Ultrashort Optical Pulses Research Articles

Vector breathers for the coupled fourth-order nonlinear Schrödinger system in a birefringent optical fiber

Abstract Optical fiber communication is widely applied in the information transmission and capacity handling of information. In this paper, coupled fourth-order nonlinear Schrodinger system, which describes the propagation of ultrashort optical pulses in a birefringent optical fiber, is studied. The Nth-order Darboux transformation and corresponding vector breather solutions are constructed, where N is a positive integer. Based on such solutions, we graphically show four different types of breathers: (1) the one with the one component containing the anti-eye-shaped breather and the other component containing the eye-shaped breather; (2) the one with each component containing the four-petaled breather; (3) the one with each component containing the eye-shaped breather; (4) the one with each component containing the Y-shaped breather. Moreover, we find that the range of the breather along the time axis decreases, and the angle between the breather and the time axis increases as the value of |γ| decreases, where γ represents the strength of higher-order linear and nonlinear effects.

Double-pulse characterization by self-referenced spectral interferometry

The reconstruction of ultrashort optical pulses with a complex intensity substructure is demonstrated using the Self-Referenced Spectral Interferometry (SRSI) pulse characterization technique with a modified phase retrieval algorithm. A correction spectral phase term is extracted by the manipulation of the temporal interferogram, allowing the treatment of scenarios with complicated pulse shapes, where the original algorithm fails. The improved SRSI algorithm is verified through the application on two temporally well-separated pulses having the same polarization direction and spectral shape, generated by duplicating 37 fs-long amplified pulses of a Ti:Sa based laser system. The spectral phase of highly chirped double pulses with equal or different amplitude ratios is numerically retrieved. The collinear and achromatic experimental arrangement results in a compact and easy-to-align system.

Ultrashort Optical Pulses and Their Generation in Resonant Media (Scientific Summary)

Our recent studies of methods for obtaining ultrashort light pulses and analysis of the impact of ultrashort optical pulses on classical and quantum micro-objects with the identification of the determining role of the degree of unipolarity of pulses (maximum for strictly unipolar pulses) in the efficiency of direct laser acceleration of charged particles and excitation of atoms and molecules have been reviewed. Special attention has been paid to the coherent mode locking regime in lasers, which is implemented when the laser pulse duration is less than the relaxation time of the working transition in media with resonance amplification and absorption (laser analog of the phenomenon of self-induced transparency). Experimental data on coherent mode locking in a titanium-sapphire laser with a cell with rubidium vapor at self-induced transparency in rubidium have been presented. The interaction of ultrashort pulses in resonant media has also been analyzed.

Influence of Average Cavity Dispersion and Spectral Bandwidth on Passively Harmonic Mode Locked L-Band Er-Doped Fiber Laser

We systematically study the impact of average cavity dispersion and pulse spectral bandwidth on harmonic mode locking in the long-wavelength band from an Er-doped fiber laser using carbon nanotubes polyvinyl alcohol (CNTs-PVA) film mode locker. By carrying out pulse energy management through optimizing the average cavity dispersion and optical spectral bandwidth, 2.08 GHz repetition rate corresponding to 201st harmonic with 36.5 dB side mode suppression ratio (SMSR) can be realized under 205 mW pump power at 1597.53 nm. Furthermore, we systematically investigate the characteristics of the harmonically mode locked ultrashort optical pulses with different spectral bandwidths versus pump power under fixed cavity dispersion first. Key laser parameters have been studied including pumping efficiency, duration, energy, SMSR, and time bandwidth product. Enlightened by the experimental results, a simple law on preliminary and fast judgment of pulses frequency under fixed pump power is proposed, namely, by monitoring the pulse spectral bandwidth. The laser source featuring high repetition rate and L-band operation is greatly sought-after in some specific applications such as modern optical communication system etc.

Real-time and high-precision interrogation of a linearly chirped fiber Bragg grating sensor array based on dispersive time delay and optical pulse compression.

A novel technique to achieve real-time and high-precision interrogation of a linearly chirped fiber Bragg (LCFBG) grating sensor array based on dispersive time delay and optical pulse compression is proposed and experimentally demonstrated. In the proposed system, an ultra-short optical pulse is launched into an LCFBG sensor array consisting of N identical LCFBGs, to produce N reflected pulses with their time delay changes corresponding to the strain or temperature changes. The reflected pulses are sent to another LCFBG having an opposite dispersion coefficient to achieve optical pulse compression to improve the measurement accuracy. A proof-of-concept experiment is demonstrated. A 2×3 LCFBG sensor array using six identical LCFBGs is implemented, and the performance is evaluated experimentally. The sensing speed can be as high as 48.6MHz, and the sensing accuracy can be as high as 0.26 με for strain and 0.045°C for temperature.

Subpicosecond flat-top pulse shaping using a hybrid plasmonic microring-based temporal differentiator

Design of a fractional-order photonic temporal differentiator, based on the silicon hybrid plasmonic add-drop microring resonators, is proposed. Because of the strong light confinement in the hybrid plasmonic waveguides, the overall footprint of the differentiator is significantly reduced. The numerical simulation results show that the differentiator can reach considerably wide 3 dB bandwidth of about 2.5 THz (20 nm) with the microring radius of 1.2 μm. It is also shown that the differentiation order and the 3 dB bandwidth of the proposed structure can be tuned in the range of [0.6 1.0] and [1.74 2.5] THz ([14 20] nm), respectively, by modifying the geometrical parameters of the differentiator. Mentioned bandwidth is higher than the previously reported values for microring-based photonic differentiators. Furthermore, the wide bandwidth and the tunable differentiation order of the structure along with its compact footprint make it a promising choice for the processing of ultrashort optical pulses. Generation of short flat-top pulses from input Gaussian pulses is then considered as an example of such applications. It is shown through three-dimensional finite-difference time-domain simulations that the proposed differentiator can be used to generate a flat-top pulse with the flat duration of 330 fs and the FWHM of ∼1 ps, from an ultrashort Gaussian input pulse, with the FWHM of 490 fs.

Rogue wave solutions for a coupled nonlinear Schrödinger equation in the birefringent optical fiber

In this paper, we investigate a fourth-order coupled nonlinear Schrödinger equation, which describes the propagation of ultrashort optical pulses in the birefringent optical fiber. Lax pair is constructed through the symbolic computation, along with the corresponding Darboux transformation (DT) which is different from that given in the existing literatures. Rogue wave solutions are obtained by virtue of the DT. Three different types of the rogue waves based on the solutions are exhibited, i.e., the anti-eye-shaped, eye-shaped four-petaled ones. Moreover, we find that the wave structure is affected by the relative background amplitudes and certain parameter in the solutions, and the range of the first-order rogue wave along the x axis increases with the increase of the fourth order term γ, while the range of the rogue wave along the t axis decreases.

The 2018 Nobel Prize in Physics: optical tweezers and chirped pulse amplification.

The 2018 Nobel Prize in Physics was awarded to Arthur Ashkin (prize share ½), Gérard Mourou (prize share ¼), and Donna Strickland (prize share ¼) for "groundbreaking inventions in the field of laser physics." This feature article summarizes the development of "optical tweezers and their application to biological systems" by Arthur Ashkin, as well as the Mourou/Strickland method of "generating high-intensity, ultrashort optical pulses" known as chirped pulse amplification. Further developments are also briefly discussed.

Supervised learning of an opto-magnetic neural network with ultrashort laser pulses

The explosive growth of data and its related energy consumption is pushing the need to develop energy-efficient brain-inspired schemes and materials for data processing and storage. Here, we demonstrate experimentally that Co/Pt films can be used as artificial synapses by manipulating their magnetization state using circularly polarized ultrashort optical pulses at room temperature. We also show an efficient implementation of supervised perceptron learning on an opto-magnetic neural network, built from such magnetic synapses. Importantly, we demonstrate that the optimization of synaptic weights can be achieved using a global feedback mechanism, such that the learning does not rely on external storage or additional optimization schemes. These results suggest that there is high potential for realizing artificial neural networks using optically controlled magnetization in technologically relevant materials, which can learn not only fast but also energy-efficient.

Two dimensional electron transports for terahertz emission fromIn0.53Ga0.47As/In0.52Al0.48Asmultilayer structures illuminated by 1.55 μm-laser

Two dimensional electron gas (2DEG) transports in In0.53Ga0.47As/In0.52Al0.48As multilayer structure (MLS) illuminated by an ultrashort optical pulse with the central wavelength at 1.55 μm is investigated by ensemble Monte Carlo simulations. Terahertz (THz) pulses are calculated according to the transient photocurrent in the InGaAs layers. It is found that InGaAs/InAlAs MLS with narrower InGaAs layers has an advantage in generating large temporal change in the transient photocurrent, which thereby is able to increase the intensity of THz emission. Beryllium (Be)-doping in InGaAs layers provides a scattering channel to speed the decay of photocurrent, and is shown to be a factor in shaping the bipolar structure of THz temporal waveforms. Bandwidth of the generated THz emission is found to be mainly controlled by the laser pulse duration at low doping level, but at high doping level, the bandwidth is determined together by laser pulse duration and doping density.

A robust numerical integrator for the short pulse equation near criticality

Abstract The short pulse equation was introduced by Schafer–Wayne (2004) for modeling the propagation of ultrashort optical pulses. While it can describe a wide range of solutions, its ultrashort pulse solutions with a few cycles, which the conventional nonlinear Schrodinger equation does not possess, have drawn much attention. In such a region, the solutions can become quite close to a singularity, and thus existing numerical methods cease to work stably, or even if they do, they require high computational cost. In this paper, we propose a robust numerical integration method which is obtained by combining a hodograph transformation and some structure-preserving methods. The resulting scheme successfully works even when the singularity occurs, and thus gives a highly robust method for resolving near singular solutions of interest. It is confirmed by numerical experiments, and some new insights about derivative blow-up are obtained.

Construction of modulation instability analysis and optical soliton solutions of pertubed nonlinear Schrödinger dynamical equation with power law nonlinearity in non-kerr medium

Abstract In this paper the perturbed nonlinear Schrodinger equation (PNLSE) with power law nonlinearity in the medium of non-kerr is analyzed by employing Reccati equation mapping method. Perturbed nonlinear Schrodinger equation depict the effect of quantic non-linearity on propagation of the ultra-short optical pulses in the medium of non-kerr, similar to optical fibers. We achieved various types of soliton solutions, some of them are novel and does not exist previously. Graphical presentation of some obtained exact solutions are also given through assigning suitable values to the parameters that aids to understand the physical phenomenon of this models. Modulation Instability (MI) is also discussed by standard linear-stability analysis that shows about all achieved results are exact and stable. The computational exertion and achieved outputs shows that the current proposed technique is powerful and effectual. Furthermore many higher order non-linear Schrodinger equations can be solved using current method.

Pulse Cluster Dynamics in Passively Mode-Locked Semiconductor Vertical-External-Cavity Surface-Emitting Lasers

Passively mode-locked lasers have become a topic of substantial research, as they are efficient sources of ultrashort optical pulses and essential to applications such as multiphoton microscopy and dual-comb spectroscopy. Here external cavity geometry has a great influence on performance, though, and also can lead to detrimental multipulse emission. The authors use a delay differential equation model, derived for these types of lasers and accounting for the external cavity geometry, to better understand the emergence of detrimental dynamics. The results are expected to further improve the performance of these systems.

Generating ultrashort flat-top optical pulses with a fiber-loop time-lens system

For generating short flat-top optical pulses, traditional methods are either bandwidth limited or have low controllability (in pulse width and shape). We propose a fiber-loop based time-lens system to realize ps-level flat-top pulses, and theoretically study their features under various parameter circumstances. This time-lens system, functioning as many stacked time-lenses, introduces great controllability for the generated pulse’s characteristics through tuning both the phase modulation device and the dispersion-compensating setup. To achieve high-quality narrow flat-top pulses (with steep pulse edges), several factors including phase modulation function, modulation strength and dispersion compensating status must be optimized simultaneously. In simulation, after 50 loops of parabolic phase modulation and chirp compensation, the flat-top pulse’s duration can be narrowed to 2.8 ps with edge widths of 1.7 ps. This kind of ps-scale flat-top pulse is very desirable for application in various areas.

A quantum dot as a source of time-bin entangled multi-photon states

A quantum computer has the potential to revolutionize multiple industries by enabling a drastic speed-up relative to classical computers for certain quantum algorithms and simulations. Linear optical quantum computing is an approach that uses photons as qubits, which are known for suffering little from decoherence. A source of multiple entangled and indistinguishable photons would be a significant step in the development of an optical quantum computer. Consequently, multiple proposals for the generation of such a stream of photons have recently been put forward. Here we introduce an alternative scheme based on a semiconductor quantum dot (QD) embedded in an optical microcavity in a magnetic field. A single charge carrier trapped in the dot has an associated spin that can be controlled by ultrashort optical pulses. Photons are sequentially generated by resonant scattering from the QD, while the charge spin is used to determine the encoding of the photons into time-bins. In this way a multi-photon entangled state can be gradually built up. With a simple optical pulse sequence we demonstrate a proof of principle experiment of our proposal by showing that the time-bin of a single photon is dependent on the measured state of the trapped charge spin.

The Power of Light: Nobel Prize in Physics 2018.

The 2018 Nobel Prize in Physics was awarded to three scientists in the field of laser science: Dr. Arthur Ashkin for his invention of the optical tweezers and their application to biological systems, and Dr. Gérard Mourou and Dr. Donna Strickland for their method of generating high-intensity, ultrashort optical pulses. The awards integrate the far reaches of time and intensity scales in laser technologies, from the extremely high-intensity chirped pulse lasers (by Mourou and Strickland) to the ultralow-power beams (by Ashkin) that are capable of handling delicate biological objects and molecules [1], [2]. The IEEE family is indeed delighted to see two of its Life Fellows, Arthur Ashkin and Gérard Mourou, as co-recipients of the awards from the Royal Swedish Academy of Science. Mourou is a past recipient of the IEEE Photonics Quantum Electronics Award and the IEEE David Sarnoff Award. Strickland has been an active author in the IEEE Journal of Quantum Electronics and IEEE Journal of Selected Topics in Quantum Electronics.

Optical soliton molecular complexes in a passively mode-locked fibre laser

Ultrashort optical pulses propagating in a dissipative nonlinear system can interact and bind stably, forming optical soliton molecules. Soliton molecules in ultrafast lasers are under intense research focus and present striking analogies with their matter molecules counterparts. The recent development of real-time spectral measurements allows probing the internal dynamics of an optical soliton molecule, mapping the dynamics of the pulses’ relative separations and phases that constitute the relevant internal degrees of freedom of the molecule. The soliton-pair molecule, which consists of two strongly bound optical solitons, has been the most studied multi-soliton structure. We here demonstrate that two soliton-pair molecules can bind subsequently to form a stable molecular complex and highlight the important differences between the intra-molecular and inter-molecular bonds. The dynamics of the experimentally observed soliton molecular complexes are discussed with the help of fitting models and numerical simulations, showing the universality of these multi-soliton optical patterns.

Periodic Spectral Modulations Arise from Nonrandom Spacing of Spectral Absorption Lines

In recent papers, Borra in 2013 and 2017, and Borra & Trottier in 2016, those authors claimed that the discovery of ultrashort (10−12 s) optical pulses originating from stars and galaxies may be sent by extraterrestrial intelligence. I show that these signals are not astrophysical or instrumental in nature, but that they originate due to the nonrandom spacings of spectral absorption lines. They can be shown to arise in their clearest form in synthetic solar spectra, as these do not suffer from noise.

Sub-Femtosecond Stark Control of Molecular Photoexcitation with Near Single-Cycle Pulses.

Electric fields can tailor molecular potential energy surfaces by interaction with the electronic state-dependent molecular dipole moment. Recent developments in optics have enabled the creation of ultrashort few-cycle optical pulses with precise control of the carrier envelope phase (CEP) that determines the offset of the maxima in the field and the pulse envelope. This opens news ways of controlling ultrafast molecular dynamics by exploiting the CEP. In this work, we show that the photoabsorption efficiency of oriented H2CSO (sulfine) can be controlled by tuning the CEP. We further show that this control emanates from a resonance condition related to Stark shifting of the electronic energy levels.

Analysis of nonlinear polarization rotation by an ultrashort optical pump and probe pulse in a strained semiconductor optical amplifier

In this paper, a comprehensive dynamic model is used to study the nonlinear polarization rotation (NPR) of a probe signal in the presence of a copropagating pump signal in a strained semiconductor optical amplifier (SOA). Pump and probe signals are Gaussian pulse with 200 fs pulse width, propagating in a 500 μm SOA. In the present model, the effects of carrier dynamics on the SOA gain and phase are considered and the NPR of the probe signal is measured by the ellipticity angle using the Stokes vector and Mueller matrices. The effects of several important factors on the NPR of the probe signal are investigated. These factors include pump signal energy, free carrier absorption and two-photon-absorption nonlinear effects, tensile/compressive strain, pump-probe pulse width, and pump-probe delay time. The results show that the pulse width and strain have a considerable effect on the ellipticity angle deviation (EAD); we especially see that the tensile strain increases the EAD, and the compressive strain reduces the EAD compared to the no strain structure. For a specific range of pulse width (here 0.2 ps to 1 ps), the EAD increases noticeably with the pulse width. It is also shown that, for the pump-probe delay time, the maximum EAD is obtained when the delay time is 0.1 ps.