| 1. |
- He, Sailing, et al.
(författare)
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Graphene nano-ribbon waveguides of recordsmall mode area and ultra-high effective refractive indices for future VLSI
- 2013
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Ingår i: Optics Express. - 1094-4087. ; 21:25, s. 30664-30673
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Tidskriftsartikel (refereegranskat)abstract
- Electronics circuits keep shrinking in dimensions, as requested by Moore's law. In contrast, photonic waveguides and circuit elements still have lateral dimensions on the order of the wavelength. A key to make photonics have a microelectronics-like development is a drastic reduction of size. To achieve this, we need a low-loss nanoscale waveguide with a drastically reduced mode area and an ultra-high effective refractive index. For this purpose, we propose here several low-loss waveguide structures based on graphene nano-ribbons. An extremely small mode area (∼10-7λ0 2, one order smaller than the smallest mode area of any waveguide that has ever been reported in the literature; here λ0 is the operating wavelength in vacuum) and an extremely large effective refractive index (several hundreds) are achieved. As a device example, a nano-ring cavity of ultrasmall size (with a diameter of ∼10-2λ0) is designed. Our study paves the way for future VLSI (very-large-scale integration) optoelectronics.
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| 2. |
- He, Sailing, et al.
(författare)
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Revealing the truth about 'trapped rainbow' storage of light in metamaterials
- 2012
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 2, s. 583-
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Tidskriftsartikel (refereegranskat)abstract
- It was claimed that the incident light can be gradually slowed down and finally trapped in a tapered metamaterial waveguide. Here we show that the energy incident from the input port of the tapered metamaterial waveguide will be totally reflected (instead of being trapped) due to the strong intermodal coupling between the forward and backward modes. The underlying physical mechanism for this strong intermodal-coupling is given. The occurrence of energy reflection is unambiguously proved using several independent methods, (1) the semi-analytical mode matching technique, (2) the numerical finite element simulation, (3) the requirement of energy and momentum conservation, and (4) an experimental verification at microwave frequency. The dream of 'trapped rainbow' for storage of light might still be possible if this intermodal coupling could be blocked, and our study provides a useful guidance for such an endeavor.
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| 3. |
- He, Y., et al.
(författare)
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CONSISTENT FORMALISM FOR THE MOMENTUM OF ELECTROMAGNETIC WAVES IN LOSSLESS DISPERSIVE METAMATERIALS AND THE CONSERVATION OF MOMENTUM
- 2011
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Ingår i: PROGRESS IN ELECTROMAGNETICS RESEARCH-PIER. - 1559-8985. ; 116, s. 81-106
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Tidskriftsartikel (refereegranskat)abstract
- A new formalism for electromagnetic and mechanical momentum in a metamaterial is developed by means of the technique of wave-packet integrals. The medium has huge mass density and can therefore be regarded as almost stationary upon incident electromagnetic waves. A clear identification of the momentum density and momentum flow, including their electromagnetic and mechanical parts, is obtained by employing this formalism in a lossless dispersive metamaterial (including the cases of impedance matching and mismatching with vacuum). It is found that the ratio of the electromagnetic momentum density to the mechanical momentum density depends on the impedance and group velocity of the electromagnetic wave inside the metamaterial. One of the definite results is that both the electromagnetic momentum and the mechanical momentum in the metamaterial are in the same direction as the energy flow, instead of in the direction of the wave vector. The conservation of total momentum is verified. In addition, the law of energy conservation in the process of normal incidence is also verified by using the wave-packet integral of both the electromagnetic energy density and the mechanical energy density, of which the latter is caused by the interaction between the induced electric/magnetic currents and the electric/magnetic field components of the electromagnetic wave.
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| 4. |
- He, Yingran, et al.
(författare)
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Plasmon induced transparency in a dielectric waveguide
- 2011
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 99:4, s. 043113-
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Tidskriftsartikel (refereegranskat)abstract
- A classical effect of electromagnetically induced transparency (EIT) is demonstrated in a dielectric slab waveguide at visible frequencies. Two nano-sized elliptical silver particles are placed inside the waveguide core layer, and their localized plasmonic resonances are utilized to obtain bright and dark states. The destructive interference between the two resonance paths leads to an EIT-like transmission spectrum of the waveguide. The contrast between the transmission peak and dip can be further enhanced by incorporating the Fabry-Perot resonance effect. The influence of Joule loss on the EIT performance is also investigated.
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| 5. |
- He, Z., et al.
(författare)
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A broadband UHF RFID Tag antenna with a novel T-matching network
- 2014
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Ingår i: Progress in Electromagnetics Research Symposium. - 1559-9450. ; , s. 978-981
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, an-ultra-high frequency (UHF) passive broadband radio frequency identification (RFID) Tag Antenna with a novel T-matching network is presented. By slightly tuned the arm lengths of the T-matching network, the impedance matching between the antenna and the chip and a broad impedance bandwidth is obtained. Thanks to the bent radiating element, the size reduction of the proposed antenna is realized. The bandwidth (S11 < -20 dB) and the corresponding 3 dB PRC bandwidth of the proposed antenna are 133MHz (835-968 MHz) and 88MHz (882-970 MHz) respectively, which means that both bandwidths are wide enough to cover the whole global UHF RFID frequency band. In the simulated results, a smooth and stable gain curve between 0.04 dBi to 1.86 dBi is found throughout the entire operating frequency band, and a gain of 1.38 dBi is obtained at the desired operating frequency point (915 MHz). In conclusion, the designed antenna owns the advantages of low-profile, compact size (56×56mm2), low cost and stable gain. Based on the simple structure, the designed tag antenna can be easily manufacture and widely used in practical applications.
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| 6. |
- Liu, H., et al.
(författare)
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Printed inverted-F MIMO antenna for TD-LTE mobile terminal
- 2014
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Ingår i: Progress in Electromagnetics Research Symposium. - 9781934142288 ; , s. 1562-1566
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Konferensbidrag (refereegranskat)abstract
- With the rapid growth and development of the mobile communication technologies in recent years, many mobile communication technologies appeared one after another, of particu-lar concern is 3GPP long term evolution (LTE). TD-LTE is growing rapidly in China and is also widely considered in the forth generation (4G) mobile communication now. MIMO technology, which utilizes multiple antenna to improve spectrum efficiency and increase the system channel capacity, is one of the 4G key technologies. In this paper a MIMO antenna, operating on TD-LTE frequency band for TD-LTE mobile ter-minal is designed. The proposed MIMO antenna consists of two modified IFA structures has the advantage of compact structure and multiband for 4G handheld devices. The antenna designed to cover the TD-LTE frequency band of 1880-1900MHz and 2575-2635MHz for China Mobile. The simulated and test results show that the isolation and S11 parameters of the proposed MIMO antenna can meet TD-LTE mobile communication requirements.
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| 7. |
- Pan, T., et al.
(författare)
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Compact circularly polarized RFID tag antenna with an embedded U-shaped feedline for metallic surfaces
- 2014
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Ingår i: Progress in Electromagnetics Research Symposium. - 9781934142288 ; , s. 1567-1571
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Konferensbidrag (refereegranskat)abstract
- A passive radio frequency identification (RFID) tag antenna with circular polarization (CP) radiation is proposed to operate at 902-928MHz and mount on metallic surfaces. A U-shaped terminal short-circuited feedline welded to a tag-chip is embedded in a rectangular slot to achieve a coupled feeding and a good impedance matching. By employing two truncated corners and two L-shaped slots with unequal length on the patch, a good left-hand circular polarization (LHCP) and compact size are obtained. The measured impedance bandwidth of the antenna is 85MHz (875-960 MHz), while the simulated 3-dB CP bandwidth is 6MHz (912-918 MHz). The proposed tag antenna shows reasonable read ranges when mounted on the metal plate in the following experiment.
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| 8. |
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| 9. |
- Wang, J., et al.
(författare)
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Sub-μm2 power splitters by using silicon hybrid plasmonic waveguides
- 2011
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 19:2, s. 838-847
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Tidskriftsartikel (refereegranskat)abstract
- Nano-scale power splitters based on Si hybrid plasmonic waveguides are designed by utilizing the multimode interference (MMI) effect as well as Y-branch structure. A three-dimensional finite-difference time-domain method is used for simulating the light propagation and optimizing the structural parameters. The designed 1×2 50:50 MMI power splitter has a nano-scale size of only 650 nm×530 nm. The designed Y-branch power splitter is also very small, i.e., about 900 nm×600 nm. The fabrication tolerance is also analyzed and it is shown that the tolerance of the waveguide width is much larger than±50 nm. The power splitter has a very broad band of over 500 nm. In order to achieve a variable power splitting ratio, a 2×2 two-mode interference coupler and an asymmetric Y-branch are used and the corresponding power splitting ratio can be tuned in the range of 97.1%:2.9%-1.7%:98.3% and 84%:16%-16%:84%, respectively. Finally a 1×4 power splitter with a device footprint of 1.9 μm×2.6 μm is also presented using cascaded Y-branches.
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| 10. |
- Ao, Xianyu, et al.
(författare)
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Black silicon with controllable macropore array for enhanced photoelectrochemical performance
- 2012
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 101:11, s. 111901-
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Tidskriftsartikel (refereegranskat)abstract
- Macroporous silicon with multiscale texture for reflection suppression and light trapping was achieved through a controllable electrochemical etching process. It was coated with TiO2 by atomic layer deposition, and used as the photoanode in photocatalytic water splitting. A conformal pn-junction was also built-in in order to split water without external bias. A 45% enhancement in photocurrent density was observed after black silicon etching. In comparison with nano-structured silicon, the etching process here has neither metal contamination nor requirement of vacuum facilities.
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