Endre søk
Begrens søket
2345678 201 - 250 of 615
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 201. Li, Q.
    et al.
    Liu, F.
    Zhang, Ziyang
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Ye, T.
    Su, Y.
    Performance of a silicon-microring slow-light delay line for advanced modulation formats2008Inngår i: Slow and Fast Light - Applications in Optical Communications (2008), Optical Society of America, 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We experimentally demonstrate a delay line in silicon microring resonator with a 20-μm radius. The delay performances of six advanced modulation formats are investigated, including NRZ, RZ, DPSK, CSRZ, RZ-DB and RZ-AMI.

  • 202. Li, Qiang
    et al.
    Chang, Qingjiang
    Liu, Fangfei
    Zhang, Ziyang
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Su, Yikai
    Optically tuneable microwave-photonic phase shifter based on silicon microring resonator2008Inngår i: European Conference on Optical Communication, ECOC, Brussels, 2008Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    We demonstrate a microwave-photonic phase shifter based on a 20-ÎŒm-radius silicon microring resonator, providing a tunable phase shift for a 20-GHz signal in a range of 0-4.6 rad.

  • 203. Li, Qiang
    et al.
    Liu, Fangfei
    Zhang, Ziyang
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Su, Yikai
    System Performances of On-Chip Silicon Microring Delay Line for RZ, CSRZ, RZ-DB and RZ-AMI Signals2008Inngår i: Journal of Lightwave Technology, ISSN 0733-8724, E-ISSN 1558-2213, Vol. 26, nr 21-24, s. 3744-3751Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We theoretically study the group-delay characteristics of a silicon microring resonator based on the coupled mode theory, and experimentally demonstrate error-free operations of an on-chip delay line using a silicon-on-insulator (SOI) microring resonator with a 20-mu m radius. Four signals of different modulation formats are examined at 5 Gb/s, including return-to-zero (RZ), carrier-suppressed return-to-zero (CSRZ), return-to-zero duobinary (RZ-DB), and return-to-zero alternate-mark-inversion (RZ-AMI). Bit error rate (BER) measurements show that the maximal delay times with error-free operations are 80,95, 110, and 65 ps, respectively, corresponding to a fractional group delay of similar to 0.4, similar to 0.5, similar to 0.55, and similar to 0.35. The differences in delay and signal degradations have been investigated based on the signal spectra and pattern dependences. Although the delays are demonstrated in a single ring resonator, the analysis is applicable in slow-light resonance structures such as all-pass filters (APF) and coupled resonator optical waveguides (CROW).

  • 204. Li, Qiang
    et al.
    Ye, Tong
    Lu, Yuanyuan
    Zhang, Ziyang
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Su, Yikai
    All-optical NRZ-to-AMI conversion using linear filtering effect of silicon microring resonator2009Inngår i: Chinese optics letters, ISSN 1671-7694, Vol. 7, nr 1, s. 12-14Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We experimentally demonstrate 10-Cb/s format conversion from non-return-to-zero (NRZ) to alternate-mark-inversion (AMI) using the linear filtering effect of silicon microring resonator. Our discussion and analysis in simulation further show that a 10-Gb/s AMI signal with good quality can be obtained by a resonator with a notch depth larger than 25 dB when the 3-dB bandwidth is 0.4 nm.

  • 205. Li, Qiang
    et al.
    Zhang, Ziyang
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Liu, Fangfei
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Su, Yikai
    Dense wavelength conversion and multicasting in a resonance-split silicon microring2008Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, nr 8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We experimentally demonstrate all-optical wavelength conversions in a 10 mu m radius resonance-split silicon microring resonator based on free carrier dispersion effect. The split resonance is caused by the mutual coupling between the two countertraveling modes inside the ring resonator. Dense wavelength conversions are performed at data rates from 500 Mbytes/s to 5 Gbytes/s and a dual-channel wavelength multicasting is realized at a data rate of 1.25 Gbytes/s. The resonance splitting phenomenon opens up opportunities to convert more closely spaced wavelengths, thus effectively increasing the system capacity.

  • 206. Li, Qiang
    et al.
    Zhang, Ziyang
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Wang, Jing
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Su, Yikai
    Fast light in silicon ring resonator with resonance-splitting2009Inngår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 17, nr 2, s. 933-940Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report experimental demonstration of fast light in an over-coupled ultra-compact silicon ring resonator with resonance-splitting. Strong mutual-coupling induced by the grating inside the ring leads to split resonances and accompanying large anomalous dispersion, thus providing a new approach to realizing fast light in the over-coupled region of the ring resonator. In the experiment, a maximum pulse advancement of 130 ps with low distortion is achieved for a 1-ns signal pulse in a 10-mu m-radius silicon ring resonator. The observed pulse advancement agrees well with the theoretical calculation based on coupled mode theory.

  • 207.
    Li, Shanghua
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Fabrication of Nanostructured Materials for Energy Applications2008Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    World energy crisis has triggered more attention to energy saving and energy conversion systems with high efficiency. There is a growing awareness that nanoscience and nanotechnology can have a profound impact on energy generation, conversion, and recovery. Nanotechnology-based solutions are being developed for a wide range of energy problems such as, solar electricity, hydrogen generation and storage, batteries, fuel cells, heat pumps and thermoelectrics. This thesis deals with the design and fabrication of novel functional materials/architectures for energy-related applications. The study includes two parts: Nanostructured thermoelectric (TE) materials for energy conversion and nanostructured metallic surfaces for energy heat transfer.

    In the first part, the focus is given to the fabrication of novel nanostructured TE materials and architectures. TE materials are very important functional materials that can convert heat to electrical energy and vice versa. Recently, nanostructuring TE materials showed very promising potential to improve their TE figure of merit which opens a new venue for the TE world. As a result, some advanced nanostructured TE architectures are proposed as the state-of-the-art TE materials/structures. Among these advanced TE architectures, bismuth telluride nanowires/thick films and skutterudite nanocomposites with nanoinclusions have been successfully fabricated and some of their advantageous TE performance has been demonstrated. For example, an improvement of 11% on the figure of merit, ZT, was achieved in the CoSb3 nanocomposite with 5 mole% ZrO2 as nanoinclusion. Comprehensive physico-chemical characterization techniques have been used for the synthesized TE materials. The potential-Seebeck microprobe, 4-point probe and laser flash apparatus have been used for the measurement of TE parameters on the TE materials.

    In the second part of the thesis, we developed a nanostructured macro-porous (NMp) surface for enhancing heat transfer in boiling process. Enhanced surfaces for boiling improve the energy efficiency of heat pumping equipment such as air conditioners, refrigerators, etc. Conventional techniques currently used for fabricating enhanced surfaces are often based on the use of complicated mechanical machine tools and require a large consumption of materials and give only limited enhancement of the boiling heat transfer. In this thesis, we present a new approach to fabricate enhanced surfaces by using electrodeposition under specific conditions forming in-situ dynamic gas bubble templates. As a result, the NMp metallic surface layer comprising of dendritically ordered copper branches is obtained. Since the structure is formed during the evolution of the dynamic bubbles, it is ideal for the bubble generation applications such as boiling. The efficiency of the NMp surfaces for boiling heat transfer was evaluated in pool boiling experiments. At the heat flux of 1 W/cm2, the heat transfer coefficient for the NMp surface is found to be more than 17 times higher than the reference surface. It's estimated that such an effective boiling surface would improve the energy efficiency of many heat pumping machines with 10 - 30 %. The extraordinary enhancement of boiling performance is explained by the structure characteristics, which assist in enhancing nucleation of the gas bubbles, subsequent coalescence, and facilitated departure from the surfaces.

  • 208.
    Li, Shanghua
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    He, Zeming
    Institute of Materials Research, German Aerospace Center (DLR).
    Toprak, Muhammet
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Stiewe, Christian
    Institute of Materials Research, German Aerospace Center (DLR).
    Müller, Eckhard
    Institute of Materials Research, German Aerospace Center (DLR).
    Muhammed, Mamoun
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Thermoelectric properties of CoSb3 with maize-like structure2007Inngår i: Physica Status Solidi-Rapid Research Letter, ISSN 1862-6254, Vol. 1, nr 6, s. 259-261Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Maize-like CoSb3 powders were obtained via the chemical alloying method. After the consolidation of the nanopowder using hot press, the CoSb3 compact shows a higher Seebeck coefficient and lower thermal conductivity. For the investigated CoSb3, a ZT of 0.15 at 673 K is shown. Though the achieved ZT does not reach the optimal value (0. 17 to 0. 18) for pure CoSb3, due to its lower electrical conductivity, the novel structure fabrication provides an interesting and promising approach to enhancing the thermoelectric performance.

  • 209.
    Li, Shanghua
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Liang, Yibin
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Qin, Jian
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Toprak, Muhammet
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Muhammed, Mamoun
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Template electrodeposition of ordered bismuth telluride nanowire arrays2009Inngår i: Journal of Nanoscience and Nanotechnology, ISSN 1533-4880, E-ISSN 1533-4899, Vol. 9, nr 2, s. 1543-1547Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Thermoelectric bismuth telluride nanowire arrays have been synthesized by direct-current electrodeposition into porous anodic alumina membranes both galvanostatically and potentiostatically. The as-synthesized Bi2Te3 nanowire arrays are highly ordered in large area, stoichiometric, uniform, with high aspect ratio (above 100) and high filling ratio (>90%) of the membrane. The effects of different electrochemical deposition parameters on crystal structures, morphology and composition have been investigated. Field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) have been used to characterize the physical and chemical properties of the nanowires.

  • 210.
    Li, Shanghua
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Soliman, Hesham M. A.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Zhou, Jian
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Toprak, Muhammet
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Muhammed, Mamoun
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Platzek, Dieter
    Ziolkowski, Pawel
    Müller, Eckhard
    Effects of annealing and doping on nanostructured bismuth telluride thick films2008Inngår i: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 20, nr 13, s. 4403-4410Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Bismuth telluride is the state-of-the-art thermoelectric (TE) material for cooling applications with a figure of merit of ∼1 at 300 K. There is a need for the development of TE materials based on the concept of thick films for miniaturized devices due to mechanical and manufacturing constraints for the thermoelement dimensions. We reported earlier a method for the fabrication of high-quality nanostructured bismuth telluride thick films with thickness from 100 to 350 μm based on electrochemical deposition techniques. In this paper, annealing is performed to further improve the TE performance of the nanostructured bismuth telluride thick films and n/p-type solid solutions are successfully fabricated by doping Se and Sb, respectively. The conditions for both annealing and doping for the thick films are investigated, and the effects of annealing and doping on morphology, crystalline phase, grain size, Seebeck coefficient, homogeneity, electrical conductivity, and power factor of the bismuth telluride thick films have been studied.

  • 211. Li, X.
    et al.
    Zhang, Ziyang
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Qin, S.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Su, Y.
    Label-free biosensor based on silicon-on-insulator micro-ring resonators2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We propose a label-free biosensor based on concentric micro-ring resonators in silicon on insulator (SOI). The concentric micro-ring resonators offer another freedom to obtain deeper notches for higher detection sensitivity. The expanded modes also provide larger sensing area. A resonant frequency shift of ∼1.37 nm is demonstrated, by numerical simulations, between the situation of using a single strand DNA and a double strand DNA.

  • 212. Li, X.
    et al.
    Zhang, Ziyang
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Qin, S.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Su, Y.
    Ultra-compact parallel label-free biosensors based on concentric micro-ring resonators in silicon-on-insulator2008Inngår i: 2008 Asia Optical Fiber Communication and Optoelectronic Exposition and Conference, AOE 2008, 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We propose an ultra-compact, label-free, parallel detection method by using an array of micro-ring resonators. Simulations of concentric micro-ring resonators with different parameters show that the device is suitable for such bio-sensing purpose.

  • 213. Li, Xiaohui
    et al.
    Zhang, Ziyang
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Li, Qiang
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Su, Y.
    Concentric silicon micro-ring resonators with enhanced transmission notch depth2008Inngår i: Proceedings of SPIE - The International Society for Optical Engineering, 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this work, we have analyzed, fabricated and demonstrated concentric micro-ring resonators in silicon-on-insulator (SOI) structure for enhanced transmission notches. The operation principles of the concentric ring resonators are studied by time-domain coupled-mode theory. Directional coupling between concentric rings offers another freedom in designing deep notch optical filters and ultra-sensitive biosensors. The finite-difference-time-domain (FDTD) simulations have shown the improvement of the notch depth, evenly distributed mode field and the effect of the resonance shift. The device is demonstrated in silicon-on-insulator structure. Transmission notch depth improvement of ~ 15dB is demonstrated for the 21-20.02-μm-radius double-ring structure comparing with the single 21-μm-radius ring.

  • 214. Li, Xiaohui
    et al.
    Zhang, Ziyang
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Qin, Shenying
    Wang, Tao
    Liu, Fangfei
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Su, Yikai
    Sensitive label-free and compact biosensor based on concentric silicon-on-insulator microring resonators2009Inngår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 48, nr 25, s. F90-F94Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We propose an ultracompact parallel label-free biosensor based on concentric silicon-on-insulator microring resonators. Our numerical studies show that the proposed biosensor offers higher sensitivity and a larger detection area than conventional single-ring-based sensors. We analyze the detection sensitivity of the DNA hybridization by immobilizing the probe on top of the double concentric ring resonators and in the ring-ring air gap. For a concentric double-ring system with an area of 27: 646 mu m(2), the bulk detection sensitivity is 683 nm RIU-1. The sensitive uniformity of the system related to the optical field distribution is also studied.

  • 215.
    Li, Yanlu
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Popov, Sergei
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Friberg, Ari T.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Rigorous modeling and physical interpretation of terahertz near-field imaging using SNOM techniques2009Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Apertureless scanning near-field optical microscopy (SNOM) operating with terahertz (THz) laser pulses is a subject of great research interest. The Mie scattering theory is commonly used to explain the features of the optical waves produced by field interactions with SNOM tips and microstructures. However, since Mie scattering fails with SNOMs at submillimeter wavelengths, a rigorous model and analysis are desirable to assess the feasibility of the THz tip-enhanced scanning near-field techniques. In this paper, we present a numerical simulation of an apertureless SNOM imaging system in the THz band. A 2-dimensional model based on the finite element method (FEM) is investigated and discussed. The modeling results are in good agreement with the experimental data obtained for this system at 2 THz radiation [8]. Additionally, a physical interpretation using the antenna theory is successfully confirmed by the simulation results. [DOI: 10.2971/jeos.2009.09007]

  • 216. Liang, H. L.
    et al.
    Mei, Z. X.
    Liu, Z. L.
    Guo, Y.
    Azarov, A.Yu.
    Kuznetsov, A.Yu.
    Hallén, Anders
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Du, X. L.
    High Zn content single-phase RS-MgZnO suitable for solar-blind frequency applications2010Inngår i: 2010 Wide Bandgap Cubic Semiconductors: From Growth To Devices, American Institute of Physics (AIP), 2010, s. 185-190Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Single-phase rock-salt MgZnO films with high Zn content were successfully fabricated on the templates of MgO (111)/α-sapphire (0001) by radio-frequency plasma assisted molecular beam epitaxy. The influence of growth temperature on epitaxy of MgZnO alloy films was investigated by the combined studies of crystal structures, compositions, and optical properties. It is found that the incorporation of Zn atoms into the rock-salt MgZnO films is greatly enhanced at low temperature, confirmed by in-situ reflection high-energy electron diffraction observations and ex-situ X-ray diffraction characterization. Zn fraction in the single-phase rock-salt Mg 0.53Zn0.47O film was determined by Rutherford backscattering spectrometry. Optical properties of the films were investigated by transmittance spectroscopy and reflectance spectroscopy, both of which demonstrate the solar-blind band gap and its dependence on Zn content.

  • 217.
    Lin, Zhili
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Thylén, Lars
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    An analytical derivation of the optimum source patterns for the pseudospectral time-domain method2009Inngår i: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 228, nr 19, s. 7375-7387Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the computational electromagnetics and acoustics, spatially smoothed sources are often utilized to alleviate the aliasing errors in the pseudospectral time-domain (PSTD) algorithms. In our work, an analytical derivation of the optimum source patterns is presented according to the accurately derived expressions of the dominant source-introduced aliasing errors according to the circular discrete convolution and Tailor series expansion method. We quantitatively demonstrate, for the first time in literature, that the aliasing errors can be optimally suppressed and rapidly reduced to the negligible levels by these optimum patterns and with the increment of source cells. We also provide the different implementation schemes of the optimal patterns both for the soft and hard source cases. The numerical calculation and 1D PSTD transient simulations are conducted to verify the excellent performance of these optimum sources.

  • 218. Lin, Zhili
    et al.
    Thylén, Lars
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    On the Accuracy and Stability of Several Widely Used FDTD Approaches for Modeling Lorentz Dielectrics2009Inngår i: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 57, nr 10, s. 3378-3381Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A rigorous and comparative study on the approximation accuracy and stability limits of several widely used finite-difference time-domain (FDTD) approaches, namely the auxiliary differential equation (ADE) approach, the bilinear transform (BT) approach, the Z-transform approach (ZT) and the piecewise linear recursive convolution (PLRC) approach, for modeling dispersive Lorentz dielectrics is presented following the given updating equations between the electric flux density and the electric field intensity. We find the ZT approach with modified material parameters is much more accurate than the original ZT approach and the other three approaches for modeling Lorentz dielectrics. The stability limits of the ADE, ZT and PLRC approaches in simulating Lorentz dielectrics are also shown to be a bit more stringent than that of BT approach which preserves the Courant stability limit as previously reported.

  • 219. Lindgren, S.
    et al.
    Ahlfeldt, H.
    Backlin, L.
    Forssen, L.
    Vieider, C.
    Elderstig, H.
    Svensson, M.
    Granlund, L.
    Kerzar, B.
    Broberg, B.
    Kjebon, Olle
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Schatz, Richard
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP. KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Forzelius, E.
    Nilsson, S.
    Laser flip-chip mounting for passive alignment and high-frequency modulation1996Inngår i: Optical Communication, 1996. ECOC ’96. 22nd European Conference on, 1996, Vol. 1, s. 103-106Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We have developed a silicon motherboard for flip-chip mounting of lasers in a way that is compatible with high-frequency modulation (24 GHz) and which allows passive alignment of the lasers to single-mode fibres.

  • 220.
    Lindgren, Stefan
    et al.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Åhlfeldt, Henrik
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Bäcklin, Lennart
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Forssén, Lili
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Vieider, Christian
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Elderstig, Håkan
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Svensson, Magnus
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Granlund, Lennart
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Andersson, Lars
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Kerzar, Boris
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Broberg, Björn
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Kjebon, Olle
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Schatz, Richard
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP. KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Forzelius, Elisabeth
    KTH, Tidigare Institutioner, Elektronik.
    Nilsson, Stefan
    KTH, Tidigare Institutioner, Elektronik.
    24-GHz modulation bandwidth and passive alignment of flip-chip mounted DFB laser diodes1997Inngår i: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 9, nr 3, s. 306-308Artikkel i tidsskrift (Fagfellevurdert)
  • 221.
    Linnarsson, Margareta K.
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Janson, Martin S.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Nordell, Nils
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Electrumlaboratoriet, ELAB.
    Wong-Leung, J.
    Schoner, A.
    Formation of precipitates in heavily boron doped 4H-SiC2006Inngår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 252, nr 15, s. 5316-5320Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM) are utilized to study precipitation and the solubility of B in 4H-SiC epitaxial layers super saturated with B. Heat treatments are performed in Ar atmosphere in an rf-heated furnace at temperatures between 1700 and 2000 degrees C. SIMS ion images, and TEM micrographs reveal the formation of two types of precipitates where the larger, more thermally stable one is suggested to be B4C. The boron solubility is determined from SIMS depth profiles and is shown to follow the Arrhenius expression: 7.1 x 10(22) exp(-1.4 eV/k(B)T) cm(-3) over the studied temperature range.

  • 222.
    Linnros, Jan
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Gregorkiewicz, Tom
    Elliman, Rob
    Kimerling, Lionel
    Silicon-based photonics2006Inngår i: Journal of Luminescence, ISSN 0022-2313, E-ISSN 1872-7883, Vol. 121, nr 2, s. V-VArtikkel i tidsskrift (Annet vitenskapelig)
  • 223. Liu, F.
    et al.
    Li, Qiang
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Zhang, Ziyang
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Su, Y.
    Ultra-compact mode-split silicon microring resonator for format conversion from NRZ to FSK2008Inngår i: Proceedings of SPIE - The International Society for Optical Engineering, 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We propose and experimentally demonstrate all optical format conversion from non-return-to-zero (NRZ) format to frequency-shift-keying (FSK) format based on free carrier dispersion effect in a silicon mode-split microring resonator. The injection of the high-power NRZ signal generates free carriers leading to the blue shift of the spectrum when a '1' comes. Therefore, there is a selective filtering for the two probes with certain separation located at different position of the split mode according to the information carried by the NRZ signal. Then the NRZ signal is converted to the FSK format. The microring resonator features ultra-compact size with a radius of 10 urn thus is suitable for integration with silicon-on-insulator (SOI) based optical and electronic devices. The split mode can provide large and variable frequency deviation for the FSK signal. 1 Gb/s NRZ signal is successfully converted to FSK format with a frequency deviation of 40 GHz, which can find application for interconnection between a metropolitan area networks (MAN) and a passive optical network (PON) system.

  • 224. Liu, F.
    et al.
    Wang, T.
    Zhang, L.
    Wang, Jing
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Su, Y.
    Silicon-chip-based frequency quadrupling for optical millimeter-wave signal generation2009Inngår i: Optoelectronic Materials and Devices IV, SPIE - International Society for Optical Engineering, 2009, s. 763105-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We propose a prototype of a silicon-chip-based frequency quadrupling system integrating a single-drive silicon Mach-Zehnder modulator and a race-track resonator as an optical differentiator. A proof-of-concept demonstration of 40-GHz millimeter-wave signal generation using 10-GHz driving signal is experimentally provided. The factors that impacting the purity of the RF spectrum are discussed through simulation.

  • 225. Liu, F.
    et al.
    Wang, T.
    Zhang, L.
    Wang, Jing
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Yikai, S. U.
    Silicon-chip-based frequency quadrupling for optical millimeter-wave signal generation2009Inngår i: 2009 Asia Communications and Photonics Conference and Exhibition, ACP 2009, 2009, s. 5377263-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We propose a prototype of a silicon-chip-based frequency quadrupling system integrating a single-drive silicon Mach-Zehnder modulator and a microring resonator. A proof-of-concept demonstration of 40-GHz millimeter-wave signal generation using 10-GHz driving signal is experimentally provided.

  • 226. Liu, F.
    et al.
    Wang, T.
    Zhang, Z.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Su, Y.
    On-chip photonic generation of ultra-wideband monocycle pulses2009Inngår i: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 45, nr 24, s. 1247-1248Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Proposed and experimentally demonstrated is photonic generation of ultra-wideband (UWB) monocycle pulses using a silicon microring resonator to perform phase-modulation-to-intensity-modulation conversion. The microring resonator features compact size and thus is cost-effective especially for applications in UWB communication systems that support multiple users. As a microring resonator with a pin diode can function as a modulator, the use of the microring resonator to realise bi-phase modulation is discussed.

  • 227. Liu, F.
    et al.
    Wang, T.
    Zhang, Ziyang
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Su, Y.
    Demonstration of wavelength multicasting using a silicon mode-split microring resonator2009Inngår i: 2009 15th Asia-Pacific Conference on Communications, APCC 2009, 2009, s. 626-629Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We experimentally demonstrate wavelength multicasting based on free carrier dispersion effect in a silicon mode-split microring resonator with a radius of ∼10 μm. The mode-split of the resonator is caused by mutual coupling between the co-propagating and counter-propagating modes inside the microring resonator, which is induced by the periodic grating-like roughness of the sidewalls. The free carriers are generated through the two photon absorption (TPA) effect and blue shift the resonance spectrum. 1.25-Gb/s data carried by the pump is simultaneously converted to two probe channels placed in the split resonances separated by ∼0.326 nm.

  • 228.
    Liu, Fangfei
    et al.
    State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Electronic Engineering, Shanghai Jiao Tong University.
    Li, Qiang
    State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Electronic Engineering, Shanghai Jiao Tong University.
    Zhang, Ziyang
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Su, Yikai
    State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Electronic Engineering, Shanghai Jiao Tong University.
    Optically Tunable Delay Line in Silicon Microring Resonator Based on Thermal Nonlinear Effect2008Inngår i: IEEE Journal of Selected Topics in Quantum Electronics, ISSN 1077-260X, E-ISSN 1558-4542, Vol. 14, nr 3, s. 706-712Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We experimentally demonstrate optically tunable delay fine in a silicon microring resonator with a 20-mu m radius. The delay-tuning mechanism is based on the red shift of the resonance induced by thermal nonlinear effect. We investigate the delay performance of three modulation formats-non-return-to-zero (NRZ), return-to-zero (RZ), and differential phase-shift keying (DPSK) signals at different data rates. Tunable delay is achieved by controlling the power of the continuous-wave (CW) pump with very low tuning threshold, which could be used in microring-resonator-based slow-light structure.

  • 229. Liu, Fangfei
    et al.
    Wang, Tao
    Qiang, Li
    Ye, Tong
    Zhang, Ziyang
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Su, Yikai
    Compact optical temporal differentiator based on silicon microring resonator2008Inngår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 16, nr 20, s. 15880-15886Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We propose and experimentally demonstrate a temporal differentiator in optical field based on a silicon microring resonator with a radius of 40 mu m. The microring resonator operates near the critical coupling region, and can take the first order derivative of the optical field. It features compact size thus is suitable for integration with silicon-on-insulator (SOI) based optical and electronic devices. The performance of this optical differentiator is tested using signals with typical shapes such as Gaussian, sinusoidal and square-like pulses at data rates of 10 Gb/s and 5 Gb/s.

  • 230.
    Liu, X. Y.
    et al.
    Chalmers University of Technology.
    Aggerstam, Thomas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Holmström, P.
    Lourdudoss, Sebastian
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Andersson, T.G.
    Cracks in GaN/AlN multiple quantum well structures grown by MBE2008Inngår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 100, s. 042026-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Due to the large lattice constant mismatch and thermal expansion coefficient difference between GaN and AlN, large strain is generated inside the GaN/AlN multiple quantum wells, which causes cracks in the structure. We investigated such cracks by optical microscopy and AFM. The crack density was studied with buffer and cap layer thickness, the number of quantum well periods, and the temperature reduction rate after growth as parameters. It was found that the crack density increased exponentially, with the number of periods above 4. Besides, a very thin, 100 nm, GaN buffer layer and similar to 300 nm GaN cap layer greatly reduced the crack density.

  • 231.
    Lourdudoss, Sebastian
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT. KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP. KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Halvledarmaterial, HMA.
    Kjebon, Olle
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT. KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Fotonik.
    Schatz, Richard
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP. KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT. KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik, Fotonik.
    Nilsson, Stefan
    Stålnacke, Björn
    Fabrication and analysis of directly modulated 1.55 µm semiconductor lasers of bandwidth up to 30 GHz1997Inngår i: 4th Annual meeting of European Research Network of Excellence on the Physics and Technology of Mesoscopic Systems (Phantoms), March 1997, Aachen, Germany, paper D2.11., 1997Konferansepaper (Fagfellevurdert)
  • 232. Lu, Yuanyuan
    et al.
    Liu, Fangfei
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Su, Yikai
    All-optical format conversions from NRZ to BPSK and QPSK based on nonlinear responses in silicon microring resonators2007Inngår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 15, nr 21, s. 14275-14282Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We propose and numerically verify a novel scheme of all-optical format conversion from non-return-to-zero (NRZ) to binary phase-shift-keying (BPSK) at 160 Gb/s using cascaded microring resonators (CMRR) on a single silicon chip. The conversion is based on large phase shift and flattened intensity-response characteristics in the CMRR. A continuous-wave light experiences different phase shifts controlled by the power of an input NRZ signal with an similar to 8.8-dB extinction ratio, while maintaining approximately the constant intensity. All-optical format conversion from NRZ to quadrature phase-shift-keying (QPSK) is also demonstrated based on parallel NRZ/BPSK converters in a Mach-Zehnder interferometer structure.

  • 233. Lysak, V. V.
    et al.
    Schatz, Richard
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP. KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Shulika, A. V.
    Sukhoivanov, I. A.
    Influence of gain nonlinearity on the second order harmonic distortion in semiconductor lasers2003Inngår i: Laser and Fiber-Optical Networks Modeling, 2003. Proceedings of LFNM 2003. 5th International Workshop on, 2003, s. 236-238Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The semiconductor laser is commonly used as a light source in fiber-optical telecommunication systems. In order to be able to send as much information as possible in a short time, it is important that the laser has a large modulation bandwidth, i.e., the turn-on and turn-off time should be as short as possible. In analogue fiber optic systems for transmission of radio or television signals, it is also important that the light from the laser increases linearly with driving current. Otherwise, the transmitted signal will become distorted. The modulation bandwidth and the modulation distortion are dependent both on the laser structure and the gain characteristics of the active material. In order to develop a correct laser model for calculation of, e.g., distortion one need an accurate model of the dependence of gain on carrier and photon density. We show that different gain models, fitted to give exactly the same modulation response can have significantly different distortion behavior.

  • 234.
    Malm, B. Gunnar
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Kolahdouz, Mohammadreza
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Radamson, Henry H.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Östling, Mikael
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Comprehensive temperature modeling of strained epitaxial silicon-germanium alloy thermistors2009Inngår i: 2009 International Semiconductor Device Research Symposium, ISDRS '09, 2009, s. 5378337-Konferansepaper (Fagfellevurdert)
  • 235.
    Marcinkevicius, Saulius
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Gusterov, A.
    Reithmaier, J. P.
    Transient electromagnetically induced transparency in InGaAs quantum dots2008Inngår i: 2008 Conference On Lasers And Electro-Optics & Quantum Electronics And Laser Science Conference: Vols 1-9, 2008, s. 3597-3598Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Electromagnetically induced transparency (EIT) based on exciton spin transitions is observed in InGaAs quantum dots. Inhomogeneous broadening of the quantum dot ensemble, detrimental for EIT, is effectively reduced by using spectrally narrow pulses.

  • 236.
    Marcinkevicius, Saulius
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Pinos, Andrea
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Liu, K.
    Veksler, D.
    Shur, M. S.
    Zhang, J.
    Gaska, R.
    Intrinsic electric fields in AlGaN quantum wells2007Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, nr 8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Intrinsic electric fields in AlxGa1-xN/AlyGa1-yN quantum wells embedded into p-i-n structures are studied using photoluminescence experiments. Spectral shifts induced by external bias and screening by photoexcited carriers allow evaluating the intrinsic fields caused by piezoelectric and spontaneous polarizations. In quantum wells with low Al content, the field is about 1 MV/cm, which is in agreement with theoretical estimations. For high Al molar fractions (35% well, 50% barrier), the extracted intrinsic field is lower and, most importantly, has the opposite sign to that predicted by the theory.

  • 237.
    Marcinkevicius, Saulius
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Siegert, Jörg
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Zhao, Qing Xiang
    Carrier spin dynamics in modulation-doped InAs/GaAs quantum dots2006Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 100, nr 5, s. 054310-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Photoexcited electron and hole spin relaxation was studied in modulation-doped and undoped InAs/GaAs quantum dots by means of time-resolved photoluminescence. After excitation into the barriers or the wetting layer, the electron spin polarization is preserved during the capture and relaxation in the dots, especially in the p-doped structures, and decays with a characteristic time of about 100 ps. Spin state admixture in combination with electron interaction with acoustic phonons is suggested as the spin relaxation mechanism. Rapid spin polarization decay during carrier relaxation in undoped quantum dots is attributed to electron-optical phonon interaction. For carrier excitation directly into the dots, no significant spin polarization was observed, which points to the mixed nature of hole levels in quantum dots. The hole spin polarization randomizes on a much shorter time scale and is not detected in the experiment.

  • 238.
    Marcks von Würtemberg, Rickard
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Design and fabrication of long wavelength vertical cavity lasers on GaAs substrates2008Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Vertical cavity surface emitting lasers (VCSELs) are today a commodity on the short wavelength laser market due to the ease with which they are manufactured. Much effort has in the last decade been directed towards making long wavelength VCSELs as successful in the marketplace. This has not been achieved due to the much more difficult fabrication technologies needed for realising high performance long wavelength VCSELs. At one point, GaInNAs quantum wells gain regions grown on GaAs substrates seemed to be the solution as it enabled all-epitaxial VCSELs that could make use of high contrast AlGaAs-based distributed Bragg reflectors (DBRs) as mirrors and lateral selective oxidation for optical and electrical confinement, thereby mimicking the successful design of short wavelength VCSELs. Although very good device results were achieved, reproducible and reliable epitaxial growth of GaInNAs quantum wells proved difficult and the technology has not made its way into high-volume production. Other approaches to the manufacturing and material problems have been to combine mature InP-based gain regions with high contrast AlGaAs-based DBRs by wafer fusion or with high contrast dielectric DBRs. Commonly, a patterned tunnel junction provides the electrical confinement in these VCSELs. Excellent performance has been achieved in this way but the fabrication process is difficult.

    In this work, we have employed high strain InGaAs quantum wells along with large detuning between the gain peak and the emission wavelength to realize GaAs-based long wavelength VCSELs. All-epitaxial VCSELs with AlGaAs-based DBRs and lateral oxidation confinement were fabricated and evaluated. The efficiency of these VCSELs was limited due to the optical absorption in the doped DBRs. To improve the efficiency and manufacturability, two novel optical and electrical confinement schemes based on epitaxial regrowth of current blocking layers were developed. The first scheme is based on a single regrowth step and requires very precise processing. This scheme was therefore not developed beyond the first generation but single mode power of 0.3 mW at low temperature, -10ºC, was achieved. The second scheme is based on two epitaxial regrowth steps and does not require as precise processing. Several generations of this design were manufactured and resulted in record high power of 8 mW at low temperature, 5ºC, and more than 3 mW at high temperature, 85ºC. Single mode power was more modest with 1.5 mW at low temperature and 0.8 mW at high temperature, comparable to the performance of the single mode lateral oxidation confined VCSELs. The reason for the modest single mode power was found to be a non-optimal cavity shape after the second regrowth that leads to poor lateral overlap between the gain in the quantum wells and the intensity of the optical field.

  • 239.
    Marcks von Würtemberg, Rickard
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Berggren, Jesper
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Dainese, Matteo
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Hammar, Mattias
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    High-power InGaAs/GaAs 1.3 mu m VCSELs based on novel electrical confinement scheme: Erratum2008Inngår i: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 44, nr 13Artikkel i tidsskrift (Fagfellevurdert)
  • 240.
    Marcks von Würtemberg, Rickard
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Berggren, Jesper
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Dainese, Matteo
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Hammar, Mattias
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    High-power InGaAs/GaAs 1.3 μm VCSELs based on novel electrical confinement scheme2008Inngår i: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 44, nr 6, s. 414-416Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Reported are 1.3 mu m InGaAs/GaAs vertical-cavity surface-emitting lasers (VCSELs) with a novel electrical confinement scheme based on lithographic definition and selective area epitaxial regrowth in the cavity region. More than 6 mW of output power with a record high differential efficiency of more than 70% is emitted from 10 mu m large devices.

  • 241.
    Marcks von Würtemberg, Rickard
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Yu, Xingang
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Berggren, Jesper
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Hammar, Mattias
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Performance optimisation of epitaxially regrown 1.3-μm vertical-cavity surface-emitting lasers2009Inngår i: IET Optoelectronics, ISSN 1751-8768, Vol. 3, nr 2, s. 112-121Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A number of GaAs-based long-wavelength, vertical-cavity, surface-emitting laser structures with optical and electrical confinement based on selective area epitaxy have been fabricated and evaluated. The influence on output power, threshold current, thermal stability and modal properties from design parameters such as bottom-distributed Bragg reflector (DBR) doping, cavity doping, dielectric top DBR design and carrier confinement barriers is evaluated. More than 7 mW of output power is emitted from multimode devices with a square active region size of 10 mm. Single-mode power from smaller devices is restricted to 1.5 mW because of a non-optimal cavity shape.

  • 242.
    Marcks von Würtemberg, Rickard
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Zhang, Zhenzhong
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Berggren, Jesper
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Hammar, Mattias
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    A novel electrical and optical confinement scheme for surface emitting optoelectronic devices2006Inngår i: WORKSHOP ON OPTICAL COMPONENTS FOR BROADBAND COMMUNICATION / [ed] Fonjallaz, PY; Pearsall, TP, BELLINGHAM, WA: SPIE-INT SOC OPTICAL ENGINEERING , 2006, Vol. 6350, s. 63500J-1-63500J-10Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A novel electrical and optical confinement scheme for surface emitting optoelectronic devices is presented. The scheme is based on epitaxial regrowth of a pnp current blocking layer structure around a mesa etched in the vertical cavity region of the device. The lateral size and orientation of the mesa is defined lithographically and dry etching is used to create vertical mesa sidewalls. By orienting the mesa sidewalls in certain crystallographic directions, it is possible to selectively grow a current blocking pnp layer structure on the exposed n-type lower cladding layer of the cavity whithout obstructing the electrical injection into the active region. The concept is evaluated in 1.2-mu m GaAs-based light emitting diodes with InGaAs quantum wells. This type of structure can easily be used as the amplifying region of a vertical cavity laser, providing a good alternative to selective oxidation confinement.

  • 243. Martijn, H.
    et al.
    Asplund, C.
    Malm, H.
    Smuk, S.
    Höglund, L.
    Gustafsson, Oscar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Hammar, Mattias
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Hellström, Staffan
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Development of IR imaging at IRnova2009Inngår i: Infrared Technology and Applications XXXV, 2009, Vol. 7298Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Historically IRnova has exclusively been a company, focused on manufacturing of QWIP detectors. Nowadays, besides continuous improvements of the performance of QWIP FPAs and development of new formats IRnova is involved in development of QWIP detectors for special applications and has started the development of the next generation infrared detectors, as well. In the light of the development of new formats we validate experimentally theoretical calculations of the response of QWIPs for smaller pixel size. These results allow for the development of high performance megapixel QWIP FPA that exhibit the high uniformity and operability QWIP detectors are known for. QWIP is also being considered for space applications. The requirements on dark current and operating temperature are however much more stringent as compared to the terrestrial applications. We show ways to improve the material quality with as a result a higher detector operating temperature. IRnova is also looking at antimony-based strained superlattice material for the LWIR region together with partners at theIMAGIC centre of excellence. One of the ways to overcome the problem with surface currents is passivating overgrowth. We will report the status and results of overgrowing the detector mesas with AlGa(As)Sb in a MOVPE system. At the same centre of excellence a novel material concept is being developed for LWIR detection. This new material contains a superlattice of vertically aligned and electronically coupled InAs and GaSb quantum dots. Simulations show that it should be possible to have LWIR detection in this material. We will present the current status and report results in this research.

  • 244.
    Martinsson, Per
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Lajunen, Hanna
    Friberg, Ari
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Scanning optical near-field resolution analyzed in terms of communication modes2006Inngår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 14, nr 23, s. 11392-11401Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present an analysis of scanning near-field optical microscopy in terms of the so-called communication modes using scalar wave theory. We show that the number of connected modes increases when the scanning distance is decreased, but the number of modes decreases when the size of the scanning aperture is decreased. In the limit of small detector aperture the best-connected mode reduces effectively to the Green function, evaluated at the center of the scanning aperture. We also suggest that the resolution of a scanning optical near-field imaging system is essentially given by the width of the lowest-order communication mode.

  • 245.
    Martinsson, Per
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Lajunen, Hanna
    Ma, Ping
    Friberg, Ari T.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Communication modes in vector diffraction2010Inngår i: Optik (Stuttgart), ISSN 0030-4026, E-ISSN 1618-1336, Vol. 121, nr 22, s. 2087-2093Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The communication modes, which mathematically correspond to singular value decomposition, have proven a useful concept in optical scalar-field diffraction, with applications in resolution studies, image synthesis, and wave propagation. For optical near-field geometries the communication modes have to be extended to electromagnetic field accounting for the polarization properties. In this paper we present the vector-valued communication modes method based on the rigorous electric-field diffraction integral. As a special case the transverse-electric scalar field modes are obtained. The intensity and polarization properties of the leading electromagnetic communication modes in near-field arrangements with rectangular apertures are discussed in terms of the Stokes parameters. For small separations between the transmitting and receiving apertures the fundamental mode possesses a ring-shaped hollow structure. The polarization properties of the near-field modes show features on spatial scales smaller than the wavelength of light. The system symmetries lead to degenerate communication modes.

  • 246.
    Mathieu, Roland
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    He, J. P.
    Kaneko, Y.
    Yoshino, H.
    Asamitsu, A.
    Tokura, Y.
    Logarithmic growth law in the two-dimensional Ising spin glass state resulting from the electron doping in single-layered manganites2007Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, nr 1, s. 014436-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The ac susceptibility of the electron-doped single-layered manganite La1.1 Sr0.9 Mn O4 is analyzed in detail. A quasi-two-dimensional antiferromagnetic (AFM) order with Ising anisotropy is stabilized below TN ∼80 K. We show that below TN, a rare two-dimensional (2D) spin-glass (SG) correlation develops with the same Ising anisotropy as the AFM state. Using simple scaling arguments of the droplet model, we derive a scaling form for the ac susceptibility data of a 2D SG, which our experimental data follow fairly well. Due to simplifications in this 2D case, the proposed scaling form only contains two unknown variables, ψν and τ0. Hence, the logarithmic growth law of the SG correlation predicted by the droplet model is convincingly evidenced by the scaling of our experimental data. The origin and nature of this 2D SG state are also discussed.

  • 247.
    Mathieu, Roland
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    He, J. P.
    Yu, X. Z.
    Kaneko, Y.
    Uchida, M.
    Lee, Y. S.
    Arima, T.
    Asamitsu, A.
    Tokura, Y.
    Coexistence of long-ranged charge and orbital order and spin-glass state in single-layered manganites with weak quenched disorder2007Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 80, nr 3, s. 37001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The relationship between orbital and spin degrees of freedom in the single crystals of the hole-doped Pr1-xCa1+xMnO4, 0.3 <= x <= 0.7 has been investigated by means of ac-magnetometry and charge transport. We show that in an intermediate underdoped region, with 0.35 <= x < 0.5, the "orbital-master spin-slave" relationship commonly observed in half-doped manganites does not take place. The long-ranged charge-orbital order is not accompanied by an antiferromagnetic transition at low temperatures, but by a frustrated short-ranged magnetic state bringing forth a spin-glass phase. We discuss in detail the nature and origin of this true spin-glass state, which, as in the half-doped manganites with large quenched disorder, is not related to the macroscopic phase separation observed in crystals with minor defects or impurities.

  • 248.
    Mathieu, Roland
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Tokura, Yoshinori
    The nanoscale phase separation in hole-doped manganites2007Inngår i: Journal of the Physical Society of Japan, ISSN 0031-9015, E-ISSN 1347-4073, Vol. 76, nr 12, s. 124706-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A macroscopic phase separation, in which ferromagnetic clusters are observed in an insulating matrix, is sometimes observed, and believed to be essential to the colossal magnetoresistive (CMR) properties of manganese oxides. The application of a magnetic field may indeed trigger large magnetoresistance effects due to the percolation between clusters allowing the movement of the charge carriers. However, this macroscopic phase separation is mainly related to extrinsic defects or impurities, which hinder the long-ranged charge-orbital order of the system. We show in the present article that rather than the macroscopic phase separation, an homogeneous short-ranged charge-orbital order accompanied by a spin glass state occurs, as an intrinsic result of the uniformity of the random potential perturbation induced by the solid solution of the cations on the A-sites of the structure of these materials. Hence the phase separation does occur, but in a more subtle and interesting nanoscopic form, here referred as "homogeneous". Remarkably, this "nanoscale phase separation" alone is able to bring forth the colossal magnetoresistance in the perovskite manganites, and is potentially relevant to a wide variety of other magnetic and/or electrical properties of manganites, as well as many other transition metal oxides, in bulk or thin film form as we exemplify throughout the article.

  • 249.
    Mathieu, Roland
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Uchida, M.
    Kaneko, Y.
    He, J. P.
    Yu, X. Z.
    Kumai, R.
    Arima, T.
    Tomioka, Y.
    Asamitsu, A.
    Matsui, Y.
    Tokura, Y.
    Bandwidth-disorder phase diagram of half-doped layered manganites2006Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, nr 2Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Phase diagrams in the plane of rA (the average ionic radius, related to the one-electron bandwidth W) and σ2 (the ionic radius variance, measuring the quenched disorder), or bandwidth-disorder phase diagrams, have been established for perovskite manganites, with a three-dimensional (3D) Mn-O network. Here we establish the intrinsic bandwidth-disorder phase diagram of half-doped layered manganites with a two-dimensional (2D) Mn-O network, examining in detail the parent state of the colossal magnetoresistance phenomenon in crystals without ferromagnetic instability. The consequences of the reduced dimensionality, from 3D to 2D, for the order-disorder phenomena in the charge-orbital sectors are also highlighted.

  • 250.
    Mbairi, Felix
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    On the processing issued of SU-8 photoresistInngår i: IEEE transactions on components and packaging technologies (Print), ISSN 1521-3331, E-ISSN 1557-9972Artikkel i tidsskrift (Fagfellevurdert)
2345678 201 - 250 of 615
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf