Gaylord, Thomas K.

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Now showing 1 - 10 of 11
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    Optimization of sawtooth surface-relief gratings: effects of substrate refractive index and polarization
    (Georgia Institute of Technology, 2006-05) Wu, Shun-Der ; Gaylord, Thomas K. ; Glytsis, Elias N.
    The effect of the refractive index of the substrate together with the incident polarization on the optimization of sawtooth surface-relief gratings (SRGs) is investigated. The global optimum diffraction efficiencies of the −1st forward-diffracted order of sawtooth SRGs are 63 .3% occurring at n ₂ =1.47 for TE polarization and 73.8% occurring at n ₂ =2.88 for TM polarization. Incident TE polarization has higher optimum diffraction efficiency than TM polarization for all n ₂ <1.85 . In contrast, TM polarization has higher optimum diffraction efficiency than TE polarization for all n ₂ >1.85 . A polymer (n ₂ =1.5) optimum sawtooth SRG exhibits 62.6% efficiency for TE polarization. A silicon (n ₂ =3.475) optimum sawtooth SRG exhibits 68.6% efficiency for TM polarization. These sawtooth SRGs are compared to right-angle-face trapezoidal SRGs. It is found that the optimum profiles of right-angle-face trapezoidal SRGs have only very slightly increased efficiencies over sawtooth SRGs (0.04% for TE and 0.55% for TM).
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    Optimization of anisotropically etched silicon surface-relief gratings for substrate-mode optical interconnects
    (Georgia Institute of Technology, 2006-01) Wu, Shun-Der ; Gaylord, Thomas K. ; Maikisch, Jonathan S. ; Glytsis, Elias N.
    The optimum profiles of right-angle-face anisotropically etched silicon surface-relief gratings illuminated at normal incidence for substrate-mode optical interconnects are determined for TE, TM, and random linear (RL) polarizations. A simulated annealing algorithm in conjunction with the rigorous coupled-wave analysis is used. The optimum diffraction efficiencies of the −1 forward-diffracted order are 37.3% , 67.1% , and 51.2% for TE-, TM-, and RL-polarization-optimized profiles, respectively. Also, the sensitivities to grating thickness, slant angle, and incident angle of the optimized profiles are presented.
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    Three-dimensional converging-diverging Gaussian beam diffraction by a volume grating
    (Georgia Institute of Technology, 2005-07) Wu, Shun-Der ; Gaylord, Thomas K. ; Glytsis, Elias N. ; Wu, Yu-Ming
    The diffraction characteristics of a volume grating (VG) illuminated by a three-dimensional (3-D) converging-diverging Gaussian beam at conical incidence are investigated by applying 3-D finite-beam (FB) rigorous coupled-wave analysis (RCWA) based on the conventional 3-D RCWA in conjunction with two-dimensional plane-wave decomposition. The Gaussian beam is assumed to have an arbitrary incidence angle, an arbitrary azimuthal angle, and any linear polarization. The two cases with linear polarizations of the central beam of the Gaussian (E _|_ K and H _|_ K) are investigated. The diffraction efficiencies and the diffracted beam profiles for both unslanted VGs and slanted VGs (designed for substrate-mode optical interconnects) are presented. In general, the diffraction efficiencies of a converging-diverging spherical Gaussian beam diffracted by both unslanted VGs and slanted VGs increase and approach the central-beam results as the refractive-index modulation increases.
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    Angular sensitivities of volume gratings for substrate-mode optical interconnects
    (Georgia Institute of Technology, 2005-07) Wu, Shun-Der ; Gaylord, Thomas K. ; Glytsis, Elias N. ; Wu, Yu-Ming
    The angular sensitivities of slanted volume gratings (VGs) illuminated by three-dimensional (3-D) converging-diverging spherical Gaussian beams for substrate-mode optical interconnects in microelectronics are analyzed by application of 3-D finite-beam rigorous coupled-wave analysis. Angular misalignments about the z, y, and x axes that correspond to yaw, pitch, and roll misalignments resulting from manufacturing tolerances of chips are investigated. Two cases of linear polarization of the central beam of the Gaussian are considered: E _|_ K and H _|_ K, where K is the grating vector. From worst-case manufacturing tolerances, the ranges of yaw, pitch, and roll misalignment angles are alpha=±1.17°, beta=±3.04°, and gamma=±3.04°, respectively. Based on these ranges of misalignment angles, the decreases of diffraction efficiencies for slanted VGs that are due to both the yaw and the roll misalignments are relatively small. However, the efficiency of substrate-mode optical interconnects achieved by slanted VGs could be reduced by 61.04% for E _|_ K polarization and by 58.63% for H _|_ K polarization because of the pitch misalignment. Thus the performance of a VG optical interconnect is most sensitive to pitch misalignment.
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    Optimization of finite-length input volume holographic grating couplers illuminated by finite-width incident beams
    (Georgia Institute of Technology, 2005-07) Wu, Shun-Der ; Glytsis, Elias N. ; Gaylord, Thomas K.
    A finite volume holographic grating coupler (VHGC) normally illuminated with various incident-beam profiles (such as a Gaussian beam, a flat cosine-squared beam, and an exponential-decay beam) with finite beam widths for input coupling is rigorously analyzed by use of the finite-difference frequency-domain method. The effects of the incident-beam width, the incident-beam position, the incident-beam profile, and the incident-beam angle of incidence on the input coupling efficiency are investigated. The optimum conditions for input coupling are determined. Both a VHGC embedded in the waveguide film region and a VHGC placed in the waveguide cover region are investigated. For a given finite VHGC, the input coupling efficiencies are strongly dependent on incident-beam widths, incident-beam positions, and incident-beam angles of incidence, but are only weakly dependent on incident-beam profiles.
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    Wavelength response of waveguide volume grating couplers for optical interconnects
    (Georgia Institute of Technology, 2004-09) Villalaz, Ricardo A. ; Glytsis, Elias N. ; Gaylord, Thomas K. ; Nakai, Tsuyoshi
    The wavelength response of a waveguide volume grating coupler (WVGC) is analyzed for coupling light from a slab waveguide into the superstrate. A leaky-mode approach is used in conjunction with rigorous coupled-wave analysis. A quantitative theoretical study of the effect of index modulation, waveguide index, and grating thickness on the wavelength bandpass of a WVGC is also presented. The FWHM wavelength bandpasses found for high-efficiency couplers range from 173 to 525 nm. The various Bragg conditions that can be used in designing a WVGC are also presented and compared. The use of the propagation constant of the mode being outcoupled as the incident wave vector in the Bragg condition is shown to produce the highest coupling efficiency.
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    Planar lightwave integrated circuits with embedded actives for board and substrate level optical signal distribution
    (Georgia Institute of Technology, 2004-05) Jokerst, Nan Marie ; Gaylord, Thomas K. ; Glytsis, Elias N. ; Brooke, Martin A. ; Cho, S. ; Nonaka, T. ; Suzuki, T. ; Geddis, Demetris L. ; Shin, Jaemin ; Villalaz, R. ; Hall, J. ; Chellapa, Ananthasayanam ; Vrazel, M.
    As the data rate of integrated circuits dramatically increases, interconnection speed at the backplane and board levels are beginning to limit system performance, which drives investigations into alternative interconnection technologies. Critical factors to consider when evaluating alternative interconnection approaches include interconnect speed, power consumption, area, and compatibility with current backplane and board integration technologies. Optical interconnections can achieve very high speed with a significant reduction in interconnect footprint compared to transmission lines, robust signal quality in high-density interconnection systems because of immunity to electromagnetic interference, and potentially simple to design (compared to transmission lines) lines with materials which can be postprocessed onto printed wiring boards or integrated into the board structure. This paper explores design options for planar optical interconnections integrated onto boards, discusses fabrication options for both beam turning and embedded interconnections to optoelectronic devices, describes integration processes for creating embedded planar optical interconnections, and discusses measurement results for a number of integration schemes that have been demonstrated by the authors. In the area of optical interconnections with beams coupled to and from the board, the topics covered include integrated metal-coated polymer mirrors and volume holographic gratings for optical beam turning perpendicular to the board. Optical interconnections that utilize active thin film (approximately 1-5 µm thick) optoelectronic components embedded in the board are also discussed, using both Si and high temperature FR-4 substrates. Both direct and evanescent coupling of optical signals into and out of the waveguide are discussed using embedded optical lasers and photodetectors.
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    Optical transmission of polymer pillars for chip I/O optical interconnections
    (Georgia Institute of Technology, 2004-01) Bakir, Muhannad S. ; Gaylord, Thomas K. ; Ogunsola, O. O. ; Glytsis, Elias N. ; Meindl, J. D.
    In the pursuit of high-density wafer-level input–output optical interconnections, microscopic polymer pillars have recently been fabricated. The optical performance of these pillars is critical for their potential application to gigascale integration. In the present work, the optical transmission of these pillars is analyzed and measured. It is shown that these polymer pillars act as precision many-moded waveguides, thus, verifying the cross-sectional uniformity, smoothness of surfaces, and optical quality of the material.
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    Substrate-embedded and flip-chip-bonded photodetector polymer-based optical interconnects: Analysis, design, and performance
    (Georgia Institute of Technology, 2003-10) Glytsis, Elias N. ; Jokerst, Nan Marie ; Villalaz, Ricardo A. ; Cho, Sang-Yeon ; Wu, Shun-Der ; Huang, Zhaoran ; Brooke, Martin A. ; Gaylord, Thomas K.
    The performance of three optoelectronic structures incorporating substrate-embedded InP-based inverted metal–semiconductor–metal photodetectors and/or volume holographic gratings are analyzed and compared at the primary optical communication wavelengths. These structures, in conjunction with optical-quality polymer layers, can be easily integrated into silicon microelectronic substrates for the purpose of implementing potentially low-cost high-data-rate chip-level or substrate-level optical interconnects. The structures are as follows: a) an evanescent-coupling architecture with a substrate- embedded photodetector, b) a volume-holographic-grating coupler architecture with a substrate-embedded photodetector, and c) a volume-holographic-grating coupler architecture with a flip-chip-bonded photodetector. It is found that the primary characteristic of the evanescent coupling architectures is the efficient performance for both TE and TM polarizations with the disadvantage of exponentially decreasing efficiency with increasing separation between the waveguide film layer and the photodetector layer. On the other hand, the primary characteristic of the volume holographic grating architectures is the possibility of wavelength and polarization selectivity and their independence on the separation between the photodetector layer and the waveguide. Comparison of the analysis with experimental results is also included in the case of the evanescent coupling into a substrate-embedded photodetector.
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    Quantum-well infrared photodetector structure synthesis: Methodology and experimental verification
    (Georgia Institute of Technology, 2003-03) Imam, Neena ; Glytsis, Elias N. ; Gaylord, Thomas K. ; Choi, Kwong-Kit ; Newman, Peter G. ; Detter-Hoskin, Lisa