| 1. |
- He, Sailing, et al.
(author)
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Focusing properties of a photonic crystal slab with negative refraction
- 2004
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In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 70:11, s. 115113-
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Journal article (peer-reviewed)abstract
- A layered Korringa-Kohn-Rostoker method is exploited to study the subwavelength imaging through a slab of rods-in-air photonic crystal. Both the intensity and phase spectra of transmission are investigated. The high transmission of evanescent waves arises due to the excitation of some slab-guided bound modes and the high coupling between the incident evanescent field and some bulk-guided Bloch modes. Through a study of the phase spectrum of transmission, it is shown that the self-collimation effect occurs at smaller incident angles whereas the negative refraction effect occurs at relatively larger incident angles. The existence of imaging aberrations is also explained with the phase spectrum. The focusing properties of the photonic crystal slab are mainly due to the negative-refraction effect for large incident angles, rather than the self-collimation effect.
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| 2. |
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| 3. |
- Hu, Liangbing, et al.
(author)
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Transparent and conductive paper from nanocellulose fibers
- 2013
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In: Energy & Environmental Science. - 1754-5692 .- 1754-5706. ; 6:2, s. 513-518
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Journal article (peer-reviewed)abstract
- Here we report on a novel substrate, nanopaper, made of cellulose nanofibrils, an earth abundant material. Compared with regular paper substrates, nanopaper shows superior optical properties. We have carried out the first study on the optical properties of nanopaper substrates. Since the size of the nanofibrils is much less than the wavelength of visible light, nanopaper is highly transparent with large light scattering in the forward direction. Successful depositions of transparent and conductive materials including tin-doped indium oxide, carbon nanotubes and silver nanowires have been achieved on nanopaper substrates, opening up a wide range of applications in optoelectronics such as displays, touch screens and interactive paper. We have also successfully demonstrated an organic solar cell on the novel substrate.
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| 4. |
- Meng, Lijun, et al.
(author)
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Optimized grating as an ultra-narrow band absorber or plasmonic sensor
- 2014
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In: Optics Letters. - 0146-9592 .- 1539-4794. ; 39:5, s. 1137-1140
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Journal article (peer-reviewed)abstract
- Lamellar gratings are investigated via temporal coupled-mode theory and numerical simulations. Total absorption can be achieved by an optimized grating with shallow grooves under normal incidence and the full width at half-maximum (FWHM) is only 0.4 nm. For certain wavelengths, the structure shows high absorption only within an ultra-narrow angle, which suggests that it can be used as a highly directional thermal emitter according to Kirchhoff's law. Besides, the resonant wavelength is sensitive to the refractive index of the environmental dielectric. The large sensitivity (1400 nm/RIU) and simultaneous small FWHM result in a huge figure-of-merit of 2300/RIU, which enables the structure to have great potential in plasmonic sensing.
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| 5. |
- Qiu, Min, et al.
(author)
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Negative refraction in semiconductor photonic crystals
- 2005
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In: SEMICONDUCTOR AND ORGANIC OPTOELECTRONIC MATERIALS AND DEVICES. - : SPIE. ; , s. 345-352
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Conference paper (peer-reviewed)abstract
- The coupling efficiency between external plane waves and the Bloch waves in photonic crystals are investigated. It is found that the coupling coefficient is highly angular dependent even for an interface between air n=l and a photonic crystal with effective index -1. It is also shown that, for point imaging by a photonic crystal slab owing to the negative refraction, the influence of the surface termination to the transmission and the imaging quality is significant. Finally, we present results demonstrating experimentally negative refraction in a two-dimensional photonic crystal.
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| 6. |
- Ruan, Zhichao, et al.
(author)
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Coupling between plane waves and Bloch waves in photonic crystals with negative refraction
- 2005
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 71:4, s. 045111-
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Journal article (peer-reviewed)abstract
- A comprehensive analysis of the coupling coefficients between plane waves in conventional dielectric media and Bloch waves of photonic crystals with effective negative refractions is performed by the layer Korringa-Kohn-Rostoker method. Employing the infinite layers refraction operator, semi-infinite size photonic crystals are considered. Some special coupling properties are discussed. In particular, the strong angular dependence of coupling coefficients is found even for an interface between air (n=1) and a photonic crystal with effective refractive index (n(eff)=-1). Thus, a negative refractive index defined by the radius of a circular equal-frequency contour does not guarantee an isotropic behavior.
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| 7. |
- Ruan, Zhichao, 1980-
(author)
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Dispersion Engineering : Negative Refraction and Designed Surface Plasmons in Periodic Structures
- 2007
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Doctoral thesis (other academic/artistic)abstract
- The dispersion property of periodic structures is a hot research topic in the last decade. By exploiting dispersion properties, one can manipulate the propagation of electromagnetic waves, and produce effects that do not exist in conventional materials. This thesis is devoted to two important dispersion effects: negative refraction and designed surface plasmons. First, we introduce negative refraction and designed surface plasmons, including a historical perspective, main areas for applications and current trends. Several numerical methods are implemented to analyze electromagnetic effects. We apply the layer-KKR method to calculate the electromagnetic wave through a slab of photonic crystals. By implementing the refraction matrix for semi-infinite photonic crystals, the layer-KKR method is modified to compute the coupling coefficient between plane waves and Bloch modes in photonic crystals. The plane wave method is applied to obtain the band structure and the equal-frequency contours in two-dimensional regular photonic crystals. The finite-difference time-domain method is widely used in our works, but we briefly discuss two calculation recipes in this thesis: how to deal with the surface termination of a perfect conductor and how to calculate the frequency response of high-Q cavities more efficiently using the Pad\`{e} approximation method. We discuss a photonic crystal that exhibits negative refraction characterized by an effective negative index, and systematically analyze the coupling coefficients between plane waves in air and Bloch waves in the photonic crystal. We find and explain that the coupling coefficients are strong-angularly dependent. We first propose an open-cavity structure formed by a negative-refraction photonic crystal. To illuminate the physical mechanism of the subwavelength imaging, we analyze both intensity and phase spectrum of the transmission through a slab of photonic crystals with all-angle negative refraction. It is shown that the focusing properties of the photonic crystal slab are mainly due to the negative refraction effect, rather than the self-collimation effect. As to designed surface plasmons, we design a structured perfectly conducting surface to achieve the negative refraction of surface waves. By the average field method, we obtain the effective permittivity and permeability of a perfectly conducting surface drilled with one-dimensional periodic rectangle holes, and propose this structure as a designed surface plasmon waveguide. By the analogy between designed surface plasmons and surface plasmon polaritons, we show that two different resonances contribute to the enhanced transmission through a metallic film with an array of subwavelength holes, and explain that the shape effect is attributed to localized waveguide resonances.
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| 8. |
- Ruan, Zhichao, et al.
(author)
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Enhanced Transmission through Periodic Arrays of Subwavelength Holes : The Role of Localized Waveguide Resonances
- 2006
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 96:23, s. 233901-
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Journal article (peer-reviewed)abstract
- By using the rigid full-vectorial three-dimensional finite-difference time-domain method, we show that the enhanced transmission through a metallic film with a periodic array of subwavelength holes results from two different resonances: (i) localized waveguide resonances where each air hole can be considered as a section of metallic waveguide with both ends open to free space, forming a low-quality-factor resonator, and (ii) well-recognized surface plasmon resonances due to the periodicity. These two different resonances can be characterized from electromagnetic band structures in the structured metal film. In addition, we show that the shape effect in the enhanced transmission through the Au film with subwavelength holes is attributed to the localized waveguide resonance.
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| 9. |
- Ruan, Zhichao, et al.
(author)
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Ideal cylindrical cloak : Perfect but sensitive to tiny perturbations
- 2007
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 99:11
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Journal article (peer-reviewed)abstract
- A cylindrical wave expansion method is developed to obtain the scattering field for an ideal two-dimensional cylindrical invisibility cloak. A near-ideal model of the invisibility cloak is set up to solve the boundary problem at the inner boundary of the cloak shell. We confirm that a cloak with the ideal material parameters is a perfect invisibility cloak by systematically studying the change of the scattering coefficients from the near-ideal case to the ideal one. However, because of the slow convergence of the zeroth-order scattering coefficients, a tiny perturbation on the cloak would induce a noticeable field scattering and penetration.
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| 10. |
- Ruan, Zhichao, et al.
(author)
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Ideal cylindrical cloak : perfect but sensitive to tiny perturbations
- 2007
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In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 99:11
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Journal article (peer-reviewed)abstract
- A cylindrical wave expansion method is developed to obtain the scattering field for an ideal two-dimensional cylindrical invisibility cloak. A near-ideal model of the invisibility cloak is set up to solve the boundary problem at the inner boundary of the cloak shell. We confirm that a cloak with the ideal material parameters is a perfect invisibility cloak by systematically studying the change of the scattering coefficients from the near-ideal case to the ideal one. However, because of the slow convergence of the zeroth-order scattering coefficients, a tiny perturbation on the cloak would induce a noticeable field scattering and penetration.
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