Rm TE Research Articles

Plasmon-magnon interactions in two-dimensional honeycomb magnets

Two-dimensional honeycomb ferromagnets offer the unprecedented opportunity to study interactions between collective modes that in standard bulk ferromagnets do not cross paths. Indeed, they harbor an optical spin-wave branch, i.e. a spin wave which disperses weakly near the Brillouin zone center. When doped with free carriers, they also host the typical gapless plasmonic mode of 2D itinerant electron/hole systems. When the plasmon branch meets the optical spin-wave branch, energy and momentum matching occurs, paving the way for interactions between the charge and spin sector. In this Letter we present a microscopic theory of such plasmon-magnon interactions, which is based on a double random phase approximation. We comment on the possibility to unveil this physics in recently isolated 2D honeycomb magnets such as ${\rm Cr}_2{\rm Ge}_2{\rm Te}_6$.

Wideband Substrate Integrated Waveguide Antenna for Full-Duplex Systems

In this letter, a low-profile and wideband substrate integrated waveguide (SIW) antenna is proposed and validated for full-duplex systems. The proposed antenna operates at 4.9 and 5.8 GHz wireless local area network bands. Each resonator of the antenna consists of a modified half-mode SIW (HMSIW) cavity, and excited by a 50 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Omega$</tex-math></inline-formula> coaxial probe. The wideband response is achieved by coupling the fundamental <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\rm TE}_{10}$</tex-math></inline-formula> mode with the perturbed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\rm TE}_{10}$</tex-math></inline-formula> mode of the HMSIW cavity. The compactness of the proposed design is obtained using two rectangular slots near the closed-ends of the cavities. By properly optimizing the overall geometry, the proposed design exhibits a 10 dB fractional bandwidth of 8.2% (4.78–5.2 GHz) and 7.7% (5.70–6.16 GHz) in the lower (4.9 GHz) and upper (5.8 GHz) frequency bands, respectively. The bandwidths of both frequency bands can be controlled by adjusting the coupling between modes. A high isolation ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&gt;$</tex-math></inline-formula> 30 dB) between the two ports is observed due to series of metallic vias between them. This antenna has compact size (0.007 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _{g}^{3}$</tex-math></inline-formula> ) with high gains of 5.24 and 5.37 dBi at 4.9 and 5.8 GHz, respectively. The proposed design is suitable for emerging full-duplex systems, thanks to its small size, high isolation, wide bandwidth, and independent resonance and bandwidth control.

Cosmology with the Planck T−E correlation coefficient

Tensions in cosmological parameters measurement motivate a revisit of the effects of instrumental systematics. In this article, we focus on the Pearson's correlation coefficient of the cosmic microwave background temperature and polarization E modes $\mathcal{R}_\ell^{\rm TE}$ which has the property of not being biased by multiplicative instrumental systematics. We build a $\mathcal{R}_\ell^{\rm TE}$-based likelihood for the Planck data, and present the first constraints on $\Lambda$CDM parameters from the correlation coefficient. Our results are compatible with parameters derived from a power spectra based likelihood. In particular the value of the Hubble parameter $H_0$ characterizing the expansion of the Universe today, 67.5 $\pm$ 1.3 km/s/Mpc, is consistent with the ones inferred from standard CMB analysis. We also discuss the consistency of the Planck correlation coefficient with the one computed from the most recent ACTPol power spectra.

Broadband chiral silicon photonic circuits based on fork-type inversely tapered nanowire waveguides.

Optical spin or circular polarization provides a new degree of freedom to control light-matter interaction in the fundamentals and applications of light. To broaden the bandwidth of chiral (spin-controlled) coupling in photonic integrated circuits, we propose fork-type inversely tapered nanowire waveguides to compensate for the out-of-step phase evolution of adiabatic coupling between ${{\rm TE}_0}$ and ${{\rm TM}_0}$ (${{\rm TE}_1}$) modes excited from the $x$- and $y$-polarization components of spin polarized light in free space, respectively. We design and simulate two kinds of devices based on air and ${{\rm Si}_3}{{\rm N}_4}$ up-claddings to show the feasibility of broadening the bandwidth of chiral silicon photonic circuits by using fork-type inverse tapers. Numerical results show that the bandwidth can approach 70 nm under high directionality of above 0.90. This broadband chiral coupling via the new phase synchronizing technique with fork-type inverse tapers may pave the way to develop on-chip spin photonics or polarization-based photonic integrated devices.

The impact of isomers on a kilonova associated with neutron star mergers

ABSTRACT We investigate the significance of isomers on a kilonova associated with neutron star mergers (NSMs) for the first time. We calculate the evolution of abundances and energy generation rates ($\dot{\epsilon }_{\rm nuc}$) of ejecta from NSMs, taking into account β− decay through isomers. We find that for ejecta with electron fraction (Ye) of 0.2–0.3, $\dot{\epsilon }_{\rm nuc}$ is appreciably changed from those without isomers, due to the large change in timing of β− decay through the isomeric states (ISs) of ${}^{123,125,127} \rm Sn$ and ${}^{128} \rm Sb$. In particular, the effects of the isomers on $\dot{\epsilon }_{\rm nuc}$ are prominent for ejecta of Ye ∼ 0.25, which could emit a fraction of an early, blue component of a kilonova observed in GW170817. When the excitation from a ground state to its IS is important, the isomers of ${}^{129} \rm Sb$ and ${}^{129, 131} \rm Te$ also cause additional and appreciable change in $\dot{\epsilon }_{\rm nuc}$. Furthermore, we demonstrate that larger amounts of lanthanide-free ejecta result in a better fit of an observed light curve of the kilonova in GW170817 if the isomers are taken into account.

Heat flow of laser-ablated gold plasma in inertial confinement fusion hohlraum

When evaluating the plasma parameters in inertial confinement fusion, the flux-limited local Spitzer-Härm (S-H) model in radiation hydrodynamics simulations may be invalid when electron temperature gradient is too large. In other publications, the electron distribution function (EDF) could be explained by comparing the energy equipartition rate &lt;inline-formula&gt;&lt;tex-math id="M7"&gt;\begin{document}$R_{\rm eq}=\dfrac{1}{2}m_{\rm e}v_{\rm te} ^2\nu_{\rm ee}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M7.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M7.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; with the heating rate &lt;inline-formula&gt;&lt;tex-math id="M8"&gt;\begin{document}$R_{\rm heat}=\dfrac{1}{2}m_{\rm e}v_{\rm os} ^2\nu_{\rm ei}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M8.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M8.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;. When the condition &lt;inline-formula&gt;&lt;tex-math id="M9"&gt;\begin{document}$R_{\rm heat}\sim R_{\rm eq}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M9.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M9.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; is satisfied, the EDF deviates from Maxwell equilibrium distribution, and is well fitted to the super-Gaussian distribution &lt;inline-formula&gt;&lt;tex-math id="M10"&gt;\begin{document}$f({{ v}})=C_m{\rm e}^{-(v/v_m)^m}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M10.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M10.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; with the index &lt;i&gt;m &lt;/i&gt;(&lt;inline-formula&gt;&lt;tex-math id="M11"&gt;\begin{document}$2&lt;m&lt;5$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M11.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M11.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;). The number of energetic electrons of the super-Gaussian distribution is less than that of the Maxwell distribution, which plays an important role in electron heat flux, especially for electrons of 3.7&lt;inline-formula&gt;&lt;tex-math id="M12"&gt;\begin{document}$v_{\rm te}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M12.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M12.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;. So electron heat flux of the super-Gaussian distribution is smaller than that of the Maxwell distribution. In this paper, EDF and electron heat flux in laser-produced Au plasma are simulated by using 1D3V PIC code (Ascent). It is found that in the coronal region, the laser intensity is larger, and the electron temperature is lower than the high-density region. So &lt;inline-formula&gt;&lt;tex-math id="M13"&gt;\begin{document}$\alpha=Z(v_{\rm os}/v_{\rm te})^2&gt;1$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M13.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M13.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, &lt;inline-formula&gt;&lt;tex-math id="M14"&gt;\begin{document}$R_{\rm heat}&gt;R_{\rm eq}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M14.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M14.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, the EDF is well fitted to super-Gaussian distribution, where the index &lt;i&gt;m&lt;/i&gt; is evaluated to be 3.34. In this region, the large electron temperature gradient leads to a small temperature scale length (&lt;inline-formula&gt;&lt;tex-math id="M15"&gt;\begin{document}$L_{\rm e}=T_{\rm e}/(\partial T_{\rm e}/\partial x)$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M15.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M15.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;), but the low e-e and e-i collision frequencies lead to a large electron mean-free-path (&lt;inline-formula&gt;&lt;tex-math id="M16"&gt;\begin{document}$\lambda_{\rm e}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M16.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M16.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;). So the Knudsen number &lt;inline-formula&gt;&lt;tex-math id="M17"&gt;\begin{document}$\lambda_{\rm e}/L_{\rm e}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M17.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M17.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; is evaluated to be 0.011, which is much larger than the critical value &lt;inline-formula&gt;&lt;tex-math id="M18"&gt;\begin{document}$2\times10^{-3}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M18.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M18.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; of the S-H model, flux-limited local S-H electron heat flux is invalid. As a result, the limited-flux S-H predicts too large an electron heat flux, which results in much higher electron temperature of radiation hydrodynamics simulation than that of SG experiments. This heat flux inhibition phenomenon in coronal region cannot be explained by the flux-limited local S-H model, and non-local electron heat flux should be considered. In the high density region, the laser intensity is weaker, and the electron temperature is higher, so &lt;inline-formula&gt;&lt;tex-math id="M19"&gt;\begin{document}$\alpha=Z(v_{\rm os}/v_{\rm te})^2&lt;1$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M19.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M19.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, &lt;inline-formula&gt;&lt;tex-math id="M20"&gt;\begin{document}$R_{\rm heat}&lt;R_{\rm eq},$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M20.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M20.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; but EDF is still well fitted to super-Gaussian distribution, where the index m is evaluated to be 2.93. In this region, &lt;inline-formula&gt;&lt;tex-math id="M21"&gt;\begin{document}$L_{\rm e}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M21.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M21.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; is larger, &lt;inline-formula&gt;&lt;tex-math id="M22"&gt;\begin{document}$\lambda_{\rm e}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M22.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M22.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; is smaller, so the Knudsen number is smaller, which is evaluated to be &lt;inline-formula&gt;&lt;tex-math id="M23"&gt;\begin{document}$7.58\times10^{-4}&lt;2\times10^{-3}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M23.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M23.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;. As a result, The flux-limited local S-H electron heat flux is valid. However, the electron heat flux depends on the flux limiting factor (&lt;inline-formula&gt;&lt;tex-math id="M24"&gt;\begin{document}$f_{\rm e}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M24.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20191423_M24.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;) that varies with laser intensity and electron temperature.

On-chip silicon dual-mode multiplexer via a subwavelength grating-based directional coupler and a mode blocker.

An on-chip silicon dual-mode multiplexer (MUX) is proposed via a subwavelength grating (SWG)-based directional coupler and a mode blocker. The proposed mode MUX is optimized by utilizing the three-dimensional full-vectorial finite-difference time-domain-based band structure and propagation calculations. The simulated results indicate that an ultralow mode cross talk of $ - {40}\,\,{\rm dB}$-40dB at the operating wavelength of 1550 nm can be achieved by introducing a ${{\rm TE}_0}$TE0 mode blocker. Benefiting from the triple SWG coupler, the mode-coupling strength can be significantly enhanced inside the proposed mode MUX, which can achieve a compact coupling length of 8.75 µm, a low insertion loss of 0.39 dB at 1550 nm, an ultrabroad bandwidth of 310 nm for the mode CT $ \lt - {15.0}\,\,{\rm dB}$<-15.0dB, and insensitivity to fabrication errors.

Ferromagnetic insulator Cr2Ge2Te6 as a modulator for generating near-infrared bright-dark soliton pairs.

Novel two-dimensional (2D)-materials-based ultra-fast modulators exhibit significance in extending the fundamental investigations and practical applications of mode-locked fiber lasers. In our work, employing the liquid-phase exfoliation method, a ${{\rm Cr}_2}{{\rm Ge}_2}{{\rm Te}_6}$Cr2Ge2Te6 (CGT) optical modulator with a modulation depth and a saturable intensity of 1.64% and ${6.31}\,\,{{\rm MW/cm}^2}$6.31MW/cm2 was fabricated. Due to its suitable modulation properties and high nonlinear coefficient, a stable bright-dark soliton pair was successfully achieved within an Er-doped fiber laser. Under the pump power of 560 mW, the maximum average output power was 5.36 mW with a pulse repetition rate of 1.835 MHz. Our results fully present the capacity of CGT in designing bright-dark soliton operations and provide a meaningful reference for promoting the ultra-fast modulation applications of ferromagnetic insulators.

Transport in magnetically doped topological insulators: Effects of magnetic clusters

We study the electron transport in a magnetically doped three dimensional topological insulator (TI) by taking the effects of impurity-impurity exchange interactions into account. The interactions between magnetic impurities give rise to the formation of {\it magnetic clusters} with temperature dependent mean sizes, randomly distributed on the surface of the TI. Instead of dealing with single magnetic impurities, we consider surface Dirac electrons to be scattered off magnetic clusters, and define the scattering potential in terms of clusters mean sizes. Within the semiclassical Boltzmann approach, employing a generalized relaxation time approximation, we obtain the surface conductivity of the TI by solving four sets of recursive relations and demonstrate that, the system is highly anisotropic and the surface conductivities possess non-monotonic behaviors, they strongly depends on the direction, the mean size and the number of magnetic clusters. We demonstrate that the dependence of the anisotropic magnetoresistance (AMR) to the spin direction of the magnetic clusters is inconsistent with the angular dependence of the TI doped with non-interacting magnetic impurities. Our results are consistent with the recent experiment on the AMR of the Cr-doped $\rm {(Bi, Sb)}_2{\rm Te}_3$ TI.

First-principles study of In mXn (X = Se, Te; m + n = 5 clusters: Structural, electronic, magnetic and spectral properties

Using the density functional theory (DFT) method, the geometrical structures of $ {\rm In}_{m}X_{n}$ ( $ X={\rm Se}$ , Te; $ m+n=5$ clusters are optimized, and their relative stability as well as electronic, magnetic and spectral properties are calculated. The ground state structures of $ {\rm In}_{m}X_{n}$ clusters are found to be largely similar for $ X={\rm Se}$ and Te, with the exception of $ {\rm In}_{2}X_{3}$ . The energy gap exhibits the maximum for $ {\rm In}_{2}{\rm Se}_{3}$ or $ {\rm In}_{3}{\rm Te}_{2}$ . The electronic properties of $ {\rm In}_{m}X_{n}$ clusters depend on their geometrical structures and, hence, on the value of m ; and $ {\rm In}_{2}{\rm Se}_{3}$ shows a low vertical electron affinity (VEA) of about 1.60eV and a high vertical ionization potential (VIP) of about 9.33eV. The total magnetic moment is 1 or 0μ_B for the clusters with $ m={\rm odd}$ (1, 3) or even (2, 4) , respectively. The local magnetic moments of X atoms amount to about 99.9% of the total magnetic moment, while those of In atoms are merely 0.1%. The IR and Raman spectra of $ {\rm In}_{m}X_{n}$ clusters exhibit similarity for $ X={\rm Se}$ and Te with an exception of $ {\rm In}_{2}X_{3}$ . The energies of the strongest peaks of $ {\rm In}_{m}{\rm Te}_{n}$ are largely smaller than the corresponding $ {\rm In}_{m}{\rm Se}_{n}$ in both IR and Raman spectra. For UV-Vis spectra, the absorption peaks at 200-400nm for all clusters and 390–780 nm for m = 1 and 3 (except $ {\rm In}_{3}{\rm Te}_{2}$ are likely to hint useful properties of UV and visible light absorption, respectively.

Substrate integrated waveguide fed dual-frequency dual-linearly-polarized dielectric resonator antenna

In this paper, a single-feed dual-frequency dual-linearly-polarized dielectric resonator antenna is proposed which finds application in two- way internet satellite system and modern radar system. In order to achieve dual linear polarization at distinct frequencies, two rectangular dielectric resonators of same dimensions are excited in ${\rm TE}^{x}_{\delta 11}$ and ${\rm TE}^{y}_{1\delta 1}$ modes by a narrow longitudinal and transverse slot, respectively, etched on the top wall of the substrate integrated waveguide. The −10 dB impedance bandwidth of the proposed antenna is 6.76% for both the frequency bands. The antenna radiates along the broadside direction and the gain of the antenna varies from 5.37 to 6.24 dBi and 5.62–7.96 dBi across 8.14–8.71 GHz and 10.29–11.01 GHz, respectively.

Graphene-Bi2Te3 Heterostructure as Broadband Saturable Absorber for Ultra-Short Pulse Generation in Er-Doped and Yb-Doped Fiber Lasers

A new type of broadband saturable absorber made of graphene-Bi2Te3 heterostructure was reported, which synergistically combines light–matter interaction in graphene with that in a small bandgap semiconductor material Bi2Te3 to achieve an improved broadband nonlinear optical response. The graphene-Bi2Te3 heterostructure films were grown by chemical vapor deposition with 15% ${\rm Bi}_{2}{\rm Te}_{3}$ coverage on graphene, in which most of the Bi2Te3 nanoplatelets are less than 30 nm thick. It is interesting to find that the heterostructure thin film shows broadband saturable absorption property. At the communication band (around 1560 nm), the saturable intensity and modulation depth are measured to be 4.95 MW/cm2 and 18.98%, respectively. While around 1067 nm, the corresponding saturable intensity and modulation depth are experimentally measured to be 2.61 MW/cm2 and 23.11%, respectively. By incorporating this optical saturable absorber inside either an Er-doped or Yb-doped fiber laser, we are able to generate ultra-short pulse with very stable operation at 1565.6 and 1049.1 nm. Our experimental results clearly demonstrate that the graphene-Bi 2Te3 heterostructure can be a promising broadband nonlinear optical material for broadband ultra-fast laser photonics.

Electronic and transport properties of the Mn-doped topological insulatorBi2Te3: A first-principles study

We present a first-principles study of the electronic, magnetic, and transport properties of the topological insulator Bi$_{2}$Te$_{3}$ doped with Mn atoms in substitutional (Mn$_{\rm Bi}$) and interstitial van der Waals gap positions (Mn$_{\rm i}$), which act as acceptors and donors, respectively. The effect of native Bi$_{\rm Te}$- and Te$_{\rm Bi}$-antisite defects and their influence on calculated electronic transport properties is also investigated. We have studied four models representing typical cases, namely (i) Bi$_{2}$Te$_{3}$ with and without native defects, (ii) Mn$_{\rm Bi}$ defects with and without native defects, (iii) the same but for Mn$_{\rm i}$ defects, and (iv) the combined presence of Mn$_{\rm Bi}$ and Mn$_{\rm i}$. It was found that lattice relaxations around Mn$_{\rm Bi}$ defects play an important role for both magnetic and transport properties. The resistivity is strongly influenced by the amount of carriers, their type, and by the relative positions of the Mn-impurity energy levels and the Fermi energy. Our results indicate strategies to tune bulk resistivities, and also help to uncover the location of Mn atoms in measured samples. Calculations indicate that at least two of the considered defects have to be present simultaneously in order to explain the experimental observations, and the role of interstitials may be more important than expected.

Spoof Plasmon-Based Slow-Wave Excitation of Dielectric Resonator Antennas

A spoof plasmon (SP)-based slow-wave feeding configuration is proposed, experimentally verified and exploited to excite the fundamental horizontally polarized mode of dielectric resonator antennas (DRAs). As an example, a cylindrical DRA operating at 3 GHz is fed by the proposed feeding structure. The simulation and measurement evidence the unique features of ${\rm TE}_{01\updelta}$ mode such as lower thickness-dependency of the resonant frequencies, superb miniaturization and ultra-compactness, and omnidirectional radiation for horizontally polarized waves. We anticipate that the ground-free SP-based feeding technique could be applied to effectively excite the more “unusual” modes of the isolated DRAs.

A Novel to Mode Converter Designed With Radially Loaded Dielectric Slabs

A novel linear shaped ${\rm TM}_{01}$ to ${\rm TE}_{11}$ mode converter having high efficiency and wide bandwidth is proposed. The design consists of a circular waveguide sectored by a horizontal metallic plate partition, and dielectric slabs radially attached in the lower semicircular waveguide. The mode converter is designed and simulated at an operating frequency of 3 GHz. A maximum bandwidth of 504 MHz (2.81–3.35 GHz) with conversion efficiency greater than 90% is achieved when three Polytetrafluoroethylene (PTFE/Teflon) slabs are placed radially in the mode converter. The mode convertor was fabricated and experiments were performed with PTFE as the dielectric slab material. The mode conversion was verified by measuring the far-field radiation pattern. The proposed mode converter is symmetric, compact, linear, and easy to fabricate. It can be used for S-band high-power microwave applications where wide bandwidth of mode conversion is required.

On Polarization of Compensated Detectors

This paper presents analyses of polarization effects in ohmic and junction sensors by detailed three-dimensional modeling. It is shown for the example of compensated ${{\rm Cd}_{1 - {\rm x}}}{{\rm Zn}_{\rm x}}{\rm Te}$ detectors that the compensating deep-levels can be also responsible for both bias-induced and ionization-induced polarization phenomena. The capture cross sections of the deep levels are shown to play a dominant role in the formation of the polarizing space charge. Calculations show that bias-induced polarization is not expected to occur in ohmic MSM structures as long as the mobility remains constant. Ionization-induced polarization is expected to occur equally in ohmic and Schottky devices, but the sign and the distribution of the polarizing space charge depend on deep level cross sections.

Wideband Equivalent Circuit for Multi-Aperture Multi-Resonant Waveguide Irises

In this paper it is shown that the traditional shunt admittance represented by a rational function yields an accurate wideband equivalent circuit for multi-aperture waveguide irises. The electromagnetic analysis of the structures reveals two different types of resonant phenomena. The first type of resonance is associated with the cutoff frequency of the ${\rm TE}_{10}$ mode. The second type or antiresonace corresponds to short-circuit TEM modes. These antiresonances are generated when the asymmetry of the iris allows the excitation of electric fields with opposite phases at contiguous apertures. The proposed equivalent circuit is a shunt admittance represented by a rational function. This rational function is analytically obtained from the singular points (resonances and antiresonances) identified in the full-wave analysis. It is straightforward to obtain the circuit elements from the rational function by following the classical one-port synthesis leading to Foster’s or Cauers’s canonical realizations. One advantage of the proposed equivalent circuit is that it represents the electromagnetic behavior of complicated structures with a minimum number of circuit elements or degrees of freedom. Several examples, with different number of apertures and symmetry, are presented to illustrate the proposed general equivalent circuit. Finally, the proposed procedure is extended to the case of arbitrary shaped irises, such as those used in frequency-selective surfaces.

Wideband Circularly Polarized Rectangular Dielectric Resonator Antennas Using Square-Shaped Slots

Two wideband single fed circularly polarized (CP) rectangular dielectric resonator antennas (DRAs) comprising square-shaped slots are proposed. Initially, two wideband linearly polarized DRAs are designed with high aspect ratio to simultaneously excite and merge two resonant modes, ${\rm TE}_{{111}}$ and ${\rm TE}_{{113}}$ . Then, CP is obtained by the technique of perturbation in the form of four and two square slots along the diagonal. The slots excite two orthogonal modes with same magnitude and quadrature in phase. Two antenna prototypes are experimentally verified. The measured impedance bandwidths are 48% (4.7–7.7 GHz) and 41% (4.6–7 GHz) in conjunction with the 3-dB axial-ratio bandwidth of 11.5% (5.7–6.4 GHz) and 24% (4.7–6 GHz).

An Isolated Radial Power Divider via Circular Waveguide &lt;formula formulatype="inline"&gt;&lt;tex Notation="TeX"&gt;${\rm TE}_{01}$&lt;/tex&gt;&lt;/formula&gt;-Mode Transducer

A $Ka$ -band isolated radial power divider via circular waveguide ${\rm TE}_{01}$ -mode converter is presented in this paper. By redesigning and using the circular waveguide ${\rm TE}_{01}$ -mode transducer to feed the 20-way radial power divider–combiner, the overall structure is miniaturized. Moreover, the resistive septum is inserted into the waveguide to improve the return loss and the isolation of the output ports. A measured return loss at the output port has improved by around 15 dB, while the worst case isolation is more than 12 dB over 28–36 GHz after using the resistive septum.

Propagating Waveguide Filters Using Dielectric Resonators

In this paper a new class of propagating waveguide in-line pseudoelliptic filters exploiting dielectric resonators is presented. The basic structure is a singlet, which is implemented by a ${\rm TE}_{01 \delta}$ mode dielectric resonator placed into a rectangular waveguide above cutoff. Couplings are controlled by a proper positioning of the puck. The fundamental propagating mode of the waveguide is exploited to both excite and bypass the resonator so as to obtain bypass coupling capability, allowing the generation of transmission zeros. Higher order filters are obtained by cascading singlets through quarter-wave or half-wave waveguide sections. The quarter-wave section behaves as an admittance inverter, while the half-wave section behaves as a resonator, the latter resulting in filters which combine dielectric and cavity resonators. Thanks to this combination, unique performances such as wide bandwidth and sharp transition bands can be obtained. To validate the proposed method a third-order filter with 2.3% fractional bandwidth (FBW) and a fifth-order filter with 8.15% FBW have been designed and manufactured, thus demonstrating the approach feasibility.