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  • 1.
    Akram, Nadeem
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Chacinski, Marek
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Olsson, Fredrik
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Lourdudoss, Sebastian
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Berrier, Audrey
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Experimental characterization of high-speed 1.55 mu m buried heterostructure InGaAsP/InGaAlAs quantum-well lasers2009In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 26, no 2, p. 318-327Article in journal (Refereed)
    Abstract [en]

    Detailed experimental characterization is performed for 1550 nm semi-insulating regrown buried heterostructure Fabry-Perot (FP) lasers having 20 InGaAsP/InGaAlAs strain-balanced quantum wells (QWs) in the active region. Light-current-voltage performance, electrical impedance, small-signal response below and above threshold, amplified spontaneous emission spectrum below threshold and relative intensity noise spectrum are measured. Different laser parameters such as external differential quantum efficiency eta(d), background optical loss alpha(i), K-factor, D-factor, characteristic temperature T-0, differential gain dg/dn, gain-compression factor epsilon, carrier density versus current, differential carrier lifetime tau(d), optical gain spectrum below threshold, and chirp parameter alpha are extracted from these measurements. The FP lasers exhibited a high T-0 (78-86.5 degrees C) and very high-resonance frequency (23.7 GHz). The results indicate that appropriately designed lasers having a large number of InGaAsP well/InGaAlAs barrier QWs with shallow valence-band discontinuity can be useful for un-cooled high-speed direct-modulated laser applications.

  • 2. Baev, A.
    et al.
    Kimberg, Viktor
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Polyutov, Sergey
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Gelmukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Bi-directional description of amplified spontaneous emission induced by three-photon absorption2005In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 22, no 2, p. 385-393Article in journal (Refereed)
    Abstract [en]

     A semiclassical dynamic theory of the nonlinear propagation of a few interacting intense light pulses is applied to study the nonlinear counterpropagation of amplified spontaneous emission (ASE) induced by three-photon absorption of short intense laser pulses in a chromophore solution. Several important results from the modeling are reached for the ASE process developing in the regime of strong saturation. Accounting for ASE in both forward and backward directions with respect to the pump pulse results in a smaller efficiency of nonlinear conversion for the forward ASE compared with the case in which forward emission is considered alone, something that results from the partial repump of the absorbed energy to the backward ASE component; the overall efficiency is nevertheless higher than for the forward emission considered alone. The efficiency of nonlinear conversion of the pump energy to the counterpropagating ASE pulses is strongly dependent on the concentration of active molecules so that a particular combination of concentration versus cell length optimizes the conversion coefficient. Under certain specified conditions, the ASE effect is found to be oscillatory; the origin of oscillations is dynamical competition between stimulated emission and off-resonant absorption. This result can be considered one of the possible explanations of the temporal fluctuations of the forward ASE pulse [Nature 415, 767 (2002)].

  • 3.
    Baev, Alexander
    et al.
    KTH, Superseded Departments, Biotechnology.
    Gel'mukhanov, Faris
    KTH, Superseded Departments, Biotechnology.
    Rubio-Pons, Oscar
    KTH, Superseded Departments, Biotechnology.
    Cronstrand, Peter
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Upconverted lasing based on many-photon absorption: an all dynamic description2004In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 21, no 2, p. 384-396Article in journal (Refereed)
    Abstract [en]

    A theory is developed for the propagation through a nonlinear medium of strong pump and amplifiedspontaneous-emission pulses. The theory is based on a solution of the density matrix equations that aims at providing an adequate treatment of the nonlinear polarization of the material without addressing the Taylor expansion over the powers of intensity. The theory has been applied for modeling of three-photon absorption induced upconverted stimulated emission of organic molecules in solvents. Numerical results are presented for the organic chromophore 4-[N-(2-hydroxyethyl)-N-(methyl)amino phenyl]-4'-(6-hydroxyhexyl sulfonyl) stilbene dissolved in dimethyl sulfoxide. The results are in good agreement with available experimental results.

  • 4.
    Björk, Gunnar
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Romero, Jose L.
    Klimov, Andrei B.
    Sanchez-Soto, Luis L.
    Mutually unbiased bases and discrete Wigner functions2007In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 24, no 2, p. 371-378Article in journal (Refereed)
    Abstract [en]

    Mutually unbiased bases and discrete Wigner functions are closely but not uniquely related. Such a connection becomes more interesting when the Hilbert space has a dimension that is a power of a prime N=d(n), which describes a composite system of n qudits. Hence, entanglement naturally enters the picture. Although our results are general, we concentrate on the simplest nontrivial example of dimension N=8=2(3). It is shown that the number of fundamentally different Wigner functions is severely limited if one simultaneously imposes translational covariance and that the generating operators consist of rotations around two orthogonal axes, acting on the individual qubits only.

  • 5. Boudrioua, A.
    et al.
    Loulergue, J. C.
    Laurell, Fredrik
    KTH, Superseded Departments, Physics.
    Moretti, P.
    Nonlinear optical properties of (H+,He+)-implanted planar waveguides in z-cut lithium niobate: annealing effect2001In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 18, no 12, p. 1832-1840Article in journal (Refereed)
    Abstract [en]

    Reflection second-harmonic generation from the polished waveguide end face was used to investigate the nonlinear properties of LiNbO3-implanted waveguides fabricated by use of 2-MeV He+ and 1.5-Mev H+ beams. Results were compared with waveguides obtained by protonic exchange in benzoic acid, In contrast to the exchanged sample where the nonlinearity is strongly reduced, the implanted samples showed that the guiding region presents rather the same response as the substrate. The area where the optical barrier is located showed a strongly enhanced second-harmonic signal that was likely to be due to structural modifications in this area. Moreover, the investigation of the annealing effect showed strong interaction of protons with the lattice compared with that of He+ ions.

  • 6.
    Cai, Yangjian
    et al.
    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.
    Zhang, Lei
    Coherent and partially coherent dark hollow beams with rectangular symmetry and paraxial propagation properties2006In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 23, no 7, p. 1398-1407Article in journal (Refereed)
    Abstract [en]

    A theoretical model is proposed to describe coherent dark hollow beams (DHBs) with rectangular symmetry. The electric field of a coherent rectangular DHB is expressed as a superposition of a series of the electric field of a finite series of fundamental Gaussian beams. Analytical propagation formulas for a coherent rectangular DHB passing through paraxial optical systems are derived in a tensor form. Furthermore, for the more general case, we propose a theoretical model to describe a partially coherent rectangular DHB. Analytical propagation formulas for a partially coherent rectangular DHB passing through paraxial optical systems are derived. The beam propagation factor (M-2 factor) for both coherent and partially coherent rectangular DHBs are studied. Numerical examples are given by using the derived formulas. Our models and method provide an effective way to describe and treat the propagation of coherent and partially coherent rectangular DHBs.

  • 7. Cui, Y. X.
    et al.
    Hu, Jun
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Nanocavity antenna array for enhancing extraordinary optical transmission of light through a metallic nanoslit2009In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 26, no 11, p. 2131-2135Article in journal (Refereed)
    Abstract [en]

    The transmission of light through a single nanoslit milled in the metallic film is enhanced by using an array of nanocavity antennas. It is shown that transmission efficiency through a 25-nm-wide silver nanoslit can be enhanced to eta = 151 when six pairs of nanostrips are placed 50 nm away from the input surface of the silver film at wavelength lambda(0) = 1 mu m. The influences of both the nanoslit position and the slit-to-strip distance on the extraordinary transmission are investigated, and the physical mechanism is explained.

  • 8. Cui, Yanxia
    et al.
    Fung, Kin Hung
    Xu, Jun
    Yi, Jin
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Fang, Nicholas X.
    Exciting multiple plasmonic resonances by a double-layered metallic nanostructure2011In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 28, no 11, p. 2827-2832Article in journal (Refereed)
    Abstract [en]

    By placing a metallic layer of a periodic nanostrip array above a metallic layer of a periodic nanogroove array with a separation of 120nm, we obtain a triple-band thin film absorber with all its resonant wavelengths displaying absorptivity greater than 90%. Through a systematic study of the current compound structure, we find these three absorption peaks mainly depend on some simple resonances, i.e., the modes supported by the nanostrip array in the top layer, the nanogroove array in the bottom layer, and the horizontal cavity between the two layers. In addition, we show that this kind of absorber is quite robust and fairly insusceptible to the parallel shift between the two different layers. This study should contribute to the design of thin film absorbers/ emitters.

  • 9. Dai, Daoxin
    et al.
    He, Sailing
    Highly sensitive sensor based on an ultra-high-Q Mach-Zehnder interferometer-coup led microring2009In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 26, no 3, p. 511-516Article in journal (Refereed)
    Abstract [en]

    A high-Q Mach-Zehnder interferometer (MZI)-coupled microring is presented for optical sensing with high sensitivity and a large measurement range. By optimizing the length difference, between the two arms of the MZI coupler, the MZI-coupled microring with a high-Q factor and high extinction ratio is obtained. In the present example, the Q factor of the designed silicon-nanowire-based microring is as high as 1.8 x 10(5) when the silicon nanowire has a propagation loss L=2 dB/cm. Due to this high-Q factor, the sensitivity for the change Delta n of the effective refractive index is about 10(-5)-10(-6) by measuring the shift of the resonant wavelength. Because of the wavelength dependence of the coupling ratio of the MZI coupler, it is possible to have only one resonant wavelength with a high extinction ratio in a very large wavelength span [i.e., the quasi-free spectral range of the MZI-coupler microring], which offers a very large measurement range covering the refractive index change

  • 10.
    Dai, Daoxin
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Sheng, Zhen
    Numerical analysis of silicon-on-insulator ridge nanowires by using a full-vectorial finite-difference method mode solver2007In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 24, no 11, p. 2853-2859Article in journal (Refereed)
    Abstract [en]

    The characteristics of silicon-on-insulator (SOI) ridge waveguides are analyzed by using a cylindrical full-vectorial finite-difference method mode solver with a perfectly-matched layer treatment. First, the single-mode condition for an SOI ridge nanowire with different Si core thicknesses is obtained. The obtained single-mode condition is different from that for the conventional micrometrical SOI ridge waveguides with a large cross section. By adjusting the cross section (the core width and the etching depth), one can have a nonbirefringent SOI ridge nanowire. The analysis on the bending loss of S01 ridge nanowires shows that one can have a relatively small bending radius even with a shallow etching (i.e., a small ratio γ between the etching depth and the total thickness). For example, even when one chooses a small ratio γ= 0.4, one still has a low bending loss with a small bending radius of 15 μm for an SOI nanowire with a thin core h∞= 250 nm, which is very different from a conventional large SOI ridge waveguide.

  • 11. El-Kallassi, Pascale
    et al.
    Ferrini, Rolando
    Zuppiroli, Libero
    Le Thomas, Nicolas
    Houdré, Romuald
    Berrier, Audrey
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Talneau, Anne
    Optical tuning of planar photonic crystals infiltrated with organic molecules2007In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 24, no 9, p. 2165-2171Article in journal (Refereed)
    Abstract [en]

    The optical tuning of InP-based planar photonic crystals (PhCs) infiltrated with a photoresponsive liquid crystal system is presented. Photoinduced phase transitions of a liquid crystal blend doped with azobenzene molecules are used to tune the optical response of PhC cavities. This process is found to be reversible and stable. Several tuning conditions are analyzed in terms of the blend phase diagram.

  • 12. Fallah, Hoorieh
    et al.
    Harun, S. W.
    Mohammed, W. S.
    Dutta, Joydeep
    Center of Excellence in Nanotechnology, Asian Institute of Technology, Patumthani 12120, Thailand.
    Excitation of core modes through side coupling to multimode optical fiber by hydrothermal growth of ZnO nanorods for wide angle optical reception2014In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 31, no 9, p. 2232-2238Article in journal (Refereed)
    Abstract [en]

    Side coupling to core modes through zinc oxide (ZnO) nanorods grown around the fiber is demonstrated in this work. The scheme utilizes wet etching of the cladding region followed by hydrothermal growth of the nanorods. The combination of nanostructures and the optical fiber system is used to demonstrate a simple wide field of view (FOV) optical receiver. Core modes are excited by the light scattered in the region where the fiber core is exposed. The angular response of the receiver was tested using a nephlometer. Light coupling efficiency was extracted by deconvoluting the finite beam extinction from the measured power. The results were compared to a first-order analytical model in which the phase function is assumed to linearly shift with the incident angle. The trend of the experimental measurements agrees with the model. 180 degrees FOV is verified, and maximum coupling efficiency of around 2.5% for a single fiber is reported. Excitation of core modes through side coupling shows potential for the application of these devices in optical receivers and sensors.

  • 13. Ferrini, R.
    et al.
    Houdre, R.
    Benisty, H.
    Qiu, Min
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Moosburger, J.
    Radiation losses in planar photonic crystals: two-dimensional representation of hole depth and shape by an imaginary dielectric constant2003In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 20, no 3, p. 469-478Article in journal (Refereed)
    Abstract [en]

    Waveguide modes in two-dimensional (2-D) photonic crystals (PhCs) deeply etched through monomode slab waveguides, e.g., AlGaAs/GaAs, GaAs/AlOx, or InP/GaInAsP, suffer from radiation losses that are strongly affected by the air hole depth and shape. The issue of three-dimensional (3-D) out-of-plane losses is addressed analytically by means of an incoherent approximation. Assuming separability both for the dielectric map and for the electric field, this approach is valid for defects such as in-plane microcavities, PhC-based waveguides, bends and couplers. Out-of-plane scattering is translated into an effective imaginary index in the air holes, so that 3-D losses can be cast in a simple 2-D calculation. The case of cylindroconical holes is treated, and the validity of this approach is experimentally confirmed by transmission measurements through simple PhC slabs.

  • 14.
    Fokine, Michael
    KTH, Superseded Departments, Physics.
    Formation of thermally stable chemical composition gratings in optical fibers2002In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 19, no 8, p. 1759-1765Article in journal (Refereed)
    Abstract [en]

    Experimental results and a discussion of possible chemical pathways in the formation of thermally stable chemical composition gratings in optical fibers are presented. Gratings are formed through high-temperature treatment of UV-exposed hydrogen-loaded fibers. The final refractive-index modulation is ascribed to variations in fluorine concentration attained by periodically increased diffusion of fluorine. The mechanism behind this increase is the formation of mobile hydrogen fluoride from chemical reactions of fluorine and UV-induced hydroxyl, which occur with the spatial periodicity of the UV pattern. A hydroxyl-assisted increase in fluorine diffusion has been verified by time-of-flight secondary-ion mass spectroscopy. Formation of ultrastable grating by periodic variation of oxygen concentration through diffusion of molecular water is also discussed.

  • 15.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Berglind, Eilert
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Thylén, Lars
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Optical transmission and waveguiding by excitonic quantum dot lattices2006In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 23, no 11, p. 2441-2447Article in journal (Refereed)
    Abstract [en]

    Metal-dielectric-metal configurations of optical waveguides have a very high laterally packaging density at the cost of high optical loss. Photonic crystals based on refractive-index-modulation materials have been used in optics, e.g., two materials having different refractive indices form a well-defined Bragg refraction mirror. Such a waveguide has lower loss but also lower packaging density. From the outset of these two notions, we propose a photonic-crystal device based on the exciton-polariton effect in a three-dimensional array of semiconductor quantum dots (QDs) for ultradense optical planar circuit applications. Excitons are first photogenerated in the QDs by the incident electromagnetic field, the exciton-polariton effect in the QD photonic crystal then induces an extra optical dispersion in QDs. The high contrast ratio between the optical dispersions of the QDs and the background therefore creates clear photonic bandgaps. By carefully designing the QD size and the QD lattice structure, perfect electromagnetic field reflection can be obtained at a specific wavelength in the lossless case, thus providing the fundamental basis for ultradense optical waveguide applications.

  • 16.
    Gao, Shiming
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Yang, Changxi
    Two channels of entangled twin photons generated by quasi-phase-matched spontaneous parametric down-conversion in periodically poled lithium niobate crystals2008In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 25, no 5, p. 734-740Article in journal (Refereed)
    Abstract [en]

    We propose the generation of two-channel time-energy entangled twin photons based on two simultaneous first-order quasi-phase-matched (QPM) spontaneous parametric down-conversion processes in a periodically poled lithium niobate (PPLN) with a monochromatic pump. The theoretical model for the generation of the entangled photons is established, and the analytical solution is obtained in a lossless crystal with an undepleted pump assumption. The generated condition of entangled photons is achieved in terms of the QPM grating period and the pump wavelength. It is shown that two channels of entangled twin photons with different wavelengths can be created by suitably choosing the PPLN grating period once the pump wavelength is fixed, which provides the potential to introduce the wavelength division multiplexed technique into quantum information systems.

  • 17.
    Gel'mukhanov, Faris
    et al.
    KTH, Superseded Departments, Biotechnology.
    Baev, A.
    Macak, P.
    Luo, Yi
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Dynamics of two-photon absorption by molecules and solutions2002In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 19, no 5, p. 937-945Article in journal (Refereed)
    Abstract [en]

    A dynamic density-matrix based theory of two-photon absorption (TPA) of molecules and solutions is presented. The theory highlights the influence of pulse duration, dephasing, and resonant conditions on the final TPA cross section as well as that of saturation, including a hierarchy of saturation intensities. A breakdown of the conventional identification of TPA with coherent one-step TPA is predicted for the long-pulse regime in which incoherent two-step TPA can even dominate the coherent one-step TPA process. The major role of the solvent is to enhance the off-resonant contributions to TPA furnished by collisional dephasing.

  • 18. Genty, Goery
    et al.
    Surakka, Minna
    Turunen, Jari
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Complete characterization of supercontinuum coherence2011In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 28, no 9, p. 2301-2309Article in journal (Refereed)
    Abstract [en]

    Using second-order coherence theory of nonstationary light we examine in detail the coherence properties of supercontinuum radiation generated in nonlinear fibers. We show that the supercontinuum can be divided into quasi-coherent and quasi-stationary parts and that the relative contributions depend on the dynamics involved in the spectral broadening process. We establish the correspondence between the quasi-coherent part of the two-frequency correlation function of the second-order theory and the usual Dudley-Coen degree of coherence used to characterize the shot-to-shot stability of supercontinuum sources. Experimental implementation for measuring separately the quasi-coherent and quasi-stationary contributions is further addressed. Our results open the route for complete characterization of supercontinuum coherence.

  • 19.
    Guo, Shuwei
    et al.
    JORCEP, Ctr Opt & Electromagnet Res, Zhejiang Prov Key Lab Sensing Technol.
    Sun, Fei
    JORCEP, Ctr Opt & Electromagnet Res, Zhejiang Prov Key Lab Sensing Technol.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. JORCEP, Ctr Opt & Electromagnet Res, Zhejiang Prov Key Lab Sensing Technol.
    Optical surface transformation for reshaping the field intensity distribution2016In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 33, no 9, p. 1847-1851Article in journal (Refereed)
    Abstract [en]

    In this study, we focus on how to reshape the field intensity distribution on the wavefront of an incident beam and produce special optical beams (e.g., asymmetric Gaussian beams, hollow beams, and zeroth-order Bessel beams) using optical surface transformation (OST). The key design method of this paper is based on OST, which is the extension of transformation optics. Numerical simulations are given to verify the performance of the proposed devices.

  • 20.
    Holmberg, Patrik
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Thermometric study of CO2-laser heated optical fibers in excess of 1700 degrees C using fiber Bragg gratings2013In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 30, no 7, p. 1835-1842Article in journal (Refereed)
    Abstract [en]

    The thermal response of optical fibers during CO2 laser irradiation has been characterized by using thermally stable short-period fiber Bragg gratings, referred to as chemical composition gratings. CO2 laser beam profiling was performed by scanning the beam across a 1 mm long grating, providing a spatial resolution given by the fiber diameter. The thermal dynamics during square pulse irradiation has been recorded for temperatures in excess of 1700°C, with heating and cooling rates as high as 10,500°C  s−1 and 6500°C  s−1, respectively.

  • 21. Jelger, Pär
    et al.
    Engholm, M.
    Norin, L.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Degradation free operation of 980 nm laser in Yb/Ce7Al-doped silica fiber2010In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 27, no 338Article in journal (Refereed)
  • 22.
    Jelger, Pär
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Engholm, M
    Norin, L
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Degradation-resistant lasing at 980 nm in a Yb/Ce/Al-doped silica fiber2010In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 27, no 2, p. 338-342Article in journal (Refereed)
    Abstract [en]

    In this work we measure how photodarkening affects the optical efficiency for three different Yb/Al-doped silica fibers operating at 980 nm, one of which is codoped with cerium. A volume Bragg grating is used for linewidth control and added rejection of amplified spontaneous emission. Several hours of degradation-resistant operation is obtained with the Ce-codoped fiber, while for the Yb/Al doped fibers a large drop in efficiency is observed within the first hour of operation. Our results show that Yb/Ce/Al-doped fibers could be excellent candidates for high-power 980 nm fiber laser sources.

  • 23. Kabakova, Irina V.
    et al.
    Yu, Zhangwei
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Halliwell, David
    Fonjallaz, Pierre-Yves
    Tarasenko, Oleksandr
    de Sterke, C. Martijn
    Margulis, Walter
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Switching and dynamic wavelength conversion in a fiber grating cavity2012In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 29, no 1, p. 155-160Article in journal (Refereed)
    Abstract [en]

    Switching and dynamic wavelength conversion of light are demonstrated in a fiber grating cavity detuned by high-voltage electrical pulses. The cavity dynamics is studied using a heterodyne technique in which the frequency-shifted light, trapped by the cavity, mixes with the backreflected light at the incident frequency. We find that the frequency shift scales linearly with the energy of the electric driving pulses.

  • 24. Khoptyar, D.
    et al.
    Jaskorzynska, Bozena
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Experimental determination of the energy-transfer parameters for homogeneous upconversion in Er-doped silica2005In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 22, no 10, p. 2091-2098Article in journal (Refereed)
    Abstract [en]

    Applying a nonlinear spectroscopic technique, we accurately monitor the dynamics of the homogeneous upconversion (HUC) in Er-doped fibers. We provide the first experimental confirmation, to our knowledge, of the earlier theoretical predictions that, for low erbium concentrations, a decay of HUC-influenced excitation probability of Er ions can be well approximated by the formula describing the static HUC. By correlating the experimentally obtained HUC dynamics with the results of our analytical model in a wide range of Er concentrations, we accurately estimate energy-transfer parameters for Er-doped silica glass and experimentally assess the validity of the model.

  • 25. Khoptyar, D.
    et al.
    Sergeyev, S.
    Jaskorzynska, Bozena
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Homogeneous upconversion in Er-doped fibers under steady state excitation: analytical model and its Monte Carlo verification2005In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 22, no 3, p. 582-590Article in journal (Refereed)
    Abstract [en]

    We present an extension to our earlier proposed statistical model for studying migration-assisted homogeneous upconversion in erbium-doped fibers. The extension takes into account minimum proximity distance between erbium ions randomly distributed in the host material and the nonuniformity of the excitation distribution among them. We derive a transcendental equation for the population inversion and find the dependence of the upconversion rate on the population inversion and the pump power for the entire range of feasible Er concentrations. We verify the validity and accuracy of the model by means of time-resolved Monte Carlo simulations.

  • 26. Korhonen, Minna
    et al.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Turunen, Jari
    Genty, Goery
    Elementary field representation of supercontinuum2013In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 30, no 1, p. 21-26Article in journal (Refereed)
    Abstract [en]

    We describe the second-order coherence functions of supercontinuum (SC) in terms of elementary fields that can be obtained from measurable average quantities. The representation is based on the partition of the second-order correlation functions of SC into quasi-coherent and quasi-stationary contributions. Numerical simulations of statistical ensembles of SC pulses with different coherence properties are used to illustrate the elementary field model. Comparison with the SC coherent-mode expansion is presented, and we also simulate the propagation of the elementary fields in a dispersive fiber to demonstrate the benefits of the model.

  • 27. Laine, T. A.
    et al.
    Friberg, Ari T.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Self-guided waves and exact solutions of the nonlinear Helmholtz equation2000In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 17, no 5, p. 751-757Article in journal (Refereed)
    Abstract [en]

    The paraxial wave theory is known to lead to inaccurate predictions in self-focusing of optical beams. The nonlinear Helmholtz equation describes more accurately wave propagation in dispersive, spatially local, Kerr-type media. We derive rigorous bright and dark solutions to the nonlinear Helmholtz equation in a full three-dimensional form. These expressions are new and unique. The solutions are obtained with a multidimensional extension of the (paraxial) nonlinear Schrodinger equation. We also establish energy conservation laws for both nonlinear wave equations in terms of spatial currents. Our results give insight, for example, into the diffraction and breakup of tightly confined nonlinear fields.

  • 28. Laine, T. A.
    et al.
    Friberg, Ari T.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Thin-layer theory of nonlinear fields2000In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 17, no 10, p. 1711-1715Article in journal (Refereed)
    Abstract [en]

    We derive a local nonlinear thin-layer theory for electromagnetic fields that propagate in layered structures of isotropic, dispersive, and spatially local Kerr media. By use of an ansatz of plane waves together with a thin-layer approximation, the two-dimensional Kerr-Maxwell equation is rigorously solved within a very thin slab, and the characteristic matrix of the nonlinear medium is determined. The theory makes use of periodicity and allows a direct calculation of the nonlinear field throughout the structure on the basis of the transmitted field. The method is applied in the two polarizations, TE and TM, and is illustrated with a numerical example. The nonlinear thin-layer technique provides a simple and accurate analytical theory that includes multiple plane-wave incident fields and takes rigorously into account all nonlinear interactions of these waves.

  • 29. Laine, T. A.
    et al.
    Friberg, Ari T.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Variational analysis and angular bistability in layered nonlinear Kerr media with phase conjugation2000In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 17, no 6, p. 977-984Article in journal (Refereed)
    Abstract [en]

    The calculus of variations is applied to electromagnetic fields in a layered nonlinear structure supporting a guided wave. The system also includes a phase-conjugate mirror (PCM). By introducing a variational dimension and using a collection of plane waves as a trial function, we approximate the exact solution of the nonlinear Kerr-Maxwell equation. The formalism is new, and it involves the nonlinear interference of multiple plane waves. A simple analytical expression for the nonlinear field in the presence of the PCM is derived, and the fact that the scattered intensities may become bistable when the angle of incidence is varied is demonstrated. In particular, our theory predicts the angular bistability in the backscattering direction, where the effect of the guided waves is subtle. Our numerical results are also in good agreement with other theoretical approaches and with the experimental data.

  • 30.
    Laurell, Fredrik
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Arvidsson, G.
    Frequencydoubling in Ti:MgO:LiNbO3 channel waveguides1986In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540Article in journal (Refereed)
  • 31.
    Myrén, Niklas
    et al.
    KTH, Superseded Departments, Physics.
    Margulis, Walther
    Acreo.
    Fokine, Michael
    Acreo.
    Tarasenko, Oleksandr
    Acreo.
    Nilsson, Lars-Erik
    Acreo.
    Olsson, Håkan
    Acreo.
    In-fiber electrode lithography2004In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 21, no 12, p. 2085-2088Article in journal (Refereed)
    Abstract [en]

    The fabrication of meter-long continuous internal fiber electrodes is achieved through deposition of a silver film inside a twin-hole fiber. Photolithography of the electrodes with 5-μm resolution inside the fiber is demonstrated by point-by-point side exposure to 0.53-μm radiation through the unharmed acrylate coating, causing laser ablation. A proof-of-principle experiment demonstrates the creation of a phase-matched structure for frequency doubling.

  • 32. Pitois, C.
    et al.
    Hult, Anders
    KTH, Superseded Departments, Polymer Technology.
    Wiesmann, D.
    Absorption and scattering in low-loss polymer optical waveguides2001In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 18, no 7, p. 908-912Article in journal (Refereed)
    Abstract [en]

    The absolute absorption spectra of low-loss optical waveguides, together with their intrinsic and extrinsic scatterings, were measured in the near infrared. Photothermal deflection spectroscopy was used to measure the full absorption spectra of a series of fluorinated cross-linked polymers. Assignment of-CH3,-CH2-, and -OH overtones as well as of combinations of overtones were made by use of the theory of anharmonic vibrations based on a Morse potential for local modes. Details of the molecular potential are given. The total attenuation in slab waveguides made with these polymers was measured by a prism-coupling technique and compared with the absolute absorption. Losses that are due to the material itself and those that are due to the processing are quantified.

  • 33. Prawiharjo, Jerry
    et al.
    Gallo, Katia
    Optoelectronics Research Centre, University of Southampton (UK).
    Broderick, Neil
    Richardson, David
    Frequency-resolved optical gating in the 1.55 um band via cascaded chi-2 processes2005In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 22, no 9, p. 1985-1993Article in journal (Refereed)
    Abstract [en]

    We investigate ultrashort-pulse interactions based on cascaded second-harmonic generation and difference-frequency generation and propose their use for frequency-resolved optical gating (FROG) at telecom wavelengths in a waveguide configuration. We show how a chi((2))-chi((2)) FROG device could allow the efficient characterization of ultrashort pulses, with time resolutions well beyond the limits normally imposed by walk-off effects on single-step chi((2)) FROG devices.

  • 34.
    Qiu, Min
    et al.
    KTH, Superseded Departments, Electromagnetic Theory.
    He, Sailing
    KTH, Superseded Departments, Electromagnetic Theory.
    Optimal design of a two-dimensional photonic crystal of square lattice with a large complete two-dimensional bandgap2000In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 17, no 6, p. 1027-1030Article in journal (Refereed)
    Abstract [en]

    Optimal design of a two-dimensional photonic crystal with a square lattice of air holes in GaAs is considered. It is shown how a maximum complete two-dimensional band gap is obtained by optimally connecting the dielectric rods with veins. The complete two-dimensional bandgap of our optimal design reaches Delta omega = 0.0762(2 pi c/a) (a is the lattice constant).

  • 35. Sergeyev, Sergey
    et al.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Khoptyar, Dmitry
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Flavin, Donal
    Statistical model of migration-assisted upconversion in a high-concentration erbium-doped fiber amplifier2006In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 23, no 8, p. 1540-1543Article in journal (Refereed)
    Abstract [en]

    We report a new model of a high-concentration erbium-doped fiber amplifier (EDFA) accounting for the statistical nature of the migration and up-conversion processes. By fitting experimental results, we conclude that the statistical model shows better applicability for the characterization of high-concentration EDFAs than the model accounting for the homogeneous upconversion and pair-induced quenching.

  • 36.
    Shen, Jian Qi
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Double-negative atomic vapor assisted by two-photon quantum coherence2012In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 29, no 11, p. 3192-3200Article in journal (Refereed)
    Abstract [en]

    A scenario for realizing simultaneously negative permittivity and permeability of a two-photon quantum-coherent atomic vapor is suggested in order to achieve a left-handed atomic medium with a negative refractive index. One of the remarkable features of the present scheme is that it can lead to a controllable manipulation of the negative refractive index of the atomic vapor. Since the electric- and magnetic-dipole allowed transitions of atoms can be excited by visible and infrared lightwaves, the refractive index of the atomic vapor can exhibit its negative refractive index at optical and near-optical frequency bands. This may be a new scheme to fabricate a negatively refracting material based on the quantum optical approach. Such a three-dimensionally isotropic negative refractive index at visible and infrared wavelengths induced by the two-photon-resonant quantum coherence would find a potential application in fabrication of superlenses for perfect imaging and subwavelength focusing.

  • 37.
    Shen, Jianqi
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Field quantization and vacuum effects in a chiral medium2008In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 25, no 11, p. 1864-1872Article in journal (Refereed)
    Abstract [en]

    A chiral medium can create an anisotropic electromagnetic environment, which leads to anisotropic quantum-vacuum fields (and observable quantum-vacuum effects). As the noncompensation effect of a pair of counterpropagating (and counterpolarized) vacuum modes will arise in the chiral medium, the physical effects resulting from the quantum-vacuum fluctuation of left- and right-handed polarized modes will no longer be exactly canceled. This may lead to an observable quantum vacuum contribution to the Berry phases of circularly polarized modes in a time-dependent quantum system (e.g., a coiled light propagating in a noncoplanarly curved fiber). A scheme to separate the quantum-vacuum Berry phase of one polarized mode from another by using a chiral-medium fiber is suggested, and the time evolution of the vacuum zero-point energy in a coiled fiber is considered.

  • 38. Shirai, Tomohiro
    et al.
    Setala, Tero
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Temporal ghost imaging with classical non-stationary pulsed light2010In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 27, no 12, p. 2549-2555Article in journal (Refereed)
    Abstract [en]

    Temporal ghost imaging with classical pulses is described as a temporal counterpart of conventional ghost imaging with thermal light. A temporal object to be imaged is located in the test arm, while the reference arm consists of some simple temporal optical elements. It is shown by illustrative examples that, when a certain condition is satisfied, the correlation between intensity fluctuations in these two arms gives basically the squared modulus of the object, but it is generally distorted by the effect of the incident pulse. The resultant temporal image depends only on the single temporal variable in the reference arm, although the light in this arm never interacts with the object. Potential applications of this system are briefly discussed.

  • 39. Sobon, Grzegorz
    et al.
    Lindberg, Robert
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Martynkien, Tadeusz
    Sotor, Jarosław
    Shot-to-shot performance analysis of an all-fiber supercontinuum source pumped at 2000  nm2018In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 36, no 2, p. A15-A21Article in journal (Refereed)
    Abstract [en]

    In this paper, we report an all-fiber supercontinuum source pumped with ultra-short pulses at 1.9–2.0 μm, covering over an octave (1200–2400 nm). We investigated the shot-to-shot stability of the supercontinuum generated in a commercially available highly nonlinear fiber (HNLF) of different lengths, ranging from 5 to 80 cm, by employing the dispersive Fourier transform method. Our study shows that using shorter HNLFs significantly improves the shot-to-shot stability while maintaining the broad spectral coverage. The supercontinuum generated in HNLFs shorter than 10 cm is characterized by excellent stability despite the anomalous-dispersion characteristic of the fiber. The presented source is characterized by exceptional simplicity, showing readiness for outside-of-lab applications.

  • 40.
    Strömqvist, Gustav
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Canalias, Carlota
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Aschieri, Pierre
    Picozzi, Antonio
    Montes, Carlos
    Temporal coherence in mirrorless optical parametric oscillators2012In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 29, no 6, p. 1194-1202Article in journal (Refereed)
    Abstract [en]

    One of the unique features of mirrorless optical parametric oscillators based on counterpropagating three-wave interactions is the narrow spectral width of the wave generated in the backward direction. In this work, we investigate experimentally and numerically the influence that a strong phase modulation in the pump has on the spectral bandwidths of the parametric waves and on the efficiency of the nonlinear interaction. The effects of group-velocity mismatch and group-velocity dispersion are elucidated. In particular, it is shown that the substantial increase in temporal coherence of the backward-generated wave can be obtained even for pumping with a temporally incoherent pump. A configuration of a mirrorless optical parametric oscillator is proposed where this gain in spectral coherence is maximized without a penalty in conversion efficiency by employing group-velocity matching of the pump and the forward-generated parametric wave.

  • 41. Sun, F.
    et al.
    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.
    Waveguide bends by optical surface transformations and optic-null media2018In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 35, no 4, p. 944-949Article in journal (Refereed)
    Abstract [en]

    We propose what we believe is a novel method to design waveguide bends for metallic waveguides with arbitrary bending angles. The proposed method is based on a new theoretical branch from transformation optics that is referred as to optic surface transformation. Compared with waveguide bends designed by traditional transformation optics, the design process of our method can be made in a graphical way that is very simple and convenient. To realize any waveguide bend designed by the method proposed in this study, one needs only one homogeneous material, i.e., an optic-null medium (even if the bending angles are different for various cases). After some reductions, we find that the optic-null media here can be approximately realized by some anisotropic zero refractive index materials. 2D numerical simulations verify the performance of the designed waveguide bends. The design principle can be extended to the 3D case.

  • 42. Thoss, A.
    et al.
    Richardson, M.
    Korn, G.
    Faubel, M.
    Stiel, H.
    Vogt, Ulrich
    Elsaesser, T.
    Kilohertz sources of hard x rays and fast ions with femtosecond laser plasmas2003In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 20, no 1, p. 224-228Article in journal (Refereed)
    Abstract [en]

    We demonstrate a new, stable, kilohertz femtosecond laser plasma source of hard-x-ray continuum and K-alpha emission that uses a microscopic liquid jet target that is continuous and debris free. Plasmas produced by ultrashort (50-fs) intense laser pulses from a fine (10-30-mum diameter) liquid Ga jet emit bright 9.3- and 10.3-keV K-alpha and K-beta lines superimposed on a multikilovolt bremmstrahlung continuum. Kilohertz femtosecond x-ray sources will find many applications in time-resolved x-ray diffraction and microscopy studies. As high-intensity lasers become more compact and operate at increasingly high repetition-rates, they require a target configuration that is both repeatable from shot to shot and debris free. Our target provides a pristine, unperturbed filament surface at rates >100 kHz. A number of liquid metal targets are considered. We show the hard-x-ray spectrum described above. The source was generated by a 50-fs-duration, 1-kHz, 2-W, high-intensity Ti:sapphire laser. Using the same technology, we also generate forward-going sub-mega-electron-volt (sub-MeV) protons from a 10-mum liquid water target at 1-kHz repetition rates. Kilohertz sources of high-energy ions will find many applications in time-resolved particle interaction studies and will lead to efficient generation of short-lived isotopes for use in nuclear medicine and other applications. The protons were detected with CR-39 track detectors in both the forward and the backward directions up to energies of similar to500 keV. As the intensity of compact high-repetition-rate lasers sources increases, we can expect improvements in the energy, conversion efficiency, and directionality to occur. The effect of these developments is discussed. As compact, high-repetition-rate femtosecond laser technology reaches focused intensities of similar to10(19) W/cm(2), many new applications of high-repetition-rate hard-x-ray and MeV ion sources will become practical.

  • 43. Tillman, K. A.
    et al.
    Reid, D. T.
    Artigas, D.
    Hellstrom, J.
    Pasiskevicius, Valdas
    KTH, Superseded Departments, Physics.
    Laurell, Fredrik
    KTH, Superseded Departments, Physics.
    Low-threshold, high-repetition-frequency femtosecond optical parametric oscillator based on chirped-pulse frequency conversion2003In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 20, no 6, p. 1309-1316Article in journal (Refereed)
    Abstract [en]

    We report a quasi-phase-matched optical parametric oscillator that incorporates a chirped nonlinear crystal and uses prechirped pulses matched to the crystal chirp to improve the conversion efficiency and reduce the operational threshold. A 20-mm crystal of aperiodically poled KTiOPO4 is phase matched to stretched Ti:sapphire pump pulses. The Ti:sapphire laser produces 104-MHz output pulses at 850 nm that are stretched from 190 to 900 fs with an average output power of 750 mW The system has demonstrated a pump depletion of more than 80%, a signal slope efficiency of 35%, and a threshold of 14.4 mW The cavity showed tuning from 1194 to 1455 nm. over a length range of 130 mum. The approach described demonstrates the potential of using chirped-pulse-chirped-crystal quasi-phase matching in long nonlinear crystals as a method to reduce ultrafast optical parametric oscillator thresholds.

  • 44.
    Tjörnhammar, Staffan
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Jacobsson, Björn
    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.
    Thermal limitations of volume Bragg gratings used in lasers for spectral control2013In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 30, no 6, p. 1402-1409Article in journal (Refereed)
    Abstract [en]

    In this paper we present experiments and calculations of the property changes of a highly reflecting volume Bragg grating (VBG) when it is used as a laser cavity mirror. A small absorption of the reflected laser beam resulted in a laser output power roll-off, increased coupling through the VBG, and a change of the spectrum from a single to a double peak at high power. The simulations revealed that an inhomogeneous temperature distribution deformed the grating such that the diffraction efficiency was reduced and the light penetrated deeper into the VBG, which accelerated the deteriorating effects. We extrapolated the power limit found in our investigations for various beam radii and absorption coefficients.

  • 45.
    Tjörnhammar, Staffan
    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.
    Numerical modeling and determination of limiting powers for volume Bragg gratings used in lasers for spectral control2013In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 30, no 8, p. 2326-2332Article in journal (Refereed)
    Abstract [en]

    In this paper we present a model to investigate the thermal limitations of volume Bragg gratings (VBGs) used in lasers for spectral control. Also presented are the limiting optical powers, to which intracavity VBGs of different length could be subjected, before the laser operation rapidly deteriorates. The results revealed that the power limit of a VBG-locked laser is highly dependent on the length of the employed VBG. Furthermore, the power limit expressed in incident power related linearly to the radius of the laser beam irradiating the VBG.

  • 46. Torres-Company, Victor
    et al.
    Lajunen, Hanna
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Coherence theory of noise in ultrashort-pulse trains2007In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 24, no 7, p. 1441-1450Article in journal (Refereed)
    Abstract [en]

    We study the influence of noise in ultrashort-pulse trains in terms of the concepts of optical coherence theory. Specifically, we consider the effects of temporal partial coherence and the timing jitter, including their possible statistical dependence. Analytical expressions for the optical power spectrum, average intensity, mutual coherence function, and the cross-spectral density function of different partially coherent pulse trains affected by stationary noise are given. We show that the new frequencies appearing due to the presence of noise are always fully uncorrelated, unless they are separated by an integral multiple of the repetition rate of the pulses in the train. We also find that spikes appear in the optical power spectrum when the noise and timing jitter are correlated.

  • 47. Wachulak, P.
    et al.
    Grisham, M.
    Heinbuch, S.
    Martz, Dale
    Department of Electrical and Computer Engineering, Colarado State University.
    Rockward, W.
    Hill, D.
    Rocca, J. J.
    Menoni, C. S.
    Anderson, E.
    Marconi, M.
    Interferometric lithography with an amplitude division interferometer and a desktop extreme ultraviolet laser2008In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 25, no 7, p. B104-B107Article in journal (Refereed)
    Abstract [en]

    We demonstrate a compact interferometric lithography nanopatterning tool based on an amplitude division interferometer (ADI) and a 46.9 nm wavelength desktop size capillary discharge laser. The system is designed to print arrays of lines, holes, and dots with sizes below 100 nm on high resolution photoresists for the fabrication of arrays of nanostructures with physical and biological applications. The future combination of this ADI with high repetition rate tabletop lasers operating at shorter wavelengths should allow the printing of arrays of sub-10 nm size features with a tabletop setup.

  • 48. Wang, B.
    et al.
    Shen, L. F.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Superlens formed by a one-dimensional dielectric photonic crystal2008In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 25, no 3, p. 391-395Article in journal (Refereed)
    Abstract [en]

    A simple superlens formed by a one-dimensional dielectric photonic crystal is introduced. Off-axis subwave-length focusing is achieved and studied with the equifrequency contour analysis and finite-difference time-domain simulation. Besides its advantage of simplicity, the present superlens can give a spot size much smaller than that achieved by a slab of some high-dimensional photonic crystal of negative refraction. The properties of an on-axis image achieved by the combination of two slabs of the one-dimensional photonic crystal are also studied.

  • 49. Wang, Chuan-Kui
    et al.
    Liu, Ji-Cai
    Zhao, Ke
    Sun, Yu-Ping
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Breakdown of optical power limiting and dynamical two-photon absorption for femtosecond laser pulses in molecular medium2007In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 24, no 9, p. 2436-2442Article in journal (Refereed)
    Abstract [en]

    We solve numerically the Maxwell-Bloch equations using an iterative predictor-corrector finite-difference time-domain technique to study the propagation of femtosecond laser pulses in a strong two-photon absorption (TPA) organic molecular medium [4,4'-bis(dimethylamino) stilbene]. The hybrid density functional theory is used to calculate electronic structures of the compound. The molecular system is described by a three-level model in an optical regime and has demonstrated a good optical power limiting behavior in a certain intensity region. Thresholds for the breakdown of optical power limiting are observed that are dependent on the input pulse width and, slightly, the propagation distance. The dynamical two-photon absorption cross section is obtained, which is almost a linearly increasing function of the pulse width in the femtosecond time domain. The propagation distance also has an obvious influence on the measurement of the TPA cross section, and non-monotonic dependence of the TPA cross section on propagation distance is observed. The input pulse width and the thickness of the molecular samples thus should be taken into account when the TPA cross section is measured.

  • 50.
    Wang, Zhechao
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Dai, Daoxin
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Ultrasmall Si-nanowire-based polarization rotator2008In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 25, no 5, p. 747-753Article in journal (Refereed)
    Abstract [en]

    A polarization rotator based on asymmetrical Si nanowires is presented and optimized for high polarization rotation efficiency (almost 100%). The present polarization rotator has a very small conversion length (similar to 10 mu m) and consequently becomes very compact. The analysis of the wavelength dependence shows the present polarization rotator has a broad bandwidth (similar to 120 nm) for high conversion efficiency (> 97%). The tolerance to various fabrication errors is also numerically studied. To compensate the fabrication error, a post-compensation method is introduced by modifying the refractive index of the up-cladding. (c) 2008 Optical Society of America.

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