Extra loss due to Fano resonances in inhibited coupling fibers based on a lattice of tubes

Confinement loss of inhibited coupling fibers with a cladding composed of a lattice of tubes of various shapes is theoretically and numerically investigated. Both solid core and hollow core are taken into account. It is shown that in case of polygonal shaped tubes, confinement loss is affected by extra loss due to Fano resonances between core modes and cladding modes with high spatial dependence. This explains why hollow core Kagome fibers exhibit much higher confinement loss with respect to tube lattice fibers and why hypocycloid core cladding interfaces significantly reduce fiber loss. Moreover it is shown that tube deformations, due for example to fabrication process, affect fiber performances. A relationship between the number of polygon sides and the spectral position of the extra loss is found. This suggests general guide lines for the design and fabrication of fibers free of Fano resonance in the spectral range of interest

Analytical Formulas for Dispersion and Effective Area in Hollow-Core Tube Lattice Fibers

In this work, we propose analytical formulas for the estimation of dispersion properties and effective area of the fundamental mode of hollow-core inhibited coupling fibers with a microstructured cladding composed by a ring of dielectric tubes. The formulas are based on a model which has already been successfully applied to the estimation of confinement loss. The model takes into account the effects of the coupling of the fundamental core mode with the cladding modes in the context of the single-tube approximation. Effective index, group velocity dispersion, and effective area of the fundamental mode are estimated and compared with the results obtained from numerical simulations, by considering ten different fibers. The comparison shows a good accuracy of the proposed formulas, which do not require any tuning of fitting parameters. On the basis of the analysis carried out, a scaling law relating the effective area to the core radius is also given. Finally, the formulas give a good estimation of the same parameters of other Hollow-core inhibited coupling fibers, such as nested, ice-cream, and kagome fibers

Inhibited coupling guiding hollow fibers for label-free DNA detection

The potentialities in using hollow core tube lattice fibers based on inhibited coupling wave-guiding for label-free DNA detection are numerically investigated and discussed here. The proposed sensing approach does not require any additional transducer component such as Bragg gratings, amplifying techniques such as nanoparticles nor coherent sources. It simply consists of the measurement of the transmittance of a piece of fiber some ten centimeters long. In case of matching DNA sequence, an additional bio-layer is laid down the dielectric-air interface causing a red shift of the transmission spectrum of the fiber. Results show a spectral sensitivity on the bio-layer with shift as high as 42 nm for every 10 nm of bio-layer and robustness against imperfect fiber coupling. The proposed approach can be easily applied to sensing of other complex molecular structures where the presence/absence of analyte can generate or not an additional layer

Flexible tube lattice fibers for terahertz applications

In this paper a flexible hollow core waveguide for the terahertz spectral range is demonstrated. Its cladding is composed of a circular arrangement of dielectric tubes surrounded by a heat-shrink jacket that allows the fiber to be flexible. Characterization of straight samples shows that the hollow core allows the absorption caused by the polymethylmethacrylate tubes of the cladding to be reduced by 31 times at 0.375 THz and 272 times at 0.828 THz with respect to the bulk material, achieving losses of 0.3 and 0.16 dB/cm respectively. Bending loss is also experimentally measured and compared to numerical results. For large bending radii bending loss scales as R−2b, whereas for small bending radii additional resonances between core and cladding appear. The transmission window bandwidth is also shown to shrink as the bending radius is reduced. An analytical model is proposed to predict and quantify both of these bending effects

Reconfigurable RF Energy Harvester with Customized Differential PCB Antenna

In this work, a RF Energy harvester comprised of a differential RF-DC CMOS converter realized in ST130nm CMOS technology and a customized broadband PCB antenna with inductive coupling feeding is presented. Experimental results show that the system can work with different carrier frequencies and thanks to its reconfigurable architecture the proposed converter is able to provide a regulated output voltage of 2 V over a 14 dB of RF input power range. The conversion efficiency of the whole system peaks at 18% under normal outdoor working conditions

A new approach to the analysis of electromagnetic FEM simulations results at electric field singularities

A new methodology to the analysis of the results of Finite-Element Modeling (FEM) simulations at electric field singularities is proposed. The method, that can be easily applied in the post-processing phase of the electromagnetic FEM analysis workflow, is based on the weighted averaging of the calculated electric field magnitude within small volumes including the singularity point under investigation. In the paper, the proposed approach is applied to the electrical stress analysis of a high-voltage device modeled by means of a commercial electromagnetic FEM tool. In comparison to the conventional metric of the maximum field evaluation usually adopted for the analysis of electrical stress in insulators, our approach features several advantages: (i) the outcome of the analysis is independent of the numerical grid refinement at the singularity, thus allowing direct comparison of calculated electric field with the material dielectric strength; (ii) the method is robust against slight modifications of the geometrical shape of the singularity; (iii) on the other hand, for a given shape, the analysis outcome responds to significant variations of the singularity size or, in other words, of its sharpness; (iv) in the analysis of high-voltage devices, the approach can be applied for the estimation of the discharge volumes corresponding to different singularity types of different device geometries. In the paper, the new methodology is explained in details and is applied to simple but significant case studies

Integrated RF-DC converter and PCB antenna for UHF wireless powering applications

In this work, a broadband differential RF-DC CMOS converter realized in CMOS 130 nm technology with a customized PCB antenna with inductive coupling feeding for RF energy scavenging is presented. Experimental results show that output DC voltage higher than 1V from 800MHz to 970MHz can be obtained with a load of 1kohm