Propagation of transverse photonic orbital angular momentum through few-mode fiber

Spatiotemporal optical vortex(STOV)pulses can carry transverse orbital angular momentum(OAM)that is perpendicular to the direction of pulse propagation.For a STOV pulse,its spatiotemporal profile can be significantly distorted due to unbalanced dispersive and diffractive phases.This may limit its use in many research applications,where a long interaction length and a tight confinement of the pulse are needed.The first demonstration of STOV pulse propagation through a few-mode optical fiber is presented.Both numerical and experimental analysis on the propagation of STOV pulse through a commercially available SMF-28 standard telecommunication fiber is performed.The spatiotemporal phase feature of the pulse can be well kept after the pulse propagates a few-meter length through the fiber even with bending.Further propagation of the pulse will result in a breakup of its spatiotemporal spiral phase structure due to an excessive amount of modal group delay dispersion.The stable and robust transmission of transverse photonic OAM through optical fiber may open new opportunities for transverse photonic OAM studies in telecommunications,OAM lasers,and nonlinear fiber-optical research.

Optical spatiotemporal vortices

Spatiotemporal vortices of light,featuring transverse orbital angular momentum(OAM)and energy circulation in the spatiotemporal domain,have received increasing attention recently.The experimental realization of the controllable generation of spatiotemporal vortices triggers a series of research in this field.This review article covers the latest developments of spatiotemporal vortices of light ranging from theoretical physics,experimental generation schemes,and characterization methods,to applications and future perspectives.This new degree of freedom in photonic OAM endowed by spatiotemporal vortices paves the way to the discovery of novel physical mechanisms and photonic applications in light science.

Tilted spatiotemporal optical vortex with partial temporal coherence [Invited]

We report the experimental and theoretical investigation of tilted spatiotemporal optical vortices with partial temporal coherence.The theoretical study shows that the instantaneous spatiotemporal optical vortex is widely variable with the statistical orbital angular momentum(OAM)direction.While decreasing temporal coherence results in a larger variability of OAM tilt,the average OAM direction is relatively unchanged.

Temporal manipulation of spatiotemporal optical vortices with an Airy pulse[Invited]

We demonstrate the temporal manipulation of spatiotemporal optical vortices(STOVs)by utilizing Airy pulses.By combining a STOV with an Airy temporal profile,the STOV exhibits nondispersive,self-accelerating,and self-healing features inherited from the Airy pulse propagation.Such features will enhance the control of STOVs in time.

Generation of ultrafast spatiotemporal wave packet embedded with time-varying orbital angular momentum

It was not until 1992 did scientists realize that light beams with a helical phase carry orbital angular momentum(OAM)[1].The discovery of optical OAM has spurred a wealth of applications such as high-speed optical communications,optical spanners and spinorbit angular momentum coupling[2-4].To date,the majority of OAM beams are temporally static,i.e.,the OAM does not vary in time.Recently,Rego et al.[5]generated extreme-ultraviolet selftorqued beams in high-harmonic generation driven by timedelayed pulses that differ by one unit of OAM.The temporal OAM variation could potentially be utilized to manipulate nanostructures and launch chiral excitations on ultrafast time scales[6].

Non-spreading Bessel spatiotemporal optical vortices

Non-spreading nature of Bessel spatiotemporal wavepackets is theoretically and experimentally investigated and orders of magnitude improvement in the spatiotemporal spreading has been demonstrated.The spatiotemporal confinement provided by the Bessel spatiotemporal wavepacket is further exploited to transport transverse orbital angular momentum through embedding spatiotemporal optical vortex into the Bessel spatiotemporal wavepacket, constructing a new type of wavepacket: Bessel spatiotemporal optical vortex. Both numerical and experimental results demonstrate that spatiotemporal vortex structure can be well maintained and confined through much longer propagation. High order spatiotemporal optical vortices can also be better confined in the spatiotemporal domain and prevented from further breaking up, overcoming a potential major obstacle for future applications of spatiotemporal vortex.

Ultrabroadband,few-cycle pulses directly from a Mamyshev fiber oscillator

While the performance of mode-locked fiber lasers has been improved significantly,the limited gain bandwidth restricts them from generating ultrashort pulses approaching a few cycles or even shorter.Here we present a novel method to achieve few-cycle pulses(~5 cycles)with an ultrabroad spectrum(~400 nm at-20 dB)from a Mamyshev oscillator configuration by inserting a highly nonlinear photonic crystal fiber and a dispersion delay line into the cavity.A dramatic intracavity spectral broadening can be stabilized by the unique nonlinear processes of a self-similar evolution as a nonlinear attractor in the gain fiber and a"perfect"saturable absorber action of the Mamyshev oscillator.To the best of our knowledge,this is the shortest pulse width and broadest spectrum directly generated from a fiber laser.

Sculpturing spatiotemporal wavepackets with chirped pulses

Pulse shaping has become a powerful tool in generating complicated ultrafast optical waveforms to meet specific application needs.Traditionally,pulse shaping focuses on the temporal waveform synthesis.Recent interests in structuring light in the spatiotemporal domain rely on Fourier analysis.A space-to-time mapping technique allows us to directly imprint complex spatiotemporal modulation through taking advantage of the relationship between frequency and time of chirped pulses.The concept is experimentally verified through the generation of spatiotemporal optical vortex(STOV)and STOV lattice.The power of this method is further demonstrated by STOV polarity reversal,vortex collision,and vortex annihilation.Such a direct mapping technique opens tremendous potential opportunities for sculpturing complex spatiotemporal waveforms.

Generation of three-dimensional versatile vortex linear light bullets(Invited Paper)

We generate and measure the versatile vortex linear light bullet, which combines a high-order Bessel beam and an Airy pulse. This three-dimensional optical wave packet propagates without distortion in any medium, while carrying an orbital angular momentum. Its non-varying feature in linear propagation is verified by a three- dimensional measurement. Such a novel versatile linear light bullet can be useful in various applications such as micromachining.

Scalar optical hopfions

Hopfions are three-dimensional(3D)topological states discovered in field theory,magnetics,and hydrodynamics that resemble particle-like objects in physical space.Hopfions inherit the topological features of the Hopf fibration,a homotopic mapping from unit sphere in 4D space to unit sphere in 3D space.Here we design and demonstrate dynamic scalar optical hopfions in the shape of a toroidal vortex and expressed as an approximate solution to Maxwell’s equations.Equiphase lines correspond to disjoint and interlinked loops forming complete ring tori in 3D space.The Hopf invariant,product of two winding numbers,is determined by the topological charge of the poloidal spatiotemporal vortices and toroidal spatial vortices in toroidal coordinates.Optical hopfions provide a photonic testbed for studying topological states and may be utilized as high-dimensional information carriers.

光子飓风——具有光子横向轨道角动量的时空涡旋

众所周知,光子具有沿传播方向的线性动量。光子的线性动量在光与物质的相互作用中具有重要的作用。光子与物质的动量交换可以产生光压。2018年获得诺贝尔物理学奖的光镊技术基于微纳米颗粒对光子动量改变产生的光场梯度力。光子也具有沿传播方向的角动量,包括与圆偏振相关的自旋角动量和与涡旋相位关联的轨道角动量。近年来,研究表明在高数值孔径聚焦光场和隐失波光场中存在垂直于光束传播方向的光子横向自旋角动量[1]。那么是否存在垂直于光束传播方向的光子横向轨道角动量呢(图1)?我们最新的研究给出了肯定的答案,成果发表于《自然—光子学》[2]。

Complex Swift Hohenberg equation dissipative soliton fiber laser

Complex Swift Hohenberg equation(CSHE)has attracted intensive research interest over the years,as it enables realistic modeling of mode-locked lasers with saturable absorbers by adding a fourth-order term to the spectral response.Many researchers have reported a variety of numerical solutions of CSHE which reveal interesting pulse patterns and structures.In this work,we have demonstrated a CSHE dissipative soliton fiber laser experimentally using a unique spectral filter with a complicated transmission profile.The behavior and performance of the laser agree qualitatively with the numerical simulations based on CSHE.Our findings bring insight into dissipative soliton dynamics and make our mode-locked laser a powerful testbed for observing dissipative solitons of CSHE,which may open a new course in ultrafast fiber laser research.