Browsing by Subject "Infrared"

Now showing 1 - 13 of 13

Open Access
Asymptotic wave-like modeling of dielectric lenses
(IEEE, 2007) Yurchenko, V. B.; Altıntaş, Ayhan
We propose asymptotic wave-like approximations for the accurate modeling of dielectric lenses used in quasi-optical systems of millimeter, submillimeter, and infrared wave applications. For the comparison, we obtain an exact full-wave solution of two-dimensional focusing lens problem and use it as a benchmark for testing and validation of asymptotic models being proposed.
Open Access
A Comparative Passivation Study for InAs / GaSb Pin Superlattice Photodetectors
(IEEE Institute of Electrical and Electronics Engineers, 2013-08) Salihoglu, O.; Muti, A.; Aydınlı, Atilla
In the quest to find ever better passivation techniques for infrared photodetectors, we explore several passivation layers using atomic layer deposition (ALD). We compare the impact of these layers on detectors fabricated under same conditions. We use ALD deposited Al2O3, HfO2, TiO2, ZnO, plasma enhanced chemical vapor deposition deposited SiO2, Si3N4, and sulfur containing octadecanethiol self assembled monolayer passivation layers on InAs/GaSb p-i-n superlattice diodes with an average cutoff wavelength of 5.1 mu m. Passivated and unpassivated photodetectors compared for their electrical performances.
Open Access
Compressive sensing based flame detection in infrared videos
(IEEE, 2013) Günay, Osman; Çetin, A. Enis
In this paper, a Compressive Sensing based feature extraction algorithm is proposed for flame detection using infrared cameras. First, bright and moving regions in videos are detected. Then the videos are divided into spatio-temporal blocks and spatial and temporal feature vectors are exctracted from these blocks. Compressive Sensing is used to exctract spatial feature vectors. Compressed measurements are obtained by multiplying the pixels in the block with the sensing matrix. A new method is also developed to generate the sensing matrix. A random vector generated according to standard Gaussian distribution is passed through a wavelet transform and the resulting matrix is used as the sensing matrix. Temporal features are obtained from the vector that is formed from the difference of mean intensity values of the frames in two neighboring blocks. Spatial feature vectors are classified using Adaboost. Temporal feature vectors are classified using hidden Markov models. To reduce the computational cost only moving and bright regions are classified and classification is performed at specified intervals instead of every frame. © 2013 IEEE.
Open Access
Cooperative localization in hybrid infrared/visible light networks: Theoretical limits and distributed algorithms
(Institute of Electrical and Electronics Engineers, 2019) Keskin, M. Furkan; Erdem, Osman; Gezici, Sinan
Light emitting diode (LED) based visible light positioning (VLP) networks can provide accurate location information in environments where the global positioning system (GPS) suffers from severe signal degradation and/or cannot achieve high precision, such as indoor scenarios. In this manuscript, we propose to employ cooperative localization for hybrid infrared/visible light networks that involve multiple LED transmitters having known locations (e.g., on the ceiling) and visible light communication (VLC) units equipped with both LEDs and photodetectors (PDs) for the purpose of cooperation. In the considered scenario, downlink transmissions from LEDs on the ceiling to VLC units occur via visible light signals, while the infrared spectrum is utilized for device-to-device communications among VLC units. First, we derive the Cramer-Rao lower bound (CRLB) and the maximum likelihood estimator (MLE) for the localization of VLC units in the proposed cooperative scenario. To tackle the nonconvex structure of the MLE, we adopt a set-theoretic approach by formulating the problem of cooperative localization as a quasiconvex feasibility problem, where the aim is to find a point inside the intersection of convex constraint sets constructed as the sublevel sets of quasiconvex functions resulting from the Lambertian formula. Next, we devise two feasibility-seeking algorithms based on iterative gradient projections to solve the feasibility problem. Both algorithms are amenable to distributed implementation, thereby avoiding high-complexity centralized approaches. Capitalizing on the concept of quasi-Fej\'er convergent sequences, we carry out a formal convergence analysis to prove that the proposed algorithms converge to a solution of the feasibility problem in the consistent case. Numerical examples illustrate the improvements in localization performance achieved via cooperation among VLC units and evidence the convergence of the proposed algorithms to true VLC unit locations in both the consistent and inconsistent cases. IEEE
Open Access
Design of metamaterial-based nanostructures for 5G applications & thermal radiation management
(2023-06) Boşdurmaz, Ekin Bircan;
The properties of natural materials can be the only limiting factor in today’s technologies. For this, researchers in the last decades found that engineering the features of naturally occurring materials in the subwavelength scales can drasti-cally change their properties. These materials beyond the natural ones are called “metamaterials”, where “meta” means “beyond” in Greek. Although the fabrica-tion of these materials can be quite challenging, clever designs and exploitation of physical phenomena can lead to tunable responses, eliminating the need for multi-ple structures. Here, diﬀerent strategies for designing tunable meta-surfaces for a wide range of applications will be presented by giving two examples. These appli-cations are namely: 1. Graphene-based Metasurface Absorber for the Active and Broadband Manipulation of Terahertz Radiation, 2. Adaptive Thermally Tunable Radiative Cooling with Angle Insensitivity Using Phase-Change Material-Based Metasurface.
Open Access
High-conductivity silicon based spectrally selective plasmonic surfaces for sensing in the infrared region
(Institute of Physics Publishing, 2017) Gorgulu, K.; Gok, A.; Yilmaz, M.; Topalli K.; Okyay, Ali Kemal
Plasmonic perfect absorbers have found a wide range of applications in imaging, sensing, and light harvesting and emitting devices. Traditionally, metals are used to implement plasmonic structures. For sensing applications, it is desirable to integrate nanophotonic active surfaces with biasing and amplification circuitry to achieve monolithic low cost solutions. Commonly used plasmonic metals such as Au and Ag are not compatible with standard silicon complementary metal-oxide-semiconductor (CMOS) technology. Here we demonstrate plasmonic perfect absorbers based on high conductivity silicon. Standard optical lithography and reactive ion etching techniques were used for the patterning of the samples. We present computational and experimental results of surface plasmon resonances excited on a silicon surface at normal and oblique incidences. We experimentally demonstrate our absorbers as ultra-low cost, CMOS-compatible and efficient refractive index sensing surfaces. The experimental results reveal that the structure exhibits a sensitivity of around 11 000 nm/RIU and a figure of merit of up to 2.5. We also show that the sensing performance of the structure can be improved by increasing doping density.
Open Access
High-speed GaAs-based resonant-cavity-enhanced 1.3-μm photodetector
(SPIE, 2000) Özbay, Ekmel; Kimukin, İbrahim; Bıyıklı, Necmi; Gary, T.
High-speed photodetectors operating at 1.3 and 1.55 μm are important for long distance fiber optic based telecommunication applications. We fabricated GaAs based photodetectors operating at 1.3 μm that depend on internal photoemission as the absorption mechanism. Detectors using internal photoemission have usually very low quantum efficiency. We increased the quantum efficiency using resonant cavity enhancement effect. Resonant cavity enhancement effect also introduced wavelength selectivity which is very important for wavelength division multiplexing based communication systems. The top-illuminated Schottky photodiodes were fabricated by a microwave-compatible monolithic microfabrication process. The top metal layer serves as the top mirror of the Fabry-Perot cavity. Bottom mirror is composed of 15 pair AlAs/GaAs distributed Bragg reflector. We have used transfer matrix method to simulate the optical properties of the photodiodes. Our room temperature quantum efficiency measurement and simulation of our photodiodes at zero bias show that, we have achieved 9 fold enhancement in the quantum efficiency, with respect to a similar photodetector without a cavity. We also investigated the effect of reverse bias on quantum efficiency. Our devices are RC time constant limited with a predicted 3-dB bandwidth of 70 GHz.
Open Access
High-Speed InSb photodetectors on GaAs for mid-IR applications
(IEEE, 2004) Kimukin, I.; Bıyıklı, Necmi; Kartaloǧlu, T.; Aytür, O.; Özbay, Ekmel
We report p-i-n type InSb-based high-speed photodetectors grown on GaAs substrate. Electrical and optical properties of photodetectors with active areas ranging from 7.06 × 10 -6 cm 2 to 2.25 × 10 -4 cm 2 measured at 77 K and room temperature. Detectors had high zero-bias differential resistances, and the differential resistance area product was 4.5 Ω cm 2. At 77 K, spectral measurements yielded high responsivity between 3 and 5 μm with the cutoff wavelength of 5.33 μm. The maximum responsivity tor 80-μm diameter detectors was 1.00 × 10 5 V/W at 435 μm while the detectivity was 3.41×10 9 cm Hz 1/2/W. High-speed measurements were done at room temperature. An optical parametric oscillator was used to generate picosecond full-width at half-maximum pulses at 2.5 μm with the pump at 780 mm. 30-μm diameter photodetectors yielded 3-dB bandwidth of 8.5 GHz at 2.5 V bias.
Open Access
Plasmon and phonon polaritons in planar van der Waals heterostructures
(Elsevier, 2023) Hajian, Hodjat; Erçağlar, Veysel; Özbay, Ekmel
The investigation of the characteristics of plasmon polaritons and phonon polaritons in planar systems is one of the key tools in understanding the optical response of plasmonic and phononic waveguides, metamaterials, and metasurfaces. Due to the considerable research interest in the polaritonics of van der Waals (vdW) materials in recent years, we conducted a detailed study on the infrared isotropic/anisotropic polaritons in plasmonic and phononic van der Waals heterostructures.
Open Access
The spontaneous hemin release form Lumbricus terrestris hemoglobin
(1997) Smith, M.L.; Paul J.; Ohlsson P.I.; Paul, K.G.
The slow, spontaneous release of hemin from earthworm, Lumbricus terrestris, hemoglobin has been studied under mild conditions in the presence of excess apomyoglobin. This important protein is surprisingly unstable. The reaction is best described as hemin released from the globin into water, followed by quick engulfment by apomyoglobin. The energetics of this reaction are compared with those of other types of hemoglobins. Anomalously low activation energy and enthalpy are counterbalanced by a negative entropy. These values reflect significant low frequency protein motion and dynamics of earthworm hemoglobin and may also indicate an open structure distal to the heme. This is also supported by the infrared spectrum of the carbonyl hemoprotein, which indicates several types of distal interactions with the bound CO. The reported low heme to polypeptide ratio for this protein may be due to facile heme and hemin release by the circulating protein.
Open Access
The role of semiconductors in the future of optical fibers
(Frontiers Research Foundation, 2023-07-21) Ordu, Mustafa
Semiconductors-core optical fibers have gathered attention for light guidance in the infrared spectrum. Cladded with glasses, fibers can be the ideal medium to transfer the favorable bulk properties of semiconductors into the micro/nano scaled one-dimensional form. The integration of these fibers with optical circuits, lasers and photonic crystals offers a wide variety of applications. In this perspective, the role of semiconductors in the future of optical fibers and their integration with photonic crystal structures are analyzed. The past and present efforts of semiconductor-core fibers are briefly reviewed, and the potential future application areas benefited by semiconductors as fiber materials are discussed.
Open Access
Video processing algorithms for wildfire surveillance
(2015-05) Günay, Osman
We propose various image and video processing algorithms for wild re surveillance. The proposed methods include; classi er fusion, online learning, real-time feature extraction, image registration and optimization. We develop an entropy functional based online classi er fusion framework. We use Bregman divergences as the distance measure of the projection operator onto the hyperplanes describing the output decisions of classi ers. We test the performance of the proposed system in a wild re detection application with stationary cameras that scan prede ned preset positions. In the second part of this thesis, we investigate di erent formulations and mixture applications for passive-aggressive online learning algorithms. We propose a classi er fusion method that can be used to increase the performance of multiple online learners or the same learners trained with di erent update parameters. We also introduce an aerial wild re detection system to test the real-time performance of the analyzed algorithms. In the third part of the thesis we propose a real-time dynamic texture recognition method using random hyperplanes and deep neural networks. We divide dynamic texture videos into spatio-temporal blocks and extract features using local binary patterns (LBP). We reduce the computational cost of the exhaustive LBP method by using randomly sampled subset of pixels in the block. We use random hyperplanes and deep neural networks to reduce the dimensionality of the nal feature vectors. We test the performance of the proposed method in a dynamic texture database. We also propose an application of the proposed method in real-time detection of ames in infrared videos. Using the same features we also propose a fast wild re detection system using pan-tilt-zoom cameras and panoramic background subtraction. We use a hybrid method consisting of speeded-up robust features and mutual information to register consecutive images and form the panorama. The next step for multi-modal surveillance applications is the registration of images obtained with di erent devices. We propose a multi-modal image registration algorithm for infrared and visible range cameras. A new similarity measure is described using log-polar transform and mutual information to recover rotation and scale parameters. Another similarity measure is introduced using mutual information and redundant wavelet transform to estimate translation parameters. The new cost function for translation parameters is minimized using a novel lifted projections onto convex sets method.
Open Access
Wideband 'black silicon' for mid-infrared applications
(Institute of Physics Publishing, 2017) Görgülü, Kazım; Yılmaz, Mehmet; Topallı, Kağan; Okyay, Ali Kemal
In this paper, we investigate the absorption of mid-infrared light by low resistivity silicon textured via deep reactive ion etching. An analytical description of the wave propagation in black silicon texture is presented, showing agreement with the experiment and the computational analysis. We also study the dependence of absorption spectrum of black silicon structure on the electrical conductivity of silicon substrate. The structures investigated unveil wideband, all-silicon infrared absorbers applicable for infrared imaging and spectroscopy with simple CMOS compatible fabrication suitable for optoelectronic integration.