancement of Refractive Index Sensitivity in Photonic Crystal Waveguide-Based Sensors by Selective Infiltration

100%
Bagci F., Akaoglu B.
Acta Physica Polonica A
|
2013
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vol. 124
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issue 1
50-55
EN
We present a liquid refractive index sensor based on a photonic crystal waveguide slab structure. Sensing mechanism employed in this study is based on the shift in cut-off wavelength as the lattice holes are selectively infiltrated. Three-dimensional plane-wave expansion and finite-difference time-domain methods are used to determine the band structure and transmission spectra, respectively. First, the sensitivity of the device is analyzed for the structure where only the first rows of holes adjacent to the line-defect are infiltrated. In addition, this analysis is repeated for a range of hole diameters. Second, the effects of infiltrated holes which are placed in the line-defect are investigated. As these infiltrated central holes are introduced, the proposed device exhibits 5.3 times improved sensitivity.
2
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Consequences of Unit Cell Design in Metamaterial Perfect Absorbers

100%
Bagci F., Akaoglu B.
Acta Physica Polonica A
|
2016
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vol. 129
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issue 4
792-796
EN
Metamaterials are a new class of composite materials with unusual properties that allow controlling of electromagnetic waves by properly engineering the response functions, which are not observed in constituent materials. However, since absorption of metamaterials is mainly based on electromagnetic resonances, the operating bandwidth is relatively narrow. Utilization of more than a single metallic structure with different geometrical parameters in each unit cell is a common way of accomplishing multiple band and/or broadband absorption. There are two usual approaches for this purpose: (a) multilayer unit cell design where metallic structures on dielectric substrate are stacked one on top of the other; (b) side by side unit cell design where metallic structures are distributed on a dielectric substrate. However, to the best of our knowledge, these two different approaches are not comparatively investigated. In this study, we propose metamaterial-based perfect absorbers with two different unit cell designs and simulate transmittances, reflectances and absorbances for each design by a commercial electromagnetic solver, CST Microwave Studio. It is found that each design has its own advantages in terms of device thickness, absorption bandwidth and angular dependence, which might be severely important for particular purposes.
3
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Enhanced Electro-Optic Modulation Performance in Optical Buffers by Slowing Light in Optimized Photonic Crystal Slab Structures

100%
Bagci F., Akaoglu B.
Acta Physica Polonica A
|
2014
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vol. 125
|
issue 2
611-614
EN
Slow light holds the key to advanced optical buffering and time-domain optical signal processing technologies. Photonic crystal based optical buffers are particularly attractive due to their nanoscale size, room temperature operation, and enhanced field dependent nonlinear response associated with the presence of slow light. In this study, the slow light and electro-optic modulation characteristics of a line-defect Si photonic crystal slab with triangular arrangement of holes filled with an electro-optic polymer (n = 1.6) are investigated by three-dimensional plane-wave expansion and finite-difference time-domain methods. The first rows adjacent to the line-defect are shifted gradually in the direction of light propagation and a slow light region with a high group index below the light-line is obtained for a shifting amount between 0.22a and 0.27a. For the photonic crystal configuration with 0.22a shifted rows, under modulated voltage change, the average group index is found to be decreasing with an increase in the bandwidth. The results show that the low group velocity supports a large delay time in a small modulated voltage variation. A linear change of group index with modulated voltage is obtained and the modulation sensitivity of central wavelength is obtained as 9.45 nm/V for a delay line length of 0.5 mm. Almost the same buffer capacity and bit length are found which provides the control of delay time flexibly while keeping the buffer capacity and the bit length almost unchanged.
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