The Experts below are selected from a list of 9960 Experts worldwide ranked by ideXlab platform
I D Mayergoyz - One of the best experts on this subject based on the ideXlab platform.
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micromagnetic study of phase locking in spin transfer nano oscillators driven by currents and ac fields
Journal of Applied Physics, 2011Co-Authors: M Daquino, C Serpico, R Bonin, G Bertotti, I D MayergoyzAbstract:The magnetization dynamics of a spin-transfer nano-oscillator is studied for a system subject to the combined action of dc spin-polarized electric current and microwave circularly polarized applied field. The uniform mode theory is developed for a spin-valve with an arbitrary orientation of the Polarizer. The theory enables one to predict the control parameters for the synchronization between the magnetization self-oscillation and the external microwave field. Full micromagnetic simulations are performed with the predicted control parameters, and they demonstrate the hysteretic nature of the synchronization in very good agreement with the theory.
Daoxi Dai - One of the best experts on this subject based on the ideXlab platform.
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low loss ultracompact transverse magnetic pass Polarizer with a silicon subwavelength grating waveguide
Optics Letters, 2014Co-Authors: Xiaowei Gua, Pengxi Che, Sitao Che, Yaocheng Shi, Daoxi DaiAbstract:An ultracompact and low-loss TM-pass Polarizer on silicon is proposed and demonstrated experimentally with a subwavelength-grating (SWG) waveguide. The SWG waveguide is designed to support Bloch mode for TM polarization so that the incident TM-polarized light goes through the SWG waveguide with very low excess loss. On the other hand, for TE polarization, the SWG waveguide works as a Bragg reflector, and consequently the incident TE-polarized light is reflected. For a fabricated ∼9 μm long Polarizer (with the period number N=20), the measured extinction ratio is ∼27 dB and the excess loss is ∼0.5 dB at the central wavelength 1550 nm. The bandwidth to achieve an extinction ratio of 20 dB is about 60 nm (from 1520 to 1580 nm). When increasing the period number to N=40, the measured extinction ratio is up to 40 dB (which is not as high as the expected theoretical value 65 dB due to the limit of the measurement system).
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compact broadband Polarizer based on shallowly etched silicon on insulator ridge optical waveguides
Optics Express, 2010Co-Authors: Daoxi Dai, Zhi Wang, Nicholas Julia, Joh E OwersAbstract:A new way to make broadband Polarizers on silicon-on-insulator (SOI) waveguides is proposed, analyzed and characterized. The characteristics of the eigenmodes in a shallowly-etched SOI ridge optical waveguide are analyzed by using a full-vectorial finite-different method (FV-FDM) mode solver. The theoretical calculation shows that the loss of TE fundamental mode could be made very low while at the same time the TM fundamental mode has very large leakage loss, which is strongly dependent on the trench width. The leakage loss of the TM fundamental mode changes quasi-periodically as the trench width wtr varies. The formula of the period ∆wtr is given. By utilizing the huge polarization dependent loss of this kind of waveguide, a compact and simple optical Polarizer based on a straight waveguide was demonstrated. The Polarizer is fabricated on a 700nm-thick SOI wafer and then characterized by using a free-space optical system. The measured extinction ratio is as high as 25dB over a 100nm wavelength range for a 1mm-long Polarizer.
N M R Peres - One of the best experts on this subject based on the ideXlab platform.
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unusual reflection of electromagnetic radiation from a stack of graphene layers at oblique incidence
Journal of Optics, 2013Co-Authors: Yuliy V Bludov, N M R Peres, M I VasilevskiyAbstract:We study the interaction of electromagnetic (EM) radiation with single-layer graphene and a stack of parallel graphene sheets at arbitrary angles of incidence. It is found that the behavior is qualitatively different for transverse magnetic (or p-polarized) and transverse electric (or s-polarized) waves. In particular, the absorbance of single-layer graphene attains a minimum (maximum) for the p (s)-polarization at the angle of total internal reflection when the light comes from a medium with a higher dielectric constant. In the case of equal dielectric constants of the media above and beneath graphene, for grazing incidence graphene is almost 100% transparent to p-polarized waves and acts as a tunable mirror for the s-polarization. These effects are enhanced for a stack of graphene sheets, so the system can work as a broad band Polarizer. It is shown further that a periodic stack of graphene layers has the properties of a one-dimensional photonic crystal, with gaps (or stop bands) at certain frequencies. When an incident EM wave is reflected from this photonic crystal, the tunability of the graphene conductivity renders the possibility of controlling the gaps, and the structure can operate as a tunable spectral-selective mirror.
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tunable graphene based Polarizer
Journal of Applied Physics, 2012Co-Authors: Yuliy V Ludov, M I Vasilevskiy, N M R PeresAbstract:It is shown that an attenuated total reflection structure containing a graphene layer can operate as a tunable Polarizer of the electromagnetic radiation. The polarization of the reflected electromagnetic wave is controlled by adjusting the voltage applied to graphene via external gate, as demonstrated for the cases of linearly and circularly polarized incident radiation. The mechanism is based on the resonant coupling of p-polarized waves to the surface plasmon-polaritons in graphene. The presented calculations show that, at resonance, the reflected wave is almost 100% s-polarized.
Cheng Huang - One of the best experts on this subject based on the ideXlab platform.
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multi band circular Polarizer using planar spiral metamaterial structure
Optics Express, 2012Co-Authors: Cheng Huang, Qi Feng, Xiangang LuoAbstract:A multi-band circular Polarizer is proposed by using multi layered planar spiral metamaterial structure in analogy with classic spiral antenna. At three distinct resonant frequencies, the incident linearly polarized wave with electric field paralleling to one specific direction is transformed into left/right-handed circularly polarized waves through electric field coupling. Measured and simulated results show that right-handed circularly polarized wave is produced at 13.33 GHz and 16.75 GHz while left-handed circularly polarized wave is obtained at 15.56 GHz. The surface current distributions are studied to investigate the transformation behavior for both circular polarizations. The relationship between the resonant positions and the structure parameters is discussed as well.
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multi band circular Polarizer using planar spiral metamaterial structure
Optics Express, 2012Co-Authors: Cheng Huang, Mingbo Pu, Chenggang Hu, Qin FengAbstract:A multi-band circular Polarizer is proposed by using multi layered planar spiral metamaterial structure in analogy with classic spiral antenna. At three distinct resonant frequencies, the incident linearly polarized wave with electric field paralleling to one specific direction is transformed into left/right-handed circularly polarized waves through electric field coupling. Measured and simulated results show that right-handed circularly polarized wave is produced at 13.33 GHz and 16.75 GHz while left-handed circularly polarized wave is obtained at 15.56 GHz. The surface current distributions are studied to investigate the transformation behavior for both circular polarizations. The relationship between the resonant positions and the structure parameters is discussed as well. (C) 2012 Optical Society of America
L Prejbeanubuda - One of the best experts on this subject based on the ideXlab platform.
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spin torque oscillator using a perpendicular Polarizer and a planar free layer
Nature Materials, 2007Co-Authors: D Houssameddine, U Ebels, B Delaet, B Rodmacq, I Firastrau, F Ponthenier, M Brunet, C Thirion, J P Michel, L PrejbeanubudaAbstract:Spintronics materials have recently been considered for radio-frequency devices such as oscillators by exploiting the transfer of spin angular momentum between a spin-polarized electrical current and the magnetic nanostructure it passes through. While previous spin-transfer oscillators (STOs) were based on in-plane magnetized structures, here we present the realization of an STO that contains a perpendicular spin current Polarizer combined with an in-plane magnetized free layer. This device is characterized by high-frequency oscillations of the free-layer magnetization, consistent with out-of-plane steady-state precessions induced at the threshold current by a spin-transfer torque from perpendicularly polarized electrons. The results are summarized in static and dynamic current-field state diagrams and will be of importance for the design of STOs with enhanced output signals.
