Transmission characteristics of VAD fibers using a multiple burner with single source gas nozzle

A vapor phase axial deposition (VAD) method using a multiple burner with single source gas nozzle is presented. Fibers fabricated by this technique feature very low loss and wide bandwidth characteristics, although the refractive index profile slightly deviates from the ideal, on the outer side of the core part. This technique is expected to provide a simple method of fabricating low loss and wide bandwidth fibers.     

The structure of single vortices in type II superconductors

This paper reports the first results of a program for the investigation of the detailed electronic and magnetic structure of type II superconductors. The structure of a single flux bundle or vortex in an infinite superconducting specimen is investigated, assuming weak coupling and a spherical Fermi surface of the material. The equations governing the gap parameterΔ(r) and the vector potentialA(r) are suitably scaled and simplified using the symmetry of the system. These equations can be solved numerically only; for their solution the asymptotics ofΔ(r) andA(r) far from the center of the vortex are required. These asymptotics are derived here by properly linearising the equations; they are found to be of the typer ^?1/2 exp (?r/rin0) wherer ₀ is determined by temperature and material parameters. Implicit equations forr ₀ are derived and discussed. We find that for materials withκ-values less than 1.7 (e.g. pure niobium)r ₀ becomes complex at low temperatures; i.e. the deviation ofΔ(r) andA(r) from their values at infinity is a damped oscillation as function ofr.     

Generation of single and multiple dissipative soliton in an erbium-doped fiber laser

We experimentally report on the generation of single and multiple dissipative soliton via nonlinear polarization rotation technique. The spectrum of the mode-locked dissipative soliton exhibits typical steep edges with a flat top; the pulse duration is 10.07 ps. It is found that with the pump power increasing from 110 mW to 161 mW, the top of the mode-locked spectrum becomes flater and the 3-dB spectral bandwidth is broadened, which indicates that the gain-dispersion effect is lowered under stronger pump. However, the full bandwidth of the spectrum is narrowed, which proves that the spectral filter effect increases and overcomes the effect of self-phase modulation induced spectral broadening. Such a phenomenon was not noticed nor reported before. Our experiment also demonstrates that the pulse interval is highly dependent on the input pump power: with pump power increasing, the pulse interval tends towards more uniform. So our observation qualitatively analyzes the relationship between mode-locked pulse characteristics and input pump power.     

Electromagnetic vortices in an array of carbon nanotubes

The dynamics of electromagnetic vortices in an array of carbon nanotubes is investigated. The electromagnetic field is described by Maxwell (two-dimensional wave) equations. Calculation modeling is performed. The resulting mass center velocity of the vortices is zero, and the intensity distribution its field changes periodically over time.     

Pattern formation using optical vortices in a photorefractive single feedback system

We analyze numerically the dynamics of optical patterns in a photorefractive single feedback system where a vortex beam is used as the input beam. Depending on the topological charge of the vortex and on the nonlinear photorefractive coupling strength, we observe different pattern geometries with a rotating dynamics.     

Selective generation of high-order optical vortices from a single phase wedge

We demonstrate that it is possible to generate high-order optical vortices from a single phase wedge by applying an incident beam with an annular intensity distribution. Various topological charges of optical vortices are realized by a static phase wedge when the position and radius of the annular illumination are changed accordingly.     

Statistical mechanics of vortices in an inviscid two-dimensional fluid

In this paper we study rigorously the statistical mechanics of a gas of vortices in the thermodynamic limit. In this limit, no negative temperature states are found to exist.Work supported in part by NSF Grant MCS 78-02721     

Measuring the topological charge of optical vortices with a single plate

Measuring the topological charge(TC) of optical vortex beams by the edge-diffraction pattern of a single plate is proposed and demonstrated. The diffraction fringes can keep well discernible in a wide three-dimensional range in this method. The redundant fringes of the diffracted fork-shaped pattern in the near-field can determine the TC value, and the orientation of the fork tells the handedness of the vortex. The plate can be opaque or translucent, and the requirement of the translucent plate ...     

Velocity field vortices and Mermin-Ho vortices in two-component spinor BEC

In light of the φ-mapping topological current theory, two important vortex structures in two-component spinor BEC—the velocity field vortices and the Mermin-Ho vortices are discussed. It is revealed that these two different kinds of vortices are created respectively from the zero points of two different order parameter configurations in the condensates, and both their topological charges, locations and motions can be determined by the φ-mapping theory.     

Collapse and backward motion of axisymmetric toroidal vortices in an accretion flow

The problem of the interaction of two coaxial, counter-rotating ring vortices in the presence of a convergent (accretion) flow with a sink at the center of symmetry has been solved. The vortices that would recede from each other in the absence of a flow (the problem inverse to the Helmholtz problem) are shown to be brought closer together by the flow and then ejected with acceleration along the axis of symmetry. The ejection velocity increases with sink strength. However, if the sink strength exceeds some critical value that depends on the initial conditions, then no ejection occurs and the vortices are captured by the flow and collapse. A similar capture and collapse are also possible during the motion of a single vortex in a flow. The difference from the planar case, where no collapse occurs, is significant. The detected phenomenon can be applied when studying nonlinear processes in atmospheric vortices as well as in active galactic nuclei and planetary atmospheres.     

共轴双涡旋声束形成离轴多涡旋的定位

涡旋声束具有螺旋的相位波前,中轴线上形成声强为零的相位奇点,其所携带的轨道角动量在粒子操控领域有着广阔的应用前景。传统声涡旋只在传播轴线上形成一个拓扑荷可控的涡旋波束,这限制了声涡旋的应用灵活性。基于环形点声源阵列和相位编码技术,利用奇偶声源分别产生共轴双涡旋声束的声场叠加,在传播截面上形成了具有中心涡旋和子涡旋的离轴多涡旋声场;研究了双涡旋拓扑参数对离轴涡旋的个数、位置及拓扑荷的影响,基于声涡旋的径向声压和相位分布,确定了离轴涡旋的离轴半径,并结合声源位置推导子涡旋中心方位角的计算公式,实现离轴涡旋的精确定位。本研究突破了沿轴分布的涡旋声场只能形成单点涡旋势阱的操控局限,为利用离轴多涡旋实现多点粒子捕获提供了理论依据,促进涡旋声场在精确粒子操控和传输方面的高效应用。     

共轴双涡旋声束形成离轴多涡旋的定位

涡旋声束具有螺旋的相位波前,中轴线上形成声强为零的相位奇点,其所携带的轨道角动量在粒子操控领域有着广阔的应用前景。传统声涡旋只在传播轴线上形成一个拓扑荷可控的涡旋波束,这限制了声涡旋的应用灵活性。基于环形点声源阵列和相位编码技术,利用奇偶声源分别产生共轴双涡旋声束的声场叠加,在传播截面上形成了具有中心涡旋和子涡旋的离轴多涡旋声场;研究了双涡旋拓扑参数对离轴涡旋的个数、位置及拓扑荷的影响,基于声涡旋的径向声压和相位分布,确定了离轴涡旋的离轴半径,并结合声源位置推导子涡旋中心方位角的计算公式,实现离轴涡旋的精确定位。本研究突破了沿轴分布的涡旋声场只能形成单点涡旋势阱的操控局限,为利用离轴多涡旋实现多点粒子捕获提供了理论依据,促进涡旋声场在精确粒子操控和传输方面的高效应用。     

Time evolution of an infinite number of vortices in a strip

We study the time evolution of a system of vortices in a strip in the thermodynamic limit. We prove the existence and the uniqueness of the solution of the equation of motion for a regularized version of the usual vortex dynamics. We extend this result to a system of particles interacting in one dimension via a long-range potential.Partially supported by the Italian C.N.R.     

Charged vortices in an abelian Higgs model with Chern-Simons term

The existence is shown of charged vortices of finite energy in a (2+1)-dimensional abelian Higgs model with Chern-Simons (C-S) term. Further, lower bounds on the energy and angular momentum of these vortices are obtained. Finally it is shown that the “glueballs” are absent in (2+1)-dimensional QED or QCD with C-S term for any compact gauge group.