Browsing by Subject "Grating structures"

Now showing 1 - 5 of 5

Open Access
Enhanced confined microwave transmission by single subwavelength apertures
(2005) Çağlayan, Hümeyra
Grating-coupling phenomena between surface plasmons and electromagnetic waves are studied in the microwave spectrum using metallic circular apertures surrounded by an array of grooves. The measurements are performed in the microwave spectrum of 10-18 GHz, corresponding to a wavelength region of 16.7-30 mm. The metallic samples have a subwavelength hole with a diameter of 8 mm and have concentric grooves with a periodicity of 16 mm. We first present the experimental and theoretical results of enhanced microwave transmission though a subwavelength circular aperture with concentric periodic grooves around the surface plasmon resonance frequency. This is followed by transmission studies through circular annular apertures with and without concentric periodic grooves around the aperture. We demonstrate a 145-fold enhancement factor could be obtained with a subwavelength circular annular aperture surrounded by concentric periodic grooves. Moreover, we study the diffraction of electromagnetic waves from subwavelength metallic circular annular apertures in the microwave spectrum. The theoretical and experimental demonstration of the near- and far-field EM distributions for subwavelength circular apertures and circular annular apertures surrounded by concentric periodic grooves is reported. We present the angular transmission distributions from circular apertures and circular annular apertures surrounded by concentric periodic grooves. At the surface mode resonance frequency the transmitted electromagnetic waves from the subwavelength circular annular aperture surrounded by concentric periodic grooves have a strong angular confinement with an angular divergence of ±3°. This represents a fourfold reduction when compared to the angular divergence of the beam transmitted from a subwavelength aperture. These results show, that not only high transmission but also a confined beam is achieved at the surface plasmon resonance frequency using a circular annular aperture with grooves .
Open Access
Idler-efficiency-enhanced long-wave infrared beam generation using aperiodic orientation-patterned GaAs gratings
(Optical Society of America, 2016) Figen, Z. G.; Aytür, O.; Arıkan, Orhan
In this paper, we design aperiodic gratings based on orientation-patterned gallium arsenide (OP-GaAs) for converting 2.1 μm pump laser radiation into long-wave infrared (8-12 μm) in an idler-efficiency-enhanced scheme. These single OP-GaAs gratings placed in an optical parametric oscillator (OPO) or an optical parametric generator (OPG) can simultaneously phase match two optical parametric amplification (OPA) processes, OPA 1 and OPA 2. We use two design methods that allow simultaneous phase matching of two arbitrary Ï‡ 2 processes and also free adjustment of their relative strength. The first aperiodic grating design method (Method 1) relies on generating a grating structure that has domain walls located at the zeros of the summation of two cosine functions, each of which has a spatial frequency that equals one of the phase-mismatch terms of the two processes. Some of the domain walls are discarded considering the minimum domain length that is achievable in the production process. In this paper, we propose a second design method (Method 2) that relies on discretizing the crystal length with sample lengths that are much smaller than the minimum domain length and testing each sample's contribution in such a way that the sign of the nonlinearity maximizes the magnitude sum of the real and imaginary parts of the Fourier transform of the grating function at the relevant phase mismatches. Method 2 produces a similar performance as Method 1 in terms of the maximization of the height of either Fourier peak located at the relevant phase mismatch while allowing an adjustable relative height for the two peaks. To our knowledge, this is the first time that aperiodic OP-GaAs gratings have been proposed for efficient long-wave infrared beam generation based on simultaneous phase matching.
Open Access
Plasmonic gratings for enhanced near infrared sensitivity of Silicon based Schottky photodetectors
(IEEE, 2011) Polat, Kazım Gürkan; Aygun, Levent Erdal; Okyay, Ali Kemal
Schottky photodetectors have been intensively investigated due to their high speeds, low device capacitances, and sensitivity in telecommunication standard bands, in the 0.8μm to 1.5μm wavelength range. Due to extreme cost advantage of Silicon over compound semiconductors, and seamless integration with VLSI circuits, metal-Silicon Schottky photodetectors are attractive low cost alternatives to InGaAs technology. However, efficiencies of Schottky type photodetectors are limited due to thin absorption region. Previous efforts such as resonant cavities increase the sensitivity using optical techniques, however their integration with VLSI circuits is difficult. Therefore, there is a need for increasing Schottky detector sensitivity, in a VLSI compatible fashion. To address this problem, we design plasmonic grating structures to increase light absorption at the metal-Silicon Schottky interface. There are earlier reports of plasmonic structures to increase Schottky photodetector sensitivity, with a renowned interest in the utilization of plasmonic effects to improve the absorption characteristics of metal-semiconductor interfaces. In this work, we report the design, fabrication and characterization of Gold-Silicon Schottky photodetectors with enhanced absorption in the near infrared region. © 2011 IEEE.
Open Access
Plasmonic materials based on ZnO films and their potential for developing broadband middle-infrared absorbers
(American Institute of Physics Inc., 2014) Kesim, Y.E.; Battal, E.; Okyay, Ali Kemal
Noble metals such as gold and silver have been extensively used for plasmonic applications due to their ability to support plasmons, yet they suffer from high intrinsic losses. Alternative plasmonic materials that offer low loss and tunability are desired for a new generation of efficient and agile devices. In this paper, atomic layer deposition (ALD) grown ZnO is investigated as a candidate material for plasmonic applications. Optical constants of ZnO are investigated along with figures of merit pertaining to plasmonic waveguides. We show that ZnO can alleviate the trade-off between propagation length and mode confinement width owing to tunable dielectric properties. In order to demonstrate plasmonic resonances, we simulate a grating structure and computationally demonstrate an ultra-wide-band (4-15 μm) infrared absorber. © 2014 Author(s).
Open Access
Polymeric waveguide Bragg grating filter using soft lithography
(Optical Society of American (OSA), 2006) Kocabas, A.; Aydınlı, Atilla
We use the soft lithography technique to fabricate a polymeric waveguide Bragg grating filter. Master grating structure is patterned by e-beam lithography. Using an elastomeric stamp and capillary action, uniform grating structures with very thin residual layers are transferred to the UV curable polymer without the use of an imprint machine. The waveguide layer based on BCB optical polymer is fabricated by conventional optical lithography. This approach provides processing simplicity to fabricate Bragg grating filters. © 2006 Optical Society of America.