Papers by Christian Hafner
IEEE Journal of Quantum Electronics, 2014
ABSTRACT In this paper, we propose and theoretically investigate an ultrafast, compact, and energ... more ABSTRACT In this paper, we propose and theoretically investigate an ultrafast, compact, and energy efficient all-optical switch (AOS) design based on a saturable absorbing cavity. The conceptual basis of the switch design is the material absorption saturation phenomenon. The optical cavity is used to enhance the light-matter interaction locally. As a result, the device dimension is substantially reduced. Numerical studies were carried out analytically using the temporal-coupled mode theory. Cavity structural parameters and material properties related to the switch design are discussed. The figure of merit of the switch performance in terms of the insertion loss, extinction ratio, and operating energy consumption are analyzed. Finally, as a specific practical application of the developed AOS, ultrahigh-speed optical time division multiplexing operations are demonstrated.
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2010 IEEE Antennas and Propagation Society International Symposium, 2010
Metamaterials are defined as synthetic structures which usually possess periodic symmetries and e... more Metamaterials are defined as synthetic structures which usually possess periodic symmetries and exhibit very promising electromagnetic properties. Some very wellknown examples are planar bulk metamaterials made of frequency selective surfaces (FSS) with double split ring resonator [1] or thin wires [2] as the patch unit cell. It is shown that an electromagnetic wave propagating within these structures experiences negative dielectric
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A new type of metamaterials is introduced which can be fabricated by printing metal patches on in... more A new type of metamaterials is introduced which can be fabricated by printing metal patches on inhomogeneous, periodic substrates. Such structures without periodic substrate are known as Frequency Selective Surfaces (FSS) but they are more promising for EMC shielding than common FSS structures because both the effective dielectric permittivity and loss of the substrate can be controlled. A numerical method
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A new type of metamaterial is proposed that may be considered as frequency selective surface (FSS... more A new type of metamaterial is proposed that may be considered as frequency selective surface (FSS), consisting of printed metal patches on inhomogeneous, periodic substrates. To analyze these structures a system of equations obtained from the Rigorous Coupled Wave Analysis (RCWA) is solved by the Method of Moments (MoM) with sub-domain rooftop basis functions and Galerkin testing functions. Several examples
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Optomechatronic Micro/Nano Devices and Components III, 2007
A new type of metamaterial is proposed that may be considered as frequency selective surface (FSS... more A new type of metamaterial is proposed that may be considered as frequency selective surface (FSS), consisting of printed metal patches on inhomogeneous, periodic substrates. To analyze these structures a system of equations obtained from the Rigorous Coupled Wave Analysis (RCWA) is solved by the Method of Moments (MoM) with sub-domain rooftop basis functions and Galerkin testing functions. Several examples
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Optomechatronic Micro/Nano Devices and Components III, 2007
Antireflective coatings are useful for a range of applications, from minimizing the radar cross-s... more Antireflective coatings are useful for a range of applications, from minimizing the radar cross-section of stealth aircraft, to maximizing the efficiency of solar energy panels. New low-index nanorod thin films promise broadband, broad angle performance for such coatings. We demonstrate that a bandwidth increase from 38.5% to 113% is possible by using a simple evolutionary strategy to optimize the thin
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Advances in Electromagnetics of Complex Media and Metamaterials, 2002
This chapter proposes complex materials (anisotropic, chiral, Tellegen, and general biisotropic) ... more This chapter proposes complex materials (anisotropic, chiral, Tellegen, and general biisotropic) as element base for Finite Photonic Crystal (FPC) devices, offers an effective method for their handling, illustrates possibilities of their numerical analysis and discusses results for FPC design. The approach is based on the Method of Auxiliary Sources (MAS) and its implementation to complex structures.
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International Journal of Oncology, 2003
Overexpression of various members of the Eph receptor tyrosine kinases and their ephrin ligands h... more Overexpression of various members of the Eph receptor tyrosine kinases and their ephrin ligands has been frequently reported in cancer. In contrast, a loss of EphB6 gene expression has been correlated with a poor prognosis in human neuroblastoma, suggesting a distinct role for this receptor compared to other family members. More recently, an important role of EphB6 signalling in T-cells has been described, suggesting possibly deleterious immunologic effects of a loss of EphB6 in cancer progression. We investigated the expression of EphB6 in melanocytic tumors. EphB6 mRNA of 22 microdissected tissues (7 benign nevi, 7 melanomas, 8 metastases) and 10 different cell lines (normal melanocytes, non-metastatic/metastatic melanoma cell lines) were measured by quantitative real-time RT-PCR. For visualization of EphB6 protein expression, immunohistochemistry of 32 melanocytic lesions were performed. On the mRNA level, the benign nevi revealed the highest EphB6 expression (mean = 1.43), while melanomas (mean = 0.63) and metastases (mean = 0.08; p=0.001) displayed a progressive and significant reduction of EphB6 expression. Accordingly, established melanoma cell lines with metastatic potential showed low EphB6 expression in comparison to normal melanocytes and to most of the melanoma cell lines. Immunohistochemistry revealed homogeneous staining in common nevi, whereas in malignant melanomas and metastases a heterogeneously positive to completely negative EphB6 staining was observed. Remarkably, Spitz nevi stained similarly to ordinary melanocytic nevi. Taken together, we show that melanoma progression to metastatic disease is associated with a significant reduction of EphB6 gene expression which may have considerable consequences for the prognosis of malignant melanoma patients and possible gene-therapeutic approaches.
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2007 Workshop on Computational Electromagnetics in Time-Domain, 2007
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The spectral and spatial treatment of electromagnetic fields express an essential operation regar... more The spectral and spatial treatment of electromagnetic fields express an essential operation regarding the functionality of integrated optical devices. Such mol- ding of fields can hardly be handled without sophis- ticated heuristic optimization tools. We propose evolutionary algorithm schemes being canonical by investigating numerous design examples in the field of computational optics and electromagnetics.
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The optical response of nanostructures that exhibit pronounced plasmonic effects is studied and a... more The optical response of nanostructures that exhibit pronounced plasmonic effects is studied and analyzed. Various approaches to solve light scattering problems in the time domain and in the frequency domain, using both the domain and the boundary discretization methods were used. Far-field and near-field characteristics of plasmonic nanostructures are investigated with several numerical algorithms to study the shape effect and
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In this paper, a three dimensional analysis of an ultra-compact sharp trench waveguide bend struc... more In this paper, a three dimensional analysis of an ultra-compact sharp trench waveguide bend structure modified with small local photonic crystals is presented. The structure used here is based on a previous proposal [1]. To fully investigate the behavior of the structure, especially mode coupling and off plane radiation losses - (that are ignored in two dimensional calculations [1]) as
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The focus of this paper is on the numerical analysis of ultra-small metallic waveguides at optica... more The focus of this paper is on the numerical analysis of ultra-small metallic waveguides at optical wavelengths that is very demanding 1) because the cross sections may be much smaller than the wavelength, 2) because strong plasmon-polariton effects must be accounted for, and 3) because of strong dispersion and material loss. After a short outline of available numerical methods with
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2008 IEEE Antennas and Propagation Society International Symposium, 2008
This paper presents a numerical technique for the accurate calculation of the dispersion diagram ... more This paper presents a numerical technique for the accurate calculation of the dispersion diagram of planar electromagnetic bandgap structures. The method is based on coupling the energy of an incident plane-wave in a perturbed structure, which has the same resonance frequencies, and studying the reflection spectra form the structure. In this method, solving the dispersion problem is transformed to solving
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2007 18th International Zurich Symposium on Electromagnetic Compatibility, 2007
This paper presents a numerical technique for the analysis of a metamaterial that may be consider... more This paper presents a numerical technique for the analysis of a metamaterial that may be considered as a new type of frequency selective surfaces (FSS), consisting of printed metal patches on inhomogeneous, periodic substrates. Such structures are more promising for EMC shielding than common FSS structures because both the effective dielectric permittivity and loss of the substrate can be controlled.
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Plasmonics, 2011
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Small, 2009
Densely packed plasmonic particle arrays are investigated for biosensing applications. Such parti... more Densely packed plasmonic particle arrays are investigated for biosensing applications. Such particle arrays exhibit interparticle optical coupling creating a strong field between the particles, which is useful for sensing purposes. The sensor properties, such as bulk sensitivity, layer sensitivity, and the depth of sensitivity are investigated with the aid of a multiple multipole program. Sensitivity to the analyte with low concentration is also examined by a dynamic adsorption processes. The detectable concentration limit of streptavidin within 3000 s in the detection system is expected from the signal-to-noise to be less than 150 pM.
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Papers by Christian Hafner