This paper investigates the zero dispersion wavelength and dispersion slope control of hollow-core photonic bandgap fibres （PBGFs） by using a full-vector finite element method. By simulation we found that theoretica...This paper investigates the zero dispersion wavelength and dispersion slope control of hollow-core photonic bandgap fibres （PBGFs） by using a full-vector finite element method. By simulation we found that theoretically the zero dispersion wavelength can be tailored by respectively changing the rounded diameter of air holes, pitch, refractive index, normalized thickness of core rings, and hole diameter to pitch ratio. At the same time the tailoring of dispersion slope can also be realized by changing the rounded diameter of air holes or pitch or normalized thickness of core rings. To illustrate the reasonability of fibre designs, this paper also gives the variance of normalized interface field intensity which measures the scattering loss relatively versus wavelength for different designs. From the viewpoint of loss, varying the rounded diameter and the thickness of core ring could shift zero wavelength but it is difficult to get the required parameters within so tiny range in practical drawing of PBGFs, on the other hand, it is possible in practice to respectively alter the pitch and refractive index to shift zero wavelength. But varying hole diameter to pitch ratio is not worthwhile because they each induce large increase of loss and narrowness of transmission bandwidth. The zero dispersion wavelength can be engineered by respectively varying the rounded diameter of air holes, pitch, refractive index, and normalized thickness of core rings without incurring large loss penalties.展开更多
The third-generation vortex identification method of Liutex(previously called Rortex)was introduced by the team led by Prof.Chaoqun Liu from University of Texas at Arlington to mathematically extract the rigid rotatio...The third-generation vortex identification method of Liutex(previously called Rortex)was introduced by the team led by Prof.Chaoqun Liu from University of Texas at Arlington to mathematically extract the rigid rotation part from the fluid motion,and thus to define and visualize vortices.Unlike the vorticity-based first generation and the scalar-valued second generation,Q,λ2,Δandλci methods for example,the Liutex vector provides a unique,mathematical and systematic way to define vortices and visualize vortical structures from multiple perspectives without ambiguity.In this article,we summarize the recent developments of the Liutex framework and discuss the Liutex theoretical system including its existence,uniqueness,stability,Galilean invariance,locality and globality,decomposition in tensor and vector forms,Liutex similarity in turbulence,and multiple Liutex-based vortex visualization methods including Liutex lines,Liutex magnitude iso-surfaces,Liutex-Ωmethod,and Liutex core line method,etc..Thereafter,the six core elements of vortex identification,including(1)absolute strength,(2)relative strength,(3)local rotational axis,(4)vortex rotation axes,(5)vortex core size,(6)vortex boundary,are used as touchstones against which the Liutex vortex identification system is examined.It is demonstrated with illustrative examples that the Liutex system is able to give complete and precise information of all six core elements in contrast to the failure and inaccuracy of the first and second-generation methods.The important concept that vorticity cannot represent vortex and the superiority of the Liutex system over previous methods are reiterated and stated in appropriate places throughout the paper.Finally,the article concludes with future perspectives,especially the application of the Liutex system in studying turbulence mechanisms encouraged by the discovery of Liutex similarity law.As a newly defined physical quantity,Liutex may open a door for quantified vortex and turbulence research including Liutex(vortex)dynamics and lead the community out of the shadow of turbulence research which traditionally relies on observations,graphics,assumptions,hypotheses,and other qualitative analyses.An optimistic projection is that the Liutex system could be critical to investigation of the vortex dynamics in applications from hydrodynamics,aerodynamics,oceanography,meteorology,etc.and to research of the generation,sustenance,modelling and controlling of turbulence.展开更多
提出了一种基于双芯光子晶体光纤(PCF)的具有短长度和超高消光比的偏振分束器,利用全矢量有限元法(FEM)对双芯PCF的耦合特性和偏振分束器的性能进行了数值研究。研究结果表明:增大纤芯间椭圆孔椭圆率、适当提高掺杂折射率可显著降低双芯...提出了一种基于双芯光子晶体光纤(PCF)的具有短长度和超高消光比的偏振分束器,利用全矢量有限元法(FEM)对双芯PCF的耦合特性和偏振分束器的性能进行了数值研究。研究结果表明:增大纤芯间椭圆孔椭圆率、适当提高掺杂折射率可显著降低双芯PCF的耦合长度;基于该双芯PCF设计的偏振分束器在1.55 mm波长处,长度为0.58 mm时,可以实现x,y偏振态的分离,消光比达到82.33 d B,消光比高于20 d B的带宽为70 nm,高于10 d B的带宽达到110 nm,覆盖了C+L波段。这为设计具有短长度、高消光比、宽带特性的PCF偏振分束器提供了一种新的结构。展开更多
基金supported by the National Natural Science Foundation of China (Grant No 60578043)the Beijing Education Committee Common Build Foundation (Grant No XK100130637)
文摘This paper investigates the zero dispersion wavelength and dispersion slope control of hollow-core photonic bandgap fibres （PBGFs） by using a full-vector finite element method. By simulation we found that theoretically the zero dispersion wavelength can be tailored by respectively changing the rounded diameter of air holes, pitch, refractive index, normalized thickness of core rings, and hole diameter to pitch ratio. At the same time the tailoring of dispersion slope can also be realized by changing the rounded diameter of air holes or pitch or normalized thickness of core rings. To illustrate the reasonability of fibre designs, this paper also gives the variance of normalized interface field intensity which measures the scattering loss relatively versus wavelength for different designs. From the viewpoint of loss, varying the rounded diameter and the thickness of core ring could shift zero wavelength but it is difficult to get the required parameters within so tiny range in practical drawing of PBGFs, on the other hand, it is possible in practice to respectively alter the pitch and refractive index to shift zero wavelength. But varying hole diameter to pitch ratio is not worthwhile because they each induce large increase of loss and narrowness of transmission bandwidth. The zero dispersion wavelength can be engineered by respectively varying the rounded diameter of air holes, pitch, refractive index, and normalized thickness of core rings without incurring large loss penalties.
基金This work was mainly supported by the Department of Mathematics of University of Texas at Arlington where the corresponding author,Dr.Chaoqun Liu,is the full-time professor。
文摘The third-generation vortex identification method of Liutex(previously called Rortex)was introduced by the team led by Prof.Chaoqun Liu from University of Texas at Arlington to mathematically extract the rigid rotation part from the fluid motion,and thus to define and visualize vortices.Unlike the vorticity-based first generation and the scalar-valued second generation,Q,λ2,Δandλci methods for example,the Liutex vector provides a unique,mathematical and systematic way to define vortices and visualize vortical structures from multiple perspectives without ambiguity.In this article,we summarize the recent developments of the Liutex framework and discuss the Liutex theoretical system including its existence,uniqueness,stability,Galilean invariance,locality and globality,decomposition in tensor and vector forms,Liutex similarity in turbulence,and multiple Liutex-based vortex visualization methods including Liutex lines,Liutex magnitude iso-surfaces,Liutex-Ωmethod,and Liutex core line method,etc..Thereafter,the six core elements of vortex identification,including(1)absolute strength,(2)relative strength,(3)local rotational axis,(4)vortex rotation axes,(5)vortex core size,(6)vortex boundary,are used as touchstones against which the Liutex vortex identification system is examined.It is demonstrated with illustrative examples that the Liutex system is able to give complete and precise information of all six core elements in contrast to the failure and inaccuracy of the first and second-generation methods.The important concept that vorticity cannot represent vortex and the superiority of the Liutex system over previous methods are reiterated and stated in appropriate places throughout the paper.Finally,the article concludes with future perspectives,especially the application of the Liutex system in studying turbulence mechanisms encouraged by the discovery of Liutex similarity law.As a newly defined physical quantity,Liutex may open a door for quantified vortex and turbulence research including Liutex(vortex)dynamics and lead the community out of the shadow of turbulence research which traditionally relies on observations,graphics,assumptions,hypotheses,and other qualitative analyses.An optimistic projection is that the Liutex system could be critical to investigation of the vortex dynamics in applications from hydrodynamics,aerodynamics,oceanography,meteorology,etc.and to research of the generation,sustenance,modelling and controlling of turbulence.
文摘提出了一种基于双芯光子晶体光纤(PCF)的具有短长度和超高消光比的偏振分束器,利用全矢量有限元法(FEM)对双芯PCF的耦合特性和偏振分束器的性能进行了数值研究。研究结果表明:增大纤芯间椭圆孔椭圆率、适当提高掺杂折射率可显著降低双芯PCF的耦合长度;基于该双芯PCF设计的偏振分束器在1.55 mm波长处,长度为0.58 mm时,可以实现x,y偏振态的分离,消光比达到82.33 d B,消光比高于20 d B的带宽为70 nm,高于10 d B的带宽达到110 nm,覆盖了C+L波段。这为设计具有短长度、高消光比、宽带特性的PCF偏振分束器提供了一种新的结构。
