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Logic gates have great importance in realization of rapid data transmission as well as low loss transfers. In this paper, a multi-objective inverse-design approach is implemented by using objective-first algorithm to design optical AND, OR, NAND and NOT logic gates on Si-platform at the design wavelength of 1.30 mu m. For all gates, the design area is fixed to 2.24 mu m x 2.24 mu m. The optical logic '1' output is accepted to be optical power values greater than 0.8 times of the input optical power. By implementing a Bias waveguide as well as two input ports, we made it possible to achieve logic '1' output for logic operations having no inputs such as '0 NAND 0 = 1' and '0 NOT = 1'. We binarized the proposed logic gates, and then numerically analyzed them by using finite-difference time-domain method. Proposed AND gate yields 1.20 times of input power for '1 AND 1 = 1' logic operation and highest logic '0' is obtained for logic operation of '1 AND 0 = 0' as 0.40 times of the input power at the operating wavelength. It is also observed that proposed logic gates can operate not only at the design wavelength of 1.30 mu m but also at broad wavelength regions as well. Finally, we demonstrate that it is possible to carry out complex logic operations by combining the proposed logic AND, OR and NAND gates to construct an XOR gate in the same platform.

The computational inverse design has paved the way for the design of highly efficient, compact, and novel nanophotonic structures beyond human intuition and trial-and-error approaches. Apparently, with nanophotonic design power, the exploration and implementation of multi-objective, complex, and functional nanophotonic devices become feasible. Herein, we used a recently emerged inverse design framework to demonstrate the design of a 1 x 2 polarization-insensitive wavelength division multiplexer (PIWDM) made of a low-refractive-index material with an index of 1.55. The inversely designed PIWDM structure successfully steers toward the targeted channels for 1.30 mu m and 1.55 mu m with TE and TM polarizations. Taking advantage of the design with a low refractive index material, we scaled the structural dimensions corresponding to the microwave region, fabricated the compact device using a 3D printer, and conducted an experiment as a proof of concept. The transmission values of the fabricated PIWDM device were -4.87 and -2.18 dB for TE and -2.19 and -2.23 dB for TM polarization at WG-I and WG-II, respectively., Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [116F200], This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under Project No. 116F200.

Bu tez çalışmasında bilinmeyen bir ortamda kimyasal gaz yoğunluğunun yüksek olduğu bölgenin tespiti ve bu kimyasal ortamın gerçek zamanlı üç boyutlu haritalanması gezgin robotlar kullanarak biyolojik tabanlı eniyileme yöntemleri yardımı ile gerçeklenmiştir. Kimyasal ortamın en yoğun olduğu bölgesini arama ve ortamı haritalama işlemleri için kheNose donanımı ile donatılmış Khepera~III gezgin robotlarkullanılmıştır. Arama işlemi Eşzamansız Parçacık Sürü Eniyileme, Bakteri Beslenmesi Tabanlı Enyineleme ve Karınca Kolonisi Beslenmesi Tabanlı Eniyileme yöntemleri kullanılarak gerçekleştirilmiştir. Üstelik uygulanan yöntemlerin tutarlığın denetlemek amacı ile Süpürmeyöntemi kullanılmıştır. Arama ve haritalama sırasında robotlar pozisyon bilgilerini ve algılayıcı verilerini kablosuz ağ üzerinden diğer robotlar ile paylaşmakta ve aynı zamanda kumanda merkezine aktarmaktadırlar. Kumanda merkezine gelen veriler birleştirilmiş, süzülmüş ve ortamın kimyasal gaz yoğunluğunun gerçek zamanlı 3 boyutlu haritalanması çıkarılmıştır. Ayrıca \\emph{Kriging} ve süzgeçleme yöntemi kullanarak elde edilen verilere aradeğerleme, dışdeğerleme ve pürüzsüzleştirme yapılarak daha pürüzsüz harita elde edilmiştir. Uygulanan yöntemlerin verimliliği elden edilen kimyasal harita kalitesi ve kimyasal kaynağın başarılı biçimde bulabilme özellikleri bakımından karşılaştırlmıştır., In this thesis implementations of various bio-inspired algorithms for obtaining high concentration regions of the chemical gas and real time chemical gas concentration mapping of an environment filled with a contaminant by using mobile robots are described. Khepera~III miniature mobile robots equipped with the \\emph{``kheNose''} transducer are used to search and determine the high concentration regions of the chemical gas contaminant and to build $3D$ map of the chemical gas concentration in the environment. The search and mapping process is achieved by using the Particle Swarm Optimization (PSO), Bacterial Foraging Optimization (BFO), and Ant Colony Optimization (ACO) algorithms. Moreover, we perform Sweeping algorithm as base case to compare with implemented algorithms. During the experiments at each step the robots share their sensor readings and position data through a wireless network among each other and also send to a remote computer where the data are combined, filtered, and interpolated to form the chemical concentration 3D map of the environment in real time. In order to obtain smoother chemical concentration map the Kriging method is used and an extrapolation and an interpolation algorithms are applied. The performance of the implemented algorithms are also compared in terms of the quality of the maps obtained and success of locating the contaminating gas sources.

18th International Conference on Transparent Optical Networks (ICTON) -- JUL 10-14, 2016 -- Univ Trento, Fac Letters ; Philosophy, Trento, ITALY, In this paper, differential evolution (DE) optimization algorithm is applied to design sub-wavelength focusing PCs structure for the first time to the best of our knowledge. For this purpose, the transverse cross section of the input beam is spatially shaped by optimized PC structure. Strong focusing of beam with FWHM equal to lambda/5 and with suppressed magnitude of side lobe intensities is achieved. In addition, microwave experiments to verify the numerical results are conducted. The numerical and experimental results given in the paper are in good agreement with each other., IEEE Photon Soc

The computational inverse design has paved the way for the design of highly efficient, compact, and novel nanophotonic structures beyond human intuition and trial-and-error approaches. Apparently, with nanophotonic design power, the exploration and implementation of multi-objective, complex, and functional nanophotonic devices become feasible. Herein, we used a recently emerged inverse design framework to demonstrate the design of a 1 x 2 polarization-insensitive wavelength division multiplexer (PIWDM) made of a low-refractive-index material with an index of 1.55. The inversely designed PIWDM structure successfully steers toward the targeted channels for 1.30 mu m and 1.55 mu m with TE and TM polarizations. Taking advantage of the design with a low refractive index material, we scaled the structural dimensions corresponding to the microwave region, fabricated the compact device using a 3D printer, and conducted an experiment as a proof of concept. The transmission values of the fabricated PIWDM device were -4.87 and -2.18 dB for TE and -2.19 and -2.23 dB for TM polarization at WG-I and WG-II, respectively., Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [116F200], This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under Project No. 116F200.

Spatial filtering is an important mechanism to improve the spatial quality of laser beams. Typically, a confocal arrangement of lenses with a diaphragm in the focal plane is used for intracavity spatial filtering. Such conventional filtering requires access to the far-field domain. In microlasers, however, conventional filtering is impossible due to the lack of space in microresonators to access the far-field. Therefore, a novel concept for more compact and efficient spatial filtering is necessary. In this study, a conceptually novel mechanism of spatial filtering in the near-field domain is proposed and demonstrated, by a nanostructured multilayer coating—a 2D photonic crystal structure with a periodic index modulation along the longitudinal and transverse directions to the beam propagation. The structure is built on a nanomodulated substrate, to provide the transverse periodicity. The physical vapor deposition is used to provide self-repeating modulation in the longitudinal direction. A 5 µm thick photonic multilayer structure composed of nanostructured multiple layers of alternating high- and low-index materials providing spatial filtering in the near-infrared frequencies with 2° low angle passband is experimentally demonstrated. The proposed photonic structure can be considered as an ideal component for intracavity spatial filtering in microlasers., Postprint (published version)

Photonic quasi-crystals are ordered but not periodic structures that lack translational symmetry but include rotational symmetry. The present work apply index gradient concept to the familiar inhomogeneous index forms, Maxwell fish eye, Luneburg lens, and Eaton lens for aiming enhanced light manipulations, such as strong light focusing, spiral wave guiding and phase front transformations., Ericson, Adva Opt Networking, Silicon Labs, BHE, MobiTel, Rohde ; Schwarz

We numerically investigate the design of a wavelength de-multiplexer based on a tapered photonic crystal waveguide. The tapered waveguide is generated by reducing the width of the channel which, in turn, provides a gradual change in the effective index for the guided modes. Depending on the wavelength, the grading effect enables the propagating beam to be trapped at different spatial positions along the waveguide. Furthermore, alternation on the tapering angle, i.e. changing the slope of the tapered waveguide, will result in a spatial shifting of the trapping locations. Thus, the structure can be adjusted to pick up the frequencies of interest at the chosen positions. Numerical results show that, by placing vertical line defects as drop channels at specific locations, different wavelengths can be properly guided along the drop channels that are transverse to the main waveguide., ERICSON, ADVA OPT NETWORKING, SILICON LABS, BHE, MobiTel, ROHDE ; SCHWARZ, ICREAICREA Funding Source: Custom

We present the optical investigation of crescent-shaped dielectric pillars that comprise a periodic structure named as crescent photonic crystals (CPC). The circular symmetry of individual cells of periodic dielectric structures is broken by replacing them with crescent shapes. The degree of freedom to manipulate the light propagation occurs due to the rotational sensitivity of CPC. The anisotropic equi-frequency contours allow sending light beams along any certain direction which is independent of the lattice periodicity of regular photonic crystals., IEEE Photon Soc, TUBITAK, Aselsan, KOC Univ

We present a novel design of two dimensional graded index medium that provides coupling of light with high coupling efficiency between two planar dielectric waveguides of different widths (15.46 mu m vs. 2.21 mu m). Poor light coupling performance of butt-coupler can be mitigated by implementing tapered coupler at the expense of long coupler section. In order to reduce coupling losses, a new coupling device approach based on graded index (GRIN) concept is proposed. The refractive index distribution is in the form of modified version of the Maxwell fish-eye lens. The inhomogeneous refractive index distribution is approximated by photonic crystals (PCs) such that the positions of each PC rods are appropriately arranged. Strong electric field focusing ability of the designed GRIN PC medium provides relatively high coupling efficiency that is around 90%. Spectral region corresponding to coupling efficiency over 75% has a bandwidth of Delta omega = 18.56% (284 nm). Finally, we discuss the durability of the proposed coupler against the lateral displacement and angular misalignment of output waveguides. (C) 2012 Optical Society of America, Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [110T306]; Turkish Academy of Sciences (TUBA GEBIP)Turkish Academy of Sciences, The authors gratefully acknowledge the financial support of the Scientific and Technological Research Council of Turkey (TUBITAK), project 110T306. H. K. also acknowledges partial support from the Turkish Academy of Sciences Distinguished Young Scientist Award (TUBA GEBIP).

Spatial filtering is an important mechanism to improve the spatial quality of laser beams. Typically, a confocal arrangement of lenses with a diaphragm in the focal plane is used for intracavity spatial filtering. Such conventional filtering requires access to the far-field domain. In microlasers, however, conventional filtering is impossible due to the lack of space in microresonators to access the far-field. Therefore, a novel concept for more compact and efficient spatial filtering is necessary. In this study, a conceptually novel mechanism of spatial filtering in the near-field domain is proposed and demonstrated, by a nanostructured multilayer coating-a 2D photonic crystal structure with a periodic index modulation along the longitudinal and transverse directions to the beam propagation. The structure is built on a nanomodulated substrate, to provide the transverse periodicity. The physical vapor deposition is used to provide self-repeating modulation in the longitudinal direction. A 5 mu m thick photonic multilayer structure composed of nanostructured multiple layers of alternating high- and low-index materials providing spatial filtering in the near-infrared frequencies with 2 degrees low angle passband is experimentally demonstrated. The proposed photonic structure can be considered as an ideal component for intracavity spatial filtering in microlasers., European Social FundEuropean Social Fund (ESF) [09.3.3- LMT-K712-17- 0016]; Research Council of Lithuania (LMTLT)Research Council of Lithuania (LMTLT); Research Council of LithuaniaResearch Council of Lithuania (LMTLT) [P-MIP-17-190], This project has received funding from European Social Fund (project No 09.3.3- LMT-K712-17- 0016) under grant agreement with the Research Council of Lithuania (LMTLT), D.G. and M.P. acknowledge the financial support from "FOKRILAS" (Project No. P-MIP-17-190) from Research Council of Lithuania. Authors are grateful to Dr. Algirdas Selskis from State research institute Center for Physical Sciences and Technology for SEM measurements.

The mode-order conversion characteristics of a heterostructure formed by regular photonic crystals (PCs) with high symmetry and PCs with low symmetry are analyzed numerically. The working principle of the proposed mode-order converter is based on the phase retardation of the incident beam while propagating through the PC heterostructure. This type of phase delay arises from the effective refractive index difference between the symmetrical PC and the asymmetric PC, called a modified annular PC (MAPC), at the specified frequency regimes a/lambda = 0.281-0.34. Further optimizations that are carried out improve the mode-order conversion bandwidth, reaching up to 24%. By means of such a novel-type configuration, a propagating fundamental mode can be transformed into higher-order modes at the output with adequate transmission efficiency. (C) 2013 Optical Society of America, Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [110T306]; TUBITAK-BIDEBTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK); Turkish Academy of SciencesTurkish Academy of Sciences, The authors gratefully acknowledge the financial support from the Scientific and Technological Research Council of Turkey (TUBITAK), project 110T306, and the financial support from TUBITAK-BIDEB. H. K. also acknowledges the partial support from the Turkish Academy of Sciences.

A novel (to our best knowledge) type of photonic crystal (PC) structure called modified annular PC (MAPC) that is composed of dielectric rods with off-centered air holes is thoroughly studied. The plane wave expansion method is applied for spectral analysis. A complete photonic bandgap region with a considerable value of gap width Delta omega/omega = 7.06% is achieved by optimizing the structural parameters of the proposed periodic medium. By introducing geometrical asymmetry to the primitive cell of PC, we engineer the dispersion properties of the proposed photonic structure such that conventional equifrequency contours for the second band can be transformed into tilted rectangular shapes. This feature enables us to demonstrate the polarization insensitive tilted self-collimation effect. A hybrid structure composed of dielectric nanowire and MAPCs is offered to obtain a high degree of polarization independent guiding of light. The two-dimensional finite-difference time-domain method is carried out to verify the light guiding efficiencies. Polarization insensitive optical functionalities achieved by MAPC structure can be deployed in integrated optical circuits. (C) 2012 Optical Society of America, Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [108T717, 110T306]; Turkish Academy of Sciences Distinguished Young Scientist Award (TUBA-GEBIP)Turkish Academy of Sciences, The authors gratefully acknowledge the financial support of the Scientific and Technological Research Council of Turkey (TUBITAK), project numbers 108T717 and 110T306. H. K. acknowledges support from the Turkish Academy of Sciences Distinguished Young Scientist Award (TUBA-GEBIP).

Asymmetric graded-index (GRIN) inhomogeneous medium is proposed to enable even-to-odd mode conversion. An exponential refractive index profile is implemented to induce an asymmetric refractive index distribution. A two-dimensional photonic crystal structure composed of constant dielectric radii with rectangular unit cells is deployed. Efficient mode transformation in a compact structure may promote the manipulation of light for the creation of other types of higher-order modes in asymmetric GRIN structures. (C) 2013 Optical Society of America, Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [110T306]; Turkish Academy of SciencesTurkish Academy of Sciences, The authors gratefully acknowledge the financial support of the Scientific and Technological Research Council of Turkey (TUBITAK), project 110T306. HK acknowledges partial support from the Turkish Academy of Sciences.

There have been huge efforts performed on the study of photonic crystals due to their potential to manipulate the flow of light waves at the optical domain. One of the precious features of the photonic crystals is that they have photonic band gaps, i.e. frequency bands in which optical modes are suppressed to exist. The creation of complete photonic band gap is an important concept especially for the design of polarization-insensitive optical devices. There are various studies targeting the generation of larger band gaps in two-dimensional photonic crystals by means of engineering the lattice geometry or by a change of the shape and orientation of the unit cells of the structure. In the present work, we study the creation of complete band gaps by breaking the structural symmetry of the annular photonic crystals which is called as modified annular photonic crystals. This new structure enables us to engineer dispersion characteristics of photonic crystals that facilitate the design of configurable polarization-insensitive optical devices for different practical applications such as self-collimation waveguides, defect-based linear waveguides, and beam splitters., Univ Warwick

We propose a mode conversion method that enables transformation of the propagating mode from fundamental to higher-order modes by utilizing asymmetric graded index (A-GRIN) structures. Refractive index variations of two different asymmetric gradient profiles, i.e., exponential and Luneburg lens profiles, have been approximated by two-dimensional photonic crystals (PCs). The basic structure is composed of constant radii with different lattice sizes. The designed GRIN mode converters provide relatively high transmission efficiency in the spectral region of interest and achieve the transformation in compact configuration. Numerical approaches utilizing the finite-difference time-domain and plane wave expansion methods are used to analyze the mode conversion phenomenon of proposed GRIN PC media. Analytical formulation based on ray theory is outlined to explore both ray trajectories and the physical concept of a wavefront retardation mechanism. (C) 2013 Optical Society of America, Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [110T306]; Turkish Academy of ScienceTurkish Academy of Sciences, The authors gratefully acknowledge the financial support of the Scientific and Technological Research Council of Turkey (TUBITAK), project 110T306. H. K. also acknowledges the partial support of the Turkish Academy of Science.

In this paper, a novel technique for spatial wavelength division using graded index photonic crystals (GRIN PCs) is proposed. The designed GRIN PC structure with hyperbolic-secant refractive index profile at a fixed frequency generates spatial shifts in the longitudinal direction with respect to different incident wavelengths so that distinct path trajectories are followed by propagating beams through the graded medium. Due to gradual variation of the refractive index profile (incremental decrease), an incident beam with an appropriately selected wavelength undergoes continuing refraction and finally, total internal reflection (TIR) occurs at the turning point. Due to the wavelength-dependency characteristic of GRIN PCs, TIR takes place at different positions for different wavelengths and thus, light wave emanates from the GRIN medium at different locations with different exit angles. It is revealed that the designed structure can work in three distinct frequency regimes and is able to separate a certain number of incident beams with different wavelengths, viz. from three to seven different wavelengths. This condition enables the deployment of the GRIN PC configuration for the design of wavelength selective media.

We investigate dispersive properties of two dimensional photonic crystal (PC) called star-shaped PC (STAR-PC) in order to succeed super-collimation over a broad bandwidth. Both time- and frequency-domain numerical methods are conducted. Due to introduced low-symmetry in the primitive cell, flat contours are observed at the fifth band for transverse magnetic mode. The proposed structure supports a super-collimation effect over a broad wavelength range between 1443 nm and 1701 nm with a bandwidth of Delta omega = 16.42%. The intrinsic characteristic of STAR-PC provides in-plane beam propagation with a limited diffraction length of 120a, where a is the lattice constant. By mean's of STAR-PC, one may realize super-collimation based single-mode optical devices with a low insertion loss, reduced dispersion and wide bandwidth. (C) 2012 Elsevier B.V. All rights reserved., Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [1081717, 110T306]; Turkish Academy of Sciences Distinguished Young Scientist Award (TUBA-GEBIP)Turkish Academy of Sciences, Authors gratefully acknowledge the financial support of the Scientific and Technological Research Council of Turkey (TUBITAK), Project numbers 1081717 and 110T306. H. K. acknowledges support from the Turkish Academy of Sciences Distinguished Young Scientist Award (TUBA-GEBIP).

We propose a simple realization of a 2-dimensonal (2D) PT-symmetric photonic structure: a honeycomb arrangement of alternating cylinders with gain or loss in a dielectric background. The structure provides a periodic modulation of the refractive index on the wavelength scale, which combined with an anti-symmetric gain/loss distribution on the same scale, leads to non-reciprocal light coupling at resonance frequencies. Numerical simulations show asymmetric right-left transmission of light beams., We acknowledge financial support by Spanish Ministerio de Ciencia e Innovacion, and European Union FEDER through project FIS2011-29731-0O2-01 and -02 and and Generalitat de Catalunya (2009 SGR 1168)., IEEE, IEEE Photon Soc, Light Tec, Agilent Technologies, Cerebra InformationsSysteme GmbH, IEEE Austria Sect, Inst Engn ; Technol, Natl Inst Telecommunicat, IIIE Media Event, ML11, GRAZ, Osterreichischer Verband Elektrotechnik, IEEE Photon Soc, Raiffeisen Meine Bank, GRAZ Stadt, Graz Univ Technology, TEST, Spanish Ministerio de Ciencia e InnovacionInstituto de Salud Carlos IIISpanish Government; European Union FEDEREuropean Commission [FIS2011-29731-0O2-01, FIS2011-29731-0O2-02]; Generalitat de CatalunyaGeneralitat de Catalunya [2009 SGR 1168]

In this work we explore a possibility to apply ultrafast 3D laser nanolithography in conjunction with pyrolysis to acquire glass-ceramic 3D structures in micro- and nano-scale. Laser fabrication allows for production of initial 3D structures with relatively small (hundreds nm - mu m) feature sizes out of SZ2080 hybrid material. Then, post-fabrication heating at 600 degrees C in Ar atmosphere decomposes organic part of the material leaving the glass-ceramic component of the hybrid. Resulting structures are uniformly shrunk by 40%. This brings us one step closer to fabricating highly efficient slow-light absorbers., The work was financially supported by NATO project grant No. SPS-985048 and European Commissions Seventh Framework Programme Laserlab-Europe IV JRA support BIOAPP (EC-GA 654148)., SPIE, Nanoscribe GmbH, NATO projectNATO (North Atlantic Treaty Organisation) [SPS-985048]; European Commissions Seventh Framework Programme Laserlab-Europe IV JRA support BIOAPP [EC-GA 654148]

In this manuscript, an evolutionary algorithm is applied to design a mode order converter photonic crystal structure for achieving transformation of the propagating fundamental mode to the higher order mode. In order to transform incident light mode from an even mode to an odd mode, predefined mask object functions are employed. The cross-sectional field profiles at the output face of the optimized structure are utilized to evaluate the optimization cost function to achieve mode order transformation task. In the study, the optimized structure composed of dielectric alumina (Al2O3) rods and time domain analyses of the optimization process are done by using finite-difference time domain method. Furthermore, numerical results are confirmed by experiments for designed structure at the microwave frequencies. It is shown that the numerical calculations and experimental measurements agree well with each other., This work developed under the financial support of Project 116F182 of the Scientific and Technological Research Council of Turkey (TUBITAK). The author H.K. also acknowledges the partial support from the Turkish Academy of Sciences., IEEE Photon Soc, IEEE, Univ Politehnica Bucharest, APEX Technologies, Photonics, OptoSigma, neaspec, Schaefer, Inst Lacznosci Panstwowy Inst Badawczy, Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [116F182]; Turkish Academy of SciencesTurkish Academy of Sciences

In this article we describe implementations of various bio-inspired algorithms for obtaining the chemical gas concentration map of an environment filled with a contaminant. The experiments are performed using Khepera III and miniQ miniature mobile robots equipped with chemical gas sensors in an environment with ethanol gas. We implement and investigate the performance of decentralized and asynchronous particle swarm optimization (DAPSO), bacterial foraging optimization (BFO), and ant colony optimization (ACO) algorithms. Moreover, we implement sweeping (sequential search algorithm) as a base case for comparison with the implemented algorithms. During the experiments at each step the robots send their sensor readings and position data to a remote computer where the data is combined, filtered, and interpolated to form the chemical concentration map of the environment. The robots also exchange this information among each other and cooperate in the DAPSO and ACO algorithms. The performance of the implemented algorithms is compared in terms of the quality of the maps obtained and success of locating the target gas sources., Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [106E122]; European CommissionEuropean CommissionEuropean Commission Joint Research Centre [045269], This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under Grant No. 106E122 and by the European Commission under the GUARDIANS Project (FP6 contract No. 045269).

In this study, we propose a method based on graded-index medium in order to cloak scatterer objects. We use discretized Luneburg lenses as a graded-index medium and the proposed structure consists of four discretized Luneburg lenses, i. e., it is can be considered as a quadruple Luneburg lens system. Numerical investigations for directional cloaking are performed by using finite-difference time-domain methods. It is shown that an object can be cloaked inside the dark zone of created by Luneburg lenses and the proposed structure can provide cloaking at optical wavelengths., Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [116F182]; Turkish Academy of SciencesTurkish Academy of Sciences, This work developed under the financial support of Project 116F182 of the Scientific and Technological Research Council of Turkey (TUBITAK). The author H.K. also acknowledges the partial support from the Turkish Academy of Sciences., IEEE Photon Soc, IEEE, Univ Politehnica Bucharest, APEX Technologies, Photonics, OptoSigma, neaspec, Schaefer, Inst Lacznosci Panstwowy Inst Badawczy