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Design of quad core photonic crystal fibers with flattened zero dispersion
摘要： Two photonic crystal fiber structures with quad-core have been investigated in this paper. Both the structures are geometrically similar but have different background materials. Both PCF structures exhibit very high birefringence. However, structure with silica background material reports birefringence of the order 10-2. It is to be noted that, this PCF structure has also shown zero dispersion behavior over a wide range of telecommunication wavelength. Moreover, the other structure with lead silicate as background material has also reported very low dispersion. Thus both the PCF structures simulated show ability to mitigate the effect of polarized mode dispersion. Besides this, other propagation characteristics like confinement loss, normalized frequency and non linear coefficient have been reported.
关键词： confinement loss,dispersion,birefringence,nonlinearity,Photonic crystal fibers
更新于2025-09-23 15:21:01
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[IEEE 2018 15th European Radar Conference (EuRAD) - Madrid, Spain (2018.9.26-2018.9.28)] 2018 15th European Radar Conference (EuRAD) - Lightweight Broadband Antennas for UAV based GPR Sensors
摘要： In this contribution two different types of broadband antennas namely a logarithmic-periodic dipole antenna (LPDA) and a transversal electromagnetic (TEM) horn antenna for ground penetrating synthetic aperture radar sensors are presented. These antennas are designed to be mounted on an unmanned aircraft vehicle (UAV). The antennas are evaluated in terms of their matching, radiation pattern pulse response and weight. Finally, an integration example of one of these antennas is shown on an UAV.
关键词： ultra wideband antennas,dispersion,unmanned aerial vehicles,Ground penetrating radar
更新于2025-09-23 15:21:01
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Computation of Propagating and Non-Propagating Lamb-Like Wave in a Functionally Graded Piezoelectric Spherical Curved Plate by an Orthogonal Function Technique
摘要： Non-propagating waves have great potential for crack evaluation, but it is difficult to obtain the complex solutions of the transcendental dispersion equation corresponding to the non-propagating wave. This paper presents an analytical approach based on the orthogonal function technique to investigate non-propagating Lamb-like waves in a functionally graded piezoelectric spherical curved plate. The presented approach can transform the set of partial differential equations for the acoustic waves into an eigenvalue problem that can give the generally complex wave numbers and the field profiles. A comparison of the obtained results with the well-known ones in plates is provided. The obtained solutions of the dispersion equation are shown graphically in three dimensional frequency-complex wave number space, which aids in understanding the properties of non-propagating waves better. The properties of the guided wave, including real, purely imaginary, and complex branches in various functionally graded piezoelectric spherical curved plates, are studied. The effects of material piezoelectricity, graded fields, and mechanical and electrical boundary conditions on the dispersion characteristics, are illustrated. The amplitude distributions of displacement and electric potential are also discussed, to analyze the specificities of non-propagating waves.
关键词： dispersion,orthogonal function technique,displacement distribution,functionally graded piezoelectric material,non-propagating wave
更新于2025-09-23 15:21:01
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Electronic and Vibrational Properties of TiS <sub/>2</sub> , ZrS <sub/>2</sub> , and HfS <sub/>2</sub> : Periodic Trends Studied by Dispersion-Corrected Hybrid Density Functional Methods
摘要： The electronic and vibrational properties of TiS2, ZrS2, and HfS2 have been studied using dispersion corrected hybrid density functional methods. The periodic trends in electronic band structures, electronic transport coefficients, IR and Raman spectra, and phonon dispersion relations were investigated. Comparison to the available experimental data shows that the applied DFT methodology is suitable for the investigation of the layered transition metal dichalcogenide materials with weak interlayer Van der Waals interactions. The choice of damping function in the D3 dispersion correction proved to have surprisingly large effect. Systematic investigation of the periodic trends within group 4 disulfides reveals that TiS2 shows many differences to ZrS2 and HfS2 due to the more covalent M–S bonding in TiS2. ZrS2 and HfS2 mainly show differences for properties where the atomic mass plays a role. All three compounds show similar Seebeck coefficients, but clear differences in the relative electrical conductivity of cross- and in-plane directions. The transport and vibrational properties of thin TiS2 single crystals were also investigated experimentally.
关键词： ZrS2,HfS2,dispersion corrected hybrid density functional methods,thermoelectric properties,periodic trends,vibrational properties,electronic properties,TiS2
更新于2025-09-23 15:21:01
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Impact of fourth order dispersion on modulational instabilities in asymmetrical three-core optical fiber
摘要： In this paper we investigate the impact of linear coupling coefficient and coupling coefficient dispersion on modulational instability (MI) in the presence of fourth order dispersion (FOD) in an asymmetric three core optical fiber under normal and anomalous dispersion regime. In addition, we also considered the impact of symmetric and asymmetric power ratio on MI characteristics. It is found that there is significant influence by linear coupling coefficient and frequencies is highly controlled by FOD, but the amplitude of MI gain found to be reduced with increasing FOD under each dispersion regimes. In case of CCD, the impact of FOD found to be quite insensitive and found no MI gain in the absence of CCD under symmetric power ratio under coupling coefficient dispersion (CCD) on MI under different dispersion regimes. In anomalous dispersion regime, at β4 < 0 the generation of smaller MI secondary side bands were observed at higher frequencies while at normal dispersion the effect of FOD leads to breaking of MI gain at different values of coupling coefficient. Though the appearance of the MI gain at different frequencies is highly controlled by FOD, but the amplitude of MI gain found to be reduced with increasing FOD under each dispersion regimes.
关键词： modulational instability,asymmetrical three-core optical fiber,fourth order dispersion,linear coupling coefficient,coupling coefficient dispersion
更新于2025-09-23 15:19:57
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Mid-infrared supercontinuum generation with high spectral flatness in dispersion flattened tellurite all-solid hybrid microstructured optical fibers
摘要： Tellurite all-solid hybrid microstructured optical fibers are proposed for chromatic dispersion control. An ultra-flattened chromatic dispersion profile with variation as small as ± 0.2 ps/km/nm over the wavelength range from 2.5 to 3.7 μm can be obtained. The fibers with flattened chromatic dispersion profiles have high potential for broadband mid-infrared supercontinuum generation. Fabrication of the fiber is successfully performed and by pumping the fabricated fiber at 2 μm, a broad and highly coherent supercontinuum with high spectral flatness is generated.
关键词： mid-infrared,supercontinuum generation,microstructured optical fibers,tellurite fibers,chromatic dispersion
更新于2025-09-23 15:19:57
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Wave plate-dependent lasing regimes transitions in an all-normal-dispersion fiber laser mode-locked by nonlinear polarization rotation
摘要： We address the transitions between three different working regimes of an all-normal-dispersion pulsed fiber laser, mode-locked by nonlinear polarization rotation (NPR). In particular, we investigate numerically the dynamics and study in details the transitions induced by solely rotating the cavity wave plates. We analyze the phemomenon by putting forward a model for all-normal-dispersion NPR-moded-locked fiber laser, based on the coupled Ginzburg-Landau equations and Jones matrix. Numerical results show that depending on the values of the cavity parameters, the transitions between the dissipative soliton regime and amplifier similariton one, or the transition between the dissipative soliton regime and the splitting pulse one may be realized by simply rotating the cavity wave plates. We found that the transitions are intrinsically related to the NPR mode-locking mechanism by explicitly evaluating the polarization states across the pulse at different locations of the cavity. Our numerical results are in very good agreement with experimental results reported in the relevant literature, and provide evidence that besides gain saturation and spectral filtering, the orientations of wave plates may be exploited as a suitable degree of freedom to obtain the desired pulse regimes in all-normal-dispersion fiber lasers.
关键词： Amplifier similariton,Splitting pulse,All-normal-dispersion fiber laser,Dissipative soliton,Nonlinear polarization rotation
更新于2025-09-23 15:19:57
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A Quantum Cascade Laser-Based Multi-Gas Sensor for Ambient Air Monitoring
摘要： A quantum cascade laser-based sensor for ambient air monitoring is presented and five gases, affecting the air quality, can be quantified. The light sources are selected to measure CO, NO, NO2, N2O and SO2. The footprint of the measurement setup is designed to fit in two standard 19” rack (48 cm × 65 cm) with 4 height units (18 cm) whereas one is holding the optical components and the other one contains the electronics and data processing unit. The concentrations of the individual analytes are measured using 2f-Wavelength Modulation Spectroscopy (2f-WMS) and a commercially available multipass gas cell defines the optical path. In addition, CO can also be measured with a dispersion-based technique, which allows one to cover a wider concentration range than 2f-WMS. The performance of this prototype has been evaluated in the lab and detection limits in the range of 1ppbv have been achieved. Finally, the applicability of this prototype for ambient air monitoring is shown in a five-week measurement campaign in cooperation with the Municipal Department for Environmental Protection (MA 22) of Vienna, Austria.
关键词： heterodyne phase sensitive dispersion spectroscopy,ambient air,infrared,quantum cascade laser,wavelength modulation spectroscopy
更新于2025-09-23 15:19:57
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Highly accurate space-time coupled least-squares finite element framework in studying wave propagation
摘要： Simulation of stress wave propagation through solid medium is commonly carried using Galerkin weak-form cast over decoupled space and time domains. In this paper, accuracy of this commonly utilized framework is compared to that of the variationally-consistent least-squares form of the wave equation cast over space-time domain. The two formulations are tested for numerical dispersion and numerical diffusion, through two test cases. The first case studies the dispersion in harmonic shear wave propagation through a soil column over a wide range of forcing frequencies. The second test case investigates numerical diffusion in an axial wave propagation generated by constant force; which is removed after a certain time to allow free vibration to take place. Low numerical dispersion and numerical diffusion as well as high rates of convergence are the main advantages of the coupled least-squares (CLS) computational framework; when compared to the decoupled Galerkin (DG) framework. Based on studies presented here, CLS has low dispersion; yielding errors with one to two orders of magnitude less than that of DG. Also, the numerical diffusion present in DG framework causes a %40 error in DG’s prediction of the stress-wave intensity. Furthermore, accumulative error during evolution is virtually nonexistent for CLS, whereas, the error steadily increases as the solution evolves in DG framework. It is also demonstrated that CLS feature of temporal meshing allows for faster computations.
关键词： Shear wave propagation,Variational-consistency,Higher continuity hierarchical finite elements,Numerical diffusion,Least squares,Impact wave propagation,Space-time coupled,Numerical dispersion,Wave equation
更新于2025-09-23 15:19:57
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Alexandrite laser induced uveitis & pigment dispersion: A case report and review of the literature
摘要： To describe a complication of an upper eyelid alexandrite laser procedure. Observations: A 55-year-old woman presented with left eye blurred vision and photophobia after a left upper eyelid procedure with an alexandrite laser. She had elevated intraocular pressure (IOP), anterior chamber cell and pigment, posterior synechiae, and retroillumination defects in the left eye. She was treated with topical prednisolone and brimonidine. Six months later, although her anterior chamber had cleared and IOP had normalized, the patient reported decreased vision-related quality of life from persistent photophobia. Conclusions and Importance: Alexandrite lasers are commonly used for hair removal and skin depigmentation. When used periocularly without proper eye protection, they have the potential to create irreversible ocular complications. This case demonstrates the importance of proper eye protection with periocular laser procedures.
关键词： Pigment dispersion,Anterior uveitis,Alexandrite laser
更新于2025-09-23 15:19:57