| 1. |
- Akram, Nadeem, 1971-, et al.
(författare)
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Experimental characterization of high-speed 1.55 mu m buried heterostructure InGaAsP/InGaAlAs quantum-well lasers
- 2009
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 26:2, s. 318-327
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Tidskriftsartikel (refereegranskat)abstract
- Detailed experimental characterization is performed for 1550 nm semi-insulating regrown buried heterostructure Fabry-Perot (FP) lasers having 20 InGaAsP/InGaAlAs strain-balanced quantum wells (QWs) in the active region. Light-current-voltage performance, electrical impedance, small-signal response below and above threshold, amplified spontaneous emission spectrum below threshold and relative intensity noise spectrum are measured. Different laser parameters such as external differential quantum efficiency eta(d), background optical loss alpha(i), K-factor, D-factor, characteristic temperature T-0, differential gain dg/dn, gain-compression factor epsilon, carrier density versus current, differential carrier lifetime tau(d), optical gain spectrum below threshold, and chirp parameter alpha are extracted from these measurements. The FP lasers exhibited a high T-0 (78-86.5 degrees C) and very high-resonance frequency (23.7 GHz). The results indicate that appropriately designed lasers having a large number of InGaAsP well/InGaAlAs barrier QWs with shallow valence-band discontinuity can be useful for un-cooled high-speed direct-modulated laser applications.
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| 2. |
- Baev, A., et al.
(författare)
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Bi-directional description of amplified spontaneous emission induced by three-photon absorption
- 2005
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 22:2, s. 385-393
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Tidskriftsartikel (refereegranskat)abstract
- A semiclassical dynamic theory of the nonlinear propagation of a few interacting intense light pulses is applied to study the nonlinear counterpropagation of amplified spontaneous emission (ASE) induced by three-photon absorption of short intense laser pulses in a chromophore solution. Several important results from the modeling are reached for the ASE process developing in the regime of strong saturation. Accounting for ASE in both forward and backward directions with respect to the pump pulse results in a smaller efficiency of nonlinear conversion for the forward ASE compared with the case in which forward emission is considered alone, something that results from the partial repump of the absorbed energy to the backward ASE component; the overall efficiency is nevertheless higher than for the forward emission considered alone. The efficiency of nonlinear conversion of the pump energy to the counterpropagating ASE pulses is strongly dependent on the concentration of active molecules so that a particular combination of concentration versus cell length optimizes the conversion coefficient. Under certain specified conditions, the ASE effect is found to be oscillatory; the origin of oscillations is dynamical competition between stimulated emission and off-resonant absorption. This result can be considered one of the possible explanations of the temporal fluctuations of the forward ASE pulse [Nature 415, 767 (2002)].
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| 3. |
- Berezovsky, Vladimir, et al.
(författare)
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Effect of dipole-dipole interactions between atoms in an active medium
- 2008
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 25:3, s. 458-462
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Tidskriftsartikel (refereegranskat)abstract
- On the basis of the results of numerical modeling, it is shown that dipole-dipole interactions among atoms in the active medium strongly influences the character of the associated superradiation. The main effect is to make the nuclear subsystem behave chaotically. Its strength increases with the atom density and leads to the suppression of distant collective correlations and superradiation. Near correlations between the atoms are established, causing a confinement effect: a shielding of radiation in the active medium.
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| 4. |
- Björk, Gunnar, et al.
(författare)
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Mutually unbiased bases and discrete Wigner functions
- 2007
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 24:2, s. 371-378
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Tidskriftsartikel (refereegranskat)abstract
- Mutually unbiased bases and discrete Wigner functions are closely but not uniquely related. Such a connection becomes more interesting when the Hilbert space has a dimension that is a power of a prime N=d(n), which describes a composite system of n qudits. Hence, entanglement naturally enters the picture. Although our results are general, we concentrate on the simplest nontrivial example of dimension N=8=2(3). It is shown that the number of fundamentally different Wigner functions is severely limited if one simultaneously imposes translational covariance and that the generating operators consist of rotations around two orthogonal axes, acting on the individual qubits only.
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| 5. |
- Cai, Yangjian, et al.
(författare)
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Coherent and partially coherent dark hollow beams with rectangular symmetry and paraxial propagation properties
- 2006
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 23:7, s. 1398-1407
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical model is proposed to describe coherent dark hollow beams (DHBs) with rectangular symmetry. The electric field of a coherent rectangular DHB is expressed as a superposition of a series of the electric field of a finite series of fundamental Gaussian beams. Analytical propagation formulas for a coherent rectangular DHB passing through paraxial optical systems are derived in a tensor form. Furthermore, for the more general case, we propose a theoretical model to describe a partially coherent rectangular DHB. Analytical propagation formulas for a partially coherent rectangular DHB passing through paraxial optical systems are derived. The beam propagation factor (M-2 factor) for both coherent and partially coherent rectangular DHBs are studied. Numerical examples are given by using the derived formulas. Our models and method provide an effective way to describe and treat the propagation of coherent and partially coherent rectangular DHBs.
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| 6. |
- Cui, Y. X., et al.
(författare)
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Nanocavity antenna array for enhancing extraordinary optical transmission of light through a metallic nanoslit
- 2009
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 26:11, s. 2131-2135
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Tidskriftsartikel (refereegranskat)abstract
- The transmission of light through a single nanoslit milled in the metallic film is enhanced by using an array of nanocavity antennas. It is shown that transmission efficiency through a 25-nm-wide silver nanoslit can be enhanced to eta = 151 when six pairs of nanostrips are placed 50 nm away from the input surface of the silver film at wavelength lambda(0) = 1 mu m. The influences of both the nanoslit position and the slit-to-strip distance on the extraordinary transmission are investigated, and the physical mechanism is explained.
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| 7. |
- Dai, Daoxin, et al.
(författare)
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Highly sensitive sensor based on an ultra-high-Q Mach-Zehnder interferometer-coup led microring
- 2009
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 26:3, s. 511-516
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Tidskriftsartikel (refereegranskat)abstract
- A high-Q Mach-Zehnder interferometer (MZI)-coupled microring is presented for optical sensing with high sensitivity and a large measurement range. By optimizing the length difference, between the two arms of the MZI coupler, the MZI-coupled microring with a high-Q factor and high extinction ratio is obtained. In the present example, the Q factor of the designed silicon-nanowire-based microring is as high as 1.8 x 10(5) when the silicon nanowire has a propagation loss L=2 dB/cm. Due to this high-Q factor, the sensitivity for the change Delta n of the effective refractive index is about 10(-5)-10(-6) by measuring the shift of the resonant wavelength. Because of the wavelength dependence of the coupling ratio of the MZI coupler, it is possible to have only one resonant wavelength with a high extinction ratio in a very large wavelength span [i.e., the quasi-free spectral range of the MZI-coupler microring], which offers a very large measurement range covering the refractive index change
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| 8. |
- Dai, Daoxin, et al.
(författare)
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Numerical analysis of silicon-on-insulator ridge nanowires by using a full-vectorial finite-difference method mode solver
- 2007
-
Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 24:11, s. 2853-2859
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Tidskriftsartikel (refereegranskat)abstract
- The characteristics of silicon-on-insulator (SOI) ridge waveguides are analyzed by using a cylindrical full-vectorial finite-difference method mode solver with a perfectly-matched layer treatment. First, the single-mode condition for an SOI ridge nanowire with different Si core thicknesses is obtained. The obtained single-mode condition is different from that for the conventional micrometrical SOI ridge waveguides with a large cross section. By adjusting the cross section (the core width and the etching depth), one can have a nonbirefringent SOI ridge nanowire. The analysis on the bending loss of S01 ridge nanowires shows that one can have a relatively small bending radius even with a shallow etching (i.e., a small ratio γ between the etching depth and the total thickness). For example, even when one chooses a small ratio γ= 0.4, one still has a low bending loss with a small bending radius of 15 μm for an SOI nanowire with a thin core h∞= 250 nm, which is very different from a conventional large SOI ridge waveguide.
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| 9. |
- El-Kallassi, Pascale, et al.
(författare)
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Optical tuning of planar photonic crystals infiltrated with organic molecules
- 2007
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 24:9, s. 2165-2171
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Tidskriftsartikel (refereegranskat)abstract
- The optical tuning of InP-based planar photonic crystals (PhCs) infiltrated with a photoresponsive liquid crystal system is presented. Photoinduced phase transitions of a liquid crystal blend doped with azobenzene molecules are used to tune the optical response of PhC cavities. This process is found to be reversible and stable. Several tuning conditions are analyzed in terms of the blend phase diagram.
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| 10. |
- Foltynowicz, Aleksandra, 1981-, et al.
(författare)
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Doppler-broadened noise-immune cavity-enhanced optical heterodyne molecular spectrometry signals from optically saturated transitions under low pressure conditions
- 2008
-
Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 25:7, s. 1156-1165
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Tidskriftsartikel (refereegranskat)abstract
- The influence of optical saturation on noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) signals from purely Doppler-broadened transitions is investigated experimentally. It is shown that the shape and the strength of the dispersion signal are virtually unaffected by optical saturation, whereas the strength of the absorption signal decreases as (1+G+-1)-1/2, where G+-1 is the degree of saturation induced by the sideband of the frequency modulated triplet, in agreement with theoretical predictions. This implies, first of all, that Doppler-broadened NICE-OHMS is affected less by optical saturation than other cavity enhanced techniques but also that it exhibits nonlinearities in the power and pressure dependence for all detection phases except pure dispersion. A methodology for assessments of the degree of saturation and the saturation power of a transition from Doppler-broadened NICE-OHMS signals is given. The implications of optical saturation for practical trace species detection by Doppler-broadened NICE-OHMS are discussed.
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| 11. |
- Foltynowicz, Aleksandra, 1981-, et al.
(författare)
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Wavelength modulated noise-immune cavity-enhanced optical heterodyne molecular spectroscopy signal line shapes in the Doppler limit
- 2009
-
Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 26:7, s. 1384-1394
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Tidskriftsartikel (refereegranskat)abstract
- A thorough analysis of the shape and strength of Doppler-broadened wavelength modulated noise-immune cavity-enhanced optical heterodyne molecular spectroscopy signals is presented and their dependence on modulation frequency, modulation amplitude and detection phase is investigated in detail. The conditions that maximize the on-resonance signal are identified. The analysis is based on the standard frequency modulation spectroscopy formalism and the Fourier description of wavelength modulation spectroscopy and verified by fits to experimental signals from C2H2 and CO2 measured at 1531 nm. In addition, the line strengths of two CO2 transitions in the v2→3v1+v2+v3 hot band [Pe(7) and Pe(9)] were found to differ by ~20% from those given in the HITRAN database.
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| 12. |
- Fu, Ying, et al.
(författare)
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Optical transmission and waveguiding by excitonic quantum dot lattices
- 2006
-
Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 23:11, s. 2441-2447
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Tidskriftsartikel (refereegranskat)abstract
- Metal-dielectric-metal configurations of optical waveguides have a very high laterally packaging density at the cost of high optical loss. Photonic crystals based on refractive-index-modulation materials have been used in optics, e.g., two materials having different refractive indices form a well-defined Bragg refraction mirror. Such a waveguide has lower loss but also lower packaging density. From the outset of these two notions, we propose a photonic-crystal device based on the exciton-polariton effect in a three-dimensional array of semiconductor quantum dots (QDs) for ultradense optical planar circuit applications. Excitons are first photogenerated in the QDs by the incident electromagnetic field, the exciton-polariton effect in the QD photonic crystal then induces an extra optical dispersion in QDs. The high contrast ratio between the optical dispersions of the QDs and the background therefore creates clear photonic bandgaps. By carefully designing the QD size and the QD lattice structure, perfect electromagnetic field reflection can be obtained at a specific wavelength in the lossless case, thus providing the fundamental basis for ultradense optical waveguide applications.
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| 13. |
- Gao, Shiming, et al.
(författare)
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Two channels of entangled twin photons generated by quasi-phase-matched spontaneous parametric down-conversion in periodically poled lithium niobate crystals
- 2008
-
Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 25:5, s. 734-740
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Tidskriftsartikel (refereegranskat)abstract
- We propose the generation of two-channel time-energy entangled twin photons based on two simultaneous first-order quasi-phase-matched (QPM) spontaneous parametric down-conversion processes in a periodically poled lithium niobate (PPLN) with a monochromatic pump. The theoretical model for the generation of the entangled photons is established, and the analytical solution is obtained in a lossless crystal with an undepleted pump assumption. The generated condition of entangled photons is achieved in terms of the QPM grating period and the pump wavelength. It is shown that two channels of entangled twin photons with different wavelengths can be created by suitably choosing the PPLN grating period once the pump wavelength is fixed, which provides the potential to introduce the wavelength division multiplexed technique into quantum information systems.
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| 14. |
- Jeong, H., et al.
(författare)
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Evolution of Sommerfeld and Brillouin precursors in intermediate spectral regimes
- 2009
-
Ingår i: Journal of the Optical Society of America B: Optical Physics. - 1520-8540 .- 0740-3224. ; 26:12, s. 2455-2460
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Tidskriftsartikel (refereegranskat)abstract
- We study, numerically, the transitional behavior of precursors in the intermediate spectral regime between twocontrasting regimes for which analytical solutions exist. The two opposite regimes are, respectively, defined as(1) off-resonance carrier with a spectral pulse width comparable to the medium’s absorption linewidth and (2)on-resonance carrier with the spectral width of the pulse much narrower than the absorption linewidth. Beyondthese two regimes, there have been few studies of precursors. In this paper, we investigate precursordynamics for the intermediate spectral regime using the finite-difference time domain method. The parameterthat has the strongest influence on the precursor dynamics is found to be the plasma frequency, ωp. This researchis applicable for controlling transients in fast communication systems.
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| 15. |
- Jonsson, F., et al.
(författare)
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Spectral windowing with chirped magneto-optical Bragg gratings
- 2005
-
Ingår i: Journal of the Optical Society of America B: Optical Physics. - 1520-8540 .- 0740-3224. ; 22:1, s. 293-298
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Tidskriftsartikel (refereegranskat)abstract
- We present a theory on a novel class of magneto-optical devices operated by means of magneto-optically induced refractive-index perturbations in chirped Bragg gratings. The predicted effect of the introduced perturbation is an opening of a narrow transmission window in the band-blocking transmission of the chirped grating. The narrow transmission window is tunable in wavelength, and relative transmission and the effects of multiple, spatially separated perturbations can also be superimposed, hence allowing for tunable, magneto-optically operated, multichannel add-drop multiplexors suitable for modularization in integrated optics.
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| 16. |
- Khoptyar, D., et al.
(författare)
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Experimental determination of the energy-transfer parameters for homogeneous upconversion in Er-doped silica
- 2005
-
Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 22:10, s. 2091-2098
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Tidskriftsartikel (refereegranskat)abstract
- Applying a nonlinear spectroscopic technique, we accurately monitor the dynamics of the homogeneous upconversion (HUC) in Er-doped fibers. We provide the first experimental confirmation, to our knowledge, of the earlier theoretical predictions that, for low erbium concentrations, a decay of HUC-influenced excitation probability of Er ions can be well approximated by the formula describing the static HUC. By correlating the experimentally obtained HUC dynamics with the results of our analytical model in a wide range of Er concentrations, we accurately estimate energy-transfer parameters for Er-doped silica glass and experimentally assess the validity of the model.
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| 17. |
- Khoptyar, D., et al.
(författare)
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Homogeneous upconversion in Er-doped fibers under steady state excitation : analytical model and its Monte Carlo verification
- 2005
-
Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 22:3, s. 582-590
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Tidskriftsartikel (refereegranskat)abstract
- We present an extension to our earlier proposed statistical model for studying migration-assisted homogeneous upconversion in erbium-doped fibers. The extension takes into account minimum proximity distance between erbium ions randomly distributed in the host material and the nonuniformity of the excitation distribution among them. We derive a transcendental equation for the population inversion and find the dependence of the upconversion rate on the population inversion and the pump power for the entire range of feasible Er concentrations. We verify the validity and accuracy of the model by means of time-resolved Monte Carlo simulations.
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| 18. |
- Kockaert, Pascal, et al.
(författare)
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Beyond the zero-diffraction regime in optical cavities with a left-handed material
- 2009
-
Ingår i: Journal of the Optical Society of America B: Optical Physics. - 1520-8540 .- 0740-3224. ; 26:12, s. B148-B155
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Tidskriftsartikel (refereegranskat)abstract
- The combination of right-handed and left-handed materials offers the possibility to design devices in which the mean diffraction is zero. Such systems are encountered, for example, in nonlinear optical cavities, where a true zero-diffraction regime could lead to the formation of patterns with arbitrarily small sizes. In practice, the minimal size is limited by nonlocal terms in the equation of propagation. We study the nonlocal properties of light propagation in a nonlinear optical cavity containing a right-handed and a left-handed material. We obtain a model for the propagation, including two sources of nonlocality: the spatial dispersion of the materials in the cavity, and the higher-order terms of the mean field approximation. We apply these results to a particular case and derive an expression for the parameter fixing the minimal size of the patterns.
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| 19. |
- Prawiharjo, Jerry, et al.
(författare)
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Frequency-resolved optical gating in the 1.55 um band via cascaded chi-2 processes
- 2005
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 22:9, s. 1985-1993
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Tidskriftsartikel (refereegranskat)abstract
- We investigate ultrashort-pulse interactions based on cascaded second-harmonic generation and difference-frequency generation and propose their use for frequency-resolved optical gating (FROG) at telecom wavelengths in a waveguide configuration. We show how a chi((2))-chi((2)) FROG device could allow the efficient characterization of ultrashort pulses, with time resolutions well beyond the limits normally imposed by walk-off effects on single-step chi((2)) FROG devices.
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| 20. |
- Rahachou, Aliaksandr, et al.
(författare)
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Waveguiding properties of surface states in photonic crystals
- 2006
-
Ingår i: Journal of the optical society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 23:8, s. 1679-1683
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Tidskriftsartikel (refereegranskat)abstract
- We propose and analyze novel surface-state-based waveguides in bandgap photonic crystals. We discuss the surface-mode band structure, the field localization, and the effect of imperfections on the waveguiding properties of the surface modes. We demonstrate that surface-state-based waveguides can be used to achieve directional emission out of the waveguide. We also discuss the application of the surface-state waveguides as efficient light couplers for conventional photonic crystal waveguides.
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| 21. |
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| 22. |
- Sergeyev, Sergey, et al.
(författare)
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Statistical model of migration-assisted upconversion in a high-concentration erbium-doped fiber amplifier
- 2006
-
Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 23:8, s. 1540-1543
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Tidskriftsartikel (refereegranskat)abstract
- We report a new model of a high-concentration erbium-doped fiber amplifier (EDFA) accounting for the statistical nature of the migration and up-conversion processes. By fitting experimental results, we conclude that the statistical model shows better applicability for the characterization of high-concentration EDFAs than the model accounting for the homogeneous upconversion and pair-induced quenching.
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| 23. |
- Shen, Jianqi
(författare)
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Field quantization and vacuum effects in a chiral medium
- 2008
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 25:11, s. 1864-1872
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Tidskriftsartikel (refereegranskat)abstract
- A chiral medium can create an anisotropic electromagnetic environment, which leads to anisotropic quantum-vacuum fields (and observable quantum-vacuum effects). As the noncompensation effect of a pair of counterpropagating (and counterpolarized) vacuum modes will arise in the chiral medium, the physical effects resulting from the quantum-vacuum fluctuation of left- and right-handed polarized modes will no longer be exactly canceled. This may lead to an observable quantum vacuum contribution to the Berry phases of circularly polarized modes in a time-dependent quantum system (e.g., a coiled light propagating in a noncoplanarly curved fiber). A scheme to separate the quantum-vacuum Berry phase of one polarized mode from another by using a chiral-medium fiber is suggested, and the time evolution of the vacuum zero-point energy in a coiled fiber is considered.
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| 24. |
- Torres-Company, Victor, et al.
(författare)
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Coherence theory of noise in ultrashort-pulse trains
- 2007
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 24:7, s. 1441-1450
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Tidskriftsartikel (refereegranskat)abstract
- We study the influence of noise in ultrashort-pulse trains in terms of the concepts of optical coherence theory. Specifically, we consider the effects of temporal partial coherence and the timing jitter, including their possible statistical dependence. Analytical expressions for the optical power spectrum, average intensity, mutual coherence function, and the cross-spectral density function of different partially coherent pulse trains affected by stationary noise are given. We show that the new frequencies appearing due to the presence of noise are always fully uncorrelated, unless they are separated by an integral multiple of the repetition rate of the pulses in the train. We also find that spikes appear in the optical power spectrum when the noise and timing jitter are correlated.
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| 25. |
- Wachulak, P., et al.
(författare)
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Interferometric lithography with an amplitude division interferometer and a desktop extreme ultraviolet laser
- 2008
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - : Optical Society of America. - 0740-3224 .- 1520-8540. ; 25:7, s. B104-B107
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a compact interferometric lithography nanopatterning tool based on an amplitude division interferometer (ADI) and a 46.9 nm wavelength desktop size capillary discharge laser. The system is designed to print arrays of lines, holes, and dots with sizes below 100 nm on high resolution photoresists for the fabrication of arrays of nanostructures with physical and biological applications. The future combination of this ADI with high repetition rate tabletop lasers operating at shorter wavelengths should allow the printing of arrays of sub-10 nm size features with a tabletop setup.
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| 26. |
- Wang, B., et al.
(författare)
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Superlens formed by a one-dimensional dielectric photonic crystal
- 2008
-
Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 25:3, s. 391-395
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Tidskriftsartikel (refereegranskat)abstract
- A simple superlens formed by a one-dimensional dielectric photonic crystal is introduced. Off-axis subwave-length focusing is achieved and studied with the equifrequency contour analysis and finite-difference time-domain simulation. Besides its advantage of simplicity, the present superlens can give a spot size much smaller than that achieved by a slab of some high-dimensional photonic crystal of negative refraction. The properties of an on-axis image achieved by the combination of two slabs of the one-dimensional photonic crystal are also studied.
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| 27. |
- Wang, Chuan-Kui, et al.
(författare)
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Breakdown of optical power limiting and dynamical two-photon absorption for femtosecond laser pulses in molecular medium
- 2007
-
Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 24:9, s. 2436-2442
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Tidskriftsartikel (refereegranskat)abstract
- We solve numerically the Maxwell-Bloch equations using an iterative predictor-corrector finite-difference time-domain technique to study the propagation of femtosecond laser pulses in a strong two-photon absorption (TPA) organic molecular medium [4,4'-bis(dimethylamino) stilbene]. The hybrid density functional theory is used to calculate electronic structures of the compound. The molecular system is described by a three-level model in an optical regime and has demonstrated a good optical power limiting behavior in a certain intensity region. Thresholds for the breakdown of optical power limiting are observed that are dependent on the input pulse width and, slightly, the propagation distance. The dynamical two-photon absorption cross section is obtained, which is almost a linearly increasing function of the pulse width in the femtosecond time domain. The propagation distance also has an obvious influence on the measurement of the TPA cross section, and non-monotonic dependence of the TPA cross section on propagation distance is observed. The input pulse width and the thickness of the molecular samples thus should be taken into account when the TPA cross section is measured.
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| 28. |
- Wang, Zhechao, et al.
(författare)
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Ultrasmall Si-nanowire-based polarization rotator
- 2008
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 25:5, s. 747-753
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Tidskriftsartikel (refereegranskat)abstract
- A polarization rotator based on asymmetrical Si nanowires is presented and optimized for high polarization rotation efficiency (almost 100%). The present polarization rotator has a very small conversion length (similar to 10 mu m) and consequently becomes very compact. The analysis of the wavelength dependence shows the present polarization rotator has a broad bandwidth (similar to 120 nm) for high conversion efficiency (> 97%). The tolerance to various fabrication errors is also numerically studied. To compensate the fabrication error, a post-compensation method is introduced by modifying the refractive index of the up-cladding. (c) 2008 Optical Society of America.
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| 29. |
- Xiao, Sanshui, et al.
(författare)
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Optical microcavities based on surface modes in two-dimensional photonic crystals and silicon-on-insulator photonic crystals
- 2007
-
Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 24:5, s. 1225-1229
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Tidskriftsartikel (refereegranskat)abstract
- Surface-mode optical microcavities based on two-dimensional photonic crystals and silicon-on-insulator photonic crystals are studied. We demonstrate that a high-quality-factor microcavity can be easily realized in these structures. With an increasing of the cavity length, the quality factor is gradually enhanced and the resonant frequency converges to that of the corresponding surface mode in the photonic crystals. These structures have potential applications such as sensing.
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| 30. |
- Xu, Huailiang, et al.
(författare)
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Lifetime measurements in neutral and singly ionized vanadium
- 2006
-
Ingår i: Optical Society of America. Journal B: Optical Physics. - 0740-3224. ; 23:12, s. 2597-2600
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Tidskriftsartikel (refereegranskat)abstract
- Radiative lifetimes of ten odd-parity levels of V I belonging to the 3d(3)4s4p and 3d(4)4p configurations and of 11 odd-parity levels of V II belonging to the 3d(3)4p configuration are reported. The lifetimes were measured with use of single-step excitation and time-resolved fluorescence spectroscopy. The neutral and singly ionized vanadium atoms were produced in a laser-induced vanadium plasma. (c) 2006 Optical Society of America.
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| 31. |
- Yan, Min, et al.
(författare)
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Guidance varieties in photonic crystal fibers
- 2006
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 23:8, s. 1684-1691
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Tidskriftsartikel (refereegranskat)
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| 32. |
- Yan, Min, et al.
(författare)
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Guidance varieties in photonic crystal fibers
- 2006
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - : Optical Society of America. - 0740-3224 .- 1520-8540. ; 23:8, s. 1684-1691
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Tidskriftsartikel (refereegranskat)abstract
- We study in general the property of dielectric optical waveguides that are translationally invariant along the field propagation direction. The core and the cladding can be made of either homogeneous or two-dimensional (2D) composite material (or metamaterial). When the metamaterial involved exhibits 2D periodicity, the waveguides are so-called photonic crystal fibers (PCFs). Guidance varieties in such waveguides are studied by examining separately the optical properties of the bulk core and cladding materials as well as by explicit numerical calculation of the overall waveguide structure. Our analysis reveals several neglected modal characteristics of such waveguides. For example, we show that different modes can copropagate in some PCFs with different guidance mechanisms, i.e., index guidance and photonic bandgap guidance. Such a feature can offer additional flexibility in light-wave manipulation. We also show that there exists a cutoff wavelength for the fundamental index-guided mode in some PCFs, which breaks the convention in traditional step-index fibers where such a cutoff does not exist.
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| 33. |
- Yan, Min, et al.
(författare)
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Guided plasmon polariton at 2D metal corners
- 2007
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 24:9, s. 2333-2342
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the properties of plasmon polaritons guided by 2D monoangular metal corners with a vector finite-element method. Such corner waveguides in general include both V-channel- and A-wedge-type waveguides. The influences of both geometric parameters (i.e., corner angle, tip sharpness, etc.) and operating wavelength to the mode properties, such as effective mode index, loss, and mode field size, are inspected. It is noticed that both a smaller corner angle and a sharper corner tip help to better confine the mode field. The confinement of the V-channel waveguide is found to be especially sensitive to its angle, while the confinement of the A-wedge waveguide is affected about equally by its angle and tip sharpness. Almost all superior mode field confinement is realized at the expense of higher propagation loss for such waveguides. The chromatic dispersion of such waveguides is found to be adequate for applications in integrated optical circuits. The mode behaviors of realistic corner waveguides with finite sidewalls are also studied.
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| 34. |
- Yan, Min, et al.
(författare)
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Guided plasmon polariton at 2D metal corners
- 2007
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - : Optical Society of America. - 0740-3224 .- 1520-8540. ; 24:9, s. 2333-2342
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the properties of plasmon polaritons guided by 2D monoangular metal corners with a vector finite-element method. Such corner waveguides in general include both V-channel- and Λ-wedge-type waveguides. The influences of both geometric parameters (i.e., corner angle, tip sharpness, etc.) and operating wavelength to the mode properties, such as effective mode index, loss, and mode field size, are inspected. It is noticed that both a smaller corner angle and a sharper corner tip help to better confine the mode field. The confinement of the V-channel waveguide is found to be especially sensitive to its angle, while the confinement of the Λ-wedge waveguide is affected about equally by its angle and tip sharpness. Almost all superior mode field confinement is realized at the expense of higher propagation loss for such waveguides. The chromatic dispersion of such waveguides is found to be adequate for applications in integrated optical circuits. The mode behaviors of realistic corner waveguides with finite sidewalls are also studied.
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| 35. |
- Yan, Wei, 1983-, et al.
(författare)
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Generalized compensated bilayer structure from the transformation optics perspective
- 2009
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 26:12, s. B39-B49
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Tidskriftsartikel (refereegranskat)abstract
- A systematic study on a generalized compensated bilayer structure is presented based on transformation optics. A compensated bilayer can be constructed through a general transformation plus a coordinate inversion based on a single layer in the electromagnetic (EM) space. Two outer boundaries of the obtained bilayer are mapped from the same surface. Such a bilayer has an optically zero volume (nihility) regardless of the material composition in the original single layer. This fact directly leads to the property of invariant scattering. A bilayer is also able to transfer the EM field from one side to the other with a scaling factor, which is determined by how the two side boundaries are mapped. For a properly chosen background, it is possible to achieve perfect optical imaging. Extensive numerical examples are given to demonstrate these identified properties and applications. Our study provides a more complete understanding of this class of transformation media by considering general geometries and arbitrary material properties.
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| 36. |
- Yan, Wei, et al.
(författare)
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Generalized compensated bilayer structure from the transformation optics perspective
- 2009
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - : Optical Society of America. - 0740-3224 .- 1520-8540. ; 26:12, s. B39-B49
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Tidskriftsartikel (refereegranskat)abstract
- A systematic study on a generalized compensated bilayer structure is presented based on transformation optics. A compensated bilayer can be constructed through a general transformation plus a coordinate inversion based on a single layer in the electromagnetic (EM) space. Two outer boundaries of the obtained bilayer are mapped from the same surface. Such a bilayer has an optically zero volume (nihility) regardless of the material composition in the original single layer. This fact directly leads to the property of invariant scattering. A bilayer is also able to transfer the EM field from one side to the other with a scaling factor, which is determined by how the two side boundaries are mapped. For a properly chosen background, it is possible to achieve perfect optical imaging. Extensive numerical examples are given to demonstrate these identified properties and applications. Our study provides a more complete understanding of this class of transformation media by considering general geometries and arbitrary material properties.
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| 37. |
- Zeng, Yong, et al.
(författare)
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Highly efficient generation of entangled photon pair by spontaneous parametric downconversion in defective photonic crystals
- 2007
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 24:6, s. 1365-1368
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Tidskriftsartikel (refereegranskat)abstract
- We study the process of spontaneous parametric downconversion in a one-dimensional defective quadratic nonlinear photonic crystal. It is shown that the strong confinements of both the pump and signal waves around the defective layer result in a giant enhancement of the entangled photon-pair generation. An enhancement factor as high as 3.4 X 10(6) is obtained in our defective structure based on the dual-localized modes. Furthermore, the linewidth of the downconverted fields is only 0. 1 nm. Such a photonic crystal structure can be applied as a highly efficient source of entangled photon pairs for highly integrated all-optical circuits.
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| 38. |
- Zhang, Ziyang, et al.
(författare)
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Coupled-mode analysis of a resonant channel drop filter using waveguides with mirror boundaries
- 2006
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 23:1, s. 104-113
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Tidskriftsartikel (refereegranskat)abstract
- The operation of resonant channel drop filters is analyzed using coupled-mode theory. The resonator is chosen to support a single standing-wave mode, and, in the ideal case, one can realize 100% in-plane channel transfer by properly applying mirror boundaries to the waveguides. The presence of the mirrors causes the resonant frequency to shift, and the system Q factor also changes accordingly. The two variables are related by a closed curve depending on the phase introduced by the reflection and wave propagation between the two ports. When one works on different regions of the curve, the system can be tuned to work at different resonant frequencies with minimum Q-factor variations or vice versa. The mirror can be frequency selective. The same single-mode cavity can be used as a resonant mirror to terminate the waveguide. The combined system is analyzed, and we find the conditions to achieve 100% channel transfer as well as to maintain a simple Lorentzian line shape of the transmission spectra. The analysis is verified by two-dimensional (2D) finite-difference time-domain simulations in 2D hexagonal photonic crystals.
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