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  • 1. Albert, J.
    et al.
    Fokine, Michael
    Margulis, W.
    Grating formation in pure silica-core fibers2002In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 27, no 10, 809-811 p.Article in journal (Refereed)
    Abstract [en]

    Strong grating formation in pure silica-core fibers by use of 193-nm ArF-laser radiation is reported. Unsaturated refractive-index changes of Deltan similar to 0.3 X 10(-3) were observed in nontreated fiber, and changes of Deltan similar to 0.5 X 10(-3) were observed in fibers with a high hydroxyl concentration. Possible mechanisms of photosensitivity in pure silica-core fibers are discussed.

  • 2. Albert, Jacques
    et al.
    Fokine, Mikael
    KTH, Superseded Departments, Physics.
    Margulis, Walter
    KTH, Superseded Departments, Physics.
    Grating formation in pure silica-core fibers2002In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 27, no 10, 809-811 p.Article in journal (Refereed)
    Abstract [en]

    Strong grating formation in pure silica-core fibers by use of 193-nm ArF-laser radiation is reported. Unsaturated refractive-index changes of Deltan similar to 0.3 X 10(-3) were observed in nontreated fiber, and changes of Deltan similar to 0.5 X 10(-3) were observed in fibers with a high hydroxyl concentration. Possible mechanisms of photosensitivity in pure silica-core fibers are discussed.

  • 3. Alessi, D
    et al.
    Martz, Dale
    Colorado State Univ, Engn Res Ctr Extreme Ultraviolet Sci & Technol.
    Wang, Y
    Berrill, M
    Luther, B M
    Rocca, J J
    Gain-saturated 10.9 nm tabletop laser operating at 1 Hz repetition rate2010In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 35, no 3, 414-6 p.Article in journal (Refereed)
    Abstract [en]

    We report the demonstration of a gain-saturated 10.9 nm tabletop soft x-ray laser operating at 1 Hz repetition rate. Lasing occurs by collisional electron impact excitation in the 4dS01-->4pP11 transition of nickel-like Te in a line-focus plasma heated by a chirped-pulse-amplification Ti:sapphire laser. With an average power of 1muW and pulse energy up to approximately 2microJ, this laser extends the ability to conduct tabletop laser experiments to a shorter wavelength.

  • 4.
    Ansari, Nazanin
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Khartsev, Sergiy
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Grishin, Alexander
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Multicolor filter all-garnet magneto-optical photonic crystals2012In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 37, no 17, 3552-3554 p.Article in journal (Refereed)
    Abstract [en]

    We demonstrate a multicolor optical filter and isolator based on a double-cavity magneto-optical (MO) photonic crystal. Being grown as a heteroepitaxial all-garnet multilayer, it compromises a strong MO response and high optical transmittance. Low-loss, high Faraday rotation passbands as well as strong light rejection within the stop band were achieved by optimization of distance between cavities and repetition number of distributed Bragg reflectors.

  • 5. Ao, X. Y.
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Polarization beam splitters based on a two-dimensional photonic crystal of negative refraction2005In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, no 16, 2152-2154 p.Article in journal (Refereed)
  • 6. Ao, X. Y.
    et al.
    He, Sailing
    KTH, Superseded Departments, Electromagnetic Theory.
    Subwavelength focusing and imaging by a multimode optical waveguide2004In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 29, no 24, 2864-2866 p.Article in journal (Refereed)
  • 7. Ao, X. Y.
    et al.
    He, Sailing
    Three-dimensional photonic crystal of negative refraction achieved by interference lithography2004In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 29, no 21, 2542-2544 p.Article in journal (Refereed)
  • 8. Barrios, Carlos Angulo
    et al.
    Banuls, Maria Jose
    Gonzalez-Pedro, Victoria
    Gylfason, Kristinn Björgvin
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Sanchez, Benito
    Griol, Amadeu
    Maquieira, Angel
    Sohlström, Hans
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Holgado, Miquel
    Calquel, Raphael
    Label-free optical biosensing with slot-waveguides2008In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 33, no 7, 708-710 p.Article in journal (Refereed)
    Abstract [en]

    We demonstrate label-free molecule detection by using an integrated biosensor based on a Si3N4/SiO2 Slot-waveguide microring resonator. Bovine serum albumin (BSA) and anti-BSA molecular binding events on the sensor surface are monitored through the measurement of resonant wavelength shifts with varying biomolecule concentrations. The biosensor exhibited sensitivities of 1.8 and 3.2 nm/(ng/mm(2)) for the detection of anti-BSA and BSA, respectively. The estimated detection limits are 28 and 16 pg/mm(2) for anti-BSA and BSA, respectively, limited by wavelength resolution.

  • 9. Barrios, Carlos Angulo
    et al.
    Gylfason, Kristinn Björgvin
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Sanchez, Benito
    Griol, Amadeu
    Sohlström, Hans
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Holgado, Miquel
    Casquel, Raphael
    Slot-waveguide biochemical sensor2007In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 32, no 21, 3080-3082 p.Article in journal (Refereed)
    Abstract [en]

    We report an experimental demonstration of an integrated biochemical sensor based on a slot-waveguidemicroring resonator. The microresonator is fabricated on a Si3N4-SiO2 platform and operates at a wavelength of 1.3 mu m. The transmission spectrum of the sensor is measured with different ambient refractive indices ranging from n = 1. 33 to 1.42. A linear shift of the resonant wavelength with increasing ambient refractive index of 212 nm/refractive index units (RIU) is observed. The sensor detects a minimal refractive index variation of 2 X 10(-4) RIU.

  • 10. Berrill, Mark
    et al.
    Alessi, David
    Wang, Yong
    Domingue, Scott R.
    Martz, Dale H.
    Electrical and Computer Engineering Department, Colorado State University.
    Luther, Brad M.
    Liu, Yanwei
    Rocca, Jorge J.
    Improved beam characteristics of solid-target son x-ray laser amplifiers by injection seeding with high harmonic pulses2010In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 35, no 14, 2317-2319 p.Article in journal (Refereed)
    Abstract [en]

    Injection seeding of solid-target soft x-ray laser amplifiers with high harmonic pulses is shown to dramatically improve the far-field laser beam profile and reduce the beam divergence. Measurements and two-dimensional simulations for a 13.9 nm nickel-like Ag amplifier show that the amplified beam divergence depends strongly on the seed and can therefore be controlled by selecting the divergence of the seed. The near-field beam size of both the seeded and unseeded lasers is shown to be determined by the size of the gain region and the divergence of the amplified beams.

  • 11.
    Bertilson, Michael
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    von Hofsten, Olov
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Vogt, Ulrich
    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.
    Christakou, Athanasia E.
    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.
    Laboratory soft-x-ray microscope for cryotomography of biological specimens2011In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 36, no 14, 2728-2730 p.Article in journal (Refereed)
    Abstract [en]

    Soft-x-ray cryotomography allows quantitative and high-resolution three-dimensional imaging of intact unstained cells. To date, the method relies on synchrotron-radiation sources, which limits accessibility for researchers. Here we present a laboratory water-window microscope for cryotomography. It is based on a lambda = 2.48nm liquid-jet laser-plasma source, a normal-incidence multilayer condenser, a 30nm zone-plate objective, and a cryotilt sample holder. We demonstrate high-resolution imaging, as well as quantitative tomographic imaging, of frozen intact cells. The reconstructed tomogram of the intracellular local absorption coefficient shows details down to similar to 100nm.

  • 12. Boyko, Andrey A.
    et al.
    Kostyukova, Nadezhda Y.
    Marchev, Georgi M.
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Kolker, Dmitry B.
    Zukauskas, Andrius
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Petrov, Valentin
    Rb:PPKTP optical parametric oscillator with intracavity difference-frequency generation in AgGaSe22016In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 41, no 12, 2791-2794 p.Article in journal (Refereed)
    Abstract [en]

    A 1.064 mu m pumped Rb:PPKTP optical parametric oscillator (OPO) generates mid-IR radiation by intracavity mixing the resonant signal and idler waves in AgGaSe2. The similar to 6 ns pulses at similar to 7 mu m have an energy of 670 mu J at 100 Hz, equivalent to an average power of 67 mW. The overall quantum conversion efficiency from 1.064 mu m amounts to 8%, and the power conversion efficiency is 1.2%.

  • 13. Bratfalean, Radu
    et al.
    Peacock, Anna
    Broderick, Neil
    Gallo, Katia
    Optoelectronics Research Centre, University of Southampton (UK).
    Lewen, Ruth
    Harmonic generation in a two-dimensional nonlinear quasi-crystal2005In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, no 4, 424-426 p.Article in journal (Refereed)
    Abstract [en]

    Second-harmonic generation in a two-dimensional nonlinear quasi-crystal is demonstrated for the first time to our knowledge. Temperature and wavelength tuning of the crystal reveal the uniformity of the pattern while angle tuning reveals the dense nature of the crystal's Fourier spectrum. These results compare well with theoretical predictions showing the excellent uniformity of the crystal and suggest that more-complicated nonlinear holograms should be possible.

  • 14. Brewer, Courtney A.
    et al.
    Brizuela, Fernando
    Wachulak, Przemyslaw
    Martz, Dale H.
    Natl. Science Foundation Engineering Research Center for Extreme Ultraviolet Science and Technology, Colorado State University.
    Chao, Weilun
    Anderson, Erik H.
    Attwood, David T.
    Vinogradov, Alexander V.
    Artyukov, Igor A.
    Ponomareko, Alexander G.
    Kondratenko, Valeriy V.
    Marconi, Mario C.
    Rocca, Jorge J.
    Menoni, Carmen S.
    Single-shot extreme ultraviolet laser imaging of nanostructures with wavelength resolution2008In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 33, no 5, 518-520 p.Article in journal (Refereed)
    Abstract [en]

    We have demonstrated near-wavelength resolution microscopy in the extreme ultraviolet. Images of 50 nm diameter nanotubes were obtained with a single ~1 ns duration pulse from a desktop-size 46.9 nm laser. We measured the modulation transfer function of the microscope for three different numerical aperture zone plate objectives, demonstrating that 54 nm half-period structures can be resolved. The combination of near-wavelength spatial resolution and high temporal resolution opens myriad opportunities in imaging, such as the ability to directly investigate dynamics of nanoscale structures.

  • 15.
    Burvall, Anna
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Martinsson, Per
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Friberg, Ari
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Communication modes in large-aperture approximation2007In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 32, no 6, 611-613 p.Article in journal (Refereed)
    Abstract [en]

    Simplified versions of the communication modes in the Fresnel domain are derived when the system apertures are large. The approximate modes, which are in the form of spherical waves and sinc functions with a spherical curvature, give physical insight into the communication modes approach and the basic limits of free-space optical communication systems. They also show that Gabor's information theory is readily derived from the communication modes.

  • 16.
    Cai, Yangjian
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Average intensity and spreading of an elliptical Gaussian beam propagating in a turbulent atmosphere2006In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 31, no 5, 568-570 p.Article in journal (Refereed)
    Abstract [en]

    An analytical formula for the average intensity of an elliptical Gaussian beam (EGB) propagating in a turbulent atmosphere is derived. The spreading properties of an EGB in a turbulent atmosphere are studied. It is found that an EGB will eventually become a circular Gaussian beam in a turbulent atmosphere. This interesting phenomenon is quite different from the propagation of an EGB in free space. The evolution properties are closely related to the parameters of the beam and the turbulent atmosphere

  • 17.
    Cai, Yangjian
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hu, Li
    Propagation of partially coherent twisted anisotropic Gaussian Schell-model beams through an apertured astigmatic optical system2006In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 31, no 6, 685-687 p.Article in journal (Refereed)
    Abstract [en]

    By expanding the hard-aperture function into a finite sum of complex Gaussian functions, we derived an approximate analytical formula for a partially coherent twisted anisotropic Gaussian Schell-model (AGSM) beam propagating through an apertured paraxial general astigmatic (GA) optical system by use of a tenser method. The results obtained by using the approximate analytical formula are in good agreement with those obtained by using the numerical integral calculation. Our formulas avoid time-consuming numerical integration and provide a convenient and effective way for studying the propagation and transformation of a partially coherent twisted AGSM beam through an apertured paraxial GA optical system. (c) 2006 Optical Society of America.

  • 18.
    Cai, Yangjian
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wang, Fei
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lensless imaging with partially coherent light2007In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 32, no 3, 205-207 p.Article in journal (Refereed)
    Abstract [en]

    Based on the fourth-order correlation of light, lensless imaging with incoherent or partially coherent light is investigated theoretically by use of classical optical coherence theory. A novel lensless optical system for implementing imaging is proposed. The visibility and quality of the image are influenced by the coherence and transverse size of the light source. The results suggest useful imaging applications in x-ray, gamma-ray, or other wavelengths where no effective lens is available, and they have potential applications in optical metrology and holography.

  • 19.
    Cai, Yangjian
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wang, Fei
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lensless optical implementation of the coincidence fractional Fourier transform2006In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 31, no 15, 2278-2280 p.Article in journal (Refereed)
    Abstract [en]

    A lensless optical system for implementing the coincidence fractional Fourier transform (FRT) is proposed. The conditions for the lensless optical system to implement the coincidence FRT with incoherent light and entangled photon pairs are discussed. The results offer a novel scheme for FRTs and thus suggest useful applications.

  • 20. Camacho, Miguel
    et al.
    Mitchell-Thomas, Rhiannon C.
    Hibbins, Alastair P.
    Sambles, J. Roy
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Designer surface plasmon dispersion on a one-dimensional periodic slot metasurface with glide symmetry2017In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 42, no 17, 3375-3378 p.Article in journal (Refereed)
    Abstract [en]

    In this Letter, we explore the dispersion of spoof surface plasmons supported by a single-layer glide-symmetric structure. This structure consists of an infinitely long double-notched slot perforated in a metal layer. The presence of a degeneracy of the two lowest-order modes at the Brillouin zone boundary, which have non-zero group velocity is explained and experimentally demonstrated. Further, the dependence of the band structure when glide-symmetric configuration is broken is also explored.

  • 21. Canagasabey, Albert
    et al.
    Ibsen, Morten
    Gallo, Katia
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Gladyshev, Alexey V.
    Dianov, Evgeny M.
    Corbari, Costantino
    Kazansky, Peter G.
    Aperiodically poled silica fibers for bandwidth control of quasi-phase-matched second-harmonic generation2010In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 35, no 5, 724-726 p.Article in journal (Refereed)
    Abstract [en]

    Precise control of the bandwidth of quasi-phase-matched second-harmonic generation in silica fibers is realized through chirped-period poling. The bandwidth is expanded by a factor of 33 over a uniform-period poled fiber of the same interaction length.

  • 22. Chen, D.
    et al.
    Shu, C.
    He, Sailing
    Multiple fiber Bragg grating interrogation based on a spectrum-limited Fourier domain mode-locking fiber laser2008In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 33, no 13, 1395-1397 p.Article in journal (Refereed)
    Abstract [en]

    A novel fiber Bragg grating (FBG) sensing system based on a spectrum-limited Fourier domain mode-locking (SL-FDML) fiber laser is proposed. Multiple FBGs cascaded in a long fiber are utilized as both the sensors in the system and the wavelength-selected components in the SL-FDML fiber laser. Both wavelength-division multiplexing and spatial-division multiplexing techniques are demonstrated for interrogation of multiple FBGs by mapping the wavelength measurement to the time measurement and by adjusting the driving frequency of the SL-FDML fiber laser. The proposed FBG sensing system, employing techniques of the wavelength- and spatial-domain interrogation of multiple FBGs, can be used in remote and quasi-distributed multipoint sensing.

  • 23. Chen, Xingxing
    et al.
    Gong, Hanmo
    Dai, Shuowei
    Zhao, Ding
    Yang, Yuanqing
    Li, Qiang
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Near-infrared broadband absorber with film-coupled multilayer nanorods2013In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 38, no 13, 2247-2249 p.Article in journal (Refereed)
    Abstract [en]

    Turning the surfaces of noble metals (metasurfaces) into black (highly absorptive) surfaces can be potentially applied in thermophotovoltaics, sensing, tailoring thermal emissivity, etc. Here we demonstrate an extremely broadband absorber for the 900-1600 nm wavelength range with robust high absorption efficiency. The inexpensive droplet evaporation method is implemented to create patterns of nanoparticles dispersed on a gold film spaced by a thin dielectric layer. The diversity of the complicated random stacking of the chemically synthesized gold nanorods is the major factor for the broad absorption band. Such a metamaterial absorber may pave the way for cost-effective manufacture of large-area black metasurfaces.

  • 24. Chi, Kequn
    et al.
    Yang, Liu
    Liu, Zhaolang
    Gao, Pingqi
    Ye, Jichun
    He, Sailing
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP. Zhejiang University, China.
    Large-scale nanostructured low-temperature solar selective absorber2017In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 42, no 10, 1891-1894 p.Article in journal (Refereed)
    Abstract [en]

    A large-scale nanostructured low-temperature solar selective absorber is demonstrated experimentally. It consists of a silicon dioxide thin film coating on a rough refractory tantalum substrate, fabricated based simply on self-assembled, closely packed polystyrene nanospheres. Because of the strong light harvesting of the surface nanopatterns and constructive interference within the top silicon dioxide coating, our absorber has a much higher solar absorption (0.84) than its planar counterpart (0.78). Though its absorption is lower than that of commercial black paint with ultra-broad absorption, the greatly suppressed absorption/emission in the long range still enables a superior heat accumulation. The working temperature is as high as 196.3 degrees C under 7-sun solar illumination in ambient conditions-much higher than those achieved by the two comparables.

  • 25. Conforti, Matteo
    et al.
    Baronio, Fabio
    Levenius, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Gallo, Katia
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Broadband parametric processes in chi((2)) nonlinear photonic crystals2014In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 39, no 12, 3457-3460 p.Article in journal (Refereed)
    Abstract [en]

    We develop a general model, based on a (2 + 1)D unidirectional pulse propagation equation, for describing broadband noncollinear parametric interactions in 2D quadratic lattices. We apply it to the analysis of twin-beam optical parametric generation in hexagonally poled LiTaO3, gaining further insights into experimental observations.

  • 26. Cui, Y. X.
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Enhancing extraordinary transmission of light through a metallic nanoslit with a nanocavity antenna2009In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 34, no 1, 16-18 p.Article in journal (Refereed)
    Abstract [en]

    The extraordinary transmission of light through a vertical nanoslit in a metal film is enhanced by introducing a nanocavity antenna formed by a nearby metallic nanostrip over the slit opening. For a fixed wavelength, the width of the metallic nanostrip should be chosen to make the horizontal metal-insulator-metal waveguide of finite length resonant as a Fabry-Perot cavity. When such a cavity antenna is used to enhance the transmission through a nonresonant nanoslit, the slit should be opened at a position with a maximal magnetic field in the horizontal resonant cavity. It is shown that an optimized cavity antenna can enhance greatly the transmission of light through a nonresonant nanoslit (by about 20 times) or a resonant nanoslit (by 124%). Such a transmission enhancement with a nanocavity antenna is studied for the first time, and the physical mechanism is explained.

  • 27. Dai, D. X.
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Design of a polarization-insensitive arrayed waveguide grating demultiplexer based on silicon photonic wires2006In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 31, no 13, 1988-1990 p.Article in journal (Refereed)
  • 28.
    Dev Choudhury, Bikash
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Sahoo, Pankaj Kumar
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA. Indian Institute of Technology, India.
    Sanatinia, Reza
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Andler, G.
    Stockholm University.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
    Swillo, Marcin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Surface second harmonic generation from silicon pillar arrays with strong geometrical dependence2015In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 40, no 9, 2072-2075 p.Article in journal (Refereed)
    Abstract [en]

    We present experimental demonstration and analysis of enhanced surface second harmonic generation (SHG) from hexagonal arrays of silicon pillars. Three sets of Si pillar samples with truncated cone-shaped pillar arrays having periods of 500, 1000, and 2000 nm, and corresponding average diameters of 200, 585 and 1550 nm, respectively, are fabricated by colloidal lithography and plasma dry etching. We have observed strong dependence of SHG intensity on the pillar geometry. Pillar arrays with a 1000 nm period and a 585 nm average diameter give more than a one order of magnitude higher SHG signal compared to the other two samples. We theoretically verified the dependence of SHG intensity on pillar geometry by finite difference time domain simulations in terms of the surface normal E-field component. The enhanced surface SHG light can be useful for nonlinear silicon photonics, surface/interface characterization, and optical biosensing.

  • 29.
    Dong, Hui
    et al.
    Nanyang Techbological University, Singapore.
    Zhou, Junqiang
    Yan, Min
    Nanyang Techbological University, Singapore.
    Shum, Ping
    Nanyang Techbological University, Singapore.
    Ma, Lin
    Gong, Yandong
    Wu, Chongqing
    Quasi-monochromatic fiber depolarizer and its application to polarization-dependent loss measurement2006In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 31, no 7, 876-878 p.Article in journal (Refereed)
    Abstract [en]

    We theoretically derive the relationship between the degrees of polarization (DOPs) of input and output for an optical component with polarization-dependent loss (PDL) and birefringence. Based on the theoretical result, we propose a novel depolarizer for quasi-monochromatic light that can depolarize a fully polarized light with a 50 MHz linewidth to less than 0.2% in the DOR The depolarized light is then used to measure PDL in a single-mode optical fiber link. To the best of our knowledge, our new PDL measurement method is significantly faster than all known methods. Experimental results show excellent agreement with other methods.

  • 30.
    Dong, Lin
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Ye, Fei
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Chughtai, Adnan
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Photostability of lasing process from water solution of Rhodamine 6G with gold nanoparticles2012In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 37, no 1, 34-36 p.Article in journal (Refereed)
    Abstract [en]

    We report the lasing performance and photobleaching of gain material containing a water solution of Rhodamine 6G dye and gold nanoparticles (NPs). In comparison to a pure dye solution, the investigated material demonstrated both enhancement and quenching of the lasing output, depending on the relative concentration of the gold NPs. Although the presence of NPs with an optimized concentration looks preferable in terms of the lasing output enhancement, such additives deteriorate the operational resource of the gain material; i.e., the photobleaching rate speeds up.

  • 31. Eriksson, F.
    et al.
    Johansson, G. A.
    Hertz, Hans M.
    KTH, Superseded Departments, Physics.
    Gullikson, E. M.
    Kreissig, U.
    Birch, J.
    14.5% near-normal incidence reflectance of Cr/Sc x-ray multilayer mirrors for the water window2003In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 28, no 24, 2494-2496 p.Article in journal (Refereed)
    Abstract [en]

    Cr/Sc multilayer mirrors, synthesized by ion-assisted magnetron sputter deposition, are proved to have a high near-normal reflectivity of R = 14.5% at a grazing angle of 87.5degrees measured at the wavelength A = 3.11 nm, which is an improvement of more than 31% compared with previously published results. Elastic recoil detection analyses show that the mirrors contained as much as 15 at. % of N and traces of C and O. Soft x-ray reflectivity simulations reveal interface widths of sigma = 0.34 nm and an exceptionally small layer thickness drift of similar to1.6 X 10(-5) nm/multilayer period throughout the stack. Simulations show that a reflectivity of R = 25.6% is attainable if impurities and layer thickness drift can be eliminated. The abrupt interfaces are achieved with ion assistance with a low ion energy of 24 eV and high ion-to-metal flux ratios of 7.1 and 23.1 during Cr and Se sputter deposition, respectively. In addition, a near-normal incidence reflectivity of 5.5% for the C VI emission line (lambda = 3.374 nm) from a laser plasma source was verified.

  • 32. Erkintalo, Miro
    et al.
    Surakka, Minna
    Turunen, Jari
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Genty, Goery
    Coherent-mode representation of supercontinuum2012In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 37, no 2, 169-171 p.Article in journal (Refereed)
    Abstract [en]

    We apply the coherent-mode expansion to correlation functions used to describe the coherence properties of supercontinuum generated in nonlinear fibers. We show that the leading term of the expansion represents the quasi-coherent part of the field while the quasi-stationary part is embedded into the higher-order modes. The evolution of the modal expansion and the number of modes needed to describe the supercontinuum field are also discussed.

  • 33.
    Errando-Herranz, Carlos
    et al.
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Niklaus, Frank
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Stemme, Göran
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Gylfason, Kristinn B.
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Low-power microelectromechanically tunable silicon photonic ring resonator add-drop filter2015In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 40, no 15, 3556-3559 p.Article in journal (Refereed)
    Abstract [en]

    We experimentally demonstrate a microelectromechanically (MEMS) tunable photonic ring resonator add-€“drop filter, fabricated in a simple silicon-on-insulator (SOI) based process. The device uses electrostatic parallel plate actuation to perturb the evanescent field of a silicon waveguide, and achieves a 530 pm resonance wavelength tuning, i.e., more than a fourfold improvement compared to previous MEMS tunable ring resonator add-€“drop filters. Moreover, our device has a static power consumption below 100 nW, and a tuning rate of -ˆ’62 €€‰pm/V, i.e., the highest reported rate for electrostatic tuning of ring resonator add-€“drop filters.

  • 34. Fallah, H.
    et al.
    Chaudhari, M.
    Bora, T.
    Harun, S. W.
    Mohammed, W. S.
    Dutta, Joydeep
    Center of Excellence in Nanotechnology, Asian Institute of Technology, Thailand.
    Demonstration of side coupling to cladding modes through zinc oxide nanorods grown on multimode optical fiber2013In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 38, no 18, 3620-3622 p.Article in journal (Refereed)
    Abstract [en]

    A novel concept is introduced that utilizes the scattering properties of zinc oxide nanorods to control light guidance and leakage inside optical fibers coated with nanorods. The effect of the hydrothermal growth conditions of the nanorods on light scattering and coupling to optical fiber are experimentally investigated. At optimum conditions, 5% of the incident light is side coupled to the cladding modes. This coupling scheme could be used in different applications such as distributed sensors and light combing. Implementation of the nanorods on fiber provides low cost and controllable nonlithography-based solutions for free space to fiber coupling. Higher coupling efficiencies can be achieved with further optimization.

  • 35. Fanjoux, Gil
    et al.
    Sudirman, Aziza
    Beugnot, Jean-Charles
    Furfaro, Luca
    Margulis, Walter
    Sylvestre, Thibaut
    Stimulated Raman–Kerr scattering in an integrated nonlinear optofluidic fiber arrangement2014In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 39, no 18, 5407-5410 p.Article in journal (Refereed)
    Abstract [en]

    We describe a novel optofluidic fiber arrangement that allows for nonlinear effects enhancement between fluids and laser light while suppressing the generation of cavitation bubbles. By filling this optofluidic system with toluene and pumping it with a nanosecond microchip laser, we demonstrate the efficient generation of a broadband Raman frequency comb spanning from 532 to more than 1000 nm. It is further shown that the Raman frequency comb dramatically broadens toward broadband continuum light due to the stimulated Raman–Kerr scattering.

  • 36. Ferrini, R.
    et al.
    Martz, J.
    Zuppiroli, L.
    Wild, B.
    Zabelin, V.
    Dunbar, L. A.
    Houdre, R.
    Mulot, M.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Planar photonic crystals infiltrated with liquid crystals: optical characterization of molecule orientation2006In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 31, no 9, 1238-1240 p.Article in journal (Refereed)
    Abstract [en]

    Nematic liquid crystals are infiltrated into InP-based planar photonic crystals. Optical measurements as a function of temperature and polarization are used to study the average director field configuration in the nanometer-size holes: a planar equilibrium state is found.

  • 37. Feve, J. P.
    et al.
    Pacaud, O.
    Boulanger, B.
    Menaert, B.
    Hellstrom, J.
    Pasiskevicius, Valdas
    KTH, Superseded Departments, Physics.
    Laurell, Fredrik
    KTH, Superseded Departments, Physics.
    Widely and continuously tunable optical parametric oscillator based on a cylindrical periodically poled KTiOPO4 crystal2001In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 26, no 23, 1882-1884 p.Article in journal (Refereed)
    Abstract [en]

    We report on what is to our knowledge the first realization of a quasi-phase-matched optical parametric oscillator (OPO) based on a crystal with a cylindrical shape. The main reason for interest in this device is its broad, continuous tuning. In experiments with a 1064-nm pump, the signal tuning range was equal to 525 nn (1515-2040 nm), and the corresponding idler was continuously tuned over 1340 nn (2220-3560 nm). The angular tuning was 26 degrees, with only a minor variation of the OPO threshold over the entire tuning range.

  • 38.
    Fokine, Michael
    KTH, Superseded Departments, Physics.
    Growth dynamics of chemical composition gratings in flourine-doped silica optical fibers2002In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 27, 1974-1976 p.Article in journal (Refereed)
    Abstract [en]

    The refractive-index modulation of chemical composition gratings in fluorine-germanium-doped silica fibers as a function of thermal treatment during manufacturing has been studied. The final grating strength was found to depend strongly on an intermediate annealing step, with an optimum temperature near 600-700 degrees C, before development at a fixed temperature of 1000 degrees C. Low-temperature treatment, aimed at removing any remaining hydrogen from the fiber, performed at 100 degrees C for 20 h before the annealing step, also significantly increased the final refractive-index modulation.

  • 39. Fokine, Michael
    Growth dynamics of chemical composition gratings in fluorine-doped silica optical fibers2002In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 27, no 22, 1974-1976 p.Article in journal (Refereed)
    Abstract [en]

    The refractive-index modulation of chemical composition gratings in fluorine-germanium-doped silica fibers as a function of thermal treatment during manufacturing has been studied, The final grating strength was found to depend strongly on an intermediate annealing step, with an optimum temperature near 600-700degreesC before development at a fixed temperature of 1000degreesC. Low-temperature treatment, aimed at removing any remaining hydrogen from the fiber, performed at 100degreesC for 20 h before the annealing step, also sigificantly increased the final refractive-index modulation.

  • 40.
    Fokine, Michael
    KTH, Superseded Departments, Physics.
    Thermal stability of chemical composition gratings in fluorine-germanium-doped silica fibers2002In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 27, no 12, 1016-1018 p.Article in journal (Refereed)
    Abstract [en]

    A model based on diffusion of dopants in a periodic structure has been applied to describe thermal decay of chemical composition gratings in fluorine-germanium-doped silica fibers. The good agreement between previously reported values and the diffusion coefficients derived here from experiments and models in the 1000 - 1200 degreesC temperature range indicate that fluorine diffusion is the main mechanism of grating decay. Experimental results also indicate that the presence of phosphorous significantly increases the decay rate of chemical composition gratings.

  • 41. Fokine, Michael
    Thermal stability of chemical composition gratings in fluorine-germanium-doped silica fibers2002In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 27, no 12, 1016-1018 p.Article in journal (Refereed)
    Abstract [en]

    A model based on diffusion of dopants in a periodic structure has been applied to describe thermal decay of chemical composition gratings in fluorine-germanium-doped silica fibers. The good agreement between previously reported values and the diffusion coefficients derived here from experiments and models in the 1000 - 1200 degreesC temperature range indicate that fluorine diffusion is the main mechanism of grating decay. Experimental results also indicate that the presence of phosphorous significantly increases the decay rate of chemical composition gratings.

  • 42. Fokine, Michael
    Thermal stability of oxygen-modulated chemical-composition gratings in standard telecommunication fiber2004In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 29, no 11, 1185-1187 p.Article in journal (Refereed)
    Abstract [en]

    Experimental results and a discussion on the formation and decay of oxygen-modulated chemical-composition gratings in a standard telecommunication fiber are presented. Comparison between the decay experiment and the model provides a diffusion coefficient with an activation energy of 490 kJ/mol, which is in close agreement with reported values of oxygen self-diffusion in silica. The gratings have a diffusion-controlled decay behavior, with more than 50% of the reflectivity remaining after 7.5 h at a temperature of 1230degreesC. The gratings show higher thermal stability when heated in air than in an inert argon atmosphere.

  • 43. Fokine, Michael
    et al.
    Margulis, W.
    Large increase in photosensitivity through massive hydroxyl formation2000In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 25, no 5, 302-304 p.Article in journal (Refereed)
    Abstract [en]

    We report a large increase in photosensitivity of germanium-doped silicate fibers by rapid heat treatment of hydrogen-loaded fibers at 1000 degrees C before exposure of the fibers to 242-nm radiation. The increase in photosensitivity is compared with thermally induced absorption caused by introduction of massive amounts of hydroxyl species. The absorption loss was measured to be 0.02 dB/cm mol.% OH at 1.55 mu m. Strong gratings (Delta n > 1 x 10(-4)) in germanium-free phosphorous-doped fibers in the presence of 242-nm radiation have also been manufactured by this technique.

  • 44.
    Fokine, Michael
    et al.
    KTH, Superseded Departments, Physics.
    Margulis, Walter
    KTH, Superseded Departments, Physics.
    Large increase in photosensitivity through massive hydroxyl formation2000In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 25, no 5, 302-304 p.Article in journal (Refereed)
    Abstract [en]

    We report a large increase in photosensitivity of germanium-doped silicate fibers by rapid heat treatment of hydrogen-loaded fibers at 1000 degrees C before exposure of the fibers to 242-nm radiation. The increase in photosensitivity is compared with thermally induced absorption caused by introduction of massive amounts of hydroxyl species. The absorption loss was measured to be 0.02 dB/cm mol.% OH at 1.55 mu m. Strong gratings (Delta n > 1 x 10(-4)) in germanium-free phosphorous-doped fibers in the presence of 242-nm radiation have also been manufactured by this technique.

  • 45. Fokine, Michael
    et al.
    Nilsson, L. E.
    Claesson, A.
    Berlemont, D.
    Kjellberg, L.
    Krummenacher, L.
    Margulis, W.
    Integrated fiber Mach-Zehnder interferometer for electro-optic switching2002In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 27, no 18, 1643-1645 p.Article in journal (Refereed)
    Abstract [en]

    Molten alloys under high pressure were used to obtain fibers with long internal electrodes that are solid at room temperature. An integrated Mach-Zehnder interferometer was constructed from a twin-core twin-hole fiber that permitted application of an electric field preferentially to one of the cores. Good stability and a switching voltage of 1.4 kV were measured with a 1-m-long fiber device with a quadratic voltage dependence.

  • 46.
    Fokine, Mikael
    et al.
    KTH, Superseded Departments, Physics.
    Nilsson, Lars-Erik
    Claesson, Åke
    Berlemont, D
    Kjellberg, L
    Krummenacher, L
    Margulis, Walter
    KTH, Superseded Departments, Physics.
    Integrated fiber Mach-Zehnder interferometer for electro-optic switching2002In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 27, no 18, 1643-1645 p.Article in journal (Refereed)
    Abstract [en]

    Molten alloys under high pressure were used to obtain fibers with long internal electrodes that are solid at room temperature. An integrated Mach-Zehnder interferometer was constructed from a twin-core twin-hole fiber that permitted application of an electric field preferentially to one of the cores. Good stability and a switching voltage of 1.4 kV were measured with a 1-m-long fiber device with a quadratic voltage dependence.

  • 47. Folli, V.
    et al.
    Gallo, Katia
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Conti, C.
    Purely nonlinear disorder-induced localizations and their parametric amplification2013In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 38, no 24, 5276-5279 p.Article in journal (Refereed)
    Abstract [en]

    We investigate spatial localization in a quadratic nonlinear medium in the presence of randomness. By means of numerical simulations and theoretical analyses we show that, in the down conversion regime, the transverse random modulation of the nonlinear susceptibility generates localizations of the fundamental wave that grow exponentially in propagation. The localization length is optically controlled by the pump intensity that determines the amplification rate. The results also apply to cubic nonlinearities.

  • 48.
    Fragemann, Anna
    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, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Broadband nondegenerate optical parametric amplification in the mid infrared with periodically poled KTiOPO42005In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, no 17, 2296-2298 p.Article in journal (Refereed)
    Abstract [en]

    We theoretically and experimentally demonstrate that the bandwidth in a nondegenerate optical parametric amplifier can be substantially increased by noncollinear interaction in a quasi-phase-matched single-periodicity structure. Broadband amplification of signals between 1540 and 1720 nm was realized in periodically poled KTiOPO4. The achieved signal bandwidth of 6.9 THz at 1680 nm is large enough to accommodate sub-100 fs optical pulses.

  • 49.
    Friberg, Ari T.
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Visser, T. D.
    Wolf, E.
    A reciprocity inequality for Gaussian Schell-model beams and some of its consequences2000In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 25, no 6, 366-368 p.Article in journal (Refereed)
    Abstract [en]

    A reciprocity inequality is derived, involving the effective size of a planar, secondary, Gaussian Schell-model source and the effective angular spread of the beam that the source generates. The analysis is shown to imply that a fully spatially coherent source of that class (which generates the lowest-order Hermite-Gaussian laser mode) has certain minimal properties.

  • 50.
    Gallo, Katia
    et al.
    Optoelectronics Research Centre, University of Southampton.
    Assanto, Gaetano
    Spatial solitons in chi(2) planar photonic crystals2007In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 32, no 21, 3149-3151 p.Article in journal (Refereed)
    Abstract [en]

    We analyze light self-confinement induced by multiple nonlinear resonances in a two-dimensional 2 photoniccrystal. With reference to second-harmonic generation in a hexagonal lattice, we show that the systemcan not only support two-color (1+1)D solitary waves with enhanced confinement and steering capabilitiesbut also enable novel features such as wavelength-dependent soliton routing.

1234 1 - 50 of 173
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