Dark Pulses Research Articles

Novel dark-bright optical solitons conversion system and power amplification

We propose a new system of the dark-bright solitons conversion using a micro- and nanoring resonators incorporating an optical add/drop filter, where the add/drop filter can be used to convert the dark soliton to a bright soliton. The key advantage of the system is that the detection of the dark soliton pulse is normally difficult due to the low level of input power. First, a dark soliton pulse is input into a microring resonator and then propagated into smaller micro- and nanoring resonators, respectively. Second, the add/drop filter is applied (connected) into the ring system, where the bright and dark solitons are obtained via the drop and through (or throughput) ports of the add/drop filter, respectively. The results obtained have shown that the detected soliton power can be controlled by the input soliton power and the ring resonator coupling coefficient, which is enough power to use in the transmission link. Thus, significant conversion-amplified signals can be achieved.

Rhythmic Conidiation in Constant Light inVividMutants ofNeurospora crassa

In Neurospora crassa, a circadian rhythm of conidiation (asexual spore formation) can be seen on the surface of agar media. This rhythm has a period of 22 hr in constant darkness (D/D). Under constant illumination (L/L), no rhythm is visible and cultures show constant conidiation. However, here we report that strains with a mutation in the vivid (vvd) gene, previously shown to code for the photoreceptor involved in photo-adaptation, exhibit conidiation rhythms in L/L as well as in D/D. The period of the rhythm of vvd strains ranges between 6 and 21 hr in L/L, depending upon the intensity of the light, the carbon source, and the presence of other mutations. Temperature compensation of the period also depends on light intensity. Dark pulses given in L/L shift the phase of the rhythm. Shifts from L/L to D/D show unexpected after effects; i.e., the short period of a vvd strain in L/L gradually lengthens over 2-3 days in D/D. The rhythm in L/L requires the white collar (wc-1) gene, but not the frequency (frq) gene. FRQ protein shows no rhythm in L/L in a vvd strain. The conidiation rhythm in L/L in vvd is therefore driven by a FRQ-less oscillator (FLO).

All-optical UWB pulse generation using sum-frequency generation in a PPLN waveguide

We propose and demonstrate a novel approach to optically generate ultrawideband (UWB) monocycle pulses by exploiting the parametric attenuation effect of sum-frequency generation (SFG) in a periodically poled lithium niobate (PPLN) waveguide. The SFG process changes the continuous-wave pump into dark optical pulse pump with undershoot, resulting in the generation of UWB monocycle through the combination of input signal and output pump with proper relative time advance/delay. Pairs of polarity-inverted UWB monocycle pulses meeting the UWB definition of U. S. Federal Communications Commission (FCC, part 15) are successfully obtained in the experiment.

Simultaneous Generation of Ultrafast Bright and Dark Pulse Employing Nonlinear Processes based on the Silicon Waveguides

In this paper we have proposed and demonstrated that the ultrafast bright and dark pulse can be generated simultaneously by utilizing mainly the nonlinear process such as stimulated Raman scattering (SRS), and so on, based on the silicon-on-insulator (SOI) optical waveguides. Results show that when an introduced ultrafast dark pulse is co-propagating with other two continue waves (CW) along the SOI, the ultrafast bright and dark pulse can be achieved at the end of waveguide at different wavelengths, respectively, if the frequency detuning of ∼15.6 THz between controlling pulse and CW is matched. The performance of pulse generation is strongly dependent on the waveguide length and initial conditions including the powers of the controlling pulse, and CW, and the time width of controlling pulse, respectively.

Generation of Ultrafast Bright and Dark Pulse on Silicon Chip with Integrated Mach-Zehnder Interferometer Configuration

In this paper we propose and simulate ultrafast femtosecond bright and dark pulses, obtained simultaneously at the same center wavelength, based on silicon-on-insulator (SOI) waveguides in Mach-Zehnder interferometer (MZI) configuration; the ultrafast pulsed pump is injected into one MZI's arm and a continuous wave component (CW) is divided equally into the two MZI arms. Numerical results show that properties of the generated bright and dark pulses are strongly dependent on the launching optical powers of both the pump pulse and CW carriers, and on the waveguide length.

DARK SOLITON BEHAVIORS WITHIN THE NONLINEAR MICRO AND NANORING RESONATORS AND APPLICATIONS

We propose some fascinating results regarding dark soliton pulse propagation within the nonlinear micro and nano waveguides. The system consists of nonlinear micro and nanoring resonators whereby the dark soliton is input into the system and travels within the waveguide. A continuous dark soliton pulse is sliced into smaller pulses by the nonlinear efiect which is known as chaos. The nonlinear behaviors such as chaos, bistability and bifurcation are analyzed and discussed. The broad area of applications such as dark-bright soliton conversion and power ampliflcation, binary code generation by the dark-bright soliton pair, dark soliton trapping and millimeter wave generation are proposed and discussed. The biggest advantage is that, where security is the most important consideration, power ampliflcation can be used to perform the long distance link.

Circadian and dark-pulse activation of orexin/hypocretin neurons

Temporal control of brain and behavioral states emerges as a consequence of the interaction between circadian and homeostatic neural circuits. This interaction permits the daily rhythm of sleep and wake, regulated in parallel by circadian cues originating from the suprachiasmatic nuclei (SCN) and arousal-promoting signals arising from the orexin-containing neurons in the tuberal hypothalamus (TH). Intriguingly, the SCN circadian clock can be reset by arousal-promoting stimuli while activation of orexin/hypocretin neurons is believed to be under circadian control, suggesting the existence of a reciprocal relationship. Unfortunately, since orexin neurons are themselves activated by locomotor promoting cues, it is unclear how these two systems interact to regulate behavioral rhythms. Here mice were placed in conditions of constant light, which suppressed locomotor activity, but also revealed a highly pronounced circadian pattern in orexin neuronal activation. Significantly, activation of orexin neurons in the medial and lateral TH occurred prior to the onset of sustained wheel-running activity. Moreover, exposure to a 6 h dark pulse during the subjective day, a stimulus that promotes arousal and phase advances behavioral rhythms, activated neurons in the medial and lateral TH including those containing orexin. Concurrently, this stimulus suppressed SCN activity while activating cells in the median raphe. In contrast, dark pulse exposure during the subjective night did not reset SCN-controlled behavioral rhythms and caused a transient suppression of neuronal activation in the TH. Collectively these results demonstrate, for the first time, pronounced circadian control of orexin neuron activation and implicate recruitment of orexin cells in dark pulse resetting of the SCN circadian clock.

All-Optical 40-GHz Time-Domain Fourier Transformation Using XPM With a Dark Parabolic Pulse

We demonstrate a 40-GHz all-optical time-domain Fourier transformation, in which an ideal parabolic phase modulation is applied to a signal by cross-phase modulation (XPM) with a dark parabolic pulse. The dark optical parabolic pulse is generated by the line-by-line spectral manipulation of a 40-GHz picosecond optical pulse source using an arrayed waveguide grating pulse shaper. By applying the parabolic XPM, the time interval for eliminating linear waveform distortions is expanded to a full bit slot. Dispersion slope-induced distortion is successfully eliminated with this scheme.

Entrainment and coupling of the hamster suprachiasmatic clock by daily dark pulses

The circadian rhythm of locomotor activity of hamsters kept in constant light (LL) can split into two distinct components that, in steady state, lie 180 degrees apart. The splitting phenomenon is the result of antiphase circadian oscillations between left and right sides of the suprachiasmatic nuclei (SCN), the master circadian clock in mammals. In unsplit hamsters housed in LL, a single dark pulse produces a phase-shift of the wheel-running activity rhythm, accompanied by a transient down-regulation of clock gene expression in the SCN. In the present study, we evaluated the effects of daily 1-hr dark pulses on wheel-running activity rhythm and on the expression of clock and nonclock proteins in the SCN of Syrian hamsters exposed to LL conditions. The results show that a daily 1-hr dark pulse entrained the rhythm of wheel-running activity of unsplit hamsters. In addition, in split animals, unimodal coupling of the two locomotor activity components was produced by daily 1-hr dark pulses. In the SCN, the effects of entrainment and unimodal coupling of the two separate components by dark observed in behavior were also evident in the bilateral expression of the proteins c-FOS, p-ERK, PERIOD 1, and calbindin. These results show that the bilaterally asymmetric SCN clock, underlying split circadian behavior, can be recoupled in phase and entrained by short daily dark exposure, indicating the synchronizing potency of darkness on the main circadian clock.

Characterization of the photoactive GAF domain of the CikA homolog (SyCikA, Slr1969) of the cyanobacterium Synechocystis sp. PCC 6803

Phytochromes and bacteriophytochromes in plants and some species of bacteria, respectively, are photoreceptors that bind linear tetrapyrroles and can respond to red and far-red light signals in a reversible manner. A related but distinct photoreceptor candidate, CikA (denoted ScCikA), has been reported to reset the circadian clock in the cyanobacterium Synechococcus elongatus PCC 7942 after a dark pulse. However, recent studies have indicated that ScCikA does not function as a photoreceptor but as a redox sensor. Moreover, the Cys residue that covalently ligates the chromophore in phytochromes is not conserved in the ScCikA protein. On the other hand, the CikA homolog in Synechocystis sp. PCC 6803 (Slr1969, denoted SyCikA) retains this conserved Cys residue. In our present study, we have isolated the putative chromophore-binding GAF domain of SyCikA from Synechocystis and phycocyanobilin-producing Escherichia coli. Absorption spectra of both preparations showed two peaks in the UV and violet regions. Irradiation of these proteins with violet light yielded a broad peak in a yellow region at the expense of the peaks in the UV and violet regions. Interestingly, successive irradiation with yellow light did not revert these absorption spectra but a partial dark reversion to the original form was detected. These results suggest that SyCikA may function as a violet light sensor in Synechocystis.

SYMBOLIC COMPUTATION STUDY OF BRIGHT SOLITONIC PULSES IN THE NORMAL DISPERSION REGION

New types of solitonic pulses are obtained theoretically based on the solutions for the nonlinear Schrödinger (NLS) equation. Unlike the earlier results, in the normal dispersion region, the novel bright solitonic pulses are observed. Depending on the parameters' values, the properties of both bright and dark solitonic pulses are described in the same expression. Furthermore, those solitonic pulses are found to be evolved into bright and dark ones under certain conditions. This might be a potential application in optical communication systems which can produce bright and dark solitonic pulses simultaneously.

Serotonergic potentiation of dark pulse‐induced phase‐shifting effects at midday in hamsters

In mammals, resetting of the suprachiasmatic clock (SCN) by behavioral activation or serotonin (5-HT) agonists is mimicked by dark pulses, presented during subjective day in constant light (LL). Because behavioral resetting may be mediated in part by 5-HT inputs to the SCN, here we determined whether 5-HT system can modulate dark-induced phase-shifts in Syrian hamsters housed in LL. Two hours of darkness at mid-subjective day (circadian time 6; CT-6) resulted in increased concentrations of 5-HT in the SCN tissue and induction of c-FOS expression in the raphe nuclei. Injections of the 5-HT(1A/7) agonist +8-OH-DPAT or dark pulses at CT-6 induced phase-advances of the wheel-running activity rhythm and down-regulated the expression of the clock genes Per1-2 and c-FOS in the SCN in a similar way. The combination of both treatments [+8-OH-DPAT + dark pulses], however, resulted in larger phase-advances, while associated molecular changes were not significantly modified, except for the gene Dbp, in comparison to +8-OH-DPAT or dark pulses alone. Dark resetting was blocked by pre-treatment with a 5-HT(7) antagonist, but not with a 5-HT(1A) antagonist. The additive phase-shifts of two different cues to reset the SCN clock open wide the gateway for non-photic shifting, leading to new strategies in chronotherapy.

Characterisation of radiation damage in silicon photomultipliers with a Monte Carlo model

Measured response functions and low photon yield spectra of silicon photomultipliers (SiPM) were compared to multi-photoelectron pulse-height distributions generated by a Monte Carlo model. Characteristic parameters for SiPM were derived. The devices were irradiated with 14 MeV electrons at the Mainz microtron MAMI. It is shown that the first noticeable damage consists of an increase in the rate of dark pulses and the loss of uniformity in the pixel gains. Higher radiation doses also reduced the photon detection efficiency. The results are especially relevant for applications of SiPM in fibre detectors at high luminosity experiments.

Cold exposure impairs dark‐pulse capacity to induce REM sleep in the albino rat

In the albino rat, a REM sleep (REMS) onset can be induced with a high probability and a short latency when the light is suddenly turned off (dark pulse, DP) during non-REM sleep (NREMS). The aim of this study was to investigate to what extent DP delivery could overcome the integrative thermoregulatory mechanisms that depress REMS occurrence during exposure to low ambient temperature (Ta). To this aim, the efficiency of a non-rhythmical repetitive DP (3 min each) delivery during the first 6-h light period of a 12 h:12 h light-dark cycle in inducing REMS was studied in the rat, through the analysis of electroencephalogram, electrocardiogram, hypothalamic temperature and motor activity at different Tas. The results showed that DP delivery triggers a transition from NREMS to REMS comparable to that which occurs spontaneously. However, the efficiency of DP delivery in inducing REMS was reduced during cold exposure to an extent comparable with that observed in spontaneous REMS occurrence. Such impairment was associated with low Delta activity and high sympathetic tone when DPs were delivered. Repetitive DP administration increased REMS amount during the delivery period and a subsequent negative REMS rebound was observed. In conclusion, DP delivery did not overcome the integrative thermoregulatory mechanisms that depress REMS in the cold. These results underline the crucial physiological meaning of the mutual exclusion of thermoregulatory activation and REMS occurrence, and support the hypothesis that the suspension of the central control of body temperature is a prerequisite for REMS occurrence.

Multichannel Selective Femtosecond Coherent Control Based on Symmetry Properties

We present and implement a new scheme for extended multichannel selective femtosecond coherent control based on symmetry properties of the excitation channels. Here, an atomic nonresonant two-photon absorption channel is coherently incorporated in a resonance-mediated (2+1) three-photon absorption channel. By proper pulse shaping, utilizing the invariance of the two-photon absorption to specific phase transformations of the pulse, the three-photon absorption is tuned independently over an order-of-magnitude yield range for any possible two-photon absorption yield. Noticeable is a set of "two-photon dark pulses" inducing widely tunable three-photon absorption.

Bright and dark 40 GHz parabolic pulse generation using a picosecond optical pulse train and an arrayed waveguide grating

We demonstrate parabolic optical pulse generation by manipulating the intensity and phase of individual longitudinal modes of a 40 GHz picosecond optical pulse train in the spectral domain. Bright and dark parabolic pulses were generated from a 40 GHz mode-locked fiber laser using a 64-channel arrayed waveguide grating pulse shaper. The obtained parabolic pulse, which can easily generate a linear chirping, is useful for a number of applications to optical signal processing applications, including pulse compression and time-domain optical Fourier transformation.

Proteins Found in a CikA Interaction Assay Link the Circadian Clock, Metabolism, and Cell Division in Synechococcus elongatus

Diverse organisms time their cellular activities to occur at distinct phases of Earth's solar day, not through the direct regulation of these processes by light and darkness but rather through the use of an internal biological (circadian) clock that is synchronized with the external cycle. Input pathways serve as mechanisms to transduce external cues to a circadian oscillator to maintain synchrony between this internal oscillation and the environment. The circadian input pathway in the cyanobacterium Synechococcus elongatus PCC 7942 requires the kinase CikA. A cikA null mutant exhibits a short circadian period, the inability to reset its clock in response to pulses of darkness, and a defect in cell division. Although CikA is copurified with the Kai proteins that constitute the circadian central oscillator, no direct interaction between CikA and either KaiA, KaiB, or KaiC has been demonstrated. Here, we identify four proteins that may help connect CikA with the oscillator. Phenotypic analyses of null and overexpression alleles demonstrate that these proteins are involved in at least one of the functions--circadian period regulation, phase resetting, and cell division--attributed to CikA. Predictions based on sequence similarity suggest that these proteins function through protein phosphorylation, iron-sulfur cluster biosynthesis, and redox regulation. Collectively, these results suggest a model for circadian input that incorporates proteins that link the circadian clock, metabolism, and cell division.

Effect of a Dark Pulse Under Continuous Red Light on the Arabidopsis thaliana Circadian Rhythm

The phase responses of the circadian rhythm for a 2-h dark pulse under continuous red light in the transgenic Arabidopsis thaliana CCA1::LUC were investigated using bioluminescence technology. By application of a 2-h dark pulse at subjective dusk, a small phase advance was induced (about 2 h phase advance). In contrast, by the application of a 2-h dark pulse at subjective dawn, a phase delay was induced (about 4 h phase delay). The phase response curve (PRC) was categorized as type-1 PRC and was described by a sinusoidal curve with a second harmonic component. The internal fluctuation of the circadian rhythm under continuous red light was also investigated. In addition, the establishment of a model for the control of the circadian rhythm is discussed.

Pulse repetition rate multiplication in fibre laser using higher-order passive modelocking

A simple technique that allows for the repetition rate multiplication of optical pulse trains generated in passively modelocked fibre lasers is experimentally demonstrated. This is achieved by initiating higher-order passive modelocking by using both a dual‐channel fibre Bragg grating and a Fabry-Pérot filter inside the fibre cavity. Continuous dark pulse trains with a repetition rate of 60 GHz were generated, which is a four-fold multiplication of the Fabry-Pérot free spectral range.

The effects of light on the Gonyaulax circadian system.

The circadian system of the marine unicellular alga Gonyaulax polyedra consists of at least two separate circadian oscillators. One of these controls the rhythm of bioluminescence, the other the rhythm of swimming behaviour. These two oscillators have separate light input mechanisms. The bioluminescence oscillator responds mainly to blue light whereas the aggregation oscillator is also sensitive to red light. Therefore, one of the chlorophylls is a likely candidate for the light receptor of the aggregation oscillator. Owing to their differences in spectral sensitivity, the two oscillators can be internally desynchronized when frequent dark pulses (e.g., five minutes every 20 min) are given in otherwise constant red light. Single bright red light pulses interrupting a constant dim blue background shift the bioluminescence oscillator similarly to dark pulses. They also lead to aftereffects in the period of the bioluminescence rhythm, indicating that the aggregation oscillator has a different phase response to red light pulses. In contrast, blue light pulses interrupting a dim red background shift both oscillators in a similar way and do not significantly alter the circadian period following the light pulse. The mammalian phosphagen creatine shortens the period of the bioluminescence rhythm significantly in blue light but not in red. Because it also increases the sensitivity of the phase response of the bioluminescence oscillator, we propose that creatine acts on its blue-sensitive light input mechanism.