Showing papers on "Optical polarization published in 2014"

Electronic structure of the negatively charged silicon-vacancy center in diamond

Abstract: The negatively charged silicon-vacancy (SiV${}^{\ensuremath{-}}$) center in diamond is a promising single-photon source for quantum communications and information processing. However, the center's implementation in such quantum technologies is hindered by contention surrounding its fundamental properties. Here we present optical polarization measurements of single centers in bulk diamond that resolve this state of contention and establish that the center has a $\ensuremath{\langle}111\ensuremath{\rangle}$ aligned split-vacancy structure with ${\mathrm{D}}_{3\mathrm{d}}$ symmetry. Furthermore, we identify an additional electronic level and evidence for the presence of dynamic Jahn-Teller effects in the center's 738-nm optical resonance.

DFT study of optical properties of pure and doped graphene

Abstract: Ab-initio calculations based on density functional theory (DFT) have been performed to study the optical properties of pure graphene and have been compared to that of individual boron (B), nitrogen (N) and BN co-doped graphene sheet. The effect of doping has been investigated by varying the concentrations of dopants from 3.125% (one atom of the dopant in 32 host atoms) to 18.75% (six dopant atoms in 50 host atoms) for individual B and N doping and from 6.25% (one B/N pair in 32 host atoms) to 75% for BN co-doping. Positions of the dopants have also been varied for the same concentration of substitution doping. The dielectric matrix has been calculated within the random phase approximation (RPA) using VASP (Vienna ab-initio Simulation Package) code. The dielectric function, absorption spectrum and energy loss-function of single layer graphene sheet have been calculated for light polarization parallel and perpendicular to the plane of graphene sheet and compared with doping graphene. The calculated dielectric functions and energy-loss spectra are in reasonable agreement with the available theoretical and experimental results for pure graphene. It has been found that individual B and N doping does not significantly affect the imaginary dielectric function and hence the absorption spectra. However, significant red-shift in absorption towards the visible range of the radiation at high doping is found to occur for the B/N co-doping. The results can be used to tailor the optical properties of graphene in the visible region.

Hexagonal boron nitride for deep ultraviolet photonic devices

Abstract: This paper provides a brief overview on recent advances in tackling the doping and optical polarization issues involved in the development of high performance deep ultraviolet (DUV) light emitting devices. In particular, recent developments in the exploitation of a novel DUV emitter layer structure based on a hexagonal boron nitride (hBN) and AlGaN p–n junction and doping engineering to potentially overcome the intrinsic problem of low p-type conductivity (or low free hole concentration) in Al-rich AlGaN are summarized. By implementing the wide bandgap and highly conductive hBN p-type layer strategy in nitride DUV emitters, p-type conductivities and DUV transparency of the electron blocking layer and p-type contact layer will be dramatically increased. This will significantly improve the free hole injection and quantum efficiency, reduce the operating voltage and heat generation, and increase the device operating lifetime. The growth of undoped and Mg-doped p-type hBN via a metal organic chemical vapor deposition technique has been studied. Furthermore, p-hBN/n-AlGaN p–n junctions have been fabricated and characterized to demonstrate the feasibility and potential of p-hBN/n-AlGaN p–n heterostructure based DUV light emitting devices. Further improvements in material quality, p-type conductivity control and device processing procedures would enhance the properties of these p–n structures, which could ultimately pave the way towards the realization of high efficiency nitride DUV photonic devices.

Circular polarization in the optical afterglow of GRB 121024A

Abstract: Gamma-ray bursts (GRBs) are most probably powered by collimated relativistic outflows (jets) from accreting black holes at cosmological distances Bright afterglows are produced when the outflow collides with the ambient medium Afterglow polarization directly probes the magnetic properties of the jet when measured minutes after the burst, and it probes the geometric properties of the jet and the ambient medium when measured hours to days after the burst1, 2, 3, 4, 5 High values of optical polarization detected minutes after the burst of GRB 120308A indicate the presence of large-scale ordered magnetic fields originating from the central engine5 (the power source of the GRB) Theoretical models predict low degrees of linear polarization and no circular polarization at late times6, 7, 8, when the energy in the original ejecta is quickly transferred to the ambient medium and propagates farther into the medium as a blast wave Here we report the detection of circularly polarized light in the afterglow of GRB 121024A, measured 015 days after the burst We show that the circular polarization is intrinsic to the afterglow and unlikely to be produced by dust scattering or plasma propagation effects A possible explanation is to invoke anisotropic (rather than the commonly assumed isotropic) electron pitch-angle distributions, and we suggest that new models are required to produce the complex microphysics of realistic shocks in relativistic jets9, 10, 11

Inverse cascade of nonhelical magnetic turbulence in a relativistic fluid

Abstract: The free decay of nonhelical relativistic magnetohydrodynamic turbulence is studied numerically, and found to exhibit cascading of magnetic energy toward large scales. Evolution of the magnetic energy spectrum PM (k, t) is self-similar in time and well modeled by a broken power law with subinertial and inertial range indices very close to 7/2 and –2, respectively. The magnetic coherence scale is found to grow in time as t 2/5, much too slow to account for optical polarization of gamma-ray burst afterglow emission if magnetic energy is to be supplied only at microphysical length scales. No bursty or explosive energy loss is observed in relativistic MHD turbulence having modest magnetization, which constrains magnetic reconnection models for rapid time variability of GRB prompt emission, blazars, and the Crab nebula.

Polarization-dependent optomechanics mediated by chiral microresonators.

Abstract: Chirality is one of the most prominent and intriguing aspects of nature, from spiral galaxies down to aminoacids. Despite the wide range of living and non-living, natural and artificial chiral systems at different scales, the origin of chirality-induced phenomena is often puzzling. Here we assess the onset of chiral optomechanics, exploiting the control of the interaction between chiral entities. We perform an experimental and theoretical investigation of the simultaneous optical trapping and rotation of spherulite-like chiral microparticles. Due to their shell structure (Bragg dielectric resonator), the microparticles function as omnidirectional chiral mirrors yielding highly polarization-dependent optomechanical effects. The coupling of linear and angular momentum, mediated by the optical polarization and the microparticles chiral reflectance, allows for fine tuning of chirality-induced optical forces and torques. This offers tools for optomechanics, optical sorting and sensing and optofluidics.

Inverse cascade of non-helical magnetic turbulence in a relativistic fluid

Abstract: The free decay of non-helical relativistic magnetohydrodynamic turbulence is studied numerically, and found to exhibit cascading of magnetic energy toward large scales. Evolution of the magnetic energy spectrum $P_M(k,t)$ is self-similar in time and well modeled by a broken power law with sub-inertial and inertial range indices very close to $7/2$ and $-2$ respectively. The magnetic coherence scale is found to grow in time as $t^{2/5}$, much too slow to account for optical polarization of gamma-ray burst afterglow emission if magnetic energy is to be supplied only at microphysical length scales. No bursty or explosive energy loss is observed in relativistic MHD turbulence having modest magnetization, which constrains magnetic reconnection models for rapid time variability of GRB prompt emission, blazars and the Crab nebula.

Reduction of Wavelength Dependence of Coupling Characteristics Using Si Optical Waveguide Curved Directional Coupler

Abstract: Directional couplers are widely used as one of the key components of optical integrated circuits. However, the coupling efficiency of the conventional directional coupler is highly sensitive to wavelength. This sensitivity degrades the characteristics of devices that contain directional couplers for wavelength division multiplexing transmission. A curved directional coupler has been proposed using silica optical waveguide as one of the coupler which realize wavelength insensitive, small footprint and tolerant to fabrication. In this paper, we theoretically investigated this curved coupler using Si wire waveguide and got results that the curved coupler whose bending radius of 21 $\mu$ m and coupling length of 7.40 $\mu$ m can reduce the wavelength dependence and achieve about a sevenfold enhancement of operational bandwidth in the transmittance variation range of $-$ 3 $\pm$ 0.1 dB compared with conventional directional coupler.

The RoboPol optical polarization survey of gamma-ray-loud blazars

Abstract: We present first results from RoboPol, a novel-design optical polarimeter operating at the Skinakas Observatory in Crete. The data, taken during the 2013 May–June commissioning of the instrument, constitute a single-epoch linear polarization survey of a sample of gamma-ray-loud blazars, defined according to unbiased and objective selection criteria, easily reproducible in simulations, as well as a comparison sample of, otherwise similar, gamma-ray-quiet blazars. As such, the results of this survey are appropriate for both phenomenological population studies and for tests of theoretical population models. We have measured polarization fractions as low as 0.015 down to R-mag of 17 and as low as 0.035 down to 18 mag. The hypothesis that the polarization fractions of gamma-ray-loud and gamma-ray-quiet blazars are drawn from the same distribution is rejected at the 3σ level. We therefore conclude that gamma-ray-loud and gamma-ray-quiet sources have different optical polarization properties. This is the first time this statistical difference is demonstrated in optical wavelengths. The polarization fraction distributions of both samples are well described by exponential distributions with averages of ⟨p⟩=6.4^(+0.9)_(−0.8)×10^(−2) for gamma-ray-loud blazars, and ⟨p⟩=3.2^(+2.0)_(−1.1)×10^(−2) for gamma-ray-quiet blazars. The most probable value for the difference of the means is 3.4^(+1.5)_(−2.0)×10^(−2). The distribution of polarization angles is statistically consistent with being uniform.

Optical birefringence and dichroism of cuprate superconductors in the THz regime.

Abstract: The presence of optical polarization anisotropies, such as Faraday or Kerr effects, linear birefringence, and magnetoelectric birefringence are evidence for broken symmetry states of matter. The recent discovery of a Kerr effect using near-IR light in the pseudogap phase of the cuprates can be regarded as a strong evidence for a spontaneous symmetry breaking and the existence of an anomalous long-range ordered state. In this work we present a high precision study of the polarimetry properties of the cuprates in the THz regime. While no Faraday effect was found in this frequency range to the limits of our experimental uncertainty (1.3 milli-radian or 0.07\ifmmode^\circ\else\textdegree\fi{}), a small but significant polarization rotation was detected that derives from an anomalous linear dichroism. In ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{y}$ the effect has a temperature onset that mirrors the pseudogap temperature ${T}^{*}$ and is enhanced in magnitude in underdoped samples. In $x=1/8$ ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Ba}}_{x}{\mathrm{CuO}}_{4}$, the effect onsets above room temperature, but shows a dramatic enhancement near a temperature scale known to be associated with spin- and charge-ordered states. These features are consistent with a loss of both ${C}_{4}$ rotation and mirror symmetry in the electronic structure of the ${\mathrm{CuO}}_{2}$ planes in the pseudogap state.

Multi-wavelength variability properties of Fermi blazar S5 0716+714

Abstract: S5 0716+714 is a typical BL Lacertae object. In this paper we present the analysis and results of long term simultaneous observations in the radio, near-infrared, optical, X-ray and $\gamma$-ray bands, together with our own photometric observations for this source. The light curves show that the variability amplitudes in $\gamma$-ray and optical bands are larger than those in the hard X-ray and radio bands and that the spectral energy distribution (SED) peaks move to shorter wavelengths when the source becomes brighter, which are similar to other blazars, i.e., more variable at wavelengths shorter than the SED peak frequencies. Analysis shows that the characteristic variability timescales in the 14.5 GHz, the optical, the X-ray, and the $\gamma$-ray bands are comparable to each other. The variations of the hard X-ray and 14.5 GHz emissions are correlated with zero-lag, so are the V band and $\gamma$-ray variations, which are consistent with the leptonic models. Coincidences of $\gamma$-ray and optical flares with a dramatic change of the optical polarization are detected. Hadronic models do not have the same nature explanation for these observations as the leptonic models. A strong optical flare correlating a $\gamma$-ray flare whose peak flux is lower than the average flux is detected. Leptonic model can explain this variability phenomenon through simultaneous SED modeling. Different leptonic models are distinguished by average SED modeling. The synchrotron plus synchrotron self-Compton (SSC) model is ruled out due to the extreme input parameters. Scattering of external seed photons, such as the hot dust or broad line region emission, and the SSC process are probably both needed to explain the $\gamma$-ray emission of S5 0716+714.

Multiwavelength variability properties of fermi blazar s5 0716+714

Abstract: S5 0716+714 is a typical BL Lacertae object. In this paper we present the analysis and results of long-term simultaneous observations in the radio, near-infrared, optical, X-ray, and ?-ray bands, together with our own photometric observations for this source. The light curves show that the variability amplitudes in ?-ray and optical bands are larger than those in the hard X-ray and radio bands and that the spectral energy distribution (SED) peaks move to shorter wavelengths when the source becomes brighter, which is similar to other blazars, i.e., more variable at wavelengths shorter than the SED peak frequencies. Analysis shows that the characteristic variability timescales in the 14.5?GHz, the optical, the X-ray, and the ?-ray bands are comparable to each other. The variations of the hard X-ray and 14.5?GHz emissions are correlated with zero lag, and so are the V band and ?-ray variations, which are consistent with the leptonic models. Coincidences of ?-ray and optical flares with a dramatic change of the optical polarization are detected. Hadronic models do not have the same natural explanation for these observations as the leptonic models. A strong optical flare correlating a ?-ray flare whose peak flux is lower than the average flux is detected. The leptonic model can explain this variability phenomenon through simultaneous SED modeling. Different leptonic models are distinguished by average SED modeling. The synchrotron plus synchrotron self-Compton (SSC) model is ruled out because of the extreme input parameters. Scattering of external seed photons, such as the hot-dust or broad-line region emission, and the SSC process are probably both needed to explain the ?-ray emission of S5 0716+714.

Optical Birefringence and Dichroism of Cuprate Superconductors in the THz regime

Abstract: The presence of optical polarization anisotropies, such as Faraday or Kerr effects, linear birefringence, and magnetoelectric birefringence are evidence for broken symmetry states of matter. The recent discovery of a Kerr effect using near-IR light in the pseudogap phase of the cuprates can be regarded as a strong evidence for a spontaneous symmetry breaking and the existence of an anomalous long-range ordered state. In this work we present a high precision study of the polarimetry properties of the cuprates in the THz regime. While no Faraday effect was found in this frequency range to the limits of our experimental uncertainty (1.3 milli-radian or 0.07\ifmmode^\circ\else\textdegree\fi{}), a small but significant polarization rotation was detected that derives from an anomalous linear dichroism. In ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{y}$ the effect has a temperature onset that mirrors the pseudogap temperature ${T}^{*}$ and is enhanced in magnitude in underdoped samples. In $x=1/8$ ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Ba}}_{x}{\mathrm{CuO}}_{4}$, the effect onsets above room temperature, but shows a dramatic enhancement near a temperature scale known to be associated with spin- and charge-ordered states. These features are consistent with a loss of both ${C}_{4}$ rotation and mirror symmetry in the electronic structure of the ${\mathrm{CuO}}_{2}$ planes in the pseudogap state.

The Outburst of the Blazar S4 0954+658 in 2011 March-April

Abstract: We present the results of optical ( R -band) photometric and polarimetric monitoring and Very Long Baseline Array imaging of the blazar S4 0954+658, along with Fermi γ-ray data during a multi-waveband outburst in 2011 March-April. After a faint state with a brightness level R ~ 17.6 mag registered in the first half of 2011 January, the optical brightness of the source started to rise and reached ~14.8 mag during the middle of March, showing flare-like behavior. The most spectacular case of intranight variability was observed during the night of 2011 March 9, when the blazar brightened by ~0.7 mag within 7 hr. During the rise of the flux, the position angle of the optical polarization rotated smoothly over more than 300°. At the same time, within 1σ uncertainty, a new superluminal knot appeared with an apparent speed of 19.0 ± 0.3 c . We have very strong evidence that this knot is associated with the multi-waveband outburst in 2011 March-April. We also analyze the multi-frequency behavior of S4 0954+658 during a number of minor outbursts from 2008 August to 2012 April. We find some evidence of connections between at least two additional superluminal ejecta and near-simultaneous optical flares.

The Outburst of the Blazar S40954+658 in March-April 2011

Abstract: We present the results of optical (R band) photometric and polarimetric monitoring and Very Long Baseline Array (VLBA) imaging of the blazar S4 0954+658, along with Fermi and gamma;-ray data during a multi-waveband outburst in 2011 March-April. After a faint state with a brightness level R ~17.6 mag registered in the first half of January 2011, the optical brightness of the source started to rise and reached ~14.8 mag during the middle of March, showing flare-like behavior. The most spectacular case of intranight variability was observed during the night of 2011 March 9, when the blazar brightened by ~0.7 mag within ~7 hours. During the rise of the flux the position angle of optical polarization rotated smoothly over more than 300$\deg$. At the same time, within 1$\sigma$ uncertainty a new superluminal knot appeared with an apparent speed of 19.0$\pm$0.3 c. We have very strong evidence for association of this knot with the multi-waveband outburst in 2011 March-April. We also analyze the multi-frequency behavior of S4 0954+658 during a number of minor outbursts from August 2008 to April 2012. We find some evidence of connections between at least two more superluminal ejecta and near-simultaneous optical flares.

Electrically tunable optical polarization rotation on a silicon chip using Berry’s phase

Abstract: Integrated optical devices require complete control of the polarization of light, but this is difficult to realize. By exploiting Berry’s phase, Xu et al. show out-of-plane guiding of light on a silicon chip and dynamic tuning of the optical polarization by application of electric fields.

Volterra-Based Reconfigurable Nonlinear Equalizer for Coherent OFDM

Abstract: A reconfigurable nonlinear equalizer (RNLE) based on inverse Volterra series transfer function is proposed for dual-polarization (DP) and multiband coherent optical orthogonal frequency-division multiplexing (OFDM) signals. It is shown that the RNLE outperforms by 2 dB the linear equalization in a 260-Gb/s DP-OFDM system at 1500 km. The RNLE improves the tolerance to inter/intraband nonlinearities, being independent on polarization tributaries, modulation format, signal bit rate, subcarrier number, and distance.

Influence of optical polarization on the improvement of light extraction efficiency from reflective scattering structures in AlGaN ultraviolet light-emitting diodes

Abstract: The improvement in light extraction efficiency from reflective scattering structures in AlGaN ultraviolet light-emitting diodes (UVLEDs) emitting at ∼270 nm is shown to be influenced by optical polarization. Three UVLEDs with different reflective scattering structures are investigated and compared to standard UVLEDs without scattering structures. The optical polarization and therefore the direction of light propagation within the various UVLEDs are altered by changes in the quantum well (QW) thickness. The improvement in light extraction efficiency of the UVLEDs with reflective scattering structures increases, compared to the UVLEDs without scattering structures, as the fraction of emitted light propagating parallel to the QW plane increases. Additionally, the light extraction efficiency increases as the average distance to the reflective scattering structures decreases.

Design and Implementation of Modified Signed-Digit Adder

Abstract: How to fully apply the characteristics and advantages of light in numerical computation is an important issue that attracts many scholars. Though much research has been done in this field, how to design and realize specific applications or devices is still an issue to be solved. Based on this, we present an architecture and implementation method of modified signed-digit (MSD) optical adder from the point of applicability. In the implementation, we fully consider the different procedures of the MSD addition which including optical logical operation, results decoding, special storage area design, data feedback, control of light path, etc. Meanwhile, we also introduce pipeline mechanism which guarantees that the addition operation is an automatic and continuous process. This is a carry free adder design method which guarantees the addition has high data throughput. It is very suitable to fulfill the large-scale numerical computation. The experiment shows, the MSD adder not only has a reasonable and correct design, but also has high throughput rate, can work efficiently and steadily.

Four-dimensional Rotations in Coherent Optical Communications

Abstract: To model electromagnetic wave propagation for coherent communications without polarization dependent losses, the unitary 2 ×2 Jones transfer matrix formalism is typically used. In this study, we propose an alternative formalism to describe such transformations based on rotations in four-dimensional (4d) Euclidean space. This formalism is usually more attractive from a communication theoretical perspective, since decisions and symbol errors can be related to geometric concepts such as Euclidean distances between points and decision boundaries. Since 4d rotations is a richer description than the conventional Jones calculus, having six rather than four degrees of freedom (DOF), we propose an extension of the Jones calculus to handle all six DOF. In addition, we show that the two extra DOF in the 4d description represents transformations that are nonphysical for propagating photons, since they does not obey the fundamental quantum mechanical boson commutation relations. Finally, we exemplify on how the nonphysical rotations can change the polarization-phase degeneracy of well-known constellations such as single-polarization QPSK, polarization-multiplexed (PM-)QPSK and polarization-switched (PS-) QPSK. For example, we show how PM-QPSK, which is well known to consist of four polarization states each having four-fold phase degeneracy, can be represented as eight states of polarizations, each with binary phase degeneracy.

Histology validation of mapping depth-resolved cardiac fiber orientation in fresh mouse heart using optical polarization tractography.

Abstract: Myofiber organization in cardiac muscle plays an important role in achieving normal mechanical and electrical heart functions. An imaging tool that can reveal microstructural details of myofiber organization is valuable for both basic research and clinical applications. A high-resolution optical polarization tractography (OPT) was recently developed based on Jones matrix optical coherence tomography (JMOCT). In this study, we validated the accuracy of using OPT for measuring depth-resolved fiber orientation in fresh heart samples by comparing directly with histology images. Systematic image processing algorithms were developed to register OPT with histology images. The pixel-wise differences between the two tractographic results were analyzed in details. The results indicate that OPT can accurately image depth-resolved fiber orientation in fresh heart tissues and reveal microstructural details at the histological level.

A Cost-Effective and Efficient Scheme for Optical OFDM in Short-Range IM/DD Systems

Abstract: We propose a cost-effective and efficient modulation scheme for intensity-modulated and direct-detection (IM/DD) optical orthogonal frequency division multiplexing (O-OFDM) systems, which combines complex-to-real transform (C2RT) and fast Hartley transform (FHT), named as fast-fast Fourier transform (FFT). The proposed scheme can modulate the complex constellation by the real-valued operations. Compared with the FFT method, the same OFDM signal can also be generated by fast-FFT, but the computational complexity nearly halved. Meanwhile, compared with the FHT scheme, fast-FFT can modulate the complex constellations by adding a simple C2RT module for a wide applicable range. The transmission experiment of over 50-km standard single-mode fiber (SSMF) has been implemented to verify the feasibility of fast-FFT-based IM/DD O-OFDM systems, including asymmetrically clipping and DC-bias O-OFDM systems. It reveals that fast-FFT shares the same bit-error-rate (BER) performance as FFT, but fast-FFT shows superiority on computational complexity.

Effect of thickness and carrier density on the optical polarization of Al0.44Ga0.56N/Al0.55Ga0.45N quantum well layers

Abstract: The thickness and carrier density of AlGaN quantum well (QW) layers have a strong influence on the valence subband structure, and the resulting optical polarization and light extraction of ultraviolet light-emitting diodes. An ultraviolet-emitting (270–280 nm) multiple quantum well heterostructure consisting of 3 periods of Al0.44Ga0.56N/Al0.55Ga0.45N with individual layer thicknesses between 2–3.2 nm is studied both experimentally and theoretically. The optical polarization changes to preferentially polarized perpendicular to the QW plane as the QW thickness increases or the carrier density increases. Calculations show these trends are due to (a) a larger decrease in overlap of conduction band to light and heavy hole envelope functions compared to crystal-field split-off envelope functions, and (b) coupling between the valence subbands where higher heavy hole subbands couple to lower light hole and crystal-field split-off subbands. These changes in the valence band have a profound effect on the optical p...

Electronic, magnetic, optical, and edge-reactivity properties of semiconducting and metallic WS2 nanoribbons

Abstract: First-principles density functional theory calculations are performed in one-dimensional single-layer WS2 nanoribbons with zigzag- and armchair-edges. Magnetic ordering, optical response, and chemical reactivity are investigated. Our results demonstrated that WS2 zigzag nanoribbons exhibit a ferromagnetic-metallic behavior that is attributed to the edges; the resulting magnetic moments are mainly localized in S and W edge atoms. Furthermore, the magnetic ordering along the edges depends on the zigzag nanoribbon's width. Armchair nanoribbons exhibit semiconducting behavior. Optical response results demonstrated that there exists a strong optical polarization anisotropy enhancing a well defined absorption intensity peak, with polarization along the nanoribbons axis. Regarding chemical reactivity, ribbons are exposed to water (H2O), thiophene (C4H4S), and carbon monoxide (CO) molecules. Results reveal that H2O can be covalently joined to the edges via the W-atoms in the ribbons with zigzag-edges, whereas in ribbons with armchair edges, H2O is dissociated in OH and H, and these species are joined to W and S atoms respectively. Results for thiophene on zigzag nanoribbons demonstrated that C4H4S molecules are absorbed by W-terminated edges, whereas in armchair ribbons, the C4H4S is linked to the edges by binding to the sulfur. Interestingly, CO molecules give rise to half-metallicity and surprising ferromagnetism in zigzag and armchair nanoribbons, respectively. The results discussed here could help to understand the physical and chemical properties of edges in transition metal dichalcogenides materials.

Hybrid underwater optical/acoustic link design

Abstract: The performance of duplex underwater optical wireless communication systems are limited by back-scattering of the transmitted light. This paper introduces a novel underwater wireless link design using hybrid optical/acoustic as a method to overcome it. The design comprises of highly directive, high-bandwidth optical uplinks from submersed AUVs or divers to a base station and a low bandwidth, wide-angle downlink. The limiting performance factors for the acoustic and optical aspects were found through respective channel modelling and SNRs; the maximum bitrate of the hybrid link is greater than a traditional acoustic link by a factor of 150. Main issues such as susceptibility to natural ocean variation, optical misalignment and acoustic latency are discussed.

Radio-Over-Fiber Optical Polarization-Multiplexed Networks for 3GPP Wireless Carrier-Aggregated MIMO Provision

Abstract: This paper proposes and demonstrates experimentally the application of optical polarization-multiplexed radio-over-fiber wireless backhauling of fully standard 3GPP carrier-aggregated multiple-input multiple-output (MIMO) signals. The experimental work demonstrates successful long-reach optical transmission of 3GPP carrier-aggregated LTE-Advanced (LTE-A) signals using 2×2 MIMO spatial diversity. The suitability of MIMO provision using radio-over-fiber optical links is demonstrated over different E-UTRA frequency division duplex frequency bands. The performance of electrical carrier aggregation is evaluated in different configurations comprising one, three and five LTE-A component carriers of 10 and 20 MHz bandwidth each. The experimental results demonstrate successful 2×2 MIMO radio-over-fiber polarization-multiplexed transmission of five LTE-A carriers over 25 km, three LTE-A carriers over 75 km and an LTE-A carrier over 100 km of standard single mode fiber to provide pervasive MIMO wireless service to a large number of users.

The extreme behavior of the radio-loud narrow-line Seyfert 1 galaxy J0849+5108

Abstract: Simultaneous radio, optical (both photometry and polarimetry), X-ray, and γ-ray observations of the radio-loud narrow-line Seyfert 1 (RL-NLSy1) galaxy J0849+5108 are presented. A massive three-magnitude optical flare across five nights in 2013 April is detected, along with associated flux increases in the γ-ray, infrared, and radio regimes; no comparable event was detected in the X-rays, though this may be due to poor coverage. A spectral energy distribution (SED) for the object using quasi-simultaneous data centered on the optical flare is compared to the previously published SEDs for the object by D'Ammando et al. The flare event coincided with a high degree of optical polarization. High amplitude optical microvariability is clearly detected, and is found to be of comparable amplitude when the object is observed in both faint and bright states. The object is also seen to undergo rapid shifts in polarization in both degree and electric vector position angle within a single night. J0849+5108 appears to show even more extreme variability than that previously reported for the similar object J0948+0022. These observations appear to support the growing claim that some RL-NLSy1 galaxies constitute a sub-class of blazar-like active galactic nuclei.

Guard-Band-Less and Polarization-Insensitive Tunable Wavelength Converter for Phase-Modulated Signals: Demonstration and Signal Quality Analyses

Abstract: We have designed a practical, tunable wavelength converter, using cascaded two-stage single-pump degenerated four-wave mixing processes in polarization-maintaining highly nonlinear fibers, employed in conjunction with a polarization-diversity scheme. This made it possible to achieve stable and high-quality operation of guard-band-less and polarization-insensitive tunable wavelength conversion for an 86-Gbit/s dual-polarization quadrature phase-shift keying signal over the operating bandwidth of 1535–1565 nm. Two factors of signal quality degradation during the conversion process were analyzed. First, the total amount of the amplified spontaneous emission (ASE) noise accumulated in the converter was studied theoretically. This leads to some important converter design parameters to improve the suppression of the signal quality degradation due to the ASE noise. Second, the increased phase error of the converted signal was investigated using a theoretical prediction, which was confirmed by an experimental study.

Variable optical polarization during high state in gamma-ray loud narrow line Seyfert 1 galaxy 1H 0323+342

Abstract: We present results of optical polarimetric and multi-band photometric observations for gamma-ray loud narrow-line Seyfert 1 galaxy 1H 0323+342. This object has been monitored by 1.5 m Kanata telescope since 2012 September but following a gamma-ray flux enhancement detected by Fermi-LAT on MJD 56483 (2013 July 10) dense follow-up was performed by ten 0.5-2.0 m telescopes in Japan over one week. The 2-year R_C-band light curve showed clear brightening corresponding to the gamma-ray flux increase and then decayed gradually. The high state as a whole lasted for ~20 days, during which we clearly detected optical polarization from this object. The polarization degree (PD) of the source increased from 0-1% in quiescence to ~3% at maximum and then declined to the quiescent level, with the duration of the enhancement of less than 10 days. The moderate PD around the peak allowed us to precisely measure the daily polarization angle (PA). As a result, we found that the daily PAs were almost constant and aligned to the jet axis, suggesting that the magnetic field direction at the emission region is transverse to the jet. This implies either a presence of helical/toroidal magnetic field or transverse magnetic field compressed by shock(s). We also found small-amplitude intra-night variability during the 2-hour continuous exposure on a single night. We discuss these findings based on the turbulent multi-zone model recently advocated by Marscher (2014). Optical to ultraviolet (UV) spectrum showed a rising shape in the higher frequency and the UV magnitude measured by Swift/UVOT was steady even during the flaring state, suggesting that thermal emission from accretion disk is dominant in that band.