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  • 151.
    Tiihonen, Mikael
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Two-dimensional quasi-phase-matched multiplecascaded four-wave mixing in periodically poled KTiOPO2006In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 31, no 22, p. 3324-3326Article in journal (Refereed)
    Abstract [en]

    A two-dimensional quasi-phase-matched structure is realized in a noncollinear, nondegenerate periodically poled KTiOPO4 parametric oscillator by utilizing the mutual coherence of two noncollinear pump beams. The mutually coherent pump beams form an interference pattern inside the crystal that is directed perpendicular to the existing quasi-phase-matched grating vector and acts as a parametric gain grating. The cavity itself supports two signal wavelengths around 1550 nm with tunable separation, while the gain grating reduces the operational threshold of the oscillator. Furthermore, with this two-dimensional quasi-phasematched structure, we can demonstrate the generation of new spectral components through multiple chi((2)) : chi((2))-caseaded four-wave mixing processes.

  • 152. Tillman, K. A.
    et al.
    Reid, D. T.
    Artigas, D.
    Hellstrom, J.
    Pasiskevicius, Valdas
    KTH, Superseded Departments, Physics.
    Laurell, Fredrik
    KTH, Superseded Departments, Physics.
    Low-threshold femtosecond optical parametric oscillator based on chirped-pulse frequency conversion2003In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 28, no 7, p. 543-545Article in journal (Refereed)
    Abstract [en]

    We report what is to our knowledge the first demonstration of a femtosecond optical parametric oscillator based on chirped-pulse frequency conversion in a long crystal of aperiodically poled potassium titanyl phosphate. The minimum pump threshold power was 15 mW, and a signal slope efficiency of 35% was achieved. Continuous tuning from 1190 to 1450 nm was obtained for an average pump power of 800 mW.

  • 153. Torres-Company, Victor
    et al.
    Minguez-Vega, Gladys
    Lancis, Jesus
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Controllable generation of partially coherent light pulses with direct space-to-time pulse shaper2007In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 32, no 12, p. 1608-1610Article in journal (Refereed)
    Abstract [en]

    We demonstrate the possibility of creating user-defined partially coherent light pulses by means of a slight modification of the direct space-to-time pulse shaper. Specifically, we generate a mutual coherence function that corresponds to the independent-elementary-pulse representation model. The theoretical limits in the parameter of global coherence and the efficiency of the system are studied. Our result opens the door to a new way of quantum control in laser-assisted chemical reactions, namely, control by partial coherence.

  • 154. Valerio, Guido
    et al.
    Sipus, Zvonimir
    Grbic, Anthony
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Nonresonant modes in plasmonic holey metasurfaces for the design of artificial flat lenses2017In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 42, no 10, p. 2026-2029Article in journal (Refereed)
    Abstract [en]

    This Letter discusses nonresonant modes excited on holey metasurfaces and their influence on the properties of spoof plasmonic states supported by the metasurface when a second surface is placed in its proximity. We consider here a metallic surface with periodic holes drilled in it. The field excited on each hole is projected onto a set of nonresonant modes in order to discuss their relative relevance. While previous simpler models assumed only the presence of the fundamental mode, we show that the simultaneous presence of several modes occurs when the surface is placed next to a metallic plate. Therefore, higher-order modes are responsible for the peculiar physical properties of wave propagation of spoof plasmons between two surfaces, which can lead to new gradient-index flat lenses for transceivers for space communications.

  • 155.
    Vasileva, Elena
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Baitenov, Adil
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Chen, Hui
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Li, Yuanyuan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Sychugov, Ilya
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Yan, Min
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Berglund, Lars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Popov, Sergei
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Effect of transparent wood on the polarization degree of light2019In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 44, no 12, p. 2962-2965Article in journal (Refereed)
    Abstract [en]

    We report on the study of polarization properties of light propagating through transparent wood (TW), which is an anisotropically scattering medium, and consider two cases: completely polarized and totally unpolarized light. It was demonstrated that scattered light distribution is affected by the polarization state of incident light. Scattering is the most efficient for light polarized parallel to cellulose fibers. Furthermore, unpolarized light becomes partially polarized (with a polarization degree of 50%) after propagating through the TW. In the case of totally polarized incident light, however, the degree of polarization of transmitted light is decreased, in an extreme case to a few percent, and reveals an unusual angular dependence on the material orientation. The internal hierarchical complex structure of the material, in particular cellulose fibrils organized in lamellae, is believed to be responsible for the change of the light polarization degree. It was demonstrated that the depolarization properties are determined by the angle between the polarization of light and the wood fibers, emphasizing the impact of their internal structure, unique for different wood species.

  • 156.
    Viotti, Anne-Lise
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Zukauskas, Andrius
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Canalias, Carlota
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Coherent phase transfer and pulse compressionat 1.4μm in a backward-wave OPO2019In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 44, no 12, p. 3066-3069Article in journal (Refereed)
    Abstract [en]

    The frequency modulation transfer property of a backward-wave optical parametric oscillator (BWOPO) is investigated in the context of near-IR pulse compression. The maximum transferrable bandwidth from the pump to the forward wave in a BWOPO is determined by the group dispersion mismatch. In comparison, the third-order phase introduced in a single-grating compressor setup is more detrimental to achieve optimum compression of the BWOPO forward wave. Nevertheless, we demonstrate a 220 GHz bandwidth transfer from 800 nm to 1.4 μm, with a compression factor of 115, leading to near-IR pulses as short as 1.3 ps with μJ energy.

  • 157.
    Vogt, Ulrich
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Lindblom, M.
    Charalambous, P.
    Kaulich, B.
    Wilhein, T.
    Condenser for Koehler-like illumination in transmission x-ray microscopes at undulator sources2006In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 31, no 10, p. 1465-1467Article in journal (Refereed)
    Abstract [en]

    We report on a novel condenser for full-field transmission x-ray microscopes that use synchrotron radiation from an undulator source. The condenser produces a Koehler-like homogeneous intensity distribution in the sample plane and eliminates object illumination problems connected with the high degree of spatial coherence in an undulator beam. The optic consists of a large number of small linear diffraction gratings and is therefore relatively easy to manufacture. First imaging experiments with a prototype condenser were successfully performed with the Twinmic x-ray microscope at the Elettra synchrotron facility in Italy.

  • 158.
    Vogt, Ulrich
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Lindblom, Magnus
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Jansson, Per
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Tuohimaa, Tomi
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Holmberg, Anders
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Hertz, Hans
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Wieland, M.
    University of Applied Sciences Koblenz, Rhein Ahr Campus Remagen.
    Wilhein, Thomas
    University of Applied Sciences Koblenz, Rhein Ahr Campus Remagen.
    Single-optical-element soft-x-ray interferometry with a laser-plasma x-ray source2005In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, no 15, p. 2167-Article in journal (Refereed)
    Abstract [en]

    We report on a compact interferometer for the water-window soft-x-ray range that is suitable for operation with laser-plasma sources. The interferometer consists of a single diffractive optical element that focuses impinging x rays to two focal spots. The light from these two secondary sources forms the interference pattern. The interferometer was operated with a liquid-nitrogen jet laser-plasma source at lambda = 2.88 nm. Scalar wave-field propagation was used to simulate the interference pattern, showing good correspondence between theoretical and experimental results. The diffractive optical element can simultaneously be used as an imaging optic, and we demonstrate soft-x-ray microscopy with interferometric contrast enhancement of a phase object.

  • 159.
    von Hofsten, Olof
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Bertilson, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Lindblom, M.
    Holmberg, Anders
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Vogt, Ulrich
    KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.
    Compact Zernike phase contrast x-ray microscopy using a single-element optic2008In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 33, no 9, p. 932-934Article in journal (Refereed)
    Abstract [en]

    We demonstrate Zernike phase contrast in a compact soft x-ray microscope using a single-element optic. The optic is a combined imaging zone plate and a Zernike phase plate and does not require any additional alignment or components. Contrast is increased and inversed in an image of a test object using the Zernike zone plate. This type of optic may be implemented into any existing x-ray microscope where phase contrast is of interest.

  • 160.
    von Hofsten, Olof
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Bertilson, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Reinspach, Julia
    Holmberg, Anders
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Hertz, Hans M.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Vogt, Ulrich
    KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.
    Sub-25-nm laboratory x-ray microscopy using a compound Fresnel zone plate2009In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 34, no 17, p. 2631-2633Article in journal (Refereed)
    Abstract [en]

    Improving the resolution in x-ray microscopes is of high priority to enable future applications in nanoscience. However, high-resolution zone-plate optics often have low efficiency, which makes implementation in laboratory microscopes difficult. We present a laboratory x-ray microscope based on a compound zone plate. The compound zone plate utilizes multiple diffraction orders to achieve high resolution while maintaining reasonable efficiency. We analyze the illumination conditions necessary for this type of optics in order to suppress stray light and demonstrate microscopic imaging resolving 25 nm features.

  • 161.
    Wang, S.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Laurell, H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Karlsson, H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    First-order type-II quasi-phase matched UV generation in periodically poled KTP1999In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 24, p. 978-980Article in journal (Refereed)
  • 162.
    Wang, Shunhua
    et al.
    KTH, School of Engineering Sciences (SCI).
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI).
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI).
    Karlsson, Håkan
    KTH, School of Engineering Sciences (SCI).
    First-order type-II quasi-phase matched UV generation in periodically poled KTP1999In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 24, p. 978-980Article in journal (Refereed)
  • 163.
    Wang, Shunhua
    et al.
    KTH, Superseded Departments, Physics.
    Pasiskevicius, Valdas
    KTH, Superseded Departments, Physics.
    Laurell, Fredrik
    KTH, Superseded Departments, Physics.
    Karlsson, Håkan
    Ultraviolet generation by first-order frequency doubling in periodically poled KTiOPO41998In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 23, no 24, p. 1883-1885Article in journal (Refereed)
    Abstract [en]

    First-order quasi-phase-matched frequency doubling at 780 nm in a 1-mm-thick periodically poled KTiOPO4 crystal with an inverted-domain period of 2.95 mu m has been demonstrated for the first time to the authors' knowledge. A normalized conversion efficiency of 1.1% W-1 cm(-1) has been obtained in cw mode. Experiments show that group-velocity walk-off prevents efficient frequency doubling of femtosecond pulses in KTiOPO4 in the UV spectral range. However, because of the large optical nonlinearity, periodically poled structures can be efficiently used for frequency doubling of cw and pulsed lasers with pulse lengths as short as similar to 1 ps.

  • 164.
    Wang, Zhechao
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Zhu, Ning
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Tang, Yongbo
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Wosinski, Lech
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Dai, Daoxin
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    He, Sailing
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Ultracompact low-loss coupler between strip and slot waveguides2009In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 34, no 10, p. 1498-1500Article in journal (Refereed)
    Abstract [en]

    We present both theoretical and experimental results of an ultracompact waveguide coupler that is capable of highly efficient coupling of light from strip waveguides to slot waveguides, and vice versa. By optimizing the geometrical parameters, it is possible to achieve extremely low-loss coupling. A coupling efficiency of 97% has been obtained experimentally while keeping the overall size down to the range below 10 mu m. Further analysis shows that the proposed coupler has relatively high tolerance to fabrication errors and is wavelength insensitive. (C) 2009 Optical Society of America

  • 165. Webb, Kevin J.
    et al.
    Thylén, Lars
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Perfect-lens-material condition from adjacent absorptive and gain resonances2008In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 33, no 7, p. 747-749Article in journal (Refereed)
    Abstract [en]

    We suggest, based on the principle of causality and for a material exhibiting adjacent absorptive and gain resonances, that there can be an intervening frequency where perfect imaging is in theory possible. At this frequency, both the dielectric constant and the permeability are negative, leading to a negative refractive index, and there is no loss. In such a material exhibiting a double resonance, the gain must be at the higher frequency. Through appropriate tuning of the refractive index, all propagating and evanescent fields from the object could then in principle be reconstructed at the image plane, subject to practical implementation limits.

  • 166.
    Yan, Min
    et al.
    Nanyang Techbological University, Singapore.
    Shum, Ping
    Nanyang Techbological University, Singapore.
    Improved air-silica photonic crystal with a triangular airhole arrangement for hollow-core photonic bandgap fiber design2005In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, no 15, p. 1920-1922Article in journal (Refereed)
  • 167.
    Yan, Min
    et al.
    Nanyang Techbological University, Singapore.
    Shum, Ping
    Nanyang Techbological University, Singapore.
    Hu, Juan Juan
    Design of air-guiding honeycomb photonic bandgap fiber2005In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, no 5, p. 465-467Article in journal (Refereed)
  • 168. Yang, Yuanqing
    et al.
    Zhao, Ding
    Gong, Hanmo
    Li, Qiang
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Plasmonic sectoral horn nanoantennas2014In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 39, no 11, p. 3204-3207Article in journal (Refereed)
    Abstract [en]

    In this Letter, plasmonic sectoral horn nanoantennas working at near-infrared wavelength (1550 nm) have been investigated. We demonstrate that, although there are certain differences between the plasmonic and classical radio-frequency (RF) sectoral horn antennas, the plasmonic horns still possess a number of attractive features, like their RF counterparts, such as tunable high directivities, simplicity in fabrication, and ease of coupling to waveguides. As a specific application, we further show how to exploit these findings to optimize an optical wireless nanolink using the proposed horn nanoantennas, and obtain a 60-fold increase in the received power compared with the situation of matched dipole nanoantennas.

  • 169.
    Yu, Zhangwei
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Knape, Harald
    Tarasenko, Olesandr
    Koch, Ralf
    Margulis, Walter
    All-fiber single-pulse selection and nanosecond gating2009In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 34, no 7, p. 1024-1026Article in journal (Refereed)
    Abstract [en]

    Two functions normally attributed to Pockels cells are performed with internal-electrode microstructured fiber components. Single-pulse selection out of a 100 MHz mode-locked pulse train is demonstrated using all-fiber nanosecond polarization rotation. Additionally, off-on-off gating with duration similar to 13 ns is achieved with a polarization rotator made out of a four-hole silicate fiber.

  • 170.
    Yu, Zhangwei
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Malmström, Mikael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Sterner, C.
    Tarasenko, O.
    Margulis, Walther
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Fonjallaz, P. -Y
    Dynamics of long-period gratings tuned with internal fiber electrodes2011In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 36, no 5, p. 633-635Article in journal (Refereed)
    Abstract [en]

    The physics of electrically switched long-period grating in a twin-hole fiber with internal electrodes is studied. Dynamic measurements for the two polarizations show how the grating spectra shift in time due to the mechanical stress and heat transfer in the core and the cladding.

  • 171.
    Zeil, Peter
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Voigtlaender, Christian
    Thomas, Jens
    Richter, Daniel
    Nolte, Stefan
    Femtosecond laser-induced apodized Bragg grating waveguides2013In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 38, no 13, p. 2354-2356Article in journal (Refereed)
    Abstract [en]

    We report on the inscription of apodized Bragg grating waveguides (BGWs) in fused silica using a modulated high repetition rate fs laser system. Tailoring of the grating's coupling strength is facilitated by appropriately substructuring the modulation of the inscribing laser radiation. The proposed alteration delivers an unchanged constant mean refractive index entailing homogeneous guiding properties along the entire waveguide. The BGWs fabricated using a Gaussian apodized modulation profile exhibit a 10 dB improvement in sideband suppression compared to waveguide gratings written with a uniform modulation profile.

  • 172. Zhang, A. P.
    et al.
    Burzynski, R.
    Yoon, Y. K.
    Prasad, P. N.
    He, Sailing
    Double-layer fabrication scheme for large-area polymeric photonic crystal membrane on silicon surface by multibeam interference lithography2008In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 33, no 12, p. 1303-1305Article in journal (Refereed)
    Abstract [en]

    We report on the fabrication of two-dimensional polymeric photonic crystal membranes on the surface of silicon using visible-light multibeam interference lithography. The structures are created by the interference of three beams of a green laser. A polymer buffer layer doped with a Rhodamine B laser dye, interlaid between the lithography layer and the silicon substrate, suppresses the effects of strong reflection and nonradiative absorption of silicon on the interference pattern. Large-area defect-free photonic crystal membranes are experimentally realized on silicon surface.

  • 173.
    Zhang, Lu
    et al.
    KTH, School of Information and Communication Technology (ICT). State Key Laboratory of Advanced Optical Communication System and Networks, Shanghai Jiao Tong University, Shanghai 200240, China.
    Hong, Xuezhi
    KTH, School of Information and Communication Technology (ICT). MOE International Laboratory for Optical Information Technologies, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China.
    Pang, Xiaodan
    KTH, School of Information and Communication Technology (ICT). Networking and Transmission Laboratory, RISE Acreo AB, Kista 16425, Sweden.
    Ozolins, Oskars
    Udalcovs, Aleksejs
    Schatz, Richard
    KTH, School of Engineering Sciences (SCI), Applied Physics, Optics and Photonics, OFO.
    Guo, Changjian
    Zhang, Junwei
    Nordwall, Fredrik
    Engenhardt, Klaus M.
    Westergren, Urban
    KTH, School of Engineering Sciences (SCI), Applied Physics, Optics and Photonics, OFO.
    Popov, Sergei
    KTH, School of Engineering Sciences (SCI), Applied Physics, Optics and Photonics, OFO.
    Jacobsen, Gunnar
    Xiao, Shilin
    Hu, Weisheng
    Chen, Jiajia
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab). MOE International Laboratory for Optical Information Technologies, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China.
    Nonlinearity-aware 200 Gbit/s DMT transmission for C-band short-reach optical interconnects with a single packaged electro-absorption modulated laser2018In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 43, no 2, p. 182-185Article in journal (Refereed)
    Abstract [en]

    We experimentally demonstrate the transmission of a 200 Gbit/s discrete multitone (DMT) at the soft forward error correction limit in an intensity-modulation directdetection system with a single C-band packaged distributed feedback laser and traveling-wave electro absorption modulator (DFB-TWEAM), digital-to-analog converter and photodiode. The bit-power loaded DMT signal is transmitted over 1.6 km standard single-mode fiber with a net rate of 166.7 Gbit/s, achieving an effective electrical spectrum efficiency of 4.93 bit/s/Hz. Meanwhile, net rates of 174.2 Gbit/s and 179.5 Gbit/s are also demonstrated over 0.8 km SSMF and in an optical back-to-back case, respectively. The feature of the packaged DFB-TWEAM is presented. The nonlinearity-aware digital signal processing algorithm for channel equalization is mathematically described, which improves the signal-to-noise ratio up to 3.5 dB. 

  • 174.
    Zhang, Lu
    et al.
    KTH. Shanghai Jiao Tong University, Shanghai, China.
    Pang, Xiaodan
    KTH. RISE Acreo AB, Networking & Transmiss Lab, S-16425 Kista, Sweden.
    Ozolins, Oskars
    Udalcovs, Aleksejs
    Popov, Sergei
    Xiao, Shilin
    Hu, Weisheng
    Chen, Jiajia
    KTH. South China Normal Univ, South China Acad Adv Optoelect, MOE Int Lab Opt Informat Technol, Guangzhou 510006, Guangdong, Peoples R China.
    Spectrally efficient digitized radio-over-fiber system with k-means clustering-based multidimensional quantization.2018In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 43, no 7, p. 1546-1549Article in journal (Refereed)
    Abstract [en]

    We propose a spectrally efficient digitized radio-over-fiber (D-RoF) system by grouping highly correlated neighboring samples of the analog signals into multidimensional vectors, where the k-means clustering algorithm is adopted for adaptive quantization. A 30  Gbit/s D-RoF system is experimentally demonstrated to validate the proposed scheme, reporting a carrier aggregation of up to 40 100 MHz orthogonal frequency division multiplexing (OFDM) channels with quadrate amplitude modulation (QAM) order of 4 and an aggregation of 10 100 MHz OFDM channels with a QAM order of 16384. The equivalent common public radio interface rates from 37 to 150  Gbit/s are supported. Besides, the error vector magnitude (EVM) of 8% is achieved with the number of quantization bits of 4, and the EVM can be further reduced to 1% by increasing the number of quantization bits to 7. Compared with conventional pulse coding modulation-based D-RoF systems, the proposed D-RoF system improves the signal-to-noise-ratio up to ∼9  dB and greatly reduces the EVM, given the same number of quantization bits.

  • 175.
    Zhang, Ziyang
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Influence of structural variations on high-Q microcavities in two-dimensional photonic crystal slabs2005In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, no 13, p. 1713-1715Article in journal (Refereed)
    Abstract [en]

    The influence of some critical structural variations in high-Q microcavities in two-dimensional photonic crystal slabs is investigated. All the cavities studied maintain a high Q in a wide range of structural variations, while the resonant frequencies shift on a relatively large scale when the structural variations are comparable to the physical sizes of the cavities.

  • 176. Zhou, B.
    et al.
    Guan, Z. G.
    Yan, C. S.
    He, Sailing
    Interrogation technique for a fiber Bragg grating sensing array based on a Sagnac interferometer and an acousto-optic modulator2008In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 33, no 21, p. 2485-2487Article in journal (Refereed)
    Abstract [en]

    We propose and experimentally demonstrate a novel real-time interrogation technique for a fiber Bragg grating (FBG) sensing system that is based on a frequency-shifted asymmetric Sagnac interferometer. FBG sensors are connected to the Sagnac loop by an optical coupler, and an acousto-optic modulator (AOM) is asymmetrically placed in the Sagnac loop. By linearly sweeping the driving frequency of the AOM, the environmental variation around each FBG sensor can be determined by measuring the spectrum of the interference signals of the two counterpropagating light beams reflected by the corresponding FBG. The system has the advantages of low cost and real-time sensing.

  • 177.
    Zhou, Tunhe
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Zanette, Irene
    Zdora, Marie-Christine
    Lundström, Ulf
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics. Stanford Univ, Dept Biol Struct, Stanford, CA 94305 USA.
    Larsson, Daniel H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Hertz, Hans M.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Pfeiffer, Franz
    Burvall, Anna
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Speckle-based x-ray phase-contrast imaging with a laboratory source and the scanning technique2015In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 40, no 12, p. 2822-2825Article in journal (Refereed)
    Abstract [en]

    The speckle-based scanning method for x-ray phase-contrast imaging is implemented with a liquid-metal-jet source. Using the two-dimensional scanning technique, the phase shift introduced by the object is retrieved in both transverse orientations, and the limitations on spatial resolution inherent to the speckle-tracking technique are avoided. This method opens up possibilities of new high-resolution multimodal applications for lab-based phasecontrast x-ray imaging.

  • 178.
    Zhou, Tunhe
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Zdora, Marie-Christine
    Zanette, Irene
    Romell, Jenny
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Hertz, Hans M.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Burvall, Anna
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Noise analysis of speckle-based x-ray phase-contrast imaging2016In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 41, no 23, p. 5490-5493Article in journal (Refereed)
    Abstract [en]

    Speckle-based x-ray phase-contrast imaging has drawn increasing interest in recent years as a simple, multimodal, cost-efficient, and laboratory-source adaptable method. We investigate its noise properties to help further optimization on the method and further comparison with other phase-contrast methods. An analytical model for assessing noise in a differential phase signal is adapted from studies on the digital image correlation technique in experimental mechanics and is supported by simulations and experiments. The model indicates that the noise of the differential phase signal from speckle-based imaging has a behavior similar to that of the grating-based method.

  • 179.
    Zhu, Ning
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Song, Jun
    KTH, School of Information and Communication Technology (ICT), Centres, Kista Photonics Research Center, KPRC.
    Wosinski, Lech
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Thylén, Lars
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Experimental demonstration of a cross-order echelle grating triplexer based on an amorphous silicon nanowire platform2009In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 34, no 3, p. 383-385Article in journal (Refereed)
    Abstract [en]

    We present the design, fabrication, and characterization of an ultracompact silicon-on-insulator-based echelle grating triplexer. It is based on the cross-order design, which utilizes different diffraction orders to cover a large spectral range from 1.3 to 1.5 mu m with three channels located at 1310, 1490, and 1550 nm and with a footprint of 150 mu m X 130 mu m.

  • 180. Zhu, Yinian
    et al.
    Shum, Ping
    Nanyang Techbological University, Singapore.
    Bay, Hui-Wen
    Yan, Min
    Nanyang Techbological University, Singapore.
    Yu, Xia
    Hu, Juanjuan
    Hao, Jianzhong
    Lu, Chao
    Strain-insensitive and high-temperature long-period gratings inscribed in photonic crystal fiber2005In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, no 4, p. 367-369Article in journal (Refereed)
1234 151 - 180 of 180
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