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  • 1.
    Chen, Zhihui
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Light manipulation in micro and nano photonic materials and structures2012Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Light manipulation is an important method to enhance the light-matter interactions in micro and nano photonic materials and structures by generating usefulelectric field components and increasing time and pathways of light propagationthrough the micro and nano materials and structures. For example, quantum wellinfrared photodetector (QWIP) cannot absorb normal incident radiation so thatthe generation of an electric field component which is parallel to the original incident direction is a necessity for the function of QWIP. Furthermore, the increaseof time and pathways of light propagation in the light-absorbing quantum wellregion will increase the chance of absorbing the photons.The thesis presents the theoretical studies of light manipulation and light-matter interaction in micro and nano photonic materials and structures, aiming atimproving the performance of optical communication devices, photonic integrateddevices and photovoltaic devices.To design efficient micro and nano photonic devices, it is essential to knowthe time evolution of the electromagnetic (EM) field. Two-dimensional and three-dimensional finite-difference time-domain (FDTD) methods have been adopted inthe thesis to numerically solve the Maxwell equations in micro and nano photonicmaterials and structures.Light manipulation in micro and nano material and structures studied in thisthesis includes: (1) light transport in the photonic crystal (PhC) waveguide, (2)light diffraction by the micro-scale dielectric PhC and metallic PhC structures(gratings); and (3) exciton-polaritons of semiconductor quantum dots, (4) surfaceplasmon polaritons at semiconductor-metallic material interface for subwavelengthlight control. All these aspects are found to be useful in optical devices of multiplebeam splitter, quantum well/dot infrared photodetectors, and solar cells.

  • 2.
    Chen, Zhihui
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Fu, Ying
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Yu, Zhongyuan
    Improving efficiency of quantum dot infrared photodetector by using photonic crystal framework in the active layer2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    Photonic crystal structure as a framework in both substrate and active layer in quantum dot infrared photodetector is used to improve the interaction between photons and QDs.

  • 3.
    Chen, Zhihui
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Hellström, Staffan
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Ning, Zhijun
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Yu, Z-Y
    Fu, Ying
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Exciton Polariton Contribution to the Stokes Shift in Colloidal Quantum Dots2011Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, nr 13, s. 5286-5293Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the exciton polariton contribution to the Stokes shift in colloidal quantum dots (QDs). By detailed quantum mechanical description of light-matter interaction and temporal analysis of incident electromagnetic field across the QD using the finite-difference time-domain method, we have shown that the optical excitation of an exciton in the QD and its coupling with the excitation radiation (i.e., exciton polariton) induce strong variations in the dielectric constant of the QD which contribute significantly to the Stokes shift and cause modifications 50 in the absorption spectrum that agrees well with experiments.

  • 4.
    Chen, Zhi-Hui
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Hellström, Staffan
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Yu, Zhong-Yuan
    Fu, Ying
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Comb-shaped photonic crystal structure for efficient broadband light diffraction and funnelling in solar cells2012Ingår i: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 99, s. 316-320Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a comb-shaped photonic-crystal (PhC) rods-lattice structure of broadband light diffraction and funnelling for solar cell applications. It is shown that the photonic band of this PhC structure is very dispersive over a broad bandwidth so that light will be efficiently diffracted in the wavelength region of solar radiation. The PhC structure also creates resonance modes leading to further diffraction and funnelling of light so that the light propagates in many pathways in the whole PhC lattice region, which will greatly facilitate light-matter interaction when light-absorbing elements are embedded in the PhC structure. The proposed structure is also valid for photodetection applications.

  • 5.
    Chen, Zhihui
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Hellström, Staffan
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Yu, Zhong-Yuan
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Fotonik.
    Fu, Ying
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Time-resolved photocurrents in quantum well/dot infrared photodetectors with different optical coupling structures2012Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, nr 4, s. 043502-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Temporal developments of photocurrents excited by an infrared radiation pulse in quantum well/dot infrared photodetectors with different optical coupling structures have been theoretically studied. It is shown that the light diffraction in a conventional reflective grating structure is a near-field effect containing severe crosstalk from neighboring pixels. A concave reflector not only eliminates the crosstalk but also strongly diffracts and focuses the incident electric field into deep active layers, which significantly increases the photocurrents in the photodetectors.

  • 6.
    Chen, Zhi-Hui
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Taiyuan University of Technology, China; Beijing University of Posts and Telecommunications, China .
    Wang, Yang
    KTH, Skolan för bioteknologi (BIO), Industriell bioteknologi.
    Yang, Yibiao
    Qiao, Na
    Wang, Yuncai
    Yu, Zhongyuan
    Enhanced normal-direction excitation and emission of dual-emitting quantum dots on a cascaded photonic crystal surface2014Ingår i: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 6, nr 24, s. 14708-14715Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Large normal-direction excitation and emission of dual-emitting quantum dots (QDs) are essential for practical application of QD sensors based on the ratiometric fluorescence response. We have numerically demonstrated an all-dielectric four-layer cascaded photonic crystal (CPC) structure (alternating TiO2 and SiO2/SU8 layers with two dimensional nanoscale patterns in each layer) which is capable of providing normal-direction high Q-factor leaky modes at excitation wavelengths of QDs and two low Q-factor leaky modes coinciding with the two emission peaks of a dual-emitting QD. Normal-direction excitation and far-field emission of the dual-emitting QDs are enhanced significantly when QDs are distributed on/in the top TiO2 layer of the CPC structure, especially in the spatial distribution areas of the resonant leaky modes. QDs can be positioned differently depending on the applications. Positioning QDs on the top TiO2 layer will improve the signal-to-noise ratios of QD biomedical/chemical/temperature sensors, while embedding QDs in the top TiO2 layer will increase the light extraction from the QD light emitting device, making our CPC a versatile optical coupling structure. Our CPC-QD structure is experimentally feasible and robust against the parameter perturbation in real fabrication.

  • 7.
    Chen, Zhihui
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Yu, Z. -Y
    Liu, Y. -M
    Lu, P. -F
    Fu, Ying
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Multiple beam splitting to free space from a V groove in a photonic crystal waveguide2011Ingår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 102, nr 4, s. 857-861Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present multiple-beam splitting to free space from a V groove in a two-dimensional photonic crystal waveguide (PCW) with a few additional dielectric rods at the exit of the PCW. Numerical study shows that 'one-beam-in to two-beams-out' (one-to-two, also denoted as Y-shaped), one-to-three, and one-to-five beam splittings can be easily realized over a wide bandwidth, and the split beams have remarkable properties such as symmetric energy distributions and high directional transmissions. Off-axis directional emission can also be achieved by simple displacements of the additional rods at the exit of the PCW.

  • 8.
    Hellström, Staffan
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Chen, Zhihui
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Fu, Ying
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Fotonik.
    Soltanmoradi, R.
    Wang, Q.
    Andersson, J. Y.
    Increased photocurrent in quantum dot infrared photodetector by subwavelength hole array in metal thin film2010Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 96, nr 23, s. 231110-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Photocurrent enhancement in quantum dot (QD) infrared photodetector (QDIP) with an optical grating of subwavelength hole array in a thin metal film has been studied by calculating the transmission and diffraction of the infrared optical field through the grating and the light-matter interaction between the transmitted optical field and electrons confined in the QD. It is shown that due to the small aspect ratio of realistic QDs in QDIPs, the light diffraction due to the surface plasmon effect at the metal-semiconductor surface and the photonic subwavelength hole array structure is dominant in increasing the photocurrent.

  • 9. Wong, Kwan-Yee Kenneth
    et al.
    Zhang, Guoqiang
    Chen, Zhihu
    KTH, Skolan för elektro- och systemteknik (EES), Ljud- och bildbehandling (Stängd 130101).
    A Stratified Approach for Camera Calibration Using Spheres2011Ingår i: IEEE Transactions on Image Processing, ISSN 1057-7149, E-ISSN 1941-0042, Vol. 20, nr 2, s. 305-316Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper proposes a stratified approach for camera calibration using spheres. Previous works have exploited epipolar tangents to locate frontier points on spheres for estimating the epipolar geometry. It is shown in this paper that other than the frontier points, two additional point features can be obtained by considering the bitangent envelopes of a pair of spheres. A simple method for locating the images of such point features and the sphere centers is presented. An algorithm for recovering the fundamental matrix in a plane plus parallax representation using these recovered image points and the epipolar tangents from three spheres is developed. A new formulation of the absolute dual quadric as a cone tangent to a dual sphere with the plane at infinity being its vertex is derived. This allows the recovery of the absolute dual quadric, which is used to upgrade the weak calibration to a full calibration. Experimental results on both synthetic and real data are presented, which demonstrate the feasibility and the high precision achieved by our proposed algorithm.

1 - 9 av 9
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