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  • 1. Chen, H.
    et al.
    Chen, X.
    Zeng, Yong
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512). Shanghai Institute of Technical Physics, China.
    Li, Z.
    Xiong, D.
    Lu, W.
    The distribution of grating-coupled field of quantum well infrared photodetector using FDTD method2007In: Infrared Materials, Devices, and Applications, SPIE - International Society for Optical Engineering, 2007, p. 68351E-Conference paper (Refereed)
    Abstract [en]

    For most commonly used GaAs/AlGaAs n-type quantum well infrared photodetectors (QWIPs), the normal incident absorption is not possible because of the transition rule. The optical grating is required to achieve high absorption quantum efficiencies. When some gratings are patterned on the metal plate, the polarization direction can be changed greatly because of the diffraction effect. Finite difference time domain (FDTD) method has been used to investigate the effect of a reflection metal grating on the couple efficiency previously. However, the authors only take one metal grating and apply periodic boundary condition along the grating direction due to the computation limit. For a real QWIP system, such simulation is crude. In this work we consider a real GaAs/AlGaAs QWIP with a wavelength response around 15um and use FDTD method to investigate the effect of a reflection metal grating on the electric field pattern and the couple efficiency. The simulating results show that the electric field pattern is not periodic for every metal grating in a real QWIP system. We have also studied the influence of the substrate thickness and the grating period on the electric field pattern and the couple efficiency. These results offer a guideline for the design of QWIP.

  • 2.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Zeng, Yong
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Berglind, Eilert
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Thylén, Lars
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Nanoscale excitonic-plasmonic optical waveguiding by metal-coated quantum dots2006In: Proceedings of International Symposium on Biophotonics, Nanophotonics and Metamaterials, 2006, p. 426-431Conference paper (Refereed)
    Abstract [en]

    A three-dimensional metal-coated semiconductor-quantum-dot (QD) nanoscale lattice structure is designed for optical waveguiding. It is based on three notions: i) Excitons are first photogenerated in the QDs by the incident electromagnetic field which is the optical wave to be guided: ii) The exciton-polariton effect in the QD structure induces an extra optical dispersion in the QDs: iii) The high contrast ratio between the optical dispersions of the QDs and the background material creates clear photonic bandgaps. By carefully designing the QD size and the QD lattice structure, perfect electromagnetic field reflection can be obtained for the incident wave in the lossless case, thus providing the fundamental basis of QDs for optical waveguide applications. Metal coating at the QD surface generates a surface plasmon spatially confined in the QD so that the exciton generation becomes enhanced for a better dielectric modulation.

  • 3.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Zeng, Yong
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Surface-plasmon-assisted electromagnetic field enhancement in semiconductor quantum dots2007In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 87, no 2, p. 167-169Article in journal (Refereed)
    Abstract [en]

    The temporal development of incident electromagnetic plane waves across semiconductor quantum dots (QDs) is analyzed by the finite-difference time-domain method. By coating the QDs using thin metal films, surface plasmon polaritons (SPPs) can be created. As illustration, our modeling approach is applied to fluorescent multiphoton quantum dots made of cadmium sulphide of particular size (3.7 nm) and energy band gap (2.67 eV). When such a QD is coated by a metal film, a dipole-formed SPP is generated at the external surface of the coated QD by the incident electromagnetic wave with a photon energy of 1.34 eV corresponding to a two-photon process. When the thickness of the metal film is 0.37 nm, the peak intensity of the SPP oscillates through both the thin metal film and the core QD, resulting in an electromagnetic field inside the QD enhanced by a factor of 10, and thus an increased two-photon excitation that can be useful for bioimaging applications. Further increasing the metal film thickness blockades the SPP initially generated at the external surface of the coated QD from penetrating through the metal film, reducing the electromagnetic field inside the QD.

  • 4. Wu, Yanrui
    et al.
    Chen, Xiaoshuang
    Zeng, Yong
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Lu, Wei
    Light coupling for single-mode photonic crystal waveguides2006In: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 35, no 1, p. 93-98Article in journal (Refereed)
    Abstract [en]

    We use a transfer-matrix method (TMM) to investigate light coupling into and out of single-end single-mode photonic crystal waveguides. Without multi-reflection complexity, we give clearly the unambiguous quantitative determination of the coupling efficiency of external light into guided mode and the transition among guided modes. It is shown that the waveguide with a line defect along Gamma J direction exhibits a much better coupling efficiency than that with a line-defect orientation along Gamma M direction.

  • 5.
    Zeng, Yong
    KTH, School of Biotechnology (BIO).
    Optical properties of active photonic materials2007Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Because of the generation of polaritons, which are quasiparticles possessing the characteristics of both photonics and electronics, active photonic materials offer a possible solution to transfer electromagnetic energy below the diffraction limit and further increase the density of photonic integrated circuits. A theoretical investigation of these exciting materials is, therefore, very important for practical applications.

    Four different kinds of polaritons have been studied in this thesis, (1) surface polaritons of negative-index-material cylindric rods, (2) exciton polaritons of semiconductor quantum dots, (3) localized plasmon polaritons of metallic nanoshells, and (4) surface plasmon polaritons of subwavelength hole arrays in thin metal films. All these types of polaritons were found to strongly affect the optical properties of the studied active photonic materials. More specifically, (1) for two-dimensional photonic crystals composed of negative-index-material cylindric rods, the coupling among surface polaritons localized in the rods results in dispersionless anti-crossing bands; (2) for three-dimensional diamond-lattice quantum-dot photonic crystals, the exciton polariton resonances lead to the formation of complete band gaps in the dispersion relationships; (3) for metallic nanoshells, the thickness of the metal shell strongly modifies the localized plasmon polaritons, and therefore influences the degree of localization of the electromagnetic field inside the metallic nanoshells; (4) for subwavelength hole arrays in thin metal films, high-order surface-polariton Bloch waves contribute significantly to the efficient transmission.

    To numerically simulate these active photonic materials, we introduced three approaches, (1) an extended plane-wave-based transfer-matrix approach for negative- index-material media, (2) a plane-wave method for semiconductor quantum-dot photonic crystals, and (3) an auxiliary-differential-equation finite-difference time- domain approach for semiconductor quantum-dot arrays. A brief perspective is also given at the end of this thesis.

  • 6.
    Zeng, Yong
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Chen, X. S.
    Lu, W.
    Optical limiting in defective quadratic nonlinear photonic crystals2006In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 99, no 12, p. 123107-Article in journal (Refereed)
    Abstract [en]

    By using a nonlinear transfer matrix method and an iteration method, we investigated an optical limiting in a defective quadratic nonlinear photonic crystal under strong pump-depletion conditions. Due to a giant enhancement of the second harmonic (SH) generation induced by the strong localization of light near the defective band, the progress of the energy exchange from the forward fundamental frequency (FF) channel to the SH channels (both forward and backward) and the backward FF channel is speeded up. The structure can therefore be used as a high-efficient compact optical power limiter. We have also studied the effects of two important parameters of the defective nonlinear periodic structure, the number of the periods and the nonlinear efficiency of the composite material, on the optical limiting.

  • 7.
    Zeng, Yong
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Chen, Xiaoshuang
    National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science.
    Lu, Wei
    National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Finite-difference time-domain simulations of exciton-polariton resonances in quantum-dot arrays2008In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 16, no 7, p. 4507-4519Article in journal (Refereed)
    Abstract [en]

    The optical properties of nanosize quantum-dot (QD) arrays are found to vary significantly around the exciton resonance frequency of the QDs. In order to simulate the interactions between electromagnetic waves and QD arrays, a general auxiliary-differential-equation, finite-difference time-domain approach is introduced and utilized in this article. Using this numerical method, the exciton-polariton resonances of single-layer and double-layer GaAs QD arrays are studied. The optical properties of a single-layer QD array are found to be characterized by the Mie resonance of its constituent QDs, while a double-layer QD array is characterized by the quasi-dipole formed by two QDs positioned in each of the two layers.

  • 8.
    Zeng, Yong
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Chen, Xiaoshuang
    National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science.
    Lu, Q.
    National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Optical properties of two-dimensional negative-phase-velocity-medium photonic crystals2006In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 73, no 6, p. 066625-Article in journal (Refereed)
    Abstract [en]

    By an extended plane-wave-based transfer-matrix method, the photonic band structure and the corresponding transmission spectrum have been calculated for a two-dimensional photonic crystal composed of negative-phase-velocity-medium (NPVM) cylindrical rods. Dispersionless anticrossing bands in the two-dimensional NPVM periodic structure are generated by the couplings among surface polaritons localized in the NPVM rods. In part of the negative-phase-velocity frequency region, the photonic band structures of the NPVM photonic crystal are characterized by a topographical continuous dispersion relationship accompanied by many anticrossing bands. The effect of the filling fraction of the NPVM rods on the optical properties of photonic crystals has also been studied.

  • 9.
    Zeng, Yong
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Chen, Xiaoshuang
    National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science.
    Lu, Wei
    National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Complete band gaps in three-dimensional quantum dot photonic crystals2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 11, p. 115325-Article in journal (Refereed)
    Abstract [en]

    Nonlocal investigations have been performed about exciton-photon couplings in three-dimensional quantum-dot (QD) photonic crystals and a complete photonic band gap has been found in the band structure of a diamond lattice. The width of such a band gap can be broadened by increasing the filling ratio of the QDs (increasing the QD radius or/and decreasing the lattice constant of the photonic crystal). By decomposing the diamond lattice into two interlacing face-centered-cubic (fcc) sublattices, we have found that by significantly modifying the QD radius in one fcc sublattice (the diamond lattice therefore changed to the zinc blende lattice), the band structure of the zinc blende lattice is in principle the sum of two individual fcc sublattices. However, a huge exciton-photon coupling is observed near the band gaps of the two individual fcc sublattices when the radii of the QDs in the two fcc sublattices approach each other, resulting in the complete band gaps of the diamond structure.

  • 10.
    Zeng, Yong
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Chen, Xiaoshuang
    National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science.
    Lu, Wei
    National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Extended plane-wave-based transfer-matrix approach to simulating dispersive photonic crystals2006In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 139, no 7, p. 328-333Article in journal (Refereed)
    Abstract [en]

    It has been difficult to compute the band structures and transmission spectra for photonic crystals (PCs) with dispersive components included in the periodic units. Here we show that by using an extended plane-wave-based transfer-matrix method, we are able to formulate the problem for computing optical properties of dispersive PCs, including magnetic and left-handed PCs. This approach is very general, since it can treat PCs with arbitrary Bravais lattice composed of materials with arbitrary dielectric permittivities and magnetic permeabilities. Combined with the supercell method, this method can further simulate defective PCs such as PC-based waveguides and microcavities.

  • 11.
    Zeng, Yong
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Chen, Xiaoshuang
    National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science.
    Lu, Wei
    National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Selective excitation of surface-polariton Bloch waves for efficient transmission of light through a subwavelength hole array in a thin metal film2007In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 76, no 3, p. 035427-Article in journal (Refereed)
    Abstract [en]

    Electromagnetic (EM) field was found to be able to transmit efficiently through a subwavelength hole array in a metal thin film at specific resonant frequencies. By analyzing the near-field distributions of EM fields in the array system, as well as the corresponding Fourier spectra, we show that the surface-polariton (SP) Bloch waves focus the energy of the incident plane-wave EM field to the vicinity of the hole at resonances (through SP scattering provided by the periodic hole). Furthermore, the wave vectors of the SP waves that contribute to the focusing effect are quantized as functions of the geometric shape of the holes in such a way that the focusing effect of the EM energy into the hole is maximal. The transmission efficiency and bandwidth at resonances are found to partially depend on the number of SP modes which contribute to the focusing effect.

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