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Showing papers on "Optical polarization published in 2011"


Journal ArticleDOI
TL;DR: In this paper, a review of sensitivity-enhancement techniques for surface plasmon resonance (SPR) sensors focusing both on the physical transduction mechanisms and the system performance is presented.
Abstract: Surface plasmon resonance (SPR) sensors have been a mature technology for more than two decades now, however, recent investigations show continuous enhancement of their sensitivity and their lower detection limit. Together with the recent investigations in localized SPR phenomena, extraordinary optical transmission through nanoapertures in metals, and surface-enhanced spectroscopies, drastic developments are expected to revolutionize the field of optical biosensing. Sensitivity-enhancement (SE) techniques are reviewed focusing both on the physical transduction mechanisms and the system performance. In the majority of cases the SE is associated with the enhancement of the electromagnetic field overlap integral describing the interaction energy within the analyte. Other important mechanisms are the interaction between plasmons and excitons and between the analyte molecules and the metal surface. The lower detection limit can be reduced significantly if systems with high signal-to-noise ratio are used such as common-path interferometry, ellipsometry or polarimetry systems.

391 citations


Journal ArticleDOI
TL;DR: The QD-luminescent images of these structures reveal that a complete family of phase-dependent, interferometric logic functions can be performed on these simple networks of silver nanowires with two optical inputs.
Abstract: We show that the local electric field distribution of propagating plasmons along silver nanowires can be imaged by coating the nanowires with a layer of quantum dots, held off the surface of the nanowire by a nanoscale dielectric spacer layer. In simple networks of silver nanowires with two optical inputs, control of the optical polarization and phase of the input fields directs the guided waves to a specific nanowire output. The QD-luminescent images of these structures reveal that a complete family of phase-dependent, interferometric logic functions can be performed on these simple networks. These results show the potential for plasmonic waveguides to support compact interferometric logic operations.

285 citations


Journal ArticleDOI
01 May 2011
TL;DR: This work reports the realization of an integrated beam splitter able to support polarization-encoded qubits and demonstrates quantum interference with polarization-entangled states and singlet state projection.
Abstract: We report the realization of an integrated beam splitter able to support polarization-encoded qubits. Using this device, we demonstrate quantum interference with polarization-entangled states and singlet state projection.

261 citations


Journal ArticleDOI
Zhenning Tao1, Liang Dou1, Weizhen Yan1, Lei Li1, Takeshi Hoshida1, Jens C. Rasmussen1 
TL;DR: In this paper, a low-complexity intrachannel nonlinear compensator operating at the symbol rate is proposed based on the nonlinear perturbation predistortion for the dual-polarization quadrature phase-shift keying (DP-QPSK) systems.
Abstract: Intrachannel nonlinearity is considered a major distortion in high-capacity transmission systems particular for the case without inline optical chromatic dispersion compensation. In this paper, a low-complexity intrachannel nonlinear compensator operating at the symbol rate is proposed based on the nonlinear perturbation predistortion for the dual-polarization quadrature phase-shift keying (DP-QPSK) systems. Compared with the widely studied backpropagation algorithm, the proposed algorithm achieves comparable performance with significantly reduced complexity and halved sampling speed in digital signal processing and digital-to-analog converters. The proposed algorithm is demonstrated in a 43 Gb/s DP-QPSK transmission experiment over 1500 km. In addition to the experimental demonstration, numerical simulation verifies that the proposed algorithm is quite robust by tolerating significant uncertainties of link parameters and span-by-span inhomogeneity in the links.

205 citations


Journal ArticleDOI
TL;DR: In this paper, a coherent optical orthogonal frequency-division multiplexing (CO-OFDM) scheme with reduced guard interval (RGI) was proposed for high-speed high-spectral-efficiency long-haul optical transmission.
Abstract: We propose a novel coherent optical orthogonal frequency-division multiplexing (CO-OFDM) scheme with reduced guard interval (RGI) for high-speed high-spectral-efficiency long-haul optical transmission. In this scheme, fiber chromatic dispersion is compensated for within the receiver rather than being accommodated by the guard interval (GI) as in conventional CO-OFDM, thereby reducing the needed GI, especially when fiber dispersion is large. We demonstrate the generation of a 448-Gb/s RGI-CO-OFDM signal with 16-QAM subcarrier modulation through orthogonal band multiplexing. This signal occupies an optical bandwidth of 60 GHz, and is transmitted over 2000 km of ultra-large-area fiber (ULAF) with five passes through an 80-GHz-grid wavelength-selective switch. Banded digital coherent detection with two detection bands is used to receive this 448-Gb/s signal. Wavelength-division multiplexed transmission of three 80-GHz spaced 448-Gb/s RGI-CO-OFDM channels is also demonstrated, achieving a net system spectral efficiency of 5.2 b/s/Hz and a transmission distance of 1600 km of ULAF.

178 citations


Journal ArticleDOI
TL;DR: The intensity enhancement factor was investigated using finite-difference time-domain simulations and confirmed by analytical calculations taking into account the plasmon damping and multiple reflections against the corral wall.
Abstract: Plasmonic focusing was investigated in symmetry broken nanocorrals under linearly polarized illumination. Near-field optical measurements of the perpendicular electric field show that a single subwavelength spot size of 320 nm can be generated. The interference pattern within the corral can be controlled by changing the polarization of optical excitation and the degree of symmetry breaking. The intensity enhancement factor was investigated using finite-difference time-domain simulations and confirmed by analytical calculations taking into account the plasmon damping and multiple reflections against the corral wall.

143 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present observations of a major outburst at centimeter, millimeter, optical, X-ray, and γ-ray wavelengths of the BL Lacertae object AO 0235+164.
Abstract: We present observations of a major outburst at centimeter, millimeter, optical, X-ray, and γ-ray wavelengths of the BL Lacertae object AO 0235+164. We analyze the timing of multi-waveband variations in the flux and linear polarization, as well as changes in Very Long Baseline Array images at λ = 7 mm with ~0.15 milliarcsec resolution. The association of the events at different wavebands is confirmed at high statistical significance by probability arguments and Monte Carlo simulations. A series of sharp peaks in optical linear polarization, as well as a pronounced maximum in the 7 mm polarization of a superluminal jet knot, indicate rapid fluctuations in the degree of ordering of the magnetic field. These results lead us to conclude that the outburst occurred in the jet both in the quasi-stationary "core" and in the superluminal knot, both parsecs downstream of the supermassive black hole. We interpret the outburst as a consequence of the propagation of a disturbance, elongated along the line of sight by light-travel time delays, that passes through a standing recollimation shock in the core and propagates down the jet to create the superluminal knot. The multi-wavelength light curves vary together on long timescales (months/years), but the correspondence is poorer on shorter timescales. This, as well as the variability of the polarization and the dual location of the outburst, agrees with the expectations of a multi-zone emission model in which turbulence plays a major role in modulating the synchrotron and inverse Compton fluxes.

141 citations


Journal ArticleDOI
J.P. Salvestrini1, L. Guilbert1, M.D. Fontana1, M. Abarkan, S. Gille1 
TL;DR: In this paper, the authors discuss and analyze the different sources of the drift in commercially LiNbO3 Mach-Zehnder modulators, and point out the predominant role of the intrinsic (dc) drift.
Abstract: The drift issue induces slow drifting of the optimum operating point for high efficiency or large nonlinearities in analog optical links, and requires complex control of the offset bias voltage for achieving high extinction ratio in digital optical links. We discuss and analyze the different sources of the drift in commercially LiNbO3 Mach-Zehnder modulators. The different extrinsic and intrinsic origins are compared in terms of phase shift and the different corresponding orders of magnitude are given, pointing out the predominant role of the intrinsic (dc) drift. We show the large role played by the electrical inhomogeneities at the surface of the LiNbO3 substrate by highlighting the link between the time dependence of the dc drift and the electrical conductivity measured at the surface and in the volume of the LiNbO3 substrate. This allows to propose a solution to the drift issue which consists in the engineering of the electrical conductivity of the lithium niobate substrate.

127 citations


Proceedings ArticleDOI
06 Mar 2011
TL;DR: In this article, a method of LP 01 /LP 11 dual-mode and dual-polarization coherent OFDM detection at 107 Gb/s was demonstrated over a 4.5-km two-mode fiber with a grating-based mode converter as a mode-selective element.
Abstract: We demonstrate a method of LP 01 /LP 11 dual-mode and dual-polarization coherent OFDM detection at 107 Gb/s. Successful reception is achieved over a 4.5-km two-mode fiber with a grating-based mode converter as a mode-selective element.

124 citations


Proceedings ArticleDOI
06 Mar 2011
TL;DR: In this article, the intrinsic Grid-free capabilities of LCOS and how it can be used practically in a flexible Grid architecture to maximize total fiber capacity are discussed. But the authors focus on the grid-free capability of the optical traffic.
Abstract: The increasing spectral efficiency of Optical Transmission systems is constrained by the limitations of wavelength switching and is driving a requirement for significantly more flexible approaches to routing of the optical traffic. We present the intrinsic Grid-free capabilities of LCOS and show how it can be used practically in a flexible Grid architecture to maximize total fiber capacity.

103 citations


Journal ArticleDOI
TL;DR: This work miniaturizes all features in a previously introduced polarization-independent three-dimensional carpet invisibility cloak, which leads to operation wavelengths in the visible, and studies the wavelength dependence in the range from 900 nm down to 500 nm.
Abstract: We miniaturize all features in a previously introduced polarization-independent three-dimensional carpet invisibility cloak by more than a factor of 2. This leads to operation wavelengths in the visible. The structures are characterized by electron and optical microscopy. In contrast to our previous work at IR wavelengths, we can directly measure two-dimensional images at visible frequencies, perform control experiments from the backside, and compare the images with theory. We find excellent agreement. Furthermore, we study the wavelength dependence in the range from 900 nm down to 500 nm. Cloaking action deteriorates as the woodpile stop band at around 575 nm is approached.

Journal ArticleDOI
TL;DR: In this article, the spectral properties of the Crab Pulsar have been analyzed as a function of the pulse phase and the spectral index has been measured using the Chandra X-ray Observatory.
Abstract: We present a new study of the X-ray spectral properties of the Crab Pulsar. The superb angular resolution of the Chandra X-ray Observatory enables distinguishing the pulsar from the surrounding nebulosity. Analysis of the spectrum as a function of pulse phase allows the least-biased measure of interstellar X-ray extinction due primarily to photoelectric absorption and secondarily to scattering by dust grains in the direction of the Crab Nebula. We modify previous findings that the line-of-sight to the Crab is under-abundant in oxygen and provide measurements with improved accuracy and less bias. Using the abundances and cross sections from Wilms, Allen & McCray (2000) we find [O/H] = (5.28+\-0.28) x 10(exp -4) (4.9 x 10(exp -4) is solar abundance). \rVe also measure for the first time the impact of scattering of flux out of the image by interstellar grains. \rYe find T(sub scat) = 0.147+/-0.043. Analysis of the spectrum as a function of pulse phase also measures the X-ray spectral index even at pulse minimum - albeit with increasing statistical uncertainty. The spectral variations are, by and large, consistent with a sinusoidal variation. The only significant variation from the sinusoid occurs over the same phase range as some rather abrupt behavior in the optical polarization magnitude and position angle. We compare these spectral variations to those observed in Gamma-rays and conclude that our measurements are both a challenge and a guide to future modeling and will thus eventually help us understand pair cascade processes in pulsar magnetospheres. The data were also used to set new. and less biased, upper limits to the surface temperature of the neutron star for different models of the neutron star atmosphere.

Journal ArticleDOI
TL;DR: In this article, the authors present an analysis of radio spectral properties in total intensity and polarization, sizes, optical identifications and redshifts of the sample of the 5808 extragalactic sources in the Australia Telescope 20 GHz (AT20G) survey catalogue of confirmed sources over 6.1 sr in the Southern sky (i.e. the whole Southern sky excluding the strip at Galactic latitude |b| < $1\buildrel{\circ}\over{5$ ��).
Abstract: The Australia Telescope 20 GHz (AT20G) survey is a blind survey of the whole Southern sky at 20 GHz with follow-up observations at 4.8, 8.6 and 20 GHz carried out with the Australia Telescope Compact Array (ATCA) from 2004 to 2008. In this paper we present an analysis of radio spectral properties in total intensity and polarization, sizes, optical identifications and redshifts of the sample of the 5808 extragalactic sources in the survey catalogue of confirmed sources over 6.1 sr in the Southern sky (i.e. the whole Southern sky excluding the strip at Galactic latitude |b| < $1\buildrel{\circ}\over{.}5$ ).The sample has a flux density limit of 40 mJy. Completeness has been measured as a function of scan region and flux density. Averaging over the whole survey area the follow-up survey is 78 per cent complete above 50 mJy and 93 per cent complete above 100 mJy. 3332 sources with declination δ < −15° have good quality almost simultaneous observations at 4.8, 8.6 and 20 GHz. The spectral analysis shows that the sample is dominated by flat-spectrum sources, with 69 per cent having spectral index α 20 8.6 > − 0.5 (S∝ν α ). The fraction of flat-spectrum sources decreases from 81 per cent for S 20 GHz > 500 mJy to 60 per cent for S 20 GHz < 100 mJy. There is also a clear spectral steepening at higher frequencies with the median α decreasing from −0.16 between 4.8 and 8.6 GHz to −0.28 between 8.6 and 20 GHz.Simultaneous observations in polarization are available for all the sources at all the frequencies. 768 sources have a good-quality detection of polarized flux density at 20 GHz; 467 of them were also detected in polarization at 4.8 and/or at 8.6 GHz so that it has been possible to compare the spectral behaviour in total intensity and polarization. We have found that the polarized fraction increases slightly with frequency and decreases with flux density. The spectral indices in total intensity and in polarization are, on average, close to each other, but we also found several sources for which the spectral shape of the polarized emission is substantially different from the spectral shape in total intensity. The correlation between the spectral indices in total intensity and in polarization is weaker for flat-spectrum sources.Cross-matches and comparisons have been made with other catalogues at lower radio frequencies, and in the optical, X-ray and γ-ray bands. Redshift estimates are available for 825 sources.

Journal ArticleDOI
TL;DR: This paper combines experimental dark-field imaging, scattering, and fluorescence spectroscopy with rigorous electrodynamics calculations in order to investigate light scattering from planar arrays of Au nanoparticles arranged in aperiodic spirals with diffuse, circularly symmetric Fourier space, and demonstrates polarization-insensitive planar light diffraction in the visible spectral range.
Abstract: In this paper, we combine experimental dark-field imaging, scattering, and fluorescence spectroscopy with rigorous electrodynamics calculations in order to investigate light scattering from planar arrays of Au nanoparticles arranged in aperiodic spirals with diffuse, circularly symmetric Fourier space. In particular, by studying the three main types of Vogel's spirals fabricated by electron-beam lithography on quartz substrates, we demonstrate polarization-insensitive planar light diffraction in the visible spectral range. Moreover, by combining dark-field imaging with analytical multiparticle calculations in the framework of the generalized Mie theory, we show that plasmonic spirals support distinctive structural resonances with circular symmetry carrying orbital angular momentum. The engineering of light scattering phenomena in deterministic structures with circular Fourier space provides a novel strategy for the realization of optical devices that fully leverage on enhanced, polarization-insensitive light-matter coupling over planar surfaces, such as thin-film plasmonic solar cells, plasmonic polarization devices, and optical biosensors.

Journal ArticleDOI
TL;DR: In this paper, the authors describe ultra-high capacity transmission based on spectrally efficient multi-level modulation and wideband optical amplification techniques and demonstrate 69.1 Tb/s transmission over 240 km of low loss pure silica core fibers.
Abstract: This paper describes ultrahigh capacity transmission based on spectrally-efficient multi-level modulation and wideband optical amplification techniques. 21.4-Gbaud polarization-division multiplexed (PDM) 16-ary quadrature amplitude modulation (QAM) signals are generated by utilizing an optical synthesis technique, wavelength-multiplexed with 25-GHz spacing by optical pre-filtering, and received by an intradyne coherent receiver based on digital signal processing (DSP) with pilotless algorithms. These techniques realize a spectral efficiency (SE) of 6.4 b/s/Hz. Furthermore, a hybrid amplification technique that combines distributed Raman and dual-band erbium-doped amplifiers (EDFAs) realizes 10.8-THz signal bandwidth in C- and extended L-bands. By using these techniques, we successfully demonstrate 69.1 Tb/s transmission over 240 km of low loss pure silica core fibers.

Journal ArticleDOI
TL;DR: In this article, the optical-UV polarization and spectral variability of a single knot (HST-1) has been studied and interpreted as enhanced particle acceleration in a shock, with cooling from both particle aging and the relaxation of the compression.
Abstract: During the last decade, M87's jet has been the site of an extraordinary variability event, with one knot (HST-1) increasing by over a factor 100 in brightness. Variability was also seen on timescales of months in the nuclear flux. Here we discuss the optical-UV polarization and spectral variability of these components, which show vastly different behavior. HST -1 shows a highly significant correlation between flux and polarization, with P increasing from approx 20% at minimum to > 40% at maximum, while the orientation of its electric vector stayed constant. HST-l's optical-UV spectrum is very hard (alpha(sub uv-0) approx. 0.5, F(sub v) varies as (v(exp -alpha)), and displays "hard lags" during epochs 2004.9-2005.5, including the peak of the flare, with soft lags at later epochs. We interpret the behavior of HST-1 as enhanced particle acceleration in a shock, with cooling from both particle aging and the relaxation of the compression. We set 2alpha upper limits of 0.5 delta parsecs and 1.02c on the size and advance speed of the flaring region. The slight deviation of the electric vector orientation from the jet PA, makes it likely that on smaller scales the flaring region has either a double or twisted structure. By contrast, the nucleus displays much more rapid variability, with a highly variable electric vector orientation and 'looping' in the (I, P) plane. The nucleus has a much steeper spectrum ((alpha(sub uv-0) approx. 1.5) but does not show UV-optical spectral variability. Its behavior can be interpreted as either a helical distortion to a steady jet or a shock propagating through a helical jet.

Journal ArticleDOI
TL;DR: In this paper, the optical polarization ratio of spontaneous emission was investigated by electroluminescence measurements for semipolar (202¯1¯) InGaN/GaN light-emitting diodes, covering the blue to green spectral range.
Abstract: The optical polarization ratio of spontaneous emission was investigated by electroluminescence measurements for semipolar (202¯1¯) InGaN/GaN light-emitting diodes, covering the blue to green spectral range. Devices fabricated on semipolar (202¯1¯) substrates exhibit polarization ratios ranging from 0.46 at 418 nm to 0.67 at 519 nm. These polarization ratios are significantly higher than those reported on semipolar (202¯1) devices. The valence band energy separation is extracted from spectral measurements and is consistent with the increased polarization ratio and theoretical predictions. Quantum well interdiffusion induced valence band mixing is suggested as a possible explanation for the low experimental value of polarization ratio observed for the (202¯1) devices.

Journal ArticleDOI
TL;DR: A plasmon hybridization model is applied to explain the spectral differences of all polarization dependent resonances and use geometric arguments to explain some of the respective shifts of the resonances.
Abstract: We apply colloidal lithography to construct stacked nanocrescent dimer structures with an exact vertical alignment and a separation distance of approximately 10 nm. Highly ordered, large arrays of these nanostructures are accessible using nonclose-packed colloidal monolayers as masks. Spatially separated nanocrescent dimers are obtained by application of spatially distributed colloids. The polarization dependent optical properties of the nanostructures are investigated in detail and compared to single crescents. The close proximity of the nanocrescents leads to a coupling process that gives rise to new optical resonances which can be described as linear superpositions of the individual crescents’ plasmonic modes. We apply a plasmon hybridization model to explain the spectral differences of all polarization dependent resonances and use geometric arguments to explain the respective shifts of the resonances. Theoretical calculations are performed to support the hybridization model and extend it to higher ord...

Journal ArticleDOI
TL;DR: In this article, the electronic band structure, density of states, complex dielectric function, optical absorption, and the infrared and Raman spectra of orthorhombic CaSnO{sub 3} were computed using density functional theory.

Journal ArticleDOI
TL;DR: This paper relates to the development of a high-voltage sensor system using a PZT piezoelectric crystal as a transducer and a fiber Bragg grating as a sensor for an optical VT for a 13-kV class.
Abstract: Electric power facilities, such as substations, rely on voltage transformers (VTs) for measurement and protection. These pieces of equipment are bulky and heavy and tend to explode, destroying nearby equipment and posing a threat to substation personnel. Optical voltage transducers offer many improvements on traditional inductive and capacitive VTs, such as linear performance, wider dynamic range, lighter weight, smaller size, and improved safety. This paper relates to the development of a high-voltage sensor system using a PZT piezoelectric crystal as a transducer and a fiber Bragg grating as a sensor for an optical VT for a 13.8-kV class. The results show that the developed sensor is capable of attaining the International Electrotechnical Commission 0.2%-accuracy class for the revenue metering system.

Journal ArticleDOI
TL;DR: In this paper, the authors combine the largest Lyapunov exponent (LLE) with the spin-flip model (SFM), including noise, to model a vertical-cavity surface emitting laser (VCSEL) subject to polarized optical injection.
Abstract: We report novel theoretical results obtained from combining the method of largest Lyapunov exponent (LLE) with the spin-flip model (SFM), including noise, to model a vertical-cavity surface emitting laser (VCSEL) subject to polarized optical injection. The LLE is applied to the numerical solutions in order to automatically calculate stability maps that characterize the dynamics. The SFM has been extended and generalized to allow for optical injection of arbitrary polarization. Measurements on a 1550-nm VCSEL have been used to estimate the values of key parameters for use in the model and with these we demonstrate excellent agreement between theory and experiment.

Journal ArticleDOI
TL;DR: In this paper, a tunable temporal photonic fractional differentiator implemented based on a tilted fiber Bragg grating is proposed and demonstrated, in which the phase response at a cladding mode resonant wavelength is strongly polarization-dependent and the fractional order of the photonic differentiator can be continuously tuned by changing the polarization state of the input light wave.
Abstract: A tunable temporal photonic fractional differentiator implemented based on a tilted fiber Bragg grating is proposed and demonstrated. The phase response at a cladding mode resonant wavelength is strongly polarization-dependent and the fractional order of the photonic differentiator can be continuously tuned by changing the polarization state of the input light wave. A proof-of-concept experiment is carried out. The fractional differentiation of an optical Gaussian pulse with a bandwidth of 40 GHz is demonstrated, in which the fractional order is continuously tuned from 0.81 to 1.42.

Journal ArticleDOI
TL;DR: In this article, the subband structure and optical properties of a cylindrical quantum well wire under intense non-resonant laser field are investigated by taking into account the correct dressing effect for the confinement potential.

Journal ArticleDOI
TL;DR: In this paper, a frequency-doubling optoelectronic oscillator (FD-OEO) based on a dual-parallel Mach-Zehnder modulator and a chirped fiber Bragg grating was demonstrated.
Abstract: A frequency-doubling optoelectronic oscillator (FD-OEO) based on a dual-parallel Mach-Zehnder modulator (DPMZM) and a chirped fiber Bragg grating (CFBG) has been demonstrated. The DPMZM implements a carrier phase-shifted double sideband (CPS-DSB) modulation to generate a microwave signal at the second-harmonic frequency, while the CFBG ensures the oscillation of the fundamental frequency signal by tailoring the phase relationships between the optical sidebands and the carrier. As a result, self-starting 10- and 20-GHz microwave signals with low phase noises are simultaneously generated.

Journal ArticleDOI
Ze Li1, Ming Li1, Hao Chi2, Xianmin Zhang2, Jianping Yao1 
TL;DR: In this paper, a photonic approach was proposed to generate a phase-coded mm-wave signal with large frequency tunability using a Mach-Zehnder modulator that is biased at the maximum transmission point and an optical notch filter.
Abstract: A photonic approach to generating a phase-coded millimeter-wave (mm-wave) signal with large frequency tunability is proposed and demonstrated. Two ± second-order optical sidebands are generated by using a Mach-Zehnder modulator that is biased at the maximum transmission point and an optical notch filter. A polarization-maintaining fiber Bragg grating is then utilized to make the two sidebands orthogonally polarized. By sending the two orthogonally polarized sidebands to a polarization modulator, to which a phase-coding signal is applied, a frequency-quadrupled phase-coded mm-wave signal is generated. The generation of a phase-coded mm-wave signal with tunable frequencies at 40, 42, and 50 GHz is experimentally demonstrated. A pulse compression ratio of about 128 is achieved.

Journal ArticleDOI
TL;DR: The results show that celestial orientation is as accurate during crescent Moon as it is during full Moon, and this orientation accuracy is equal to that measured for diurnal species that orient under the 100 million times brighter polarization pattern formed around the Sun.
Abstract: Prominent in the sky, but not visible to humans, is a pattern of polarized skylight formed around both the Sun and the Moon. Dung beetles are, at present, the only animal group known to use the much dimmer polarization pattern formed around the Moon as a compass cue for maintaining travel direction. However, the Moon is not visible every night and the intensity of the celestial polarization pattern gradually declines as the Moon wanes. Therefore, for nocturnal orientation on all moonlit nights, the absolute sensitivity of the dung beetle's polarization detector may limit the precision of this behaviour. To test this, we studied the straight-line foraging behaviour of the nocturnal ball-rolling dung beetle Scarabaeus satyrus to establish when the Moon is too dim—and the polarization pattern too weak—to provide a reliable cue for orientation. Our results show that celestial orientation is as accurate during crescent Moon as it is during full Moon. Moreover, this orientation accuracy is equal to that measured for diurnal species that orient under the 100 million times brighter polarization pattern formed around the Sun. This indicates that, in nocturnal species, the sensitivity of the optical polarization compass can be greatly increased without any loss of precision.

Journal ArticleDOI
TL;DR: In this article, the spectral energy distributions of the ejecta of a core-collapse supernova (CC SNe) are fitted with both analytic and numerical models, using the radiative-transfer code MOCASSIN for the latter ones.
Abstract: Aims. Core-collapse supernovae (CC SNe), especially type II-Plateau ones, are thought to be important contributors to cosmic dust production. SN 2004dj, one of the closest and brightest SN since 1987A, offered a good opportunity to examine dust-formation processes. To find signs of newly formed dust, we analyze all available mid-infrared (MIR) archival data from the Spitzer space telescope. Methods. We re-reduced and analyzed data from IRAC, MIPS, and IRS instruments obtained between +98 and +1381 days after explosion and generated light curves and spectra for each epoch. Observed spectral energy distributions are fitted with both analytic and numerical models, using the radiative-transfer code MOCASSIN for the latter ones. We also use imaging polarimetric data obtained at +425 days by the Hubble space telescope. Results. We present convincing evidence of dust formation in the ejecta of SN 2004dj from MIR light curves and spectra. Significant MIR excess flux is detected in all bands between 3.6 and 24 μm. In the optical, a ∼0.8% polarization is also detected at a 2-sigma level, which exceeds the interstellar polarization in that direction. Our analysis shows that the freshly-formed dust around SN 2004dj can be modeled assuming a nearly spherical shell that contains amorphous carbon grains, which cool from ∼700 K to ∼400 K between +267 and +1246 days. Persistent excess flux is found above 10 μ m, which is explained by ac old (∼115 K) dust component. If this cold dust is of circumstellar origin, it is likely to be condensed in a cool, dense shell between the forward and reverse shocks. Pre-existing ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ––– – +++ –– –––– –

Journal ArticleDOI
TL;DR: In this paper, an optical polarization survey of 878 stars from the Hipparcos catalog was conducted to investigate the distance of the proposed annular region and map the geometry of the Galactic magnetic field in these directions.
Abstract: The Sun is located inside an extremely low density and quite irregular volume of the interstellar medium, known as the Local Cavity (LC). It has been widely believed that some kind of interaction could be occurring between the LC and Loop I, a nearby superbubble seen in the direction of the Galactic center. As a result of such interaction, a wall of neutral and dense material, surrounded by a ring-shaped feature, would be formed at the interaction zone. Evidence of this structure was previously observed by analyzing the soft X-ray emission in the direction of Loop I. Our goal is to investigate the distance of the proposed annular region and map the geometry of the Galactic magnetic field in these directions. On that account, we have conducted an optical polarization survey of 878 stars from the Hipparcos catalog. Our results suggest that the structure is highly twisted and fragmented, showing very discrepant distances along the annular region: ≈ 100 pc on the left side and 250 pc on the right side, independently confirming the indication from a previous photometric analysis. In addition, the polarization vectors' orientation pattern along the ring also shows a widely different behavior toward both sides of the studied feature, running parallel to the ring contour on the left side and showing no relation to its direction on the right side. Altogether, these evidences suggest a highly irregular nature, casting some doubt on the existence of a unique large-scale ring-like structure.

Journal ArticleDOI
TL;DR: In this paper, a single-side band (SSB) modulator-based recirculating frequency shifter (RFS) was used to generate 50 12.5GHz-spaced optical carriers with high power flatness and stability.
Abstract: We report the generation of fifty 12.5-GHz-spaced optical carriers with high power flatness and stability by using a single-side band (SSB) modulator-based recirculating frequency shifter (RFS). The peak-to-peak power difference and the RMS power difference of the generated carriers are 2.5 and 0.3 dB, respectively. We also experimentally investigate the impact of implementation imperfections on the flatness of the generated carriers. The important factors that contribute to the flatness of the generated carriers are found to be the amplitude balance of two inphase (I) and quadrature (Q) drive signals for the SSB modulator, the time misalignment between the I and Q signals, the accuracy of the /2 phase bias of the SSB modulator and the stability of the polarization alignment in the RFS. By carefully controlling all the factors mentioned earlier, we obtain stable operation of 50 frequency-locked carriers; showing that the SSB modulator-based RFS is a promising technique for future terabit per second multicarrier transmission.

Proceedings ArticleDOI
Jianjun Yu, Ze Dong, Xin Xiao1, Yan Xia1, Sheping Shi1, Chao Ge1, Weiqing Zhou1, Nan Chi2, Yufeng Shao2 
06 Mar 2011
TL;DR: In this paper, a scheme to generate coherent 112 optical sub-carriers with subcarrier spacing of 25GHz was proposed and experimentally demonstrated and the authors have successfully generated 10.2-Tbit/s (112×100Gbps) single channel optical OFDM polarization multiplexing QPSK signal with the bandwidth of 2.8THz and the optical signal noise ratio greater than 20dB (0.1nm bandwidth for each subchannel).
Abstract: A novel scheme to generate coherent 112 optical sub-carriers with subcarrier spacing of 25GHz is proposed and experimentally demonstrated. By using these coherent optical subcarriers, we have successfully generated 10-Tbit/s (112×100Gbit/s) single channel optical OFDM polarization multiplexing QPSK signal with the bandwidth of 2.8THz and the optical signal noise ratio greater than 20dB (0.1nm bandwidth for each subchannel). We have transmitted the 11.2-Tbit/s optical OFDM signal over 640-km SMF-28 with an amplifier span of 80km and EDFA-only.