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  • 1.
    Ako, Thomas
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Design of invisibility cloaks with an open tunnel2010In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 18, no 26, p. 27060-27066Article in journal (Refereed)
    Abstract [en]

    In this paper we apply the methodology of transformation optics for design of a novel invisibility cloak which can possess an open tunnel. Such a cloak facilitates the insertion (retrieval) of matter into (from) the cloak's interior without significantly affecting the cloak's performance, overcoming the matter exchange bottleneck inherent to most previously proposed cloak designs. We achieve this by applying a transformation which expands a point at the origin in electromagnetic space to a finite area in physical space in a highly anisotropic manner. The invisibility performance of the proposed cloak is verified by using full-wave finite-element simulations. (C) 2010 Optical Society of America

  • 2. Akram, Muhammad Nadeem
    et al.
    Xiang, Yu
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Yu, Xingang
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zabel, Thomas
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Influence of base-region thickness on the performance of Pnp transistor-VCSEL2014In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 22, no 22, p. 27398-27414Article in journal (Refereed)
    Abstract [en]

    We have recently reported a 980nm GaAs-based three terminal Pnp transistor-vertical-cavity surface-emitting laser (TVCSEL) operating at room temperature with optical power up to 1.8mW. However, the current gain beta = Delta I-c/Delta I-b was near zero just before lasing and became negative after the lasing threshold. The main cause of the negative current gain was found to be a gradual and position-dependent forward-biasing (saturation) of the base-collector junction with increasing bias even before lasing threshold. In this article, detailed multi-physics device simulations are performed to better understand the device physics, and find ways to avoid the premature saturation of the base-collector junction. We have optimized the thickness of the base region as well as its doping concentration and the location of the quantum wells to ensure that the T-VCSEL is in the active mode throughout its range of operation. That is, the emitter-base junction is forward biased and base-collector junction is reversed biased for sweeping the excess charges out of the base region.

  • 3. Alcusa-Saez, E. P.
    et al.
    Diez, A.
    Rivera-Perez, E.
    Margulis, Walter
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Norin, Lars
    ACREO.
    Andres, M. V.
    Acousto-optic interaction in polyimide coated optical fibers with flexural waves2017In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 25, no 15, p. 17167-17173Article in journal (Refereed)
    Abstract [en]

    Acousto-optic coupling in polyimide-coated single-mode optical fibers using flexural elastic waves is demonstrated. The effect of the polyimide coating on the acoustooptic interaction process is analyzed in detailed. Theoretical and experimental results are in good agreement. Although the elastic attenuation is significant, we show that acousto-optic coupling can be produced with a reasonably good efficiency. To our knowledge, it is the first experimental demonstration of acousto-optic coupling in optical fibers with robust protective coating.

  • 4.
    Antelius, Mikael
    et al.
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Gylfason, Kristinn B.
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Sohlström, Hans
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    An apodized SOI waveguide-to-fiber surface grating coupler for single lithography silicon photonics2011In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, no 4, p. 3592-3598Article in journal (Refereed)
    Abstract [en]

    We present the design, fabrication, and characterization of a grating for coupling between a single mode silica fiber and the TE mode in a silicon photonic waveguide on a silicon on insulator (SOI) substrate. The grating is etched completely through the silicon device layer, thus permitting the fabrication of through-etched surface coupled silicon nanophotonic circuits in a single lithography step. Furthermore, the grating is apodized to match the diffracted wave to the mode profile of the fiber. We experimentally demonstrate a coupling efficiency of 35% with a 1 dB bandwidth of 47 nm at 1536 nm on a standard SOI substrate. Furthermore, we show by simulation that with an optimized buried oxide thickness, a coupling efficiency of 72% and a 1 dB bandwidth of 38 nm at 1550 nm is achievable. This is, to our knowledge, the highest simulated coupling efficiency for single-etch TE-mode grating couplers. In particular, simulations show that apodizing a conventional periodic through-etched grating decreases the back-reflection into the waveguide from 21% to 0.1%.

  • 5.
    Ao, Xianyu
    et al.
    KTH.
    He, Sailing
    KTH, Superseded Departments, Electromagnetic Theory.
    Two-stage design method for realization of photonic bandgap structures with desired symmetries by interference lithography2004In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 12, no 6, p. 978-983Article in journal (Refereed)
    Abstract [en]

    Interference lithography for the fabrication of photonic crystals is considered. A two-stage design method for realization of photonic bandgap structures with desired symmetries is developed. An optimal photonic crystal with a large bandgap is searched by adjusting some parameters while keeping some basic symmetry of the unit cell unchanged. A nonlinear programming method is then used to find the optimal electric field vectors of the laser beams and realize the desired interference pattern. The present method is useful for a rational and systematical design of new photonic bandgap structures.

  • 6. Arias, Augusto
    et al.
    Etcheverry, Sebastian
    Solano, Pablo
    Staforelli, Juan
    Gallardo, Maria Jose
    Rubinsztein-Dunlop, Helina
    Saavedra, Carlos
    Simultaneous rotation, orientation and displacement control of birefringent microparticles in holographic optical tweezers2013In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, no 1, p. 102-111Article in journal (Refereed)
    Abstract [en]

    We report the experimental implementation of a new method for generating multiple dynamical optical tweezers, where each one of them is generated with an independent linear polarization state with arbitrary orientation. This also allows an independent simultaneous polarization-rotation control. The laser beam, both for generating multiple traps and polarization control, has been modulated using a single reflective nematic liquid crystal with parallel alignment. We present experimental results of controlled displacement, orientation and rotation of birefringent particles. In addition, a simple method for estimating and canceling out the primary astigmatism present in the system is presented.

  • 7. Baek, In Hyung
    et al.
    Choi, Sun Young
    Lee, Hwang Woon
    Cho, Won Bae
    Petrov, Valentin
    Agnesi, Antonio
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Yeom, Dong-Il
    Kim, Kihong
    Rotermund, Fabian
    Single-walled carbon nanotube saturable absorber assisted high-power mode-locking of a Ti:sapphire laser2011In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, no 8, p. 7833-7838Article in journal (Refereed)
    Abstract [en]

    We report on passive mode-locking of a Ti:sapphire laser employing a single-walled carbon nanotube saturable absorber (SWCNT-SA) specially designed and fabricated for wavelengths near 800 nm. Mode-locked pulses as short as 62 fs were generated at a repetition rate of 99.4 MHz. We achieved output powers from the SWCNT-SA mode-locked laser as high as 600 mW with a slope efficiency of 26%. The characteristics of SWCNT-SA-assisted mode-locking were compared with those of Kerr-lens mode-locking without SWCNT-SA.

  • 8.
    Baghban, Mohammad Amin
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Schollhammer, Jean
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Errando-Herranz, Carlos
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Gylfason, Kristinn B
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Gallo, Katia
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Bragg gratings in thin-film LiNbO3 waveguides2017In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Optics Express, ISSN 1094-4087, Vol. 25, no 26, p. 32323-32332Article in journal (Refereed)
    Abstract [en]

    We design, fabricate and characterize sidewall corrugated Bragg gratings in a high confinement integrated optics lithium niobate platform, comprising submicrometric photonic wires, tapers and grating couplers to interface off-chip standard telecom optical fibers. We analyze the grating performance as band-rejection filter for TE-polarized signals in the telecom C-band, considering both rectangular and sinusoidal sidewall profiles, and demonstrate record extinction ratios as high as 27 dB and rejection bandwidths as narrow as 3 nm. The results show the potential for an efficient integration of novel photonic functionalities into low-footprint LiNbO3 nonlinear and electro-optical waveguide devices.

  • 9. Bagschik, K.
    et al.
    Frömter, R.
    Müller, L.
    Roseker, W.
    Bach, J.
    Staeck, P.
    Thönnißen, C.
    Schleitzer, S.
    Hårdensson Berntsen, Magnus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Weier, C.
    Adam, R.
    Viefhaus, J.
    Schneider, C. M.
    Grübel, G.
    Oepen, H. P.
    Spatial coherence determination from the Fourier analysis of a resonant soft X-ray magnetic speckle pattern2016In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 24, no 20, p. 23162-23176Article in journal (Refereed)
    Abstract [en]

    We present a method to determine the two-dimensional spatial coherence of synchrotron radiation in the soft X-ray regime by analyzing the Fourier transform of the magnetic speckle pattern from a ferromagnetic film in a multidomain state. To corroborate the results, a Young's double-pinhole experiment has been performed. The transverse coherence lengths in vertical and horizontal direction of both approaches are in a good agreement. The method presented here is simple and gives a direct access to the coherence properties of synchrotron radiation without nanostructured test objects.

  • 10. Barrios, Carlos Angulo
    et al.
    Sanchez, Benito
    Gylfason, Kristinn Björgvin
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Griol, Amadeu
    Sohlström, Hans
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Holgado, Miquel
    Casquel, Raphael
    Demonstration of slot-waveguide structures on silicon nitride / silicon oxide platform2007In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 15, no 11, p. 6846-6856Article in journal (Refereed)
    Abstract [en]

    We report on the first demonstration of guiding light in vertical slot-waveguides on silicon nitride/silicon oxide material system. Integrated ring resonators and Fabry-Perot cavities have been fabricated and characterized in order to determine optical features of the slot-waveguides. Group index behavior evidences guiding and confinement in the low-index slot region at O-band (1260-1370nm) telecommunication wavelengths. Propagation losses of < 20 dB/cm have been measured for the transverse-electric mode of the slot-waveguides.

  • 11.
    Bergstrand, Jan
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.
    Rönnlund, Daniel
    KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.
    Widengren, Jerker
    KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.
    Wennmalm, Stefan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Scanning inverse fluorescence correlation spectroscopy2014In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 22, no 11, p. 13073-13090Article in journal (Refereed)
    Abstract [en]

    Scanning Inverse Fluorescence Correlation Spectroscopy (siFCS) is introduced to determine the absolute size of nanodomains on surfaces. We describe here equations for obtaining the domain size from cross-and auto-correlation functions, measurement simulations which enabled testing of these equations, and measurements on model surfaces mimicking membranes containing nanodomains. Using a confocal microscope of 270 nm resolution the size of 250 nm domains were estimated by siFCS to 257 +/- 12 nm diameter, and 40 nm domains were estimated to 65 +/- 26 nm diameter. Applications of siFCS for sizing of nanodomains and protein clusters in cell membranes are discussed.

  • 12. Bertani, Stefano
    et al.
    Jacobsson, Bjorn
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Stjernström, Mårten
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry (closed 20110630).
    Stretching-tunable external-cavity laser locked by an elastic silicone grating2006In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 14, no 25, p. 11982-11986Article in journal (Refereed)
    Abstract [en]

    We demonstrate wavelength locking of a diode laser at 760 nm with feedback from an elastic transmission grating in the Littrow configuration. The laser was in a single longitudinal mode with a side-mode suppression of 20 dB. By stretching the grating the laser could be tuned over a few nm. The grating was fabricated in a silicone elastomer ( polydimethylsiloxane) by a moulding technique, and coated by a thin layer of Ti and Au to achieve an increased diffraction efficiency needed for efficient locking.

  • 13.
    Bertilson, Michael
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    von Hofsten, Olof
    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.
    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.
    High-resolution computed tomography with a compact soft x-ray microscope2009In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 17, no 13, p. 11057-11065Article in journal (Refereed)
    Abstract [en]

    Computed tomography based on high-resolution soft x-ray microscopy utilizes the natural contrast for biological specimens provided by the water window (lambda = 2.4 - 4.4 nm) and the high resolving power of zone plate objectives. It is capable of revealing the 3D structure of biological specimens at sub-visible-microscopic resolution. To date, the technique has only been available at synchrotron-based microscopes, which limits the researchers access. In the present paper we demonstrate high-resolution soft x-ray tomography with a laboratory zone-plate-based soft x-ray microscope. The specimen, a diatom mounted on a glass capillary, was reconstructed from a tilt series of 53 images covering 180 using a filtered back projection algorithm. The resolution of the tomogram was estimated to a half period of 140 nm using a differential-phase-residual method. Cryo-fixation, increased source brightness and extended-depth-of-focus objectives are important for pushing the resolution of compact systems for biological samples.

  • 14.
    Bertilson, Michael
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    von Hofsten, Olov
    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, Biomedical and X-ray Physics.
    Numerical model for tomographic image formation in transmission x-ray microscopy2011In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, no 12, p. 11578-11583Article in journal (Refereed)
    Abstract [en]

    We present a numerical image-formation model for investigating the influence of partial coherence, sample thickness and depth-of-focus on the accuracy of tomographic reconstructions in transmission x-ray microscopes. The model combines wave propagation through the object by finite difference techniques with Fourier methods. We include a ray-tracing model to analyse the origin of detrimental stray light in zone plate-based x-ray microscopes. These models allow optimization of x-ray microscopy systems for quantitative tomographic imaging of thick objects. Results show that both the depth-of-focus and the reconstructed local absorption coefficient are highly dependent on the degree of coherence of the optical system.

  • 15.
    Bogdanowicz, Janusz
    et al.
    IMEC, Kapeldreef 75, B-3000 Leuven, Belgium.
    Gilbert, Matthieu
    IMEC, Kapeldreef 75, B-3000 Leuven, Belgium.
    Innocenti, Nicolas
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Koelling, Sebastian
    IMEC, Kapeldreef 75, B-3000 Leuven, Belgium.
    Vanderheyden, Benoit
    4 Institut Montefiore, Sart-Tilman B28, B-4000 Liege, Belgium.
    Vandervorst, Wilfried
    IMEC, Kapeldreef 75, B-3000 Leuven, Belgium.
    Light absorption in conical silicon particles2013In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, no 3, p. 3891-3896Article in journal (Refereed)
    Abstract [en]

    The problem of the absorption of light by a nanoscale dielectric cone is discussed. A simplified solution based on the analytical Mie theory of scattering and absorption by cylindrical objects is proposed and supported by the experimental observation of sharply localized holes in conical silicon tips after high-fluence irradiation. This study reveals that light couples with tapered objects dominantly at specific locations, where the local radius corresponds to one of the resonant radii of a cylindrical object, as predicted by Mie theory.

  • 16. Boyko, Andrey A.
    et al.
    Marchev, Georgi M.
    Petrov, Valentin
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Kolker, Dmitry B.
    Zukauskas, Andrius
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Kostyukova, Nadezhda Y.
    Intracavity-pumped, cascaded AgGaSe2 optical parametric oscillator tunable from 5.8 to 18 mu m2015In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, no 26, p. 33460-33465Article in journal (Refereed)
    Abstract [en]

    A AgGaSe2 nonlinear crystal placed in a coupled cavity is intracavity pumped by the similar to 1.85-mu m signal pulses of a 1.064-mu m pumped Rb: PPKTP doubly-resonant optical parametric oscillator (OPO) operating at a repetition rate of 100 Hz. Using two samples cut for type-I and II phase-matching, the overall idler tunability of the singly-resonant AgGeSe2 OPO covers an unprecedented spectral range from 5.8 to similar to 18 mu m in the mid-IR.

  • 17. Brizuela, Fernando
    et al.
    Carbajo, Sergio
    Sakdinawat, Anne
    Alessi, David
    Martz, Dale H.
    Electrical and Computer Engineering, Colorado State University.
    Wang, Yong
    Luther, Bradley
    Goldberg, Kenneth A.
    Mochi, Iacopo
    Attwood, David T.
    La Fontaine, Bruno
    Rocca, Jorge J.
    Menoni, Carmen S.
    Extreme ultraviolet laser-based table-top aerial image metrology of lithographic masks2010In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 18, no 14, p. 14467-14473Article in journal (Refereed)
    Abstract [en]

    We have realized the first demonstration of a table-top aerial imaging microscope capable of characterizing pattern and defect printability in extreme ultraviolet lithography masks. The microscope combines the output of a 13.2 nm wavelength, table-top, plasma-based, EUV laser with zone plate optics to mimic the imaging conditions of an EUV lithographic stepper. We have characterized the illumination of the system and performed line-edge roughness measurements on an EUVL mask. The results open a path for the development of a compact aerial imaging microscope for high-volume manufacturing.

  • 18.
    Burvall, Anna
    et al.
    National university of Ireland, Galway.
    Barrett, Harrison H.
    University of Arizona.
    Dainty, Christopher
    National University of Ireland, Galway.
    Myers, Kyle J.
    U.S. Food and Drug Administration Laboratory for the Assessment of Medical Imaging Systems.
    Singular-value decomposition for through-focus imaging systems2006In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, no 10, p. 2440-2448Article in journal (Refereed)
    Abstract [en]

    Singular-value decomposition (SVD) of a linear imaging system gives information on the null and measurement components of object and image and provides a method for object reconstruction from image data. We apply SVD to through-focus imaging systems that produce several two-dimensional images of a three-dimensional object. Analytical expressions for the singular functions are derived in the geometrical approximation for a telecentric, laterally shift-invariant system linear in intensity. The modes are evaluated numerically, and their accuracy confirmed. Similarly, the modes are derived and evaluated for a continuous image representing the limit of a large number of image planes.

  • 19.
    Burvall, Anna
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Barrett, Harrison H.
    Myers, Kyle J.
    Dainty, Christopher
    Singular-value decomposition of a tomosynthesis system2010In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 18, no 20, p. 20699-20711Article in journal (Refereed)
    Abstract [en]

    Tomosynthesis is an emerging technique with potential to replace mammography, since it gives 3D information at a relatively small increase in dose and cost. We present an analytical singular-value decomposition of a tomosynthesis system, which provides the measurement component of any given object. The method is demonstrated on an example object. The measurement component can be used as a reconstruction of the object, and can also be utilized in future observer studies of tomosynthesis image quality.

  • 20.
    Burvall, Anna
    et al.
    National University of Ireland, Galway.
    Daly, Elisabeth
    National University of Ireland, Galway.
    Chamot, Stephane R.
    Swiss Federal Polytechnic School of Lausanne.
    Dainty, Chris
    National University of Ireland, Galway.
    Linearity of the pyramid wavefront sensor2006In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 14, no 25, p. 11925-11934Article in journal (Refereed)
    Abstract [en]

    The pyramid wavefront sensor is very similar to the Fourier knife-edge test, but employs dynamic modulation to quantify the phase derivative. For circular modulation, we compare approximate geometrical optics calculations, more exact diffraction calculations, and experimental results. We show that both the sinusoidal and the approximate linear relationship between wavefront derivative and wavefront sensor response can be derived rigorously from diffraction theory. We also show that geometrical, diffraction and experimental results are very similar, and conclude that the approximate geometrical predictions can be used in place of the more complex diffraction results.

  • 21.
    Burvall, Anna
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Lundstrom, Ulf
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Takman, Per A. C.
    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.
    Phase retrieval in X-ray phase-contrast imaging suitable for tomography2011In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, no 11, p. 10359-10376Article in journal (Refereed)
    Abstract [en]

    In-line phase-contrast X-ray imaging provides images where both absorption and refraction contribute. For quantitative analysis of these images, the phase needs to be retrieved numerically. There are many phase-retrieval methods available. Those suitable for phase-contrast tomography, i.e., non-iterative phase-retrieval methods that use only one image at each projection angle, all follow the same pattern though derived in different ways. We outline this pattern and use it to compare the methods to each other, considering only phase-retrieval performance and not the additional effects of tomographic reconstruction. We also outline derivations, approximations and assumptions, and show which methods are similar or identical and how they relate to each other. A simple scheme for choosing reconstruction method is presented, and numerical phase-retrieval performed for all methods.

  • 22.
    Burvall, Anna
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Martinsson, Per
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Friberg, Ari
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Communication modes applied to axicons2004In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 12, no 3, p. 377-383Article in journal (Refereed)
    Abstract [en]

    The communication modes, which constitute a convenient method for the propagation and information analysis of optical fields, are formulated in the generalized axicon geometry. The transmitting region is the axicon’s annular aperture, and the observation domain is the optical axis containing the focal line segment. We show that in rotational symmetry one may employ the prolate spheroidal wave functions to represent the communication modes. Further, in usual circumstances the modes can be approximated by quadratic waves in the aperture domain and by sinc functions in the image domain. Both the exact communication modes and the approximate technique are confirmed numerically, with linear axicons as examples.

  • 23.
    Cai, Yangjian
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Propagation of various dark hollow beams in a turbulent atmosphere2006In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 14, no 4, p. 1353-1367Article in journal (Refereed)
    Abstract [en]

    Propagation of a dark hollow beam (DHB) of circular, elliptical or rectangular symmetry in a turbulent atmosphere is investigated. Analytical formulas for the average intensity of various DHBs propagating in a turbulent atmosphere are derived in a tensor form based on the extended Huygens-Fresnel integral. The intensity and spreading properties of the DHBs in a turbulent atmosphere are studied numerically. It is found that after a long propagation distance a dark hollow beam of circular or non-circular eventually becomes a circular Gaussian beam (without dark hollow) in a turbulent atmosphere, which is much different from its propagation properties in free space. The conversion from a DHB to a circular Gaussian beam becomes quicker and the beam spot in the far field spreads more rapidly for a larger structure constant, a shorter wavelength, a lower beam order and a smaller waist size of the initial beam.

  • 24.
    Calil Kores, Cristine
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Department of Applied Physics, School of Engineering Sciences, Roslagstullsbacken 21, 10691 Stockholm, Sweden .
    Ismail, Nur
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Geskus, Dimitri
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Dijkstra, Meindert
    Bernhardi, Edward
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Visiting scientist .
    Pollnau, Markus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Advanced Technology Institute, Department of Electrical and Electronic Engineering, University of Surrey, Guildford GU2 7XH, UK.
    Temperature dependence of the spectral characteristics of distributed-feedback resonators2018In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, no 4, p. 4892-4905Article in journal (Refereed)
    Abstract [en]

    We characterize the spectral response of a distributed-feedback resonator when subject to a thermal chirp. An Al2O3 rib waveguide with a corrugated surface Bragg grating inscribed into its SiO2 top cladding is experimentally investigated. We induce a near-to-linear temperature gradient along the resonator, leading to a similar variation of the grating period, and characterize its spectral response in terms of wavelength and linewidth of the resonance peak. Simulations are carried out, showing good agreement with the experimental results and indicating that the wavelength of the resonance peak is a result only of the total accumulated phase shift. For any chirp profile we are able to calculate the reflectivities at the resonance wavelength, and this information largely explains how the linewidth of the resonance changes. This result shows that the increase in linewidth is governed by the increase of the resonator outcoupling losses. 

  • 25. Camara, Alexandre R.
    et al.
    Pereira, Joao M. B.
    Tarasenko, Oleksandr
    Margulis, Walter
    Acreo Swedish ICT.
    Carvalho, Isabel C. S.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Optical creation and erasure of the linear electrooptical effect in silica fiber2015In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, no 14, p. 18060-18069Article in journal (Refereed)
    Abstract [en]

    We study the creation and erasure of the linear electrooptical effect in silicate fibers by optical poling. Carriers are released by exposure to green light and displaced with simultaneous application of an internal dc field. The second order nonlinear coefficient induced grows with poling bias. The field recorded (similar to 10(8) V/m) is comparable to that obtained through classical thermal poling of fibers. In the regime studied here, the second-order nonlinearity induced (similar to 0.06 pm/V) is limited by the field applied during poling (1.2 x 10(8) V/m). Optical erasure with high-power green light alone is very efficient. The dynamics of the writing and erasing process is discussed, and the two dimensional (2D) field distribution across the fiber is simulated. (C) 2015 Optical Society of America

  • 26. Camara, Alexandre
    et al.
    Tarasenko, Oleksandr
    Margulis, Walter
    KTH, School of Engineering Sciences (SCI), Applied Physics. Acreo AB, Kista, Sweden .
    Study of thermally poled fibers with a two-dimensional model2014In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 22, no 15, p. 17700-17715Article in journal (Refereed)
    Abstract [en]

    A two-dimensional (2D) numerical model is implemented to describe the movement of ions under thermal poling for the specific case of optical fibers. Three types of cations are considered (representing Na+, Li+ and H3O+) of different mobility values. A cross-sectional map of the carrier concentration is obtained as a function of time. The role of the various cations is investigated. The assumptions of the model are validated by comparing the predictions to experimental data of the time evolution of the nonlinearity induced. A variational analysis of poling parameters including temperature, poling voltage, sign of the bias potential and initial ionic concentrations is performed for a particular fiber geometry. The analysis allows identifying the impact of these parameters on the induced second-order nonlinearity in poled fibers.

  • 27. Campbell, S.
    et al.
    Thomson, R. R.
    Hand, D. P.
    Kar, A. K.
    Reid, D. T.
    Canalias, Carlota
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Frequency-doubling in femtosecond laser inscribed periodically-poled potassium titanyl phosphate waveguides2007In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 15, no 25, p. 17146-17150Article in journal (Refereed)
    Abstract [en]

    Frequency doubling has been achieved in femtosecond-laser-inscribed single-mode waveguides written in two periodically-poled potassium titanyl phosphate crystals. A conversion efficiency of 0.22 %W-1 was obtained for first-order quasi-phase matching at 980 nm and an efficiency of 0.02 %W-1 for third-order quasi-phase matching at 800 nm.

  • 28. Cen, Min
    et al.
    Chen, Jiajia
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab). South China Normal University, China.
    Moeyaert, Veronique
    Megret, Patrice
    Wuilpart, Marc
    Full monitoring for long-reach TWDM passive optical networks2016In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 24, no 14, p. 15782-15797Article in journal (Refereed)
    Abstract [en]

    This paper presents a novel and simple fiber monitoring system based on multi-wavelength transmission-reflection analysis for long-reach time and wavelength division multiplexing passive optical networks. For the first time, the full localization functionality of long-reach passive optical networks is possible with the proposed monitoring scheme, including supporting fault detection, identification, and localization in both feeder and distribution fiber segments. By measuring the transmitted and reflected/backscattered optical powers launched by an unmodulated continuous-wave optical source, the proposed solution is able to supervise the network with good spatial accuracy, a high detection speed and a low impact on data traffic. Both the theoretical analysis and experimental validation show that the proposed scheme is capable of providing an accurate fault monitoring functionality for long-reach time and wavelength division multiplexing passive optical networks.

  • 29. Cen, Min
    et al.
    Chen, Jiajia
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Moeyaert, Veronique
    Megret, Patrice
    Wuilpart, Marc
    Multi-wavelength transmission-reflection analysis for fiber monitoring2014In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 22, no 25, p. 31248-31262Article in journal (Refereed)
    Abstract [en]

    We propose and implement a novel approach based on multi-wavelength Transmission-Reflection Analysis (MW-TRA) technique for monitoring lossy events (e.g. disconnected connectors, fiber breaks and fiber bendings) along an optical fiber link. By launching un-modulated continuous-wave lights carried by different wavelengths into the fiber and measuring their transmitted and reflected/backscattered optical powers, our proposed MW-TRA scheme is able to localize any lossy event (including both reflective and non-reflective) and to quantify the corresponding insertion and return losses with high accuracy.

  • 30. Chang, Lantian
    et al.
    Dijkstra, Meindert
    Ismail, Nur
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Pollnau, Markus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    de Ridder, Rene M.
    Worhoff, Kerstin
    Subramaniam, Vinod
    Kanger, Johannes S.
    Waveguide-coupled micro-ball lens array suitable for mass fabrication2015In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, no 17, p. 22414-22423Article in journal (Refereed)
    Abstract [en]

    We demonstrate a fabrication procedure for the direct integration of micro-ball lenses on planar integrated optical channel waveguide chips with the aim to reduce the divergence of light that arises from the waveguide in both horizontal and vertical directions. Fabrication of the lenses is based on photoresist reflow which is a procedure that allows for the use of photolithography for careful alignment of the lenses with respect to the waveguides and enables mass production. We present in detail the design and fabrication procedures. Optical characterization of the fabricated micro-ball lenses demonstrates a good performance in terms of beam-size reduction and beam shape. The beam half divergence angle of 1544 nm light is reduced from 12.4 degrees to 1.85 degrees.

  • 31. Chang, Lantian
    et al.
    Weiss, Nicolas
    van Leeuwen, Ton G.
    Pollnau, Markus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    de Ridder, Rene M.
    Worhoff, Kerstin
    Subramaniam, Vinod
    Kanger, Johannes S.
    Chip based common-path optical coherence tomography system with an on-chip microlens and multi-reference suppression algorithm2016In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 24, no 12, p. 12635-12650Article in journal (Refereed)
    Abstract [en]

    We demonstrate an integrated optical probe including an on-chip microlens for a common-path swept-source optical coherence tomography system. This common-path design uses the end facet of the silicon oxynitride waveguide as the reference plane, thus eliminating the need of a space-consuming and dispersive on-chip loop reference arm, thereby obviating the need for dispersion compensation. The on-chip micro-ball lens eliminates the need of external optical elements for coupling the light between the chip and the sample. The use of this lens leads to a signal enhancement up to 37 dB compared to the chip without a lens. The light source, the common-path arm and the detector are connected by a symmetric Y junction having a wavelength independent splitting ratio (50/50) over a much larger bandwidth than can be obtained with a directional coupler. The signal-to-noise ratio of the system was measured to be 71 dB with 2.6 mW of power on a mirror sample at a distance of 0.3 mm from the waveguide end facet. Cross-sectional OCT images of a layered optical phantom sample are demonstrated with our system. A method, based on an extended Fourier-domain OCT model, for suppressing ghost images caused by additional parasitic reference planes is experimentally demonstrated.

  • 32. Chen, D. R.
    et al.
    Yang, T. J.
    Wu, J. J.
    Shen, L. F.
    Liao, K. L.
    He, Sailing
    Band-rejection fiber filter and fiber sensor based on a Bragg fiber of transversal resonant structure2008In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 16, no 21, p. 16489-16495Article in journal (Refereed)
    Abstract [en]

    We propose a novel band-rejection fiber filter based on a Bragg fiber of transversal resonant structure, which can also be used as a fiber sensor. Defect layers are introduced in the periodic high/low index structure in the cladding of the Bragg fiber. Coupling between the core mode and the defect mode results in large confinement loss for some resonant wavelengths inside the band gap of the Bragg fiber. A segment of the Bragg fiber of transversal resonant structure can be used as a band-rejection fiber filter, whose characteristics are mainly determined by the defect layer. The loss peak wavelength of the Bragg fiber is dependent on the refractive index and the thickness of the defect layer which indicates its applications of refractive index and strain sensing.

  • 33. Chen, Daru
    et al.
    Qin, Shan
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Channel-spacing-tunable multi-wavelength fiber ring laser with hybrid Raman and erbium-doped fiber gains2007In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 15, no 3, p. 930-935Article in journal (Refereed)
  • 34. Chen, Rui-Pin
    et al.
    Chew, Khian-Hooi
    Zhou, Guoquan
    Dai, Chao-Qing
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Zhejiang University, China.
    Vectorial effect of hybrid polarization states on the collapse dynamics of a structured optical field2016In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 24, no 24, p. 28143-28153Article in journal (Refereed)
    Abstract [en]

    The collapse dynamics of a structured optical field with a distribution of spatially-variant states of polarization (SoP) and a spiral phase in the field cross section is studied using the two-dimensional coupled nonlinear Schrodinger equations. The self-focusing of a structured optical field with an inhomogeneous SoP distribution can give rise to new phenomena of collapse dynamics that is completely different from a scalar field. The collapse patterns are closely related to the topological charges of the vortexas well as the polarization, the initial power, and the SoP distribution in the field cross section. A single on-axis collapse or multiple off-axis partial collapses may occur due to the self-focusing effects of linearly, elliptically and circularly polarized components located at different positions of the field cross-section. The polarization in the core of the collapsing beam is always linearly polarized. The structured collapsing beams, which are driven by the vortex, propagate along a spiral trajectory in a saturated medium.

  • 35. Chen, Tuo
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Zhejiang University, Hangzhou, China.
    Frequency-tunable circular polarization beam splitter using a graphene-dielectric sub-wavelength film2014In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 22, no 16, p. 19748-19757Article in journal (Refereed)
    Abstract [en]

    Manipulating the circular polarization of light is of great importance in chemistry and biology, as chiral molecules exhibit different physiological properties when exposed to different circularly polarized waves. Here we suggest a graphene/dielectric-stacked structure, which has both the properties of an epsilon-near-zero material and the high Hall conductivity of graphene. The proposed sub-wavelength structure demonstrates efficient manipulation of circular polarization properties of light. In a quite broad frequency range and at a large oblique incidence angle, the present magnetically active structure is transparent for one circularly polarized wave, and opaque for another. Such an effect can be further tuned by changing the magnitude of the applied magnetic field and chemical potential of graphene.

  • 36.
    Chen, Xi
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Shi, Yuechun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO. Nanjing University, China.
    Lou, Fei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Chen, Yiting
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Wosinski, Lech
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO. Zhejiang University, China.
    Photothermally tunable silicon-microring-based optical add-drop filter through integrated light absorber2014In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 22, no 21, p. 25233-25241Article in journal (Refereed)
    Abstract [en]

    An optically pumped thermo-optic (TO) silicon ring add-drop filter with fast thermal response is experimentally demonstrated. We propose that metal-insulator-metal (MIM) light absorber can be integrated into silicon TO devices, acting as a localized heat source which can be activated remotely by a pump beam. The MIM absorber design introduces less thermal capacity to the device, compared to conventional electrically-driven approaches. Experimentally, the absorber-integrated add-drop filter shows an optical response time of 13.7 mu s following the 10%-90% rule (equivalent to a exponential time constant of 5 mu s) and a wavelength shift over pump power of 60 pm/mW. The photothermally tunable add-drop filter may provide new perspectives for all-optical routing and switching in integrated Si photonic circuits.

  • 37. Chen, Xue-Wen
    et al.
    Choy, Wallace C. H.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Efficient optical modeling of spontaneous emission in a cylindrically layered nanostructure2007In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 15, no 16, p. 10356-10361Article in journal (Refereed)
  • 38. Chen, Xue-Wen
    et al.
    Choy, Wallace C. H.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Chui, P. C.
    Highly efficient fluorescence of a fluorescing nanoparticle with a silver shell2007In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 15, no 11, p. 7083-7094Article in journal (Refereed)
  • 39.
    Chen, Yiting
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Dai, Jin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Honeycomb-lattice plasmonic absorbers at NIR: anomalous high-order resonance2013In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, no 18, p. 20873-20879Article in journal (Refereed)
    Abstract [en]

    We design, fabricate and characterize a plasmonic honeycomb lattice absorber with almost perfect absorption at 1140 nm over a wide incident angle range. This absorber also possesses a narrow-band, angle-and polarization-dependent high-order resonance in the short-wavelength range, with a bandwidth of 19 nm and angle sensitivity of 3 nm per degree. The nature of this high-order absorption band is analyzed through finite-element simulations. We believe it is due to Bragg coupling of the incident light to the backward-propagating surface plasmon polariton through the periodic modulation of the structure. Such fine absorption bands can find applications in plasmonic sensors and spectrally selective thermal emitters.

  • 40.
    Chen, Yiting
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Dai, Jin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO. Zhejiang University, China .
    Metal-insulator-metal plasmonic absorbers: influence of lattice2014In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 22, no 25, p. 30807-30814Article in journal (Refereed)
    Abstract [en]

    We experimentally demonstrate three kinds of metal-insulator-metal based plasmonic absorbers consisting of arrays of gold nanodisks distributed in different lattices, including square, triangular and honeycomb lattices. It's found that resonances originated from localized surface plasmon undergo little changes with respect to different lattice distributions of the nanodisks. The interparticle coupling results in a minor bandwidth broadening of the fundamental mode. Different from square-and triangular-lattice absorbers, honeycomb-lattice absorber possesses a unique red-shifting (with respect to incident angles) narrow-band high-order mode, which originates from coupling of incident light to propagating surface plasmon polariton (SPP) waves. Similar high-order mode can also be generated in square-lattice absorber by increasing the period so that a smaller reciprocal lattice vector can be introduced to excite the SPP mode. Furthermore, we show that two types of resonances can interact and create Fano-type resonances. The simulation results agree well with the experimental results. (C) 2014 Optical Society of America

  • 41.
    Chen, Yiting
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Wang, Jing
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Chen, Xi
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Plasmonic analog of microstrip transmission line and effect of thermal annealing on its propagation loss2013In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, no 2, p. 1639-1644Article in journal (Refereed)
    Abstract [en]

    We fabricated a plasmonic analog of the microwave microstrip transmission line and measured its propagation loss before and after thermal annealing. It is found that its propagation loss at 980 nm wavelength can be reduced by more than 50%, from 0.45 to 0.20 dB/μm, after thermal annealing at 300 °C. The reduction in loss can be attributed to the improved gold surface condition and probably also to the change in the metal's inner structure. Less evident loss reduction is noticed at 1550 nm, which is owing to extremely small portion of the modal electric field located in the metal regions at this wavelength.

  • 42. Chesini, Giancarlo
    et al.
    Cordeiro, Cristiano M. B.
    de Matos, Christiano J. S.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Carvalho, Isabel C. S.
    Knight, J. C.
    All-fiber devices based on photonic crystal fibers with integrated electrodes2009In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 17, no 3, p. 1660-1665Article in journal (Refereed)
    Abstract [en]

    A special kind of microstructured optical fiber is proposed and fabricated in which, in addition to the holey region (solid core and silica-air cladding), two large holes exist for electrode insertion. Either Bi-Sn or Au-Sn alloys were selectively inserted into the large holes forming two parallel, continuous and homogeneous internal electrodes. We demonstrate the production of a monolithic device and its use to externally control some of the guidance properties (e. g. polarization) of the fiber.

  • 43.
    Chughtai, Mohsan Niaz
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Influence of polarization state, baud rate and PMD on non-linear impairments in WDM systems with mixed PM (D)QPSK and OOK channels2012In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 20, no 7, p. 8155-8160Article in journal (Refereed)
    Abstract [en]

    In this paper we numerically investigate nonlinear impairments in a WDM system with mixed PM (D)QPSK and OOK channels. First we analyze the dependence of XPM and XPolM on SOP and baud rate in absence of PMD. In this case we find that the nonlinear impairments are highly dependent on relative SOP between the PM (D)QPSK and neighbouring OOK channels. The dependence on relative SOP is more pronounced in differential detection than in coherent detection. However, with increasing values of PMD this dependence decreases, and non-linear tolerance improves

  • 44. Cui, Y. X.
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A theoretical re-examination of giant transmission of light through a metallic nano-slit surrounded with periodic grooves2009In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 17, no 16, p. 13995-14000Article in journal (Refereed)
    Abstract [en]

    We show that the slit-to-groove distance for a maximal transmission through the nano-slit surrounded with periodic grooves cannot be predicted by the theory of constructive interference between the groove-generated surface plasmon wave (SPW) and the incident wave. A clear physical explanation is given for the dependence of the transmission on the slit-to-groove distance. It is shown that the influence to the transmission comes from three parts: the groove-generated SPW, the incident wave and the nano-slit-generated SPW. The groove-generated SPW is the main factor determining the local field distribution around the nano-slit opening. The influence of the incident wave is very weak when strong SPW is generated on the input surface by many periods of deep grooves. The nano-slit-generated SPW can also be considered as a disturbance to the light distribution on the input surface.

  • 45. Dai, D. X.
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Novel ultracompact Si-nanowire-based arrayed-waveguide grating with microbends2006In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 14, no 12, p. 5260-5265Article in journal (Refereed)
  • 46. Dai, Daoxin
    et al.
    He, Sailing
    A silicon-based hybrid plasmonic waveguide with a metal cap for a nano-scale light confinement2009In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 17, no 19, p. 16646-16653Article in journal (Refereed)
    Abstract [en]

    A hybrid plasmonic waveguide with a metal cap on a silicon-on-insulator rib (or slab) is presented. There is a low-index material nano-layer between the Si layer and the metal layer. The field enhancement in the nano-layer provides a nano-scale confinement of the optical field (e. g., 50nm x 5nm) when operates at the optical wavelength lambda = 1550nm. The theoretical investigation also shows that the present hybrid plasmonic waveguide has a low loss and consequently a relatively long propagation distance (on the order of several tens of lambda).

  • 47.
    Dai, Daoxin
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Shi, Yaocheng
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. 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), Optics and Photonics, Photonics. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Thylen, Lars
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Silicon hybrid plasmonic submicron-donut resonator with pure dielectric access waveguides2011In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, no 24, p. 23671-23682Article in journal (Refereed)
    Abstract [en]

    Characteristic analyses are given for a bent silicon hybrid plasmonic waveguide, which has the ability of submicron bending (e.g., R = 500nm) even when operating at the infrared wavelength range (1.2 mu m similar to 2 mu m). A silicon hybrid plasmonic submicron-donut resonator is then presented by utilizing the sharp-bending ability of the hybrid plasmonic waveguide. In order to enable long-distance optical interconnects, a pure dielectric access waveguide is introduced for the present hybrid plasmonic submicron-donut resonator by utilizing the evanescent coupling between this pure dielectric waveguide and the submicron hybrid plasmonic resonator. Since the hybrid plasmonic waveguide has a relatively low intrinsic loss, the theoretical intrinsic Q-value is up to 2000 even when the bending radius is reduced to 800nm. By using a three-dimensional finite-difference time-domain (FDTD) method, the spectral response of hybrid plasmonic submicron-donut resonators with a bending radius of 800nm is simulated. The critical coupling of the resonance at around 1423nm is achieved by choosing a 80nm-wide gap between the access waveguide and the resonator. The corresponding loaded Q-value of the submicron-donut resonator is about 220.

  • 48.
    Dai, Daoxin
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Shi, Yaocheng
    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), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Wosinski, Lech
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Thylén, Lars
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Gain enhancement in a hybrid plasmonic nano-waveguide with a low-index or high-index gain medium2011In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, no 14, p. 12925-12936Article in journal (Refereed)
    Abstract [en]

    A theoretical investigation of a nano-scale hybrid plasmonic waveguide with a low-index as well as high-index gain medium is presented. The present hybrid plasmonic waveguide structure consists of a Si substrate, a buffer layer, a high-index dielectric rib, a low-index cladding, a low-index nano-slot, and an inverted metal rib. Due to the field enhancement in the nano-slot region, a gain enhancement is observed, i.e., the ratio partial derivative G/partial derivative g > 1, where g and G are the gains of the gain medium and the TM fundamental mode of the hybrid plasmonic waveguide, respectively. For a hybrid plasmonic waveguide with a core width of w(co) = 30nm and a slot height of h(slot) = 50nm, the intrinsic loss could be compensated when using a low-index medium with a moderate gain of 176dB/cm. When introducing the high-index gain medium for the hybrid plasmonic waveguide, a higher gain is obtained by choosing a wider core width. For the high-index gain case with h(slot) = 50nm and w(co) = 500nm, a gain of about 200dB/cm also suffices for the compensation of the intrinsic loss.

  • 49.
    Dai, Jin
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101).
    Ye, Fei
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Chen, Yiting
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101).
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101).
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101).
    Light absorber based on nano-spheres on a substrate reflector2013In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, no 6, p. 6697-6706Article in journal (Refereed)
    Abstract [en]

    We systematically study a type of plasmonic light absorber based on a monolayer of gold nano-spheres with less than 30 nm in diameters deposited on top of a continuous gold substrate. The influences of particle size, inter-particle distance, particle-substrate spacer size etc on the resonance are studied thoroughly with a 3D finite-element method. We identified that the high-absorption resonance is mainly due to gap plasmon (coupled through particle bodies) when the separation between neighboring nano-spheres is small enough, such as close to 1 nm; at larger particle separations, the resonance is dominated by particle dipoles (coupled through the host dielectric). Experimentally, an absorber was fabricated based on chemically-synthesized gold nanoparticles coated with silica shell. The absorber shows a characteristic absorption band around 810 nm with a maximum absorbance of approximately 90%, which agrees reasonably well with our numerical calculation. The fabrication technique can be easily adapted for devising efficient light absorbers of large areas.

  • 50. Dai, S.
    et al.
    Zhao, D.
    Li, Q.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO. State Key Laboratory of Modern Optical Instrumentation, Department of Optical Engineering, Zhejiang University, Hangzhou 310027, China .
    Double-sided polarization-independent plasmonic absorber at near-infrared region2013In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, no 11, p. 13125-13133Article in journal (Refereed)
    Abstract [en]

    A double-sided polarization-independent plasmonic absorber is proposed and numerically investigated. Distinct from previously studied absorbers, it could absorb light incident from both sides of the surface through an ultrathin three-layer metal-insulator-metal nanostructure. Patterned metal particles are adopted instead of metal films in this absorber. It shows a high absorbance over a wide incident-Angle range at near-infrared region. For electromagnetic waves incident from different sides of the structure, the maximum absorption locates at different wavelengths due to asymmetry. The effective medium theory demonstrates that the whole structure exhibits different impedances for both top and bottom incidences. This double-sided-Absorption characteristic could lead to potential applications in thermal emitters, sensing, etc.

123456 1 - 50 of 292
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