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  • 1. Blomstedt, K.
    et al.
    Setala, T.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Effective degree of coherence: general theory and application to electromagnetic fields2007In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 9, no 10, p. 907-919Article in journal (Refereed)
    Abstract [en]

    The concept of overall or effective degree of coherence has proven useful and insightful in the scalar theory of light. In this paper we extend the concept to fields represented over arbitrary vector (Hilbert) spaces. We show that the effective degree of coherence remains unaltered by scaled unitary mappings, which describe for instance many physical interactions. In the context of random, vector-valued electromagnetic fields the invariance implies that the effective degree of coherence assumes the same value in commonly used representation spaces. Thereby, in contrast to the local degree of coherence, this quantity can be taken as an intrinsic property of the electromagnetic wave field. In particular, the effective degree of coherence does not change when the field is scattered by a lossless medium and it can be determined from the far-field pattern. Hence the effective degree of coherence of electromagnetic fields is readily measurable.

  • 2.
    Cai, Yangjian
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Propagation of various flat-topped beams in a turbulent atmosphere2006In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 8, no 6, p. 537-545Article in journal (Refereed)
    Abstract [en]

    The propagation of flat-topped beams with circular, elliptical and rectangular symmetries in a turbulent atmosphere is investigated. Analytical formulae for the average intensity of various flat-topped beams propagating in a turbulent atmosphere are derived in a tensor form. The formulae derived can easily be reduced to those for flat-topped beams propagating in free space (in the absence of turbulence). The propagation properties of flat-topped beams are studied in detail. We find that a flat-topped beam with circular or non-circular symmetry will evolve into a circular Gaussian beam in the far field under the influence of atmospheric turbulence, which is quite different to its properties in free space. Our method provides an effective and convenient way to analyse the propagation of various flat-topped beams in a turbulent atmosphere.

  • 3. Fernando, H. N. J.
    et al.
    Canning, J.
    Wosinski, Lech
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Jaskorzynska, Bozena
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Dainese, M.
    Characterization of ultra-violet-induced changes in planar waveguides2003In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 5, no 4, p. 335-340Article in journal (Refereed)
    Abstract [en]

    A simple, low-cost spectrophotometer system operating in reflection absorption mode is used to characterize changes in refractive index and thickness of thin films under 193 nm irradiation. The results indicate overall dilation of the glass and are confirmed by additional surface topographic measurements. We also show that in addition to the net relaxation from laser annealing of the interface, in germanosilicate samples local compaction takes place. Since the net relaxation is triggered by remote interactions, it is not spatially confined to the laser-irradiated area. However, a local positive index change is observed. These results are in agreement with previous hypotheses put forward to explain planar waveguide negative index changes. They also bring to attention the great care necessary in both conducting and interpreting measurements that do not take into account spatial variations arising from the combination of remote and local triggers of both index and thickness changes.

  • 4. Hansson, B. T.
    et al.
    Arvidsson, M.
    Friberg, Ari T.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Pump-mode influence on the performance of end-pumped passively Q-switched lasers2002In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 4, no 1, p. 29-32Article in journal (Refereed)
    Abstract [en]

    We present a simple way of adjusting the output performance of end-pumped passively Q-switched lasers. The method is based on changing the size of the pump mode within the active medium, and the approach is demonstrated both in theory and in practice. We show that it is possible to modify the repetition rate from 7 kHz to 1 MHz and the pulse length from 6 to 30 ns for the laser used in the experiments.

  • 5.
    He, Sailing
    et al.
    KTH, Superseded Departments, Electromagnetic Theory.
    Xu, J.
    Romanov, V. G.
    A simple analytical method for calculating the leakage loss of a buried rectangular waveguide2004In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 6, no 1, p. 57-62Article in journal (Refereed)
    Abstract [en]

    A simple and efficient analytical method is presented for studying leaky modes in a buried rectangular waveguide on a high-refractive-index substrate. The cross-sectional profile of the refractive index for the buried rectangular waveguide is decomposed into three parts. The two main parts correspond to two independent multilayered slab waveguide structures and the remaining part is treated as a small perturbation term. The contributions from all three parts to the leakage loss are given analytically. Numerical results are presented and compared with those calculated with the semi-vectorial finite difference method. Fast speed, satisfactory accuracy and simplicity are the main advantages of the present method.

  • 6.
    Kimberg, Victor
    et al.
    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.
    Angular anisotropy of the delay time of short pulses in impurity band based photonic crystals2005In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 7, no 3, p. 118-122Article in journal (Refereed)
    Abstract [en]

    We investigate the transmission of short pulses through one-dimensional impurity band based photonic crystals. We found a strong dependence of the delay time on the angle of incidence. The delay time is larger for larger incident angles for the transverse electrical mode, while the delay time of the transverse magnetic mode has a qualitatively different angular dependence, especially in the region below the Brewster angle. The strong anisotropy of the delay time is traced to the anisotropy of the group velocity which is directly related to the angular dependence of the impurity band structure.

  • 7.
    Kimberg, Victor
    et al.
    KTH, Superseded Departments, Biotechnology.
    Gelmukhanov, Faris
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Pent, E.
    Plekhanov, A.
    Kuchin, I.
    Rodionov, M.
    Shelkovnikov, V.
    Angular properties of band structures in one-dimensional holographic photonic crystals2004In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 6, no 10, p. 991-996Article in journal (Refereed)
    Abstract [en]

    One-dimensional photonic crystals with continuous distribution of the dielectric constant were fabricated by the use of photopolymer materials and laser holography. The angular dependence of light propagation through the system was studied experimentally and theoretically. It is shown that the Brewster angles for different bands are different, in contrast to the conventional two-layer Bragg reflector with a step-like distribution of the dielectric constant. Comparison of the theory with experimental data allowed us to define the parameters of the hologram-the dielectric contrast and the shrinkage of the structure.

  • 8. Lindberg, J.
    et al.
    Setälä, T.
    Kaivola, M.
    Friberg, Ari T.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Degree of polarization in light transmission through a near-field probe2004In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 6, no 3, p. S59-S63Article in journal (Refereed)
    Abstract [en]

    We analyse the changes in the partial polarization of random, stationary light fields in transmission through a near-field probe. The probe is modelled as a two-dimensional metal-coated optical fibre tip through which the field is propagated by applying the boundary-integral method. Both the magnitude of the opening angle and the aperture size of the probe are found to significantly influence the partial polarization of the field. We discuss the results in terms of both the conventional two-dimensional and the recent three-dimensional formalism for the degree of polarization.

  • 9. Ou, H. Y.
    et al.
    Zhu, K.
    Hu, Y.
    Fu, H. Y.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Tunable and reconfigurable multi-tap microwave photonic filter with negative coefficients based on a single laser diode2009In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 11, no 1Article in journal (Refereed)
    Abstract [en]

    A tunable and reconfigurable multi-tap microwave photonic filter with negative coefficients is proposed and demonstrated. The baseband resonance is eliminated by an electro-optic phase modulator combined with a dispersive medium. A Mach-Zehnder modulator (MZM) is used to get a multi-wavelength source out of a single laser diode. The free spectral range and spectral response of the microwave photonic filter is tuned and reconfigured by controlling the microwave signal and the bias voltage applied on the MZM. Experimental results show the enhanced flexibility of the present microwave photonic filter.

  • 10.
    Petermann, Ingemar
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Helmfrid, Sten
    Proximion AB, Kista.
    Fonjallaz, Pierre-Yves
    Acreo AB, Kista.
    Fibre Bragg characterization with ultraviolet-based interferometric side diffraction2003In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 5, no 5, p. 437-441Article in journal (Refereed)
    Abstract [en]

    The interferometric side diffraction method for fibre Bragg grating characterization is evaluated using a set-up with an ultraviolet interrogation beam. In its present configuration, the reproducibility errors are 2-5% for the index and typically 10degrees-20degrees for the phase profile. The reflection spectra of chirped test gratings have been successfully reproduced with the aid of the acquired phase and refractive index envelope data. It is verified that the power of the interrogating beam, within some limits, is unimportant as regards the phase reproducibility, and the importance of relating the analysis to the fabrication parameters of the grating under investigation is stressed.

  • 11.
    Petermann, Ingemar
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Helmfrid, Sten
    Proximion Fibre Systems AB, Kista.
    Gunnarsson, Ola
    Acreo AB, Kista.
    Kjellberg, Leif
    Acreo AB, Kista.
    Tunable and programmable optical bandpass filter2007In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 9, no 11, p. 1057-1061Article in journal (Refereed)
    Abstract [en]

    We demonstrate a novel tunable and programmable optical bandpass filter with a transmission peak less than 5 pm wide that is tunable over 18.5 nm. The number of transmission windows within the stop band, as well as each window's position and strength, is set by applying a heat profile to a chirped fibre Bragg grating with the aid of a thermal printer head comprising a 640 pixel array. It is shown that the width of a transmission peak formed by local heating is mainly determined by the refractive index modulation depth and chirp rate and not by the width of the heated region.

  • 12.
    Popov, Sergei
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Sergeyev, S.
    Friberg, Ari T.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    The impact of pump polarization on the polarization dependence of the Raman gain due to the breaking of a fibre's circular symmetry2004In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 6, no 3, p. S72-S76Article in journal (Refereed)
    Abstract [en]

    For many practical applications, the polarization dependence of the Raman gain (Raman PDG) is considered as a drawback. Most approaches used to reduce the PDG are based on depolarization or scrambling of the pump source polarization. We report on an experimentally observed effect and describe a method for reducing the Raman PDG by means of polarization control with a fully polarized pump source. The method makes it possible to maintain high efficiency of the Raman gain. The absence of circular symmetry (on average) in non-polarization maintaining fibres allows one to find a certain polarization state of the pump to minimize the Raman PDG. The observed phenomenon is inherently related to polarization mode dispersion which always exists in optical fibres.

  • 13. Sergeyev, Sergey V.
    et al.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Polarization-dependent gain and gain fluctuations in a fiber Raman amplifier2007In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 9, no 12, p. 1119-1122Article in journal (Refereed)
    Abstract [en]

    We report a new vector model of a fiber Raman amplifier with a randomly varying birefringence. We find that the analysis of gain fluctuations and polarization-dependent gain can be used for measurements of beat and birefringence correlation lengths and the polarization mode dispersion value on a long single-mode fiber. Results are consistent with a standard technique based on differential group delay measurements.

  • 14. She, J.
    et al.
    Forsberg, E.
    Ao, X. Y.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    High-efficiency polarization beam splitters based on a two-dimensional polymer photonic crystal2006In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 8, no 3, p. 345-349Article in journal (Refereed)
  • 15. Song, J.
    et al.
    He, Sailing
    KTH, Superseded Departments, Electromagnetic Theory.
    Effects of rounded corners on the performance of an echelle diffraction grating demultiplexer2004In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 6, no 8, p. 769-773Article in journal (Refereed)
    Abstract [en]

    Theeffectsof two different types ofroundedcorneron theperformance(such as the insertion loss, the polarization dependent loss (PDL) and the chromatic dispersion) of anechellediffractiongrating(EDG) demultiplexer are analysed by using an accurate method of moment (MoM). The results show that both the insertion loss and the chromatic dispersion increase rapidly as the radius ofroundedcornersincreases. It is shown that the impact ofroundedtroughs on the PDL is more significant than that ofroundedcrests. The PDL of an EDG demultiplexer can be reduced near the central wavelength at some special values for the radius of theroundedcorners.

  • 16.
    Thaning, Anna
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Martinsson, Per
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Karelin, Mikalai
    Friberg, Ari
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Limits of diffractive optics by communication modes2003In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 5, p. 153-158Article in journal (Refereed)
    Abstract [en]

    We apply the concept of communication modes, previously employed in information theory, to diffractive optics. The communication modes are used to study the resolution of one-dimensional optical systems in the Fresnel regime. Using the modes, which in this geometry are prolate spheroidal wavefunctions, the best achievable approximation to a given target field can be assessed. In this paper, the field propagation in terms of the communication modes is demonstrated numerically, and the results on resolution are confirmed by Fourier analysis.

  • 17. Turunen, J.
    et al.
    Friesem, A. A
    Friberg, Ari T.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Polarization optics2004In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 6, no 3, p. S1-S1Article in journal (Other academic)
  • 18. Wang, Q.
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A new effective model for the director distribution of a twisted nematic liquid crystal cell2005In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 7, no 8, p. 438-444Article in journal (Refereed)
  • 19. Wang, Q.
    et al.
    He, Sailing
    KTH, Superseded Departments, Electromagnetic Theory.
    A simple, fast and accurate method of designing directional couplers by evaluating the phase difference of local supermodes2003In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 5, no 5, p. 449-452Article in journal (Refereed)
  • 20. Xiao, Sanshui
    et al.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Theoretical study of the transmission properties of a metallic film with surface corrugations2007In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 9, no 4, p. 348-351Article in journal (Refereed)
    Abstract [en]

    Transmissions through a metallic film at near-infrared wavelengths with different surface corrugations on both sides are systemically studied. The calculations are performed by the three-dimensional finite-different time-domain method. Calculated results show that the transmissions are strongly dependent on the surface structures. Compared with other structures, the transmission for a film periodically drilled by cross air grooves are relatively larger. Transmission is enhanced more with symmetric conditions on both layers than the asymmetric case. The enhanced transmission can be explained by a competition between the absorption in the metal and enhanced transmission due to coupled surface plasmon resonance.

  • 21. Yu, Xia
    et al.
    Zhang, Ying
    Pan, Shanshan
    Shum, Ping
    Nanyang Techbological University, Singapore.
    Yan, Min
    Leviatan, Yehuda
    Li, Changming
    A selectively coated photonic crystal fiber based surface plasmon resonance sensor2010In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 12, no 1Article in journal (Refereed)
  • 22.
    Zhang, Liyang
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    The effect of transformation order on the invisibility performance of a practical cylindrical cloak2008In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 10, no 9Article in journal (Refereed)
    Abstract [en]

    A class of polynomial coordinate transformation functions with an arbitrary order number is used to design cylindrical invisibility cloaks. Since an ideal cylindrical cloak is inevitably unphysical at its inner boundary, our investigation involves the replacement of a thin layer of material at the cloak's inner surface by a homogeneous material layer. This approach effectively avoids the infinities in the material parameters, and at the same time produces practical near-ideal invisibility cloaks. The cloaks obtained are perfectly matched in impedance at the outer boundary. We quantitatively show the effect of the transformation order on the proposed cloak's scattering coefficients.

1 - 22 of 22
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