Bright Pulses Research Articles

InGaAsP/InP Microring Resonator (MRR) Waveguide Used to Generate Soliton Comb with Tunable Channel Spacing

A novel system of tunable channel spacing soliton comb generation is presented using a PANDA ring resonator incorporated with an add-drop filter system. The intense optical fields known as soliton comb can be generated. Results show that soliton comb can be generated with un-equal spaced or variable free spectral range (FSR) by using the input bright soliton pulse into the microring resonator (MRR) system. The proposed comb filter exhibits a large tuning range in channel spacing. Our simulations shows that the channel spacing can be continuously tuned form up to 10 GHz, where the centre wavelength of the input power has been selected at 50 GHz. The structure of the proposed MRR's waveguide (InGaAsP/InP) and mode propagation profile have been presented in this research.

Open data set of live cyanobacterial cells imaged using an X-ray laser.

Structural studies on living cells by conventional methods are limited to low resolution because radiation damage kills cells long before the necessary dose for high resolution can be delivered. X-ray free-electron lasers circumvent this problem by outrunning key damage processes with an ultra-short and extremely bright coherent X-ray pulse. Diffraction-before-destruction experiments provide high-resolution data from cells that are alive when the femtosecond X-ray pulse traverses the sample. This paper presents two data sets from micron-sized cyanobacteria obtained at the Linac Coherent Light Source, containing a total of 199,000 diffraction patterns. Utilizing this type of diffraction data will require the development of new analysis methods and algorithms for studying structure and structural variability in large populations of cells and to create abstract models. Such studies will allow us to understand living cells and populations of cells in new ways. New X-ray lasers, like the European XFEL, will produce billions of pulses per day, and could open new areas in structural sciences.

Polarization domain wall pulses in a microfiber-based topological insulator fiber laser.

Topological insulators (TIs), are novel two-dimension materials, which can act as effective saturable absorbers (SAs) in a fiber laser. Moreover, based on the evanescent wave interaction, deposition of the TI on microfiber would create an effective SA, which has combined advantages from the strong nonlinear optical response in TI material together with the sufficiently-long-range interaction length in fiber taper. By using this type of TI SA, various scalar solitons have been obtained in fiber lasers. However, a single mode fiber always exhibits birefringence, and hence can support two orthogonal degenerate modes. Here we investigate experimentally the vector characters of a TI SA fiber laser. Using the saturated absorption and the high nonlinearity of the TI SA, a rich variety of dynamic states, including polarization-locked dark pulses and their harmonic mode locked counterparts, polarization-locked noise-like pulses and their harmonic mode locked counterparts, incoherently coupled polarization domain wall pulses, including bright square pulses, bright-dark pulse pairs, dark pulses and bright square pulse-dark pulse pairs are all observed with different pump powers and polarization states.

A bright attosecond x-ray pulse train generation in a double-laser-driven cone target

By using full three-dimensional particle-in-cell and Monte Carlo simulations, we investigate the generation of a high-brightness attosecond x-ray pulse train in a double-laser-driven cone target. The scheme makes use of two lasers: the first high-intensity laser with a laser peak intensity 1.37 × 1020 W/cm2 irradiates the cone and produces overdense attosecond electron bunches; the second counterpropagating weakly relativistic laser with a laser peak intensity 4.932 × 1017 W/cm2 interacts with the produced electron bunches and a bright x-ray pulse train is generated by Thomson backscattering of the second laser off the attosecond electron bunches. It is shown that the photon flux rises by 5 times using the cone target as compared with a normal channel. Meanwhile, the x-ray peak brightness increases significantly from 1.4 × 1021/(s mm2 mrad2 0.1 keV) to 6.0 × 1021/(s mm2 mrad2 0.1 keV), which is much higher than that of the Thomson x-ray source generated from traditional accelerators. We also discuss the influence of the laser and target parameters on the x-ray pulse properties. This compact bright x-ray source may have diverse applications, e.g., the study of electric dynamics and harmonics emission in the atomic scale.

Compact bright pulse and ultrashort-pulse in the nonlinear Kerr-like media

The extended nonlinear Schrödinger equation describing the propagation of light beam in the weak nonlocal nonlinear media in general, and in the optical fibers with nearly instantaneous nonlinear response of the medium in particular, is investigated. In the zero-dispersion limit, we show that the system exhibits stable stationary compact bright pulse with an arbitrary nonlinear phase-shift both for the focusing and the defocusing media. However, in the presence of the large linear dispersion, this compact pulse become unstable and may be either disintegrate or transform into the ultrashort bright pulse according to whether the system operates in the normal or in the anomalous region. The exact analytical expressions of these two pulses are derived and the results checked through numerical simulations.

Does melatonin have a meaningful role as a sleep aid for jet lag recovery?

Does melatonin have a meaningful role as a sleep aid for jet lag recovery?

Orthogonally polarized bright–dark pulse pair generation in mode-locked fiber laser with a large-angle tilted fiber grating

We report on the generation of orthogonally polarized bright–dark pulse pair in a passively mode-locked fiber laser with a large-angle tilted fiber grating (LA-TFG). The unique polarization properties of the LA-TFG, i.e., polarization-dependent loss and polarization-mode splitting, enable dual-wavelength mode-locking operation. Besides dual-wavelength bright pulses with uniform polarization at two different wavelengths, the bright–dark pulse pair has also been achieved. It is found that the bright–dark pulse pair is formed due to the nonlinear couplings between lights with two orthogonal polarizations and two different wavelengths. Furthermore, harmonic mode-locking of bright–dark pulse pair has been observed. The obtained bright–dark pulse pair could find potential use in secure communication system. It also paves the way to manipulate the generation of dark pulse in terms of wavelength and polarization, using specially designed fiber grating for mode-locking.

Spectral-hole memory for light at the single-photon level

We demonstrate a solid state spin-wave optical memory based on stopped light in a spectral hole. A long lived narrow spectral hole is created by optical pumping in the inhomogeneous absorption profile of a Pr$^{3+}$:Y$_2$SiO$_5$ crystal. Optical pulses sent through the spectral hole experience a strong reduction of their group velocity and are spatially compressed in the crystal. A short Raman pulse transfers the optical excitation to the spin state before the light pulse exits the crystal, effectively stopping the light. After a controllable delay, a second Raman pulse is sent, which leads to the emission of the stored photons. We reach storage and retrieval efficiencies for bright pulses of up to $39\,\%$ in a $5 \,\mathrm{mm}$-long crystal. We also show that our device works at the single photon level by storing and retrieving $3\,\mathrm{\mu s}$-long weak coherent pulses with efficiencies up to $31\,\%$, demonstrating the most efficient spin-wave solid state optical memory at the single-photon level so far. We reach an unconditional noise level of $(9\pm1)\times 10^{-3}$ photons per pulse in a detection window of $4\,\mathrm{\mu s}$ leading to a signal-to-noise ratio of $33 \pm 4$ for an average input photon number of 1, making our device promising for long-lived storage of non-classical light.

Dark solitons in laser radiation build-up dynamics.

We reveal the existence of slowly decaying dark solitons in the radiation build-up dynamics of bright pulses in all-normal dispersion mode-locked fiber lasers, numerically modeled in the framework of a generalized nonlinear Schrödinger equation. The evolution of noise perturbations to quasistationary dark solitons is examined, and the significance of background shape and soliton-soliton collisions on the eventual soliton decay is established. We demonstrate the role of a restoring force in extending soliton interactions in conservative systems to include the effects of dissipation, as encountered in laser cavities, and generalize our observations to other nonlinear systems.

TEMPORAL EVOLUTION OF THE VELA PULSAR’S PULSE PROFILE

ABSTRACT The mechanisms of emission and changes in rotation frequency (“glitching”) of the Vela pulsar (J0835−4510) are not well understood. Further insight into these mechanisms can be achieved by long-term studies of integrated pulse width, timing residuals, and bright-pulse rates. We have undertaken an intensive observing campaign of Vela and collected over 6000 hr of single-pulse data. The data shows that the pulse width changes with time, including marked jumps in width after micro-glitches (frequency changes). The abundance of bright pulses also changes after some micro-glitches, but not all. The secular changes in pulse width have three possible cyclic periods that match with X-ray periodicities of a helical jet that are interpreted as free precession.

Topological Insulator-Assisted Dual-Wavelength Fiber Laser Delivering Versatile Pulse Patterns

We report on the generation of dual-wavelength mode-locked pulses in an erbium-doped fiber laser incorporating a topological insulator (TI): Bi2Se3/Polyvinyl Alcohol (PVA) film which could operate as both an excellent saturable absorber (SA) for mode-locking and a high-nonlinear medium for mitigating the mode competition of erbium-doped fiber and stabilizing the dual-wavelength oscillation. The TI: Bi2Se3/PVA film is prepared through a liquid-phase exfoliation/spin-coating method. Its saturating intensity and modulation depth are measured to be about 31.5 MW/cm2 and 3.4%, respectively. Taking advantage of the high nonlinearity and saturable absorption of the TI: Bi2Se3, three dual-wavelength pulse patterns, namely bright pulse, bright-dark soliton pair, and hybrid step-like and dark pulse, could be achieved under different lengths of single mode fiber by properly adjusting the pump power and the polarization state. For the bright pulse operation, we obtain its fundamental repetition rate of 9.75 MHz. For the bright-dark soliton pair operation, we find that it contains two distinct parts in the whole optical spectrum: one is at shorter wavelength corresponds to bright soliton and the other one is at longer wavelength corresponds to dual-wavelength dark soliton. In addition, we also achieved the harmonic mode-locking (HML) of the bright-dark soliton pair. The highest obtained repetition rate is about 433.8 MHz, which corresponds to the 280th harmonic of the fundamental repetition rate. For the hybrid step-like and dark pulse operation, we achieve its fundamental repetition rate of 8.805 MHz. Our findings suggest that TI: Bi2Se3 can operate as both an excellent SA for short pulse generation and a promising highly nonlinear photonic material for the related nonlinear optics applications.

PATIENT DOSE DURING THERAPEUTIC ENDOSCOPIC RETROGRADE CHOLANGIOPANCREATOGRAPHY PROCEDURE.

Endoscopic retrograde cholangiopancreatography (ERCP) is a standard technique for the diagnosis and treatment of disorders of the pancreas or bile ducts. The aim of this study was the measurement of the radiation dose to patients during therapeutic ERCP procedures, in order to estimate the patient effective dose (ED). Fifteen patients were studied using a fluoroscopy system equipped with automatic brightness control and pulse fluoroscopy mode. Fluoroscopy time (FT), cumulative dose (Ka,r) and air kerma-area product (PKA) were collected for ERCP procedures. The ED was calculated from PKA values. The FT was ranged from 0.68 to 5.57 min, with the mean value of 2.50 min; the Ka,r was ranged from 2.22 to 19.10 mGy, with the mean value of 7.71 mGy; and the PKA was ranged between 0.59 and 5.10 Gycm2, with the mean value of 2.03 Gycm2. The ED ranged from 0.11 to 0.97 mSv, whilst the mean and median ED values were 0.39 and 0.32 mSv, respectively. FT and radiation dose to the patients were either comparative or significantly lower than those previously reported.

OPTICAL BISTABILITY CONTROLLED USING ADD-DROP MOBIUS MICRORING RESONATOR SYSTEM

The theoretical investigation has been performed on the implementation of optical Mobius shape in add-drop microring resonator. The modified add-drop Mobius configuration is used to investigate the optical bistability and the spectral transmission. The optical bright soliton pulse is used as the input source of the resonator system. The pulses propagation of the resonator system is modelled using the iterative programming based on the transfer matrix analysis equations. The enhancement of nonlinear effect of the resonator system is achieved by the add-drop Mobius resonator configuration. The system has been modelled for a variation of coupling coefficient for increase the bistable signal properties. The Add-drop Mobius MRR generated a bistable signal with 6.01 mW hysteresis width, and 9.47 mW output switch power with optimized radius of 5 µm outer and 4.5 m inner ring parts with 50 mW controlled power and input power. Mobius configuration is found as the better shape of resonator cavity that capable of optical switching application.

Preparation and Delivery of Microcrystals in Lipidic Cubic Phase for Serial Femtosecond Crystallography

Membrane proteins (MPs) are important components of cellular membranes and primary drug targets. Rational drug design relies on the exact structural information about the protein, however MPs are difficult to handle and crystallize. Recent progress in MP structural determination has benefited greatly from the development of lipidic cubic phase (LCP) crystallization method, which yields well-diffracting but often small crystals that suffer from radiation damage during traditional crystallographic data collection at synchrotron sources. Introduction of the X-ray free-electron laser (XFEL) source that produces extremely bright femtosecond pulses enabled room temperature data collection from microcrystals with minimal, if any, radiation damage. Our recent efforts in combining LCP technology with serial femtosecond crystallography (LCP-SFX) have resulted in high-resolution structures of several human G protein-coupled receptors, the largest and the most important drug target superfamily, yet notoriously difficult for structural determination. In LCP-SFX technique, LCP is recruited as a matrix for both growth and delivery of membrane protein microcrystals to the intersection with an XFEL beam for crystallographic data collection. It has been demonstrated that LCP-SFX can significantly improve the diffraction resolution when only micron-sized crystals are available and when crystal quality is too poor to yield interpretable structural data at conventional synchrotron microfocus beamlines. Here we present the protocol for preparation, characterization and delivery of microcrystals in LCP for LCP-SFX experiments.

A pilot ASKAP survey of radio transient events in the region around the intermittent pulsar PSR J1107−5907

We use observations from the Boolardy Engineering Test Array (BETA) of the Australian Square Kilometre Array Pathfinder (ASKAP) telescope to search for transient radio sources in the field around the intermittent pulsar PSR J1107-5907. The pulsar is thought to switch between an "off" state in which no emission is detectable, a weak state and a strong state. We ran three independent transient detection pipelines on two-minute snapshot images from a 13 hour BETA observation in order to 1) study the emission from the pulsar, 2) search for other transient emission from elsewhere in the image and 3) to compare the results from the different transient detection pipelines. The pulsar was easily detected as a transient source and, over the course of the observations, it switched into the strong state three times giving a typical timescale between the strong emission states of 3.7 hours. After the first switch it remained in the strong state for almost 40 minutes. The other strong states lasted less than 4 minutes. The second state change was confirmed using observations with the Parkes radio telescope. No other transient events were found and we place constraints on the surface density of such events on these timescales. The high sensitivity Parkes observations enabled us to detect individual bright pulses during the weak state and to study the strong state over a wide observing band. We conclude by showing that future transient surveys with ASKAP will have the potential to probe the intermittent pulsar population.

The countermeasures against the blinding attack in quantum key distribution

It has been shown that the single photon detectors (SPDs) based on the avalanche photodiode (APD) can be blinded and controlled by the bright light and short trigger pulses. Eavesdropper can get the full information without causing additional quantum bit error rate. Hence, in order to guarantee the security of the quantum key distribution (QKD) systems, some countermeasures, by changing the characteristic of the SPD or monitoring the parameters of the detector, are presented by some research groups. In this paper, we provide a new and effective countermeasure against the blinding attack based on improving the optical scheme of the decoding unit in the QKD system rather than only considering the characteristic of the SPD. In our proposal we use a coupler with asymmetric splitting ratio to distinguish the detection characteristic of the SPD with blinding attack from that without blinding attack. The detailed analysis shows that the proposed scheme is feasible to defense the blinding attack.

Optical Rogue Wave Excitation and Modulation on a Bright Soliton Background**Supported by the National Natural Science Foundation of China under Grant Nos 11475135 and 11547302, and the Doctoral Program Funds of the Ministry of Education of China under Grant No 20126101110004.

We study rogue waves in an inhomogeneous nonlinear optical fiber with variable coefficients. An exact rogue wave solution that describes rogue wave excitation and modulation on a bright soliton pulse is obtained. Special properties of rogue waves on the bright soliton, such as the trajectory and spectrum, are analyzed in detail. In particular, our analytical results suggest a way of sustaining the peak shape of rogue waves on the soliton background by choosing an appropriate dispersion parameter.

Bright attosecond soft X-ray pulse trains by transient phase-matching in two-color high-order harmonic generation.

We study two-color high-order harmonic generation in Neon with 790 nm and 1300 nm driving laser fields and observe an extreme-ultraviolet continuum that extends to photon energies of 160 eV. Using a 6-mm-long, high pressure gas cell, we optimize the HHG yield at high photon energies and investigate the effect of ionization and propagation under phase-matching conditions that allow us to control the temporal structure of the XUV emission. Numerical simulations that include the 3D propagation of the two-color laser pulse show that a bright isolated attosecond pulse with exceptionally high photon energies can be generated in our experimental conditions due to an efficient hybrid optical and phase-matching gating mechanism.

Kuznetsov–Ma soliton and Akhmediev breather of higher-order nonlinear Schrödinger equation**Project supported by the Key Project of Scientific and Technological Research in Hebei Province, China (Grant No. ZD2015133).

In terms of Darboux transformation, we have exactly solved the higher-order nonlinear Schrödinger equation that describes the propagation of ultrashort optical pulses in optical fibers. We discuss the modulation instability (MI) process in detail and find that the higher-order term has no effect on the MI condition. Under different conditions, we obtain Kuznetsov–Ma soliton and Akhmediev breather solutions of higher-order nonlinear Schrödinger equation. The former describes the propagation of a bright pulse on a continuous wave background in the presence of higher-order effects and the soliton’s peak position is shifted owing to the presence of a nonvanishing background, while the latter implies the modulation instability process that can be used in practice to produce a train of ultrashort optical soliton pulses.

SINGLE-PULSE RADIO OBSERVATIONS OF THE GALACTIC CENTER MAGNETAR PSR J1745–2900

In this paper, we report radio observations of the Galactic Center magnetar PSR J1745-2900 at six epochs between June and October, 2014. These observations were carried out using the new Shanghai Tian Ma Radio Telescope at a frequency of 8.6 GHz. Both the flux density and integrated profile of PSR J1745-2900 show dramatic changes from epoch to epoch showing that the pulsar was in its "erratic" phase. On MJD 56836, the flux density of this magnetar was about 8.7 mJy, which was ten times large than that reported at the time of discovery, enabling a single-pulse analysis. The emission is dominated by narrow "spiky" pulses which follow a log-normal distribution in peak flux density. From 1913 pulses, we detected 53 pulses whose peak flux density is ten times greater than that of the integrated profile. They are concentrated in pulse phase at the peaks of the integrated profile. The pulse widths at the 50% level of these bright pulses was between 0.2 to 0.9 deg, much narrower than that of integrated profile (~12 deg). The observed pulse widths may be limited by interstellar scattering. No clear correlation was found between the widths and peak flux density of these pulses and no evidence was found for subpulse drifting. Relatively strong spiky pulses are also detected in the other five epochs of observation, showing the same properties as that detected in MJD 56836. These strong spiky pulses cannot be classified as "giant" pulses but are more closely related to normal pulse emission.