Optical Pulse Profile Research Articles

All-fiber fast acousto-optic temporal control of tunable optical pulses

We demonstrate a new all-fiber electrically tunable modulation method which significantly reduces the response time of a Bragg grating acousto-optic modulator. A 4 cm long device is fabricated with a 1 cm grating inscribed in a suspended core fiber. An acoustic pulse train is switched out of phase along the fiber, damping unwanted natural resonant vibrations inside the grating. The device rise time is decreased from 56 to 9 µs by tuning the duty cycle of the driven electrical signal, contributing to achieve the shortest switching time of 15.6 µs. This tunable temporal response reveals unique features to change the profile of optical pulses. High pulse modulation depths are achieved employing a compact acousto-optic modulator, pointing to fast switching of all-fiber photonic devices.

Identifying reliable periods in 2MASS J09213414–5939068, IGR J16167–4957, and V667 Pup

Detailed timing analyses of three cataclysmic variables, namely 2MASS J09213414−5939068, IGR J16167−4957, and V667 Pup are carried out using the long-baseline and high-cadence optical photometric data from the Transiting Exoplanet Survey Satellite (TESS). Periods of 908.12 ± 0.05 s and 990.10 ± 0.06 s are observed in the optical variation of 2MASS J09213414−5939068 that were not found in earlier studies and appear to be probable spin and beat periods of the system, respectively. The presence of multiple periods at spin, beat, and other sidebands indicates that 2MASS J09213414−5939068 likely belongs to an intermediate polar class of magnetic cataclysmic variables that seems to be accreted via a disc-overflow mechanism. Clear evidence of a period of 582.45 ± 0.04 s is found during the TESS observations of IGR J16167−4957, which can be interpreted as the spin period of the system. Strong modulation at this frequency supports its classification as an intermediate polar, where accretion may primarily be governed by a disc. The dominance of the spin pulse unveils the disc-fed dominance accretion in V667 Pup, but the detection of the previously unknown beat period of 525.77 ± 0.03 s suggests that a portion of the material is also accreted through a stream. Moreover, the double-peaked structure observed in the optical spin pulse profile of V667 Pup suggests the possibility of a two-pole accretion geometry, where each pole accretes at a different rate and is separated by 180°.

Optical Wave Phenomena in Birefringent Fibers Described by Space-Time Fractional Cubic-Quartic Nonlinear Schrödinger Equation with the Sense of Beta and Conformable Derivative

The work explores the optical wave solutions along with their graphical representations by proposing the coupled spatial-temporal fractional cubic-quartic nonlinear Schrödinger equation with the sense of two fractal derivatives (beta and conformable derivative) and Kerr law nonlinearity for birefringent fibers. The new extended direct algebraic method for the first time is implemented to achieve this goal. Many optical solutions are listed along with their existence criteria. Based on the existence criteria, the cubic-quartic bright, and singular optical soliton, periodic pulse, and rouge wave profiles are supported in birefringent fibers with the influence of both beta and conformable derivative parameter.

Effect of dispersion on indistinguishability between single-photon wave-packets

With propagating through a dispersive medium, the temporal–spectral profile of optical pulses should be inevitably modified. Although such dispersion effect has been well studied in classical optics, its effect on a single-photon wave-packet has not yet been entirely revealed. In this paper, we investigate the effect of dispersion on indistinguishability between single-photon wave-packets through the Hong–Ou–Mandel (HOM) interference. By dispersively manipulating two weak coherent single-photon wave-packets which are prepared by attenuating mode-locked laser pulses before interfering with each other, we observe that the difference of the second-order dispersion between two optical paths of the HOM interferometer can be mapped to the interference curve, indicating that (i) with the same amount of dispersion effect in both paths, the HOM interference curve must be only determined by the intrinsic indistinguishability between the wave-packets, i.e., dispersion cancellation due to the indistinguishability between Feynman paths; and (ii) unbalanced dispersion effect in two paths cannot be canceled and will broaden the interference curve thus providing a way to measure the second-order dispersion coefficient. Our results suggest a more comprehensive understanding of the single-photon wave-packet and pave ways to explore further applications of the HOM interference.

Extending the Z 2 n and H Statistics to Generic Pulsed Profiles

Abstract The search for astronomical pulsed signals within noisy data in the radio band is usually performed through an initial Fourier analysis to find “candidate” frequencies and then refined through the folding of the time series using trial frequencies close to the candidate. In order to establish the significance of the pulsed profiles found at these trial frequencies, pulsed profiles are evaluated with a χ 2 test to establish how much they depart from a null hypothesis where the signal is consistent with a flat distribution of noisy measurements. In high-energy astronomy, the χ 2 statistic has widely been replaced by the statistic and H-test, as they are more sensitive to extra information, such as the harmonic content of the pulsed profile. The statistic and H-test were originally developed for use with “event data” composed of arrival times of single photons, leaving it unclear how these methods could be used in radio astronomy. In this paper, we present a version of the statistic and H-test for pulse profiles with Gaussian uncertainties appropriate for radio or even optical pulse profiles. We show how these statistical indicators provide better sensitivity to low-significance pulsar candidates with respect to the usual χ 2 method and a straightforward way to discriminate between pulse profile shapes. Moreover, they provide an additional tool for radio frequency interference rejection.

Timing analysis and pulse profile of the Vela pulsar in the optical band from Iqueye observations

The Vela pulsar is among a number of pulsars which show detectable optical pulsations. We performed optical observations of this pulsar in January and December 2009 with the Iqueye instrument mounted at the ESO 3.5 m New Technology Telescope. Our aim was to perform phase fitting of the Iqueye data, and to measure the optical pulse profile of the Vela pulsar at high time resolution, its absolute phase and rotational period. We calculated for the first time an independent optical timing solution and obtained the most detailed optical pulse profile available to date. Iqueye detected a distinct narrow component on the top of one of the two main optical peaks, which was not resolved in previous observations, and a third statistically significant optical peak not aligned with the radio one. The quality of the Iqueye data allowed us to determine the relative time of arrival of the radio-optical-gamma-ray peaks with an accuracy of a fraction of a millisecond. We compare the shape of the Iqueye pulse profile with that observed in other energy bands and discuss its complex multi-wavelength structure.

Extensive photometry of the intermediate polar V2069 Cyg (RX J2123.7+4217)

To obtain the spin period of the white dwarf in the intermediate polar V2069 Cyg with high precision, we fulfilled extensive photometry. Observations were performed within 32 nights, which have a total duration of 119 hours and cover 15 months. We found the spin period of the white dwarf, which is equal to 743.40650+/-0.00048 s. Using our precise spin period, we derived the oscillation ephemeris with a long validity of 36 years. This ephemeris and the precise spin period can be used for future investigations of spin period changes of the white dwarf in V2069 Cyg. In addition, for the first time we detected the sideband oscillation with a period of 764.5125+/-0.0049 s. The spin and sideband oscillations revealed unstable amplitudes both in a time-scale of days and in a time-scale of years. On average, the semi-amplitude of the spin oscillation varied from 17 mmag in 2014 to 25 mmag in 2015. The semi-amplitude of the sideband oscillation varied from 12 mmag in 2014 to an undetectable level of less than 7 mmag in 2015. In a time-scale of years, the optical spin pulse profile revealed essential changes from an asymmetric double-peaked shape in 2014 to a quasi-sinusoidal shape in 2015. Such drastic changes of the optical spin pulse profile seem untypical of most intermediate polars and, therefore, are of great interest. The pulse profile of the sideband oscillation was quasi-sinusoidal. Moreover, we note that V2069 Cyg possesses strong flickering with a peak-to-peak amplitude of 0.4-0.6 mag.

Coherent-control of linear signals: Frequency-domain analysis

The dependence of various types of linear signals on the phase profile of broadband optical pulses is examined using fundamental time translation invariance symmetry of multipoint correlation functions. The frequency-domain wave-mixing analysis presented here unifies several arguments made earlier with respect to the conditions whereby coherent control schemes may be used.

Direct modelling of error statistics for data transmission through a high data rate communication line using a four-level phase modulation format

This paper presents mathematical modelling results for information transmission by optical pulses through a fibre-optic communication line at a rate of 80 Gbit s-1 per WDM channel usinga four-level phase modulation format. We examine the influence of nonlinear effects on the profile of optical pulses propagating along the fibre. Using direct optical signal detection, we analyse error statistics and demonstrate an uneven error distribution over various symbol combinations.

The first observation of optical pulsations from a soft gamma repeater: SGR 0501+4516

ABSTRACT We present high-speed optical photometry of the soft gamma repeater SGR 0501+4516, obtained with ULTRACAM on two consecutive nights approximately 4 months after the source was discovered via its gamma-ray bursts. We detect SGR 0501+4516 at a magnitude of i′= 24.4 ± 0.1. We present the first measurement of optical pulsations from a SGR, deriving a period of 5.7622 ± 0.0003 s, in excellent agreement with the X-ray spin period of the neutron star. We compare the morphologies of the optical pulse profile with the X-ray and infrared pulse profiles; we find that the optical, infrared and harder X-rays share similar double-peaked morphologies, but the softer X-rays exhibit only a single-peaked morphology, indicative of a different origin. The optical pulsations appear to be in phase with the X-ray pulsations and exhibit a root-mean-square pulsed fraction of 52 ± 7 per cent, approximately a factor of 2 greater than in the X-rays. Our results find a natural explanation within the context of the magnetar model for SGRs.

Optical pulsations from the anomalous X-ray pulsar 1E 1048.1–5937

Abstract We present high-speed optical photometry of the anomalous X-ray pulsar 1E 1048.1-5937 obtained with ULTRACAM on the 8.2-m Very Large Telescope in 2007 June. We detect 1E 1048.1-5937 at a magnitude of i′= 25.3 ± 0.2, consistent with the values found by Wang et al. and hence confirming their conclusion that the source was approximately 1 mag brighter than in 2003–06 due to an on-going X-ray flare that started in 2007 March. The increased source brightness enabled us to detect optical pulsations with an identical period (6.458 s) to the X-ray pulsations. The root-mean-square (rms) pulsed fraction in our data is 21 ± 7 per cent, approximately the same as the 2–10 keV X-ray rms pulsed fraction. The optical and X-ray pulse profiles show similar morphologies and appear to be approximately in phase with each other, the latter lagging the former by only 0.06 ± 0.02 cycles. The optical pulsations in 1E 1048.1-5937 are very similar in nature to those observed in 4U 0142+61. The implications of our observations for models of anomalous X-ray pulsars are discussed.

Impact of high-frequency spectral phase modulation on the temporal profile of short optical pulses

The impact of high-frequency spectral phase modulation on the temporal intensity of optical pulses is derived analytically and simulated in two different regimes. The temporal contrast of an optical pulse close to the Fourier-transform limit is degraded by a pedestal related to the power spectral density of the spectral phase modulation. When the optical pulse is highly chirped, its intensity modulation is directly related to the spectral phase variations with a transfer function depending on the second-order dispersion of the chirped pulse. The metrology of the spectral phase of an optical pulse using temporal-intensity measurements performed after chirping the pulse is studied. The effect of spatial averaging is also discussed.

A Novel Composite Method for Ultra-Wideband Doublet Pulses Generation

A novel composite approach to generate ultra-wideband (UWB) doublet pulses in optical domain through an electrical Gaussian pulse is proposed and demonstrated in this letter. Two pulses with reversed polarity generated by polarization modulation are fed into a differential group delay device and a semiconductor optical amplifier (SOA) wherein the optical pulse profile is modified. Doublet pulses are obtained after optical-electrical detection due to gain saturation and recovery mechanism in the SOA. The fractional bandwidth of doublet pulses exceeds 180%, fulfilling the UWB requirements.

Retrieving Optical Pulse Profiles Using a Nonlinear Optical Loop Mirror

A novel technique is proposed to characterize the power profile of short optical pulses using the transmission characteristic of a nonlinear optical loop mirror (NOLM). Under some assumptions, the power profile can be retrieved from pulse energy measurements at the NOLM output using a slow detection setup. As a fiber-based technique based on the Kerr effect, it does not require phase matching or tedious mechanical adjustments. The technique is able to characterize simultaneously pulse features from the picosecond to the nanosecond scale.

Programmable shaping of a subterawatt, femtosecond laser pulse by modulating the spectral phase of the preamplified pulse

Shaping the temporal profile of subterawatt optical pulses with a femtosecond duration is demonstrated with the help of a programmable pulse shaper, which is based on a liquid–crystal spatial light modulator. For safe operation, we place the pulse shaper between regenerative and multipass amplifiers. We generate double pulses, whose respective component pulses have 0.27-TW peak power and 74-fs duration. The possibility of variously-shaped multiterawatt pulses is also discussed.

The near-UV pulse profile and spectrum of the pulsar PSR B0656+14

We have observed the middle-aged pulsar PSR B0656+14 with the prism and the NUV MAMA detector of the Space Telescope Imaging Spectrograph (STIS) to measure the pulsar spectrum and periodic pulsations in the near-ultraviolet (NUV). The pulsations are clearly detected, double-peaked and very similar to the optical pulse profile. The NUV pulsed fraction is 70 ± 12%. The spectral slope of the dereddened phase-integrated spectrum in the ∼1800-3200 A range is ∼α v = 0.35 ±0.5 which together with the high pulse fraction indicates a non-thermal origin for the NUV emission. The total flux in the range ∼1700-3400 A is estimated to be 3.4 ± 0.3 x 10 -15 erg s -1 cm -2 when corrected for E(B - V) = 0.03 mag. At a distance of 288 pc this corresponds to a luminosity L NUV = 3.4 x 10 28 erg s -1 assuming isotropy of the emission. We compare the NUV pulse profile with observations from radio to gamma-rays. The first NUV sub-pulse is in phase with the gamma-ray pulse marginally detected with EGRET, while the second NUV sub-pulse is similar both in shape and in phase with the non-thermal pulse in hard X-rays. This indicates a single origin of the non-thermal emission in the optical-NUV and in the X-rays. This is also supported by the observed NUV spectral slope, which is compatible with a blackbody plus power-law fit extended from the X-ray range, but dominated by the power-law component in most of the NUV range.

Numerical simulation of nonuniformly time-sampled pulse propagation in nonlinear fiber

Numerical simulation of pulse propagation in nonlinear optical fiber based on nonlinear Schrodinger equation plays a significant role in the design, analysis, and optimization of optical communication systems. Unconditionally stable operator-splitting techniques such as the split-step Fourier method or the split-step wavelet method have been successfully used for numerical simulation of uniformly time-sampled pulses along nonlinear optical fibers. Even though uniform time sampling is widely used in optical communication systems simulation, nonuniform time sampling is better or even desired for certain applications. For example, a sampling strategy that uses denser sampling points in regions where the signal changes rapidly and sparse sampling in regions where the signal change is gradual would result in a better replica of the signal. In this paper, we report a novel method that extends the standard operator-splitting techniques to handle nonuniformly sampled optical pulse profiles in the time domain. The proposed method relies on using cubic (or higher order) B-splines as a basis set for representing optical pulses in the time domain. We show that resulting operator matrices are banded and sparse due to the compact support of B-splines. Moreover, we use an algorithm based on Krylov subspace to exploit the sparsity of matrices for calculating matrix exponential operators. We present a comprehensive set of analytical and numerical simulation results to demonstrate the validity and accuracy of the proposed method.

The Vela pulsar in the near-infrared

We report on the first detection of the Vela pulsar in the near-infrared with the VLT/ISAAC in the Js and H bands. The pulsar magnitudes are Js=22.71 +/- 0.10 and H=22.04 +/- 0.16. We compare our results with the available multiwavelength data and show that the dereddened phase-averaged optical spectrum of the pulsar can be fitted with a power law F_nu propto nu^(-alpha_nu) with alpha_nu = 0.12 +/- 0.05, assuming the color excess E(B-V)=0.055 +/-0.005 based on recent spectral fits of the emission of the Vela pulsar and its supernova remnant in X-rays. The negative slope of the pulsar spectrum is different from the positive slope observed over a wide optical range in the young Crab pulsar spectrum. The near-infrared part of the Vela spectrum appears to have the same slope as the phase-averaged spectrum in the high energy X-ray tail, obtained in the 2-10 keV range with the RXTE. Both of these spectra can be fitted with a single power law suggesting their common origin. Because the phase-averaged RXTE spectrum in this range is dominated by the second X-ray peak of the pulsar light curve, coinciding with the second main peak of its optical pulse profile, we suggest that this optical peak can be redder than the first one. We also detect two faint extended structures in the 1.5''-3.1'' vicinity of the pulsar, projected on and aligned with the south-east jet and the inner arc of the pulsar wind nebula, detected in X-rays with Chandra. We discuss their possible association with the nebula.

Optical Pulse‐Phased Photopolarimetry of PSR B0656+14

We have observed the optical pulse profile of PSR B0656+14 in 10 phase bins at a high signal-to-noise ratio, and have measured the linear polarization profile over 30% of the pulsar period with some significance. The pulse profile is double-peaked, with a bridge of emission between the two peaks, similar to gamma-ray profiles observed in other pulsars. There is no detectable unpulsed flux, to a 1 σ limit of 16% of the pulse-averaged flux. The emission in the bridge is highly (~100%) polarized, with a position angle sweep in excellent agreement with the prediction of the rotating vector model (RVM) as determined from radio polarization observations. We are able to account for the gross features of the optical light curve (i.e., the phase separation of the peaks) using both polar cap and outer gap models. Using the polar cap model, we are also able to estimate the height of the optical emission regions.

Spatiotemporal measurements based on spatial spectral interferometry for ultrashort optical pulses shaped by a Fourier pulse shaper

We measured the space–time profile of ultrashort optical pulses shaped with a Fourier pulse shaper. Spatial chirp, which originated in the space–time coupling at the pulse shaper, was observed directly with two-dimensional spatial spectral interferometry. By analyzing the two-dimensional fringe pattern, we successfully obtained a spatial and a temporal distribution in both amplitude and phase for shaped pulses. Numerically predicted spatiotemporal patterns were compared with experimental results.