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  • 1.
    Abd Alrahman, Chadi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Khodabakhsh, Amir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Qu, Zhechao
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Cavity-enhanced optical frequency comb spectroscopy of high-temperature H2O in a flame2014In: Optics Express, E-ISSN 1094-4087, Vol. 22, no 11, p. 13889-13895Article in journal (Refereed)
    Abstract [en]

    We demonstrate near-infrared cavity-enhanced optical frequency comb spectroscopy of water in a premixed methane/air flat flame. The detection system is based on an Er:fiber femtosecond laser, a high finesse optical cavity containing the flame, and a fast-scanning Fourier transform spectrometer (FTS). High absorption sensitivity is obtained by the combination of a high-bandwidth two-point comb-cavity lock and auto-balanced detection in the FTS. The system allows recording high-temperature water absorption spectra with a resolution of 1 GHz and a bandwidth of 50 nm in an acquisition time of 0.4 s, with absorption sensitivity of 4.2 x 10 (9) cm(-1) Hz(-1/2) per spectral element.

  • 2.
    Ako, Thomas
    et al.
    Laboratory of Photonic and Microwave Engineering, School of Information and Communication Technology, Royal Insitute of Technology, Electrum 229, Kista, Sweden.
    Yan, Min
    Laboratory of Photonic and Microwave Engineering, School of Information and Communication Technology, Royal Insitute of Technology, Electrum 229, Kista, Sweden.
    Qiu, Min
    Laboratory of Photonic and Microwave Engineering, School of Information and Communication Technology, Royal Insitute of Technology, Electrum 229, Kista, Sweden.
    Design of invisibility cloaks with an open tunnel2010In: Optics Express, E-ISSN 1094-4087, Vol. 18, no 26, p. 27060-27066Article in journal (Refereed)
    Abstract [en]

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

  • 3. Amotchkina, Tatiana
    et al.
    Trubetskov, Michael K.
    Pervak, Yurij
    Veisz, Laszlo
    Max-Planck-Institut für Quantenoptik, D-85748 Garching, Germany.
    Pervak, Vladimir
    Stress compensation with antireflection coatings for ultrafast laser applications: from theory to practice2014In: Optics Express, E-ISSN 1094-4087, Vol. 22, no 24, p. 30387-30393Article in journal (Refereed)
    Abstract [en]

    Each complicated coating, in particular, a dispersive mirror consists of dozens of layers. Thin films layers have mechanical stresses. After summing up stresses from all layers, the resulting stress is high enough to bend even a relatively thick substrate. To avoid this effect we suggest depositing an antireflection coating (AR) at the back-side of the substrate which together with suppression of unwanted reflections from the back side will also compensate this stress. We demonstrate unique, extremely thick and sophisticated AR coating consisting of 71 layers with the total physical thickness of 7.5 µm. This AR coating completely compensates stress from the dispersive mirror coated on the front side and minimizes unwanted reflections.

  • 4. Centeno, R.
    et al.
    Mandon, J.
    Cristescu, S. M.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Harren, F. J. M.
    External cavity diode laser-based detection of trace gases with NICE-OHMS using current modulation2015In: Optics Express, E-ISSN 1094-4087, Vol. 23, no 5, p. 6277-6282Article in journal (Refereed)
    Abstract [en]

    We combine an external cavity diode laser with noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) using current modulation. With a finesse of 1600, we demonstrate noise equivalent absorption sensitivities of 4.1 x 10(-10) cm(-1) Hz(-1/2), resulting in sub-ppbv detection limits for Doppler-broadened transitions of CH4 at 6132.3 cm(-1), C2H2 at 6578.5 cm(-1) and HCN at 6541.7 cm(-1). The system is used for hydrogen cyanide detection from sweet almonds.

  • 5.
    Cheddad, Abbas
    et al.
    Umeå University, Faculty of Medicine, Umeå Centre for Molecular Medicine (UCMM).
    Nord, Christoffer
    Umeå University, Faculty of Medicine, Umeå Centre for Molecular Medicine (UCMM).
    Hörnblad, Andreas
    Umeå University, Faculty of Medicine, Umeå Centre for Molecular Medicine (UCMM).
    Prunskaite-Hyyryläinen, Renata
    Oulu Center for Cell-Matrix Research, Biocenter Oulu, Laboratory of Developmental Biology and Department of Medical Biochemistry and Molecular Biology, Institute of Biomedicine, University of Oulu, Finland.
    Eriksson, Maria
    Umeå University, Faculty of Medicine, Umeå Centre for Molecular Medicine (UCMM).
    Georgsson, Fredrik
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Vainio, Seppo
    Oulu Center for Cell-Matrix Research, Biocenter Oulu, Laboratory of Developmental Biology and Department of Medical Biochemistry and Molecular Biology, Institute of Biomedicine, University of Oulu, Finland.
    Ahlgren, Ulf
    Umeå University, Faculty of Medicine, Umeå Centre for Molecular Medicine (UCMM).
    Improving signal detection in emission optical projection tomography via single source multi-exposure image fusion2013In: Optics Express, E-ISSN 1094-4087, Vol. 21, no 14, p. 16584-16604Article in journal (Refereed)
    Abstract [en]

    We demonstrate a technique to improve structural data obtained from Optical Projection Tomography (OPT) using Image Fusion (IF) and contrast normalization. This enables the visualization of molecular expression patterns in biological specimens with highly variable contrast values. In the approach, termed IF-OPT, different exposures are fused by assigning weighted contrasts to each. When applied to projection images from mouse organs and digital phantoms our results demonstrate the capability of IF-OPT to reveal high and low signal intensity details in challenging specimens. We further provide measurements to highlight the benefits of the new algorithm in comparison to other similar methods.

  • 6. Chen, Xi
    et al.
    Shi, Yuechun
    Lou, Fei
    Chen, Yiting
    Yan, Min
    Optics and Photonics, School of Information and CommunicationTechnology, KTH Royal Institute of Technology, Electrum 229, Kista, Sweden.
    Wosinski, Lech
    Qiu, Min
    Photothermally tunable silicon-microring-based optical add-drop filter through integrated light absorber2014In: Optics Express, E-ISSN 1094-4087, Vol. 22, no 21, p. 25233-25241Article in journal (Refereed)
    Abstract [en]

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

  • 7.
    Chen, Yiting
    et al.
    Optics and Photonics, School of Information and Communication Technology Royal Institute of Technology (KTH), Kista, Sweden.
    Dai, Jin
    Optics and Photonics, School of Information and Communication Technology Royal Institute of Technology (KTH), Kista, Sweden.
    Yan, Min
    Optics and Photonics, School of Information and Communication Technology Royal Institute of Technology (KTH), Kista, Sweden.
    Qiu, Min
    Optics and Photonics, School of Information and Communication Technology Royal Institute of Technology (KTH), Kista, Sweden; State Key Laboratory of Modern Optical Instrumentation and Institute of Advanced Nanophotonics, Department of Optical Engineering, Zhejiang University, Hangzhou, China.
    Honeycomb-lattice plasmonic absorbers at NIR: anomalous high-order resonance2013In: Optics Express, E-ISSN 1094-4087, Vol. 21, no 18, p. 20873-20879Article in journal (Refereed)
    Abstract [en]

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

  • 8.
    Chen, Yiting
    et al.
    Optics and Photonics, School of Information and Communication Technology Royal Institute of Technology (KTH), Kista, Sweden.
    Dai, Jin
    Optics and Photonics, School of Information and Communication Technology Royal Institute of Technology (KTH), Kista, Sweden.
    Yan, Min
    Optics and Photonics, School of Information and Communication Technology Royal Institute of Technology (KTH), Kista, Sweden.
    Qiu, Min
    Optics and Photonics, School of Information and Communication Technology Royal Institute of Technology (KTH), Kista, Sweden; 2 State Key Laboratory of Modern Optical Instrumentation and Institute of Advanced Nanophotonics, Department of Optical Engineering, Zhejiang University, Hangzhou, China.
    Metal-insulator-metal plasmonic absorbers: influence of lattice2014In: Optics Express, E-ISSN 1094-4087, Vol. 22, no 25, p. 30807-30814Article in journal (Refereed)
    Abstract [en]

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

  • 9.
    Chen, Yiting
    et al.
    Optics and Photonics, School of Information and Communication Technology Royal Institute of Technology (KTH), Kista, Sweden.
    Wang, Jing
    Optics and Photonics, School of Information and Communication Technology Royal Institute of Technology (KTH), Kista, Sweden.
    Chen, Xi
    Optics and Photonics, School of Information and Communication Technology Royal Institute of Technology (KTH), Kista, Sweden.
    Yan, Min
    Optics and Photonics, School of Information and Communication Technology Royal Institute of Technology (KTH), Kista, Sweden.
    Qiu, Min
    Optics and Photonics, School of Information and Communication Technology Royal Institute of Technology (KTH), Kista, Sweden; State Key Laboratory of Modern Optical Instrumentation and Institute of Advanced Nanophotonics, Department of Optical Engineering, Zhejiang University, Hangzhou, China.
    Plasmonic analog of microstrip transmission line and effect of thermal annealing on its propagation loss2013In: Optics Express, E-ISSN 1094-4087, Vol. 21, no 2, p. 1639-1644Article in journal (Refereed)
    Abstract [en]

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

  • 10.
    Dai, Jin
    et al.
    Optics and Photonics, School of Information and Communication Technology, KTH - Royal Institute of Technology, Kista, Sweden.
    Ye, Fei
    Functional Materials, School of Information and Communication Technology, KTH - Royal Institute of Technology, Kista, Sweden.
    Chen, Yiting
    Optics and Photonics, School of Information and Communication Technology, KTH - Royal Institute of Technology, Kista, Sweden.
    Muhammed, Mamoun
    Functional Materials, School of Information and Communication Technology, KTH - Royal Institute of Technology, Kista, Sweden.
    Qiu, Min
    Optics and Photonics, School of Information and Communication Technology, KTH - Royal Institute of Technology, Kista, Sweden.
    Yan, Min
    Optics and Photonics, School of Information and Communication Technology, KTH - Royal Institute of Technology, Kista, Sweden.
    Light absorber based on nano-spheres on a substrate reflector2013In: Optics Express, E-ISSN 1094-4087, Vol. 21, no 6, p. 6697-6706Article in journal (Refereed)
    Abstract [en]

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

  • 11.
    de Andres Gonzalez, Aitor
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Jolly, Spencer W.
    Université libre de Bruxelles, Brussels, Belgium.
    Fischer, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Muschet, Alexander A.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Schnur, Fritz
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Veisz, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Spatio-spectral couplings in optical parametric amplifiers2023In: Optics Express, E-ISSN 1094-4087, Vol. 31, no 8, p. 12036-12048Article in journal (Refereed)
    Abstract [en]

    Optical parametric amplification (OPA) is a powerful tool for the generation of ultrashort light pulses. However, under certain circumstances, it develops spatio-spectral couplings, color dependent aberrations that degrade the pulse properties. In this work, we present a spatio-spectral coupling generated by a non-collimated pump beam and resulting in the change of direction of the amplified signal with respect to the input seed. We experimentally characterize the effect, introduce a theoretical model to explain it as well as reproduce it through numerical simulations. It affects high-gain non-collinear OPA configurations and becomes especially relevant in sequential optical parametric synthesizers. In collinear configuration, however, beyond the direction change, also angular and spatial chirp is produced. We obtain with a synthesizer about 40% decrease in peak intensity in the experiments and local elongation of the pulse duration by more than 25% within the spatial full width at half maximum at the focus. Finally, we present strategies to correct or mitigate the coupling and demonstrate them in two different systems. Our work is important for the development of OPA-based systems as well as few-cycle sequential synthesizers.

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  • 12.
    Dong, H.
    et al.
    Network Technology Research Centre, Nanyang Technological University, Singapore.
    Shum, P.
    Network Technology Research Centre, Nanyang Technological University, Singapore.
    Yan, M.
    Network Technology Research Centre, Nanyang Technological University, Singapore.
    Zhou, J. Q.
    Network Technology Research Centre, Nanyang Technological University, Singapore.
    Ning, G. X.
    Network Technology Research Centre, Nanyang Technological University, Singapore.
    Gong, Y. D.
    Institute for InfoComm Research, Singapore.
    Wu, C. Q.
    School of Science, Beijing Jiaotong University, China.
    Generalized Mueller matrix method for polarization mode dispersion measurement in a system with polarization-dependent loss or gain2006In: Optics Express, E-ISSN 1094-4087, Vol. 14, no 12, p. 5067-5072Article in journal (Refereed)
    Abstract [en]

    A generalized Mueller matrix method (GMMM) is proposed to measure the polarization mode dispersion (PMD) in an optical fiber system with polarization-dependent loss or gain (PDL/G). This algorithm is based on the polar decomposition of a 4×4 matrix which corresponds to a Lorentz transformation. Compared to the generalized Poincaré sphere method, the GMMM can measure PMD accurately with a relatively larger frequency step, and the obtained PMD data has very low noise level.

  • 13. Dong, Hui
    et al.
    Shum, Ping
    Yan, Min
    Network Technology Research Centre, EEE School , Nanyang Technological University, Singapore.
    Ning, Guoxiang
    Gong, Yandong
    Wu, Chongqing
    Generalized frequency dependence of output Stokes parameters in an optical fiber system with PMD and PDL/PDG2005In: Optics Express, E-ISSN 1094-4087, Vol. 13, no 22, p. 8875-8881Article in journal (Refereed)
    Abstract [en]

    Dependence of output optical power, Stokes vector and degree of polarization on optical frequency is presented for an optical fiber system with both polarization mode dispersion and polarization-dependent loss or gain. The newly formulated equations are generalized for input light with arbitrary degree of polarization. The spectral resolved measurements of polarization mode dispersion using partially polarized light agree well with our theory.

  • 14.
    Fischer, Peter
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Muschet, Alexander
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lang, Tino
    Salh, Roushdey
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Veisz, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck-Institut für Quantenoptik, D-85748 Garching, Germany.
    Saturation control of an optical parametric chirped-pulse amplifier2021In: Optics Express, E-ISSN 1094-4087, Vol. 29, p. 4210-4218Article in journal (Refereed)
    Abstract [en]

    Optical parametric chirped-pulse amplification (OPCPA) is a light amplification technique that provides the combination of broad spectral gain bandwidth and large energy, directly supporting few-cycle pulses with multi-terawatt (TW) peak powers. Saturation in an OPCPA increases the stability and conversion efficiency of the system. However, distinct spectral components experience different gain and do not saturate under the same conditions, which reduces performance. Here, we describe a simple and robust approach to control the saturation for all spectral components. The demonstrated optimal saturation increases the overall gain, conversion efficiency and spectral bandwidth. We experimentally obtain an improvement of the pulse energy by more than 18%. This technique is easily implemented in any existing OPCPA system with a pulse shaper to maximize its output.

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  • 15.
    Foltynowicz, Aleksandra
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ma, Weiguang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Characterization of fiber-laser-based sub-Doppler NICE-OHMS for quantitative trace gas detection2008In: Optics Express, E-ISSN 1094-4087, Vol. 16, no 19, p. 14689-14702Article in journal (Refereed)
    Abstract [en]

    The potential of fiber-laser-based sub-Doppler noise-immune cavity-enhanced optical heterodyne molecular spectrometry for trace gas detection is scrutinized. The non-linear dependence of the on-resonance sub-Doppler dispersion signal on the intracavity pressure and power is investigated and the optimum conditions with respect to these are determined. The linearity of the signal strength with concentration is demonstrated and the dynamic range of the technique is discussed. Measurements were performed on C2H2 at 1531 nm up to degrees of saturation of 100. The minimum detectable sub-Doppler optical phase shift was 5 x 10-11 cm-1 Hz-1/2, corresponding to a partial pressure of C2H2 of 1 x 10-12 atm for an intracavity pressure of 20 mTorr, and a concentration of 10 ppb at 400 mTorr.

  • 16.
    Foltynowicz, Aleksandra
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wang, Junyang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ehlers, Patrick
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Distributed-feedback-laser-based NICE-OHMS
in the pressure-broadened regime2010In: Optics Express, E-ISSN 1094-4087, Vol. 18, no 18, p. 18580-18591Article in journal (Refereed)
    Abstract [en]

    A compact noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) system based on a narrow linewidth distributed-feedback laser and fiber-coupled acousto-optic and electro-optic modulators has been developed. Measurements of absorption and dispersion signals have been performed at pressures up to 1/3 atmosphere on weak acetylene transitions at 1551 nm. Multiline fitting routines were implemented to obtain transition parameters, i.e., center frequencies, linestrengths, and pressure broadening coefficients. The signal strength was shown to be linear with pressure and concentration, and independent of detection phase. The minimum detectable on-resonance absorption with a cavity with a finesse of 460 was 2 × 10−10 cm−1 for 1 minute of integration time.

  • 17.
    Ghorbani, Ramin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    ICL-based TDLAS sensor for real-time breath gas analysis of carbon monoxide isotopes2017In: Optics Express, E-ISSN 1094-4087, Vol. 25, no 11, p. 12743-12752Article in journal (Refereed)
    Abstract [en]

    We present a compact sensor for carbon monoxide (CO) in air and exhaled breath based on a room temperature interband cascade laser (ICL) operating at 4.69 µm, a low-volume circular multipass cell and wavelength modulation absorption spectroscopy. A fringe-limited (1σ) sensitivity of 6.5 × 10−8 cm−1Hz-1/2 and a detection limit of 9 ± 5 ppbv at 0.07 s acquisition time are achieved, which constitutes a 25-fold improvement compared to direct absorption spectroscopy. Integration over 10 s increases the precision to 0.6 ppbv. The setup also allows measuring the stable isotope 13CO in breath. We demonstrate quantification of indoor air CO and real-time detection of CO expirograms from healthy non-smokers and a healthy smoker before and after smoking. Isotope ratio analysis indicates depletion of 13CO in breath compared to natural abundance.

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  • 18.
    Gustafsson Coppel, Ludovic
    et al.
    Faculty of Computer Science and Media Technology, Gjøvik University College, Norway.
    Johansson, Niklas
    Department of Natural Sciences, Mid Sweden University, Örnsköldsvik, Sweden.
    Neuman, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics. Department of Natural Sciences, Mid Sweden University, Örnsköldsvik, Sweden.
    Angular dependence of fluorescence from turbid media2015In: Optics Express, E-ISSN 1094-4087, Vol. 23, no 15, p. 19552-19564Article in journal (Refereed)
    Abstract [en]

    We perform Monte Carlo light scattering simulations to study the angular distribution of the fluorescence emission from turbid media and compare the results to measured angular distributions from fluorescing white paper samples. The angular distribution of fluorescence emission is significantly depending on the concentration of fluorophores. The simulations show also a dependence on the angle of incidence that is however not as evident in the measurements. A detailed analysis of the factors affecting this angular distribution indicates that it is strongly correlated to the mean depth of the fluorescence process. The findings can find applications in fluorescence spectroscopy and are of particular interest when optimizing the impact of fluorescence on e.g.the appearance of paper as the measured values are angle dependent.

  • 19.
    Hassan, Emadeldeen
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Hannover Centre for Optical Technologies, Institute for Transport and Automation Technology (Faculty of Mechanical Engineering), and Cluster of Excellence PhoenixD, Leibniz University Hannover, Hannover, Germany; Department of Electronics and Electrical Communications, Menoufia University, Menouf, Egypt.
    Calà Lesina, Antonio
    Hannover Centre for Optical Technologies, Institute for Transport and Automation Technology (Faculty of Mechanical Engineering), and Cluster of Excellence PhoenixD, Leibniz University Hannover, 30167 Hannover, Germany.
    Topology optimization of dispersive plasmonic nanostructures in the time-domain2022In: Optics Express, E-ISSN 1094-4087, Vol. 30, no 11, p. 19557-19572Article in journal (Refereed)
    Abstract [en]

    Topology optimization techniques have been applied in integrated optics and nanophotonics for the inverse design of devices with shapes that cannot be conceived by human intuition. At optical frequencies, these techniques have only been utilized to optimize nondispersive materials using frequency-domain methods. However, a time-domain formulation is more efficient to optimize materials with dispersion. We introduce such a formulation for the Drude model, which is widely used to simulate the dispersive properties of metals, conductive oxides, and conductive polymers. Our topology optimization algorithm is based on the finite-difference time-domain (FDTD) method, and we introduce a time-domain sensitivity analysis that enables the evaluation of the gradient information by using one additional FDTD simulation. The existence of dielectric and metallic structures in the design space produces plasmonic field enhancement that causes convergence issues. We employ an artificial damping approach during the optimization iterations that, by reducing the plasmonic effects, solves the convergence problem. We present several design examples of 2D and 3D plasmonic nanoantennas with optimized field localization and enhancement in frequency bands of choice. Our method has the potential to speed up the design of wideband optical nanostructures made of dispersive materials for applications in nanoplasmonics, integrated optics, ultrafast photonics, and nonlinear optics.

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  • 20.
    Hausmaninger, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Narrowing of the linewidth of an optical parametric oscillator by an acousto-optic modulator for the realization of mid-IR noise-immune cavity-enhanced optical heterodyne molecular spectrometry down to 10(-10) cm(-1) Hz(-1/2)2015In: Optics Express, E-ISSN 1094-4087, Vol. 23, no 26, p. 33641-33655, article id UNSP 252446Article in journal (Refereed)
    Abstract [en]

    The linewidth of a singly resonant optical parametric oscillator (OPO) has been narrowed with respect to an external cavity by the use of an acousto-optic modulator (AOM). This made possible an improvement of the sensitivity of a previously realized OPO-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry instrument for the 3.2 - 3.9 mu m mid-infrared region by one order of magnitude. The resulting system shows a detection sensitivity for methane of 2.4 x 10(-10) cm(-1) Hz(-1/2) and 1.3 x 10(-10) cm(-1) at 20 s, which allows for detection of both the environmentally important (CH4)-C-13 and CH3D isotopologues in atmospheric samples. (C) 2015 Optical Society of America

  • 21.
    Johansson, Alexandra C.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rutkowski, Lucile
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Filipsson, Anna
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hausmaninger, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zhao, Gang
    Umeå University, Faculty of Science and Technology, Department of Physics. 2 State Key Laboratory of Quantum Optics and Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Broadband calibration-free cavity-enhanced complex refractive index spectroscopy using a frequency comb2018In: Optics Express, E-ISSN 1094-4087, Vol. 26, no 16, p. 20633-20648Article in journal (Refereed)
    Abstract [en]

    We present broadband cavity-enhanced complex refractive index spectroscopy (CE-CRIS), a technique for calibration-free determination of the complex refractive index of entire molecular bands via direct measurement of transmission modes of a Fabry-Perot cavity filled with the sample. The measurement of the cavity transmission spectrum is done using an optical frequency comb and a mechanical Fourier transform spectrometer with sub-nominal resolution. Molecular absorption and dispersion spectra (corresponding to the imaginary and real parts of the refractive index) are obtained from the cavity mode broadening and shift retrieved from fits of Lorentzian profiles to the individual cavity modes. This method is calibration-free because the mode broadening and shift are independent of the cavity parameters such as the length and mirror reflectivity. In this first demonstration of broadband CE-CRIS we measure simultaneously the absorption and dispersion spectra of three combination bands of CO2 in the range between 1525 nm and 1620 nm and achieve good agreement with theoretical models. This opens up for precision spectroscopy of the complex refractive index of several molecular bands simultaneously. 

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  • 22. Kataja, Mikko
    et al.
    Pourjamal, Sara
    Maccaferri, Nicolò
    CIC nanoGUNE, Donostia-San Sebastian, Spain.
    Vavassori, Paolo
    Hakala, Tommi K.
    Huttunen, Mikko J.
    Törmä, Päivi
    van Dijken, Sebastiaan
    Hybrid plasmonic lattices with tunable magneto-optical activity2016In: Optics Express, E-ISSN 1094-4087, Vol. 24, no 4, p. 3652-3652Article in journal (Refereed)
    Abstract [en]

    We report on the optical and magneto-optical response of hybrid plasmonic lattices that consist of pure nickel and gold nanoparticles in a checkerboard arrangement. Diffractive far-field coupling between the individual emitters of the lattices results in the excitation of two orthogonal surface lattice resonance modes. Local analyses of the radiation fields indicate that both the nickel and gold nanoparticles contribute to these collective resonances and, thereby, to the magneto-optical activity of the hybrid arrays. The strong effect of noble metal nanoparticles on the magneto-optical response of hybrid lattices opens up new avenues for the realization of sensitive and tunable magneto-plasmonic nanostructures.

  • 23. Krzempek, Karol
    et al.
    Tomaszewska, Dorota
    Gluszek, Aleksander
    Martynkien, Tadeusz
    Mergo, Pawel
    Sotor, Jaroslaw
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sobon, Grzegorz
    Stabilized all-fiber source for generation of tunable broadband fCEO-free mid-IR frequency comb in the 7–9 µm range2019In: Optics Express, E-ISSN 1094-4087, Vol. 27, no 26, p. 37435-37445Article in journal (Refereed)
    Abstract [en]

    A compact and robust all-fiber difference frequency generation-based source of broadband mid-infrared radiation is presented. The source emits tunable radiation in the range between 6.5 µm and 9 µm with an average output power up to 5 mW at 125 MHz repetition frequency. The all-in-fiber construction of the source along with active stabilization techniques results in long-term repetition rate stability of 3 Hz per 10 h and a standard deviation of the output power better than 0.8% per 1 h. The applicability of the presented source to laser spectroscopy is demonstrated by measuring the absorption spectrum of nitrous oxide (N2O) around 7.8 µm. The robustness and good long- and short-term stability of the source opens up for applications outside the laboratory.

  • 24. Li, Qiang
    et al.
    Wang, Tao
    Su, Yikai
    Yan, Min
    Laboratory of Photonics and Microwave Engineering, School of Information and Communication Technology, Royal Institute of Technology (KTH), Electrum 229, Kista, Sweden.
    Qiu, Min
    Coupled mode theory analysis of mode-splitting in coupled cavity system2010In: Optics Express, E-ISSN 1094-4087, Vol. 18, no 8, p. 8367-8367Article in journal (Refereed)
    Abstract [en]

    We analyze transmission characteristics of two coupled identical cavities, of either standing-wave (SW) or traveling-wave (TW) type, based on temporal coupled mode theory. Mode splitting is observed for both directly (cavity-cavity) and indirectly (cavity-waveguide-cavity) coupled cavity systems. The effects of direct and indirect couplings, if coexisting in one system, can offset each other such that no mode splitting occurs and the original single-cavity resonant frequency is retained. By tuning the configuration of the coupled cavity system, one can obtain different characteristics in transmission spectra, including splitting in transmission, zero transmission, Fano-type transmission, electromagnetically-induced-transparency (EIT)-like transmission, and electromagnetically-induced-absorption (EIA)-like transmission. It is also interesting to notice that a side-coupled SW cavity system performs similarly to an under-coupled TW cavity. The results are useful for the design of cavity-based devices for integration in nanophotonics.

  • 25.
    Liu, Hairong
    et al.
    Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, China; Laboratory of Photonics and Microwave Engineering, School of Information and Communication Technology, Royal Institute of Technology (KTH), Electrum 229, Kista, Sweden.
    Yan, Min
    Laboratory of Photonics and Microwave Engineering, School of Information and Communication Technology, Royal Institute of Technology (KTH), Electrum 229, Kista, Sweden.
    Qiu, Min
    Laboratory of Photonics and Microwave Engineering, School of Information and Communication Technology, Royal Institute of Technology (KTH), Electrum 229, Kista, Sweden.
    Liu, Deming
    Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, China.
    Yu, Xia
    Singapore Institute of Manufacturing Technology (SIMTech), Singapore, Singapore.
    Zhang, Ying
    Singapore Institute of Manufacturing Technology (SIMTech), Singapore, Singapore.
    Theoretical investigation on guiding IR light in hollow-core metallic fiber with corrugated inner surface2010In: Optics Express, E-ISSN 1094-4087, Vol. 18, no 21, p. 21959-21964Article in journal (Refereed)
    Abstract [en]

    Hollow metallic fibers (HMFs) are in general lossy primarily owing to the fact that the guided transverse-magnetic (TM) light sustains a relatively high propagation loss. In this paper, we propose a type of practical hollow-core metallic fiber (HMF) with longitudinally corrugated inner surface for transmitting infrared (IR) light. Simulation results show that the loss of the fundamental TM mode can be easily reduced by 50~100 times compared to a HMF without surface corrugation. In contrast to the traditional HMF with a dielectric coating, it is shown that the loss of the fundamental TM mode in the proposed HMF is relatively insensitive to the corrugation layer thickness or equivalently the operating frequency.

  • 26.
    Liu, Hairong
    et al.
    Dept. of Opto-electronic Engineering, Huazhong U. of Sci.& Tech., China.
    Yan, Min
    Network Technology Research Centre, Nanyang Technological University, Singapore.
    Shum, Ping
    Network Technology Research Centre, Nanyang Technological University, Singapore.
    Ghafouri-Shiraz, H.
    School of Electronic, Electrical and Computer Engineering, The University of Birmingham, Edgbaston, Birmingham, UK.
    Liu, Deming
    Dept. of Opto-electronic Engineering, Huazhong U. of Sci.& Tech., China.
    Design and analysis of anti-resonant reflecting photonic crystal VCSEL lasers2004In: Optics Express, E-ISSN 1094-4087, Vol. 12, no 18, p. 4269-4274Article in journal (Refereed)
    Abstract [en]

    Anti-resonant reflecting photonic crystal structure is employed in vertical cavity surface emitting lasers (VCSELs) to achieve photon confinement in lateral direction. Such a design is promising in supporting large-aperture single-mode emission. In the configuration, hexagonal arrays of high-index cylinders which run vertically in the cladding region are introduced in the VCSEL’s top DBR (p-DBR) mirror region. The transverse modal property of the proposed structure, especially leakage loss, has been theoretically investigated. An optimum design for the minimum radiation loss while maintaining single-mode operation has been discussed in this paper.

  • 27.
    Liu, Jianxin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, China; Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, China.
    Zhao, Gang
    State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, China; Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, China.
    Ma, Weiguang
    State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, China; Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, China.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Development of a Doppler-broadened NICE-OHMS system for trace gas detection based on a single sideband phase modulator2021In: Optics Express, E-ISSN 1094-4087, Vol. 29, no 26, p. 42411-42419Article in journal (Refereed)
    Abstract [en]

    To expand the applicability of noise-immune cavity-enhanced optical heterodyne molecular spectrometer (NICE-OHMS), a universal system incorporating a fiber-coupled singlesideband modulator (f-SSM) for control of the laser frequency has been developed. A homemade PID servo mainly composed of two integrators has been designed, resulting in a locking bandwidth of 170 kHz and a continuous tuning range of 2.2 GHz. The system exhibits a noise-equivalent Doppler-broadened absorption limit of 8.0x10-14 cm-1 for an integration time of 64 s. Since the f-SSM is the sole external frequency actuator, this opens up for NICE-OHMS based on a multitude of laser systems.

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  • 28. Liu, Jianxin
    et al.
    Zhou, Yueting
    Guo, Songjie
    Hou, Jiajuan
    Zhao, Gang
    Ma, Weiguang
    Wu, Yongqian
    Dong, Lei
    Zhang, Lei
    Yin, Wangbao
    Xiao, Liantuan
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Jia, Suotang
    A novel methodology to directly pre-determine the relative wavelength response of DFB laser in wavelength modulation spectroscopy2019In: Optics Express, E-ISSN 1094-4087, Vol. 27, no 2, p. 1249-1261Article in journal (Refereed)
    Abstract [en]

    A novel methodology to directly pre-determine the relative wavelength response (RWR) of a DFB laser, in terms of a combined current linearly scanned wavelength response and current modulated wavelength response (CMWR), in wavelength modulation spectroscopy (WMS) is presented. It is shown that the assessed RWR can be used to mimic the measured response with standard deviation of discriminations that are below 3.4 x 10(-3)cm(-1) under a variety of conditions. It is also shown that its performance supersedes two commonly used assessment models of the CMWR but is slightly worse than that of the third model. however with the benefit of solely using a single fitting parameter (the concentration) instead of more. When the novel method is applied to the assessment of CO2 concentration in a Herriot-type multipass cell by using the technique of calibration-free WMS, the results show that there is virtually no difference compared to that by use of the best of the other methods. It is concluded that the novel method is more robust and simplifies the retrieval process of gas concentration.

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  • 29.
    Lou, Fei
    et al.
    Laboratory of Photonics and Microwave Engineering, Royal Institute of Technology (KTH), Kista, Sweden .
    Yan, Min
    Laboratory of Photonics and Microwave Engineering, Royal Institute of Technology (KTH), Kista, Sweden .
    Thylen, Lars
    Laboratory of Photonics and Microwave Engineering, Royal Institute of Technology (KTH), Kista, Sweden; Hewlett-Packard Laboratories, Palo Alto, California, USA.
    Qiu, Min
    Laboratory of Photonics and Microwave Engineering, Royal Institute of Technology (KTH), Kista, Sweden; Department of Optical Engineering, Zhejiang University, Hangzhou, China.
    Wosinski, Lech
    Laboratory of Photonics and Microwave Engineering, Royal Institute of Technology (KTH), Kista, Sweden .
    Whispering gallery mode nanodisk resonator based on layered metal-dielectric waveguide2014In: Optics Express, E-ISSN 1094-4087, Vol. 22, no 7, p. 8490-8502Article in journal (Refereed)
  • 30.
    Lu, Chuang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Vieira, Francisco Senna
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Głuszek, Aleksander
    Laser & Fiber Electronics Group, Faculty of Electronics, Wrocław University of Science and Technology, Wybrzeze Wyspianskiego 27, Wrocław, Poland.
    Silander, Isak
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sobon, Grzegorz
    Laser & Fiber Electronics Group, Faculty of Electronics, Wrocław University of Science and Technology, Wybrzeze Wyspianskiego 27, Wrocław, Poland.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Robust, fast and sensitive near-infrared continuous-filtering Vernier spectrometer2021In: Optics Express, E-ISSN 1094-4087, Vol. 29, no 19, p. 30155-30167Article in journal (Refereed)
    Abstract [en]

    We present a new design of a robust cavity-enhanced frequency comb-based spectrometer operating under the continuous-filtering Vernier principle. The spectrometer is based on a compact femtosecond Er-doped fiber laser, a medium finesse cavity, a diffraction grating, a custom-made moving aperture, and two photodetectors. The new design removes the requirement for high-bandwidth active stabilization present in the previous implementations of the technique, and allows scan rates up to 100 Hz. We demonstrate the spectrometer performance over a wide spectral range by detecting CO2 around 1575 nm (1.7 THz bandwidth and 6 GHz resolution) and CH4 around 1650 nm (2.7 THz bandwidth and 13 GHz resolution). We achieve absorption sensitivity of 5 × 10−9 cm-1 Hz-1/2 at 1575 nm, and 1 × 10−7 cm-1 Hz-1/2 cm-1 at 1650 nm. We discuss the influence of the scanning speed above the adiabatic limit on the amplitude of the absorption signal.

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  • 31.
    Lu, Chuang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Vieira, Francisco Senna
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Time-resolved continuous-filtering Vernier spectroscopy of H2O and OH radical in a flame2019In: Optics Express, E-ISSN 1094-4087, Vol. 27, no 21, p. 29521-29533Article in journal (Refereed)
    Abstract [en]

    We use broadband near-infrared continuous-filtering Vernier spectroscopy (CF-VS) for time-resolved detection of H2O and OH radical in a premixed CH4/air flat flame. The CF-VS spectrometer is based on a femtosecond Er:fiber laser, an external cavity that contains the flame, and a detection system comprising a rotating diffraction grating and photodetectors. Spectra of H2O and OH radical around 1570 nm are continuously recorded with 6.6 GHz spectral resolution, 4.0 x 10-7 cm-1 absorption sensitivity, and 25 ms time resolution, while the fuel-air equivalence ratio is periodically modulated with a square wave. The concentrations of the two analytes are retrieved with percent level precision by a fit of a Vernier model to each spectrum spanning 13 nm. The temporal profiles of both concentrations in each modulation cycle are repeatable and the steady-state concentration levels are in good agreement with predictions based on one-dimensional simulations of a static flat flame. The robust CF-VS spectrometer opens up for quantitative monitoring of multiple products of time-varying combustion processes with relatively simple data acquisition procedures.

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  • 32. Ma, Guangjin
    et al.
    Yu, Wei
    Yu, M. Y.
    Shen, Baifei
    Veisz, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck-Institut für Quantenoptik, D-85748 Garching, Germany.
    Intense circularly polarized attosecond pulse generation from relativistic laser plasmas using few-cycle laser pulses2016In: Optics Express, E-ISSN 1094-4087, Vol. 24, no 9, p. 10057-10065Article in journal (Refereed)
    Abstract [en]

    We have investigated the polarization of attosecond light pulses generated from relativistic few-cycle laser pulse interaction with the surface of overdense plasmas using particle-in-cell simulation. Under suitable conditions, a desired polarization state of the generated attosecond pulse can be achieved by controlling the polarization of the incident laser. In particular, an elliptically polarized laser pulse of suitable ellipticity can generate an almost circularly polarized attosecond pulse without compromising the harmonic generation efficiency. The process is thus applicable as a new tabletop circularly-polarized XUV radiation source for probing attosecond phenomena with high temporal resolution.

  • 33.
    Maccaferri, Nicolò
    et al.
    Nanomagnetism Group, CIC nanoGUNE Consolider, Donostia / San Sebastián, Spain.
    González-Díaz, Juan B.
    Bonetti, Stefano
    Berger, Andreas
    Kataja, Mikko
    van Dijken, Sebastiaan
    Nogués, Josep
    Bonanni, Valentina
    Pirzadeh, Zhaleh
    Dmitriev, Alexandre
    Åkerman, Johan
    Vavassori, Paolo
    Polarizability and magnetoplasmonic properties of magnetic general nanoellipsoids2013In: Optics Express, E-ISSN 1094-4087, Vol. 21, no 8, p. 9875-9889Article in journal (Refereed)
    Abstract [en]

    An approach to compute the polarizability tensor of magnetic nanoparticles having general ellipsoidal shape is presented. We find a surprisingly excellent quantitative agreement between calculated and experimental magneto-optical spectra measured in the polar Kerr configuration from nickel nanodisks of large size (exceeding 100 nm) with circular and elliptical shape. In spite of its approximations and simplicity, the formalism presented here captures the essential physics of the interplay between magneto-optical activity and the plasmonic resonance of the individual particle. The results highlight the key role of the dynamic depolarization effects to account for the magneto-optical properties of plasmonic nanostructures.

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  • 34.
    Muschet, Alexander A.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    de Andres, Aitor
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fischer, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Salh, Roushdey
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Veisz, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Utilizing the temporal superresolution approach in an optical parametric synthesizer to generate multi-TW sub-4-fs light pulses2022In: Optics Express, E-ISSN 1094-4087, Vol. 30, no 3, p. 4374-4380Article in journal (Refereed)
    Abstract [en]

    The Fourier-transform limit achieved by a linear spectral phase is the typical optimum by the generation of ultrashort light pulses. It provides the highest possible intensity, however, not the shortest full width at half maximum of the pulse duration, which is relevant for many experiments. The approach for achieving shorter pulses than the original Fourier limit is termed temporal superresolution. We demonstrate this approach by shaping the spectral phase of light from an optical parametric chirped pulse amplifier and generate sub-Fourier limited pulses. We also realize it in a simpler way by controlling only the amplitude of the spectrum, producing a shorter Fourier-limited duration. Furthermore, we apply this technique to an optical parametric synthesizer and generate multi-TW sub-4-fs light pulses. This light source is a promising tool for generating intense and isolated attosecond light and electron pulses.

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  • 35.
    Qu, Zhechao
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Ghorbani, Ramin
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Valiev, Damir
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Schmidt, Florian M
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Calibration-free scanned wavelength modulation spectroscopy – application to H2O and temperature sensing in flames2015In: Optics Express, E-ISSN 1094-4087, Vol. 23, no 12, p. 16492-16499Article in journal (Refereed)
    Abstract [en]

    A calibration-free scanned wavelength modulation spectroscopy scheme requiring minimal laser characterization is presented. Species concentration and temperature are retrieved simultaneously from a single fit to a group of 2f/1f-WMS lineshapes acquired in one laser scan. The fitting algorithm includes a novel method to obtain the phase shift between laser intensity and wavelength modulation, and allows for a wavelengthdependent modulation amplitude. The scheme is demonstrated by detection of H2O concentration and temperature in atmospheric, premixed CH4/air flat flames using a sensor operating near 1.4 μm. The detection sensitivity for H2O at 2000 K was 4 × 10−5 cm−1 Hz-1/2, and temperature was determined with a precision of 10 K and absolute accuracy of ~50 K. A parametric study of the dependence of H2O and temperature on distance to the burner and total fuel mass flow rate shows good agreement with 1D simulations.

  • 36.
    Rolla, Dorota Tomaszewska
    et al.
    Laser & Fiber Electronics Group, Faculty of Electronics, Photonics and Microsystems, Wrocław University of Science and Technology, Wybrzeze Wyspianskiego 27, Wroclaw, Poland.
    Jaworski, Piotr
    Laser & Fiber Electronics Group, Faculty of Electronics, Photonics and Microsystems, Wrocław University of Science and Technology, Wybrzeze Wyspianskiego 27, Wroclaw, Poland.
    Wu, Dakun
    Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou, China.
    Yu, Fei
    Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou, China; Key Laboratory of Materials for High Power Laser, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai, China.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Krzempek, Karol
    Laser & Fiber Electronics Group, Faculty of Electronics, Photonics and Microsystems, Wrocław University of Science and Technology, Wybrzeze Wyspianskiego 27, Wroclaw, Poland.
    Sobon, Grzegorz
    Laser & Fiber Electronics Group, Faculty of Electronics, Photonics and Microsystems, Wrocław University of Science and Technology, Wybrzeze Wyspianskiego 27, Wroclaw, Poland.
    Mid-infrared optical frequency comb spectroscopy using an all-silica antiresonant hollow-core fiber2024In: Optics Express, E-ISSN 1094-4087, Vol. 32, no 6, p. 10679-10689Article in journal (Refereed)
    Abstract [en]

    We present the first mid-infrared optical frequency comb spectrometer employing an absorption cell based on self-fabricated, all-silica antiresonant hollow-core fiber (ARHCF). The spectrometer is capable of measuring sub-mL sample volumes with 26 m interaction length and noise equivalent absorption sensitivity of 8.3 × 10−8 cm−1 Hz−1/2 per spectral element in the range of 2900 cm−1 to 3100 cm−1. Compared to a commercially available multipass cell, the ARHCF offers a similar interaction length in a 1000 times lower gas sample volume and a 2.8 dB lower transmission loss, resulting in better absorption sensitivity. The broad transmission windows of ARHCFs, in combination with a tunable optical frequency comb, make them ideal for multispecies detection, while the prospect of measuring samples in small volumes makes them a competitive technique to photoacoustic spectroscopy along with the robustness and prospect of coiling the ARHCFs open doors for miniaturization and out-of-laboratory applications.

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  • 37.
    Rutkowski, Lucile
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Johansson, Alexandra C.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zhao, Gang
    Umeå University, Faculty of Science and Technology, Department of Physics. State Key Laboratory of Quantum Optics and Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China.
    Hausmaninger, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Khodabakhsh, Amir
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sensitive and broadband measurement of dispersion in a cavity using a Fourier transform spectrometer with kHz resolution2017In: Optics Express, E-ISSN 1094-4087, Vol. 25, no 18, p. 21711-21718Article in journal (Refereed)
    Abstract [en]

    Optical cavities provide high sensitivity to dispersion since their resonance frequencies depend on the index of refraction. We present a direct, broadband, and accurate measurement of the modes of a high finesse cavity using an optical frequency comb and a mechanical Fourier transform spectrometer with a kHz-level resolution. We characterize 16000 longitudinal cavity modes spanning 16 THz of bandwidth in terms of center frequency, linewidth, and amplitude. Using the center frequencies we retrieve the group delay dispersion of the cavity mirror coatings and pure N2 with 0.1 fs2 precision and 1 fs2 accuracy, as well as the refractivity of the 3ν13 absorption band of CO2 with 5 × 10‒12 precision. This opens up for broadband refractive index metrology and calibration-free spectroscopy of entire molecular bands.

  • 38.
    Schmidt, Florian
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Foltynowicz-Matyba, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ma, Weiguang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lock, Tomas
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Doppler-broadened fiber-laser-based NICE-OHMS: improved detectability2007In: Optics Express, E-ISSN 1094-4087, Vol. 15, no 17, p. 10822-10831Article in journal (Refereed)
    Abstract [en]

    The performance of fiber-laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) has been improved by elimination of the technical constraints that limited its first demonstration. Doppler-broadened detection of C2H2 and CO2 at ~1531 nm is demonstrated using a cavity with a finesse of 4800. Frequency and wavelength modulated detection at absorption and dispersion phase are compared and the optimum mode of detection is discussed. A minimum detectable absorption of 8 × 10-11 cm-1, which corresponds to a detection limit of 4.5 ppt (2 ppt·m) for C2H2, was obtained for an acquisition time of 0.7 s by lineshape fitting. The linearity of the pressure dependence of the signal strengths is investigated for both C2H2 and CO2.

  • 39.
    Silander, Isak
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Silva de Oliveira, Vinicius
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Forssén, Clayton
    Umeå University, Faculty of Science and Technology, Department of Physics. Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Foltynowicz, Aleksandra
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rubin, Tom
    Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
    Zelan, Martin
    Measurement Science and Technology, RISE Research Institutes of Sweden, Borås, Sweden.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    In situ determination of the penetration depth of mirrors in Fabry-Perot refractometers and its influence on assessment of refractivity and pressure2022In: Optics Express, E-ISSN 1094-4087, Vol. 30, no 14, p. 25891-25906Article in journal (Refereed)
    Abstract [en]

    A procedure is presented for in situ determination of the frequency penetration depth of coated mirrors in Fabry-Perot (FP) based refractometers and its influence on the assessment of refractivity and pressure. It is based on assessments of the absolute frequency of the laser and the free spectral range of the cavity. The procedure is demonstrated on an Invar-based FP cavity system with high-reflection mirrors working at 1.55 µm. The influence was assessed with such a low uncertainty that it does not significantly contribute to the uncertainties (k = 2) in the assessment of refractivity (<8 × 10−13) or pressure of nitrogen (<0.3 mPa).

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  • 40.
    Song, Yi
    et al.
    Laboratory of Photonics and Microwave Engineering, School of Information and Communication Technology, Royal Institute of Technology, Electrum 229, Kista, Sweden.
    Wang, Jing
    Laboratory of Photonics and Microwave Engineering, School of Information and Communication Technology, Royal Institute of Technology, Electrum 229, Kista, Sweden.
    Li, Qiang
    Laboratory of Photonics and Microwave Engineering, School of Information and Communication Technology, Royal Institute of Technology, Electrum 229, Kista, Sweden.
    Yan, Min
    Laboratory of Photonics and Microwave Engineering, School of Information and Communication Technology, Royal Institute of Technology, Electrum 229, Kista, Sweden.
    Qiu, Min
    Laboratory of Photonics and Microwave Engineering, School of Information and Communication Technology, Royal Institute of Technology, Electrum 229, Kista, Sweden.
    Broadband coupler between silicon waveguide and hybrid plasmonic waveguide2010In: Optics Express, E-ISSN 1094-4087, Vol. 18, no 12, article id 13173Article in journal (Refereed)
    Abstract [en]

    Efficient broadband coupling of light between a dielectric waveguide and a hybrid plasmonic waveguide is investigated theoretically. A plasmonic linear taper is used as a coupler which connects the two types of waveguides. Broadband coupling is realized by such a compact plasmonic taper with a length of only 0.4μm, which achieves a coupling efficiency of 70% (1.5dB) at the 1.55μm telecommunication wavelength.

  • 41.
    Tan, Jeryl
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Forget, Nicolas
    Borot, Antonin
    Kaplan, Daniel
    Tournois, Pierre
    Muschet, Alexander
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Veisz, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Physics. Max-Planck-Institut für Quantenoptik, Garching, Germany.
    Dispersion control for temporal contrast optimization2018In: Optics Express, E-ISSN 1094-4087, Vol. 26, no 19, p. 25003-25012Article in journal (Refereed)
    Abstract [en]

    We investigate the temporal contrast of the Light Wave Synthesizer 20 (LWS-20): a powerful, few-cycle source based on the optical parametric synthesizer principle. Saturation effects in the RF amplifier driving the acousto-optic programmable dispersive filter (AOPDF) were found to degrade the coherent contrast for non-monotonic group delay corrections. We subsequently present a new dispersion scheme and design a novel transmission grism-based stretcher optimized for LWS-20. The resulting temporal contrast of the amplified, compressed output pulses is improved by 2-4 orders of magnitude compared to the former design.

  • 42.
    Thorin, Emil
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Zhang, Kun
    Center for Combustion Energy, Department of Energy and Power Engineering, Tsinghua University 100084, Beijing, China.
    Valiev, Damir
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Center for Combustion Energy, Department of Energy and Power Engineering, Tsinghua University 100084, Beijing, China.
    Schmidt, Florian M.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Simultaneous detection of K, KOH, and KCl in flames and released from biomass using photofragmentation TDLAS2021In: Optics Express, E-ISSN 1094-4087, Vol. 29, no 26, article id 42945Article in journal (Refereed)
    Abstract [en]

    Gaseous potassium (K) species released from biomass during thermochemicalconversion pose challenges to reactors and human health. Photofragmentation tunable diodelaser absorption spectroscopy (PF-TDLAS) was used for simultaneous, high-dynamic rangemeasurements of atomic K, potassium hydroxide (KOH) and potassium chloride (KCl) inflat flames seeded with KCl salt. An expression for the PF-TDLAS signal is presented andexperimentally verified. Axial K species concentration profiles recorded at fuel-air equivalenceratios of 0.8 and 1.3 are compared to 2D axisymmetric reacting flow simulations. An overallgood agreement is found, but KOH is over-predicted in simulations of fuel-rich flames at theexpense of atomic K. Quantification of K species close to softwood and wheat straw particlesconverted in the flames is demonstrated.

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  • 43. Valerio, Aline de Matos
    et al.
    Kampel, Milton
    Vantrepotte, Vincent
    Ward, Nicholas D.
    Sawakuchi, Henrique Oliveira
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Universidade de São Paulo, USP/CENA, Piracicaba, SP, Brazil .
    Da Silva Less, Diani Fernanda
    Neu, Vania
    Cunha, Alan
    Richey, Jeffrey
    Using CDOM optical properties for estimating DOC concentrations and pCO2 in the lower Amazon river2018In: Optics Express, E-ISSN 1094-4087, Vol. 26, no 14, p. A657-A677Article in journal (Refereed)
    Abstract [en]

    Coloured dissolved organic matter (CDOM) is one of the major contributors to the absorption budget of most freshwaters and can be used as a proxy to assess non-optical carbon fractions such as dissolved organic carbon (DOC) and the partial pressure of carbon dioxide (pCO2). Nevertheless, riverine studies that explore the former relationships are still relatively scarce, especially within tropical regions. Here we document the spatial-seasonal variability of CDOM, DOC and pCO2, and assess the potential of CDOM absorption coefficient (aCDOM(412)) for estimating DOC concentration and pCO2 along the Lower Amazon River. Our results revealed differences in the dissolved organic matter (DOM) quality between clearwater (CW) tributaries and the Amazon River mainstream. A linear relationship between DOC and CDOM was observed when tributaries and mainstream are evaluated separately (Amazon River: N = 42, R2 = 0.74, p<0.05; CW: N = 13, R2 = 0.57, p<0.05). However, this linear relationship was not observed during periods of higher rainfall and river discharge, requiring a specific model for these time periods to be developed (N = 25, R2 = 0.58, p<0.05). A strong linear positive relation was found between aCDOM(412) and pCO2(N = 69, R2 = 0.65, p<0.05) along the lower river. pCO2 was less affected by the optical difference between tributaries and mainstream waters or by the discharge conditions when compared to CDOM to DOC relationships. Including the river water temperature in the model improves our ability to estimate pCO(2) (N = 69; R2 = 0.80, p<0.05). The ability to assess both DOC and pCO2 from CDOM optical properties opens further perspectives on the use of ocean colour remote sensing data for monitoring carbon dynamics in large running water systems worldwide.

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  • 44. Wang, Jing
    et al.
    Chen, Yiting
    Chen, Xi
    Hao, Jiaming
    Yan, Min
    Division of Optics and Photonics, Royal Institute of Technology (KTH), Electrum 229, Kista, Sweden.
    Qiu, Min
    Photothermal reshaping of gold nanoparticles in a plasmonic absorber2011In: Optics Express, E-ISSN 1094-4087, Vol. 19, no 15, p. 14726-14734Article in journal (Refereed)
    Abstract [en]

    We experimentally demonstrate that a metamaterial nanostructure can have a localized heating response owing to plasmonic resonances in the near-infrared wavelength range (from 1.5 to 2µm). With a broadband nanosecond-pulse light, the temperature of composing gold particles in the nanostructure can be easily increased to over 900K within only several nanoseconds, resulting in re-shaping of the particles. The photothermal effect is elaborated with finite-element based numerical simulations. The absorption resonance can in principle be tailored with a great freedom by choosing appropriate metamaterial parameters. The light-induced heating in an artificial metamaterial can be potentially used for all-optical acute temperature tuning in a micro-environment, which may open new frontiers especially in nanotechnology and biotechnology.

  • 45.
    Yan, M.
    et al.
    Network Technology Research Centre, Nanyang Technological University, Research TechnoPlaza, Singapore.
    Shum, P.
    Network Technology Research Centre, Nanyang Technological University, Research TechnoPlaza, Singapore.
    Analysis of perturbed Bragg fibers with an extended transfer matrix method2006In: Optics Express, E-ISSN 1094-4087, Vol. 14, no 7, p. 2596-2610Article in journal (Refereed)
    Abstract [en]

    We introduce an extended transfer matrix method (TMM) for solving guided modes in leaky optical fibers with layered cladding. The method can deal with fibers with circular but nonconcentric material interfaces. Validity of the method is verified by two full-vector numerical methods. The TMM is then used to investigate the guidance property of perturbed Bragg fibers. Our analysis reveals that the core modes will interact with each other when a perturbed Bragg fiber has only C 1 symmetry. Special attention is paid to the first transverse-electric (TE01) mode, which is found to experience severe degradation around spectral regions where its dispersion curve supposedly crosses a transverse-magnetic (TM) or hybrid mode.

  • 46.
    Yan, M.
    et al.
    Network Technology Research Centre, Nanyang Technological University, Singapore.
    Shum, P.
    Network Technology Research Centre, Nanyang Technological University, Singapore.
    Antiguiding in microstructured optical fibers2004In: Optics Express, E-ISSN 1094-4087, Vol. 12, no 1, p. 104-116Article in journal (Refereed)
    Abstract [en]

    Antiguiding, as opposed to positive index-contrast guiding (or index-guiding), in microstructured air-silica optical fibers is shown to have a significant influence on the fiber’s transmission property, especially when perturbations exist near the defect core. Antiguided modes are numerically analyzed in such fibers by treating the finite periodic air-silica composite (including the central defect) as the core and outer bulk silica region as the cladding. Higher-order modes, which can couple energy from the fundamental mode in the presence of waveguide irregularities, are predicted to be responsible for high leakage loss of realistic holey fibers. The modal property of an equivalent simple step-index antiguide model is also analyzed. Results show that approximation from a composite core waveguide to a simple step-index fiber always neglects some important modal characteristics.

  • 47.
    Yan, Min
    et al.
    Department of Photonics Engineering, Technical University of Denmark, Kongens Lyngby, Denmark.
    Mortensen, Niels Asger
    Department of Photonics Engineering, Technical University of Denmark, Kongens Lyngby, Denmark.
    Hollow-core infrared fiber incorporating metal-wire metamaterial2009In: Optics Express, E-ISSN 1094-4087, Vol. 17, no 17, p. 14851-14864Article in journal (Refereed)
    Abstract [en]

    Infrared (IR) light is considered important for short-range wireless communication, thermal sensing, spectroscopy, material processing, medical surgery, astronomy etc. However, IR light is in general much harder to transport than optical light or microwave radiation. Existing hollow-core IR waveguides usually use a layer of metallic coating on the inner wall of the waveguide. Such a metallic layer, though reflective, still absorbs guided light significantly due to its finite Ohmic loss, especially for transverse-magnetic (TM) light. In this paper, we show that metal-wire based metamaterials may serve as an efficient TM reflector, reducing propagation loss of the TM mode by two orders of magnitude. By further imposing a conventional metal cladding layer, which reflects specifically transverse-electric (TE) light, we can potentially obtain a low-loss hollow-core fiber. Simulations confirm that loss values for several low-order modes are comparable to the best results reported so far.

  • 48.
    Yan, Min
    et al.
    Department of Microelectronics and Applied Physics, Royal Institute of Technology, Electrum 229, Kista, Sweden.
    Ruan, Zhichao
    Department of Microelectronics and Applied Physics, Royal Institute of Technology, Electrum 229, Kista, Sweden.
    Qiu, Min
    Department of Microelectronics and Applied Physics, Royal Institute of Technology, Electrum 229, Kista, Sweden.
    Scattering characteristics of simplified cylindrical invisibility cloaks2007In: Optics Express, E-ISSN 1094-4087, Vol. 15, no 26, p. 17772-17782Article in journal (Refereed)
    Abstract [en]

    The previously reported simplified cylindrical linear cloak is improved so that the cloak’s outer surface is impedance-matched to free space. The scattering characteristics of the improved linear cloak is compared to the previous counterpart as well as the recently proposed simplified quadratic cloak derived from quadratic coordinate transformation. Significant improvement in invisibility performance is noticed for the improved linear cloak with respect to the previously proposed linear one. The improved linear cloak and the simplified quadratic cloak have comparable invisibility performances, except that the latter however has to fulfill a minimum shell thickness requirement (i.e. outer radius must be larger than twice of inner radius). When a thin cloak shell is desired, the improved linear cloak is much more superior than the other two versions of simplified cloaks.

  • 49.
    Yan, Min
    et al.
    Laboratory of Photonics and Microwave Engineering, School of Information and Communication Technology, Royal Insitute of Technology (KTH), Kista, Sweden.
    Thylén, Lars
    Laboratory of Photonics and Microwave Engineering, School of Information and Communication Technology, Royal Insitute of Technology (KTH), Kista, Sweden; Hewlett-Packard Laboratories, Palo Alto, California, USA.
    Qiu, Min
    Laboratory of Photonics and Microwave Engineering, School of Information and Communication Technology, Royal Insitute of Technology (KTH), Kista, Sweden.
    Layered metal-dielectric waveguide: subwavelength guidance, leveraged modulation sensitivity in mode index, and reversed mode ordering2011In: Optics Express, E-ISSN 1094-4087, Vol. 19, no 4, p. 3818-3824Article in journal (Refereed)
    Abstract [en]

    We describe a layered metal-dielectric waveguide, whose fundamental mode has an effective index as high as 7.35 at 1.55μm, enabling subwavelength spatial confinement. The loss is found to be reasonable in relation to the confinement. The indefinite dielectric tensor of the stratified metamaterial core generally leads to multimode operation of the waveguide, exhibiting a “reversed” mode ordering contrary to conventional waveguides. The waveguide features a strong leveraging in modal index change subject to a change of index in the dielectric layers, opening the design possibilities of very compact active electro-optic devices.

  • 50.
    Yan, Min
    et al.
    Department of Microelectronics and Applied Physics, Royal Institute of Technology, and Kista Photonics Research Center, Electrum 229, Kista, Sweden.
    Thylén, Lars
    Department of Microelectronics and Applied Physics, Royal Institute of Technology, and Kista Photonics Research Center, Electrum 229, Kista, Sweden.
    Qiu, Min
    Department of Microelectronics and Applied Physics, Royal Institute of Technology, and Kista Photonics Research Center, Electrum 229, Kista, Sweden.
    Parekh, Devang
    Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, Berkeley, USA.
    Feasibility study of nanoscaled optical waveguide based on near-resonant surface plasmon polariton2008In: Optics Express, E-ISSN 1094-4087, Vol. 16, no 10, p. 7499-7507Article in journal (Refereed)
    Abstract [en]

    Currently subwavelength surface plasmon polariton (SPP) waveguides under intensive theoretical and experimental studies are mostly based on the geometrical singularity property of such waveguides. Typical examples include the metal-insulator-metal based waveguide and the metallic fiber. Both types of waveguides support a mode with divergent propagation constant as the waveguides’ geometry (metal gap distance or fiber radius) shrinks to zero. Here we study an alternative way of achieving subwavelength confinement through deploying two materials with close but opposite epsilon values. The interface between such two materials supports a near-resonant SPP. By examining the relationship between mode propagation loss and the mode field size for both planar and fiber waveguides, we show that waveguides based on near-resonant SPP can be as attractive as those solely based on geometrical tailoring. We then explicitly study a silver and silicon based waveguide with a 25nm core size at 600nm wavelength, in its properties like single-mode condition, mode loss and group velocity. It is shown that loss values of both materials have to be decreased by ~1000 times in order to have 1dB/µm propagation loss. Hence we point out the necessity of novel engineering of low-loss metamaterials, or introducing gain, for practical applications of such waveguides. Due to the relatively simple geometry, the proposed near-resonant SPP waveguides can be a potential candidate for building optical circuits with a density close to the electronic counterpart.

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