Dark Pulses Research Articles

Timing of light pulses and photoperiod on the diurnal rhythm of hippocampal neuronal morphology of Siberian hamsters

Rapid remodeling of neurons provides the brain with flexibility to adjust to environmental fluctuations. In Siberian hamsters, hippocampal dendritic morphology fluctuates across the day. To reveal the regulatory mechanism of diurnal remodeling of hippocampal neurons, we investigated the effects of light signals applied under different photoperiodic conditions on dendritic morphology. A 4-h dark pulse during the morning of long days (LD) increased basilar dendritic length, as well as complexity of basilar dendrites of neurons in the CA1. A light pulse during the late night in short days (SD) reduced basilar dendrite branching and increased primary apical dendrites of CA1 neurons. Spine density of dentate gyrus (DG) dendrites was increased by a dark pulse in LD and spine density of CA1 basilar dendrites was decreased by a light pulse in SD. These results indicate that light signals induce rapid remodeling of dendritic morphology in a hippocampal subregion-specific manner. A light pulse in SD decreased hippocampal expression of fetal liver kinase 1 (Flk1), a receptor for vascular endothelial growth factor (VEGF), raising the possibility that VEGF–FLK1 signaling might be involved in the rapid decrease of branching or spine density of CA1 basilar dendrites by light.

Comment on ‘Evidence of slow-light effects from rotary drag of structured beams’

The paper Wisniewski-Barker E et al (2013 New J. Phys. 15 083020) is intended to distinguish experimentally between two mechanisms of pulse delay in ruby and to provide evidence in favor of the slow-light model. The proposed test is based on the idea of monitoring time delay of a ‘dark pulse’ or ‘intensity null’, rather than that of some Gaussian-like pulse. We show that, because of certain experimental inconsistencies, the results of the measurements do not allow one to prefer one of the models and, thus, are interpreted inadequately. In this comment, we propose and realize a simple modification of the experiment Wisniewski-Barker E et al (2013 New J. Phys. 15 083020), which allows us to unambiguously resolve this dilemma. We show that the effect of pulse delay in ruby is perfectly described by the simple model of pulse reshaping and does not require invoking the coherent population oscillation-based slow-light effects.

Optical Stretcher of Biological Cells Using Sub-Nanometer Optical Tweezers Generated by an Add/Drop Microring Resonator System

The design system consists of a nonlinear modified add/drop Microring Resonators (MRR) to build up optical tweezers in the form of potential wells is presented. The optical tweezers can be used for sub-nanometer objects trapping to form an optical stretcher used to deform the biological cells. The fabricated material used is InGaAsP/InP, which provide the required output signals. The optical tweezers can be formed by the dark soliton pulses and can be tuned and amplified using the Gaussian laser beam input. The optical dark soliton pulses with the central wavelengths range 1.4 to 1.55-m are fed into the system, collide with the input Gaussian laser beam at the add port and finally the optical tweezers with bandwidth of 4, 12 and 18 nm could be generated and used to trap sub-nanometer objects using a molecular buffer system. Interacting the tweezers holding the subnanometer objects with human tissue, influence the cellular surface of the cells by the generated forces. Therefore an optical stretcher can be formed to deform the biological cells of human tissue using optical tweezers.

2 µm bright–dark pulses in Tm-doped fiber ring laser with net anomalous dispersion

We demonstrate bright–dark pulses near 2 µm in a Tm-doped fiber laser (TDFL) for the first time. Bright–dark pulses could be achieved when the laser works in the passively mode-locking regime and the net group velocity dispersion is quite anomalous. A polarization controller is employed to manipulate the polarization states of the laser oscillation modes. The dark and bright pulses are confirmed to be two orthogonal linear polarization components that are coupled incoherently in the laser cavity. Experimental results also show that the dark and bright pulses have different spectral distributions.

Dark pulse emission in nonlinear polarization rotation-based multiwavelength mode-locked erbium-doped fiber laser

We experimentally show dark pulse generation in all-normal dispersion multiwavelength erbium-doped fiber laser (EDFL) with a long cavity of figure-of-eight configuration. The EDFL generates a stable multiwavelength laser with 0.47 nm spacing at 24 mW threshold pump power, while the number of lines obtained increases with the pump power. A dark pulse emission is observed as the pump power is increased above 137 mW, with fundamental repetition rate of 29 kHz and pulse width of 2.7 µs. It is observed that the dark pulse train can be shifted to second-, third-, and fourth-order harmonic dark pulses by carefully adjusting the polarization controller. For the fundamental dark pulse, the maximum pulse energy of 32.4 nJ is obtained at pump power of 146.0 mW.

基于半导体光放大器的暗脉冲的产生

基于半导体光放大器的暗脉冲的产生

Observations of three types of pulses in an erbium-doped fiber laser by incorporating a graphene saturable absorber

We experimentally observed three types of pulses generated in an erbium-doped fiber laser by incorporating a homemade graphene saturable absorber (GSA). The generated pulses from the laser oscillator include dual-wavelength dark pulses, fundamentally step-like pulses, and non-soliton second-harmonic pulses. These operation regimes are first reported by using graphene as the saturable absorber. Our results will further indicate that the GSA can function well for obtaining various ultrafast pulse phenomena, highlighting the practical potential of graphene in ultrafast photonics technologies.

T3B — an experiment to measure the time structure of hadronic showers

The goal of the T3B experiment is the measurement of the time structure of hadronic showers with nanosecond precision and high spatial resolution together with the CALICE hadron calorimeter prototypes, with a focus on the use of tungsten as absorber medium. The detector consists of a strip of 15 scintillator cells individually read out by silicon photomultipliers (SiPMs) and fast oscilloscopes with a PC-controlled data acquisition system. The data reconstruction uses an iterative subtraction technique which provides a determination of the arrival time of each photon on the light sensor with sub-nanosecond precision. The calibration is based on single photon-equivalent dark pulses constantly recorded during data taking, automatically eliminating the temperature dependence of the SiPM gain. In addition, a statistical correction for SiPM afterpulsing is demonstrated. To provide the tools for a comparison of T3B data with GEANT4 simulations, a digitization routine, which accounts for the detector response to energy deposits in the detector, has been implemented.

An Ytterbium-doped fiber laser with dark and Q-switched pulse generation using graphene-oxide as saturable absorber

We demonstrate an ytterbium-doped fiber (YDF) laser being able to generate dark pulses and Q-switched pulses by using a graphene oxide (GO) based composite as saturable absorber (SA). These operation regimes are realized for the first time in a 1-μm band fiber laser as far as our best knowledge. In the fabrication of GO based saturable absorber (GOSA), a vertical evaporation process is included, which results in a GO concentration and thickness variable SA. The generated dark pulse has pulse duration in ns-scale. In the Q-switched operation, pulses with durations from 5.321μs to 2.655μs and repetition rates from 28.47kHz to 58.95kHz can be obtained as the launched pump power is changed. The transition from the dark pulse to Q-switched operations can be clearly seen as the pump power is increased to a certain value. The radio frequency (RF) and optical spectrum variations with respect to the change of pump power have also been analyzed in detail.

Localized and periodic wave patterns for a nonic nonlinear Schrödinger equation

Abstract Propagating modes in a class of ‘nonic’ derivative nonlinear Schrodinger equations incorporating ninth order nonlinearity are investigated by application of two key invariants of motion. A nonlinear equation for the squared wave amplitude is derived thereby which allows the exact representation of periodic patterns as well as localized bright and dark pulses in terms of elliptic and their classical hyperbolic limits. These modes represent a balance among cubic, quintic and nonic nonlinearities.

Evidence of dark solitons in all-normal-dispersion-fiber lasers

In a recent paper we reported dark pulse emission of an all-normal-dispersion-fiber laser [Zhang, Tang, Zhao, and Wu, Phys. Rev. A 80, 045803 (2009)]. However, the formation mechanism of the dark pulse in the laser was unclear due to the limited temporal resolution of the measurement system. Using an improved detection system we have further investigated the phenomenon. We not only experimentally, unambiguously confirmed the existence of dark solitons in the fiber laser, but also identified that the dark pulses observed previously were bunches of the dark solitons. Moreover, we show that the dark soliton formation is a generic feature of the all-normal-dispersion-fiber lasers.

Dynamics of dark hollow Gaussian laser pulses in relativistic plasma

Optical beams with null central intensity have potential applications in the field of atom optics. The spatial and temporal evolution of a central shadow dark hollow Gaussian (DHG) relativistic laser pulse propagating in a plasma is studied in this article for first principles. A nonlinear Schrodinger-type equation is obtained for the beam spot profile and then solved numerically to investigate the pulse propagation characteristics. As series of numerical simulations are employed to trace the profile of the focused and compressed DHG laser pulse as it propagates through the plasma. The theoretical and simulation results predict that higher-order DHG pulses show smaller divergence as they propagate and, thus, lead to enhanced energy transport.

Lesions of the Intergeniculate Leaflet Lead to a Reorganization in Circadian Regulation and a Reversal in Masking Responses to Photic Stimuli in the Nile Grass Rat

Light influences the daily patterning of behavior by entraining circadian rhythms and through its acute effects on activity levels (masking). Mechanisms of entrainment are quite similar across species, but masking can be very different. Specifically, in diurnal species, light generally increases locomotor activity (positive masking), and in nocturnal ones, it generally suppresses it (negative masking). The intergeniculate leaflet (IGL), a subdivision of the lateral geniculate complex, receives direct retinal input and is reciprocally connected with the primary circadian clock, the suprachiasmatic nucleus (SCN). Here, we evaluated the influence of the IGL on masking and the circadian system in a diurnal rodent, the Nile grass rat (Arvicanthis niloticus), by determining the effects of bilateral IGL lesions on general activity under different lighting conditions. To examine masking responses, light or dark pulses were delivered in the dark or light phase, respectively. Light pulses at Zeitgeber time (ZT) 14 increased activity in control animals but decreased it in animals with IGL lesions. Dark pulses had no effect on controls, but significantly increased activity in lesioned animals at ZT0. Lesions also significantly increased activity, primarily during the dark phase of a 12:12 light/dark cycle, and during the subjective night when animals were kept in constant conditions. Taken together, our results suggest that the IGL plays a vital role in the maintenance of both the species-typical masking responses to light, and the circadian contribution to diurnality in grass rats.

An L-band graphene-oxide mode-locked fiber laser delivering bright and dark pulses

In this work we have demonstrated the generation of L-band bright and dark pulses from a graphene-oxide (GO) mode-locked erbium-doped fiber laser. The polymer-hosted graphene-oxide saturable absorber (SA) was fabricated by a vertical evaporation method, which permitted a flexible choice of GO concentration and SA thickness. Stable fundamental solitons with a width of ∼770 fs and repetition rate of ∼21.79 MHz could be directly generated from the laser cavity. The corresponding spectrum was centered at ∼1596.0 nm with a 3 dB bandwidth of ∼4.454 nm. Triple solitons and fundamentally repetitive dark pulses could also be achieved. By changing the laser cavity design, we also achieved the generation of dark pulses, which had one to three times the repetition rate. The multiple soliton and dark pulse generation were experimentally observed for the first time in such a GO mode-locked fiber laser system, to the best of our knowledge. Our experimental results indicate that the GOSA can be successfully utilized to realize different mode-locked states in the L-band.

A Novel Technique for the Stabilization of SiPM Gain Against Temperature Variations

In several applications of Silicon Photo-Multipliers (SiPM), drifts of the detector gain with the temperature represent a severe drawback which prevents from achieving optimal performance. We propose an original technique to address this issue, based upon the use of a SiPM not exposed to the light as a temperature sensor. The average amplitude of the dark pulses produced by this detector is measured and controlled to a constant reference value by means of a negative feedback loop, which automatically varies the bias voltage of the SiPM. The same bias voltage variations generated by the feedback loop are also applied to the sensitive SiPMs used in the specific application, thus making constant their gain. The effectiveness of the proposed compensation scheme has been experimentally demonstrated by using two SiPMs from FBK-irst (1 mm × 1 mm, 400 micro-cells, breakdown voltage Vbr ≅ 29 V), one as temperature sensor involved in the negative feedback loop and the other as light sensitive device. Both detectors have been enclosed in a thermally isolated box with temperature varied in the interval between 20 °C and 30 °C : the variation of the SiPM gain can be reduced from more than 20%, without compensation, to about 2%.

Harmonic mode locking counterparts of dark pulse and dark-bright pulse pairs

We have investigated experimentally different operational states of an all-normal-dispersion ytterbium-doped fiber (YDF) ring laser with a long cavity. Various operational states were obtained by adjusting a polarization controller (PC) and the pump power. Self-pulsing, bright pulses, dark-bright pulse pairs and their harmonic mode locking (HML) counterparts, as well as dark pulses and their HML counterparts have all been obtained. Numerical simulations reproduce well the formation processes of dark pulses and dark-bright pulse pairs.

Dark-Square-Pulse Generation in a Ring Cavity With a Tellurite Single-Mode Fiber

We demonstrate the generation of dark square pulses in a ring cavity with a 207-m long tellurite single-mode fiber. The duration of the pulse is tuned by adjusting the linear phase delay bias in the cavity. We obtain the dark-square pulse with a maximum full width at half maximum of 112 ns. The dark pulse is formed by the combined actions of the bright-square-pulse generation, birefringence, and polarizing effect in the cavity. The tellurite fiber can simultaneously provide the high nonlinearity, high birefringence, and large normal dispersion, which dominate the formation of a dark pulse in the cavity.

Coexistence and evolution of bright pulses and dark solitons in a fiber laser

Bright pulses and dark solitons coexisting and evolving in a fiber laser with strong normal dispersion have been observed. Experimental results show that there exists a transitional pulse regime with the pulse duty cycle of ∼0.5 that connects the bright pulse and dark soliton regimes. On adjusting polarization states and pump power, the duty cycle of pulses varies so that the laser emits bright, transitional, and dark pulses alternately. It is found that dark solitons are composed of two antiphase square pulses with very large durations and duty cycles. The experimental observations reveal that the bright and dark solitons are not completely isolated from each other. This work could provide a new perspective to the understanding of bright and dark soliton formations as well as their transformations.

Dark solitons of the power-energy saturation model: application to mode-locked lasers

The generation and dynamics of dark solitons in mode-locked lasers is studied within the framework of a nonlinear Schrödinger equation which incorporates power-saturated loss, as well as energy-saturated gain and filtering. Mode-locking into single dark solitons and multiple dark pulses are found by employing different descriptions for the energy and power of the system defined over unbounded and periodic (ring laser) systems. Treating the loss, gain and filtering terms as perturbations, it is shown that these terms induce an expanding shelf around the soliton. The dark soliton dynamics are studied analytically by means of a perturbation method that takes into regard the emergence of the shelves and reveals their importance.

Optical wireless quantum communication coding system using decimal convertor

In this study, a system of microring resonators and an add/drop filter are used to generate a large bandwidth signal as a localized multi wavelength, applicable for continuous dense coding and continuous variable encoding generation. This technique uses the Kerr nonlinear type of light in the MRR to generate multi wavelength of bright and dark soliton for quantum network cryptography. Afterwards, generated bright and dark optical pulses are converted into digital logic quantum codes using a decimal convertor system in which transmission of secured information are performed via an optical wireless communication system. Results show that ranges of multi bright and dark soliton wavelengths from 1.45 to \(1.65\,\upmu \mathrm{m}\) with central wavelength of \(1.55\,\upmu \mathrm{m}\) could be simulated, where the FWHM and FSR of 50 and 1,440 pm are obtained, respectively.