We investigate in detail the influence of line defects on focusing of electromagnetic waves in a two-dimensional photonic-crystal flat lens. Through simulations, we find that a focusing can always be observed when a l...We investigate in detail the influence of line defects on focusing of electromagnetic waves in a two-dimensional photonic-crystal flat lens. Through simulations, we find that a focusing can always be observed when a line defect in the lens is introduced along the light transmission direction and the width of the line defect is less than λ/2. However, there appear two focusings when the width of the line defect is more than λ/2. When the line defect is introduced along the direction perpendicular to the transmission, there is always one focusing.展开更多
We have investigated in detail the influence of defect on the focusing of electromagnetic waves in a two-dimensional photonic-crystal flat lens by using the finite-difference time-domain method. The result shows that ...We have investigated in detail the influence of defect on the focusing of electromagnetic waves in a two-dimensional photonic-crystal flat lens by using the finite-difference time-domain method. The result shows that many focusings can be observed at the symmetrical positions when a defect is introduced into the lens. Furthermore, the wave-guides in the lens can confine the transmission wave effectively and improve the quality of the focusing.展开更多
A novel all-fibre flat-top comb filter based on a high birefringence photonic crystal fibre loop mirror is proposed and demonstrated. We simulate theoretically its output spectra and experimentally realize a flat-top ...A novel all-fibre flat-top comb filter based on a high birefringence photonic crystal fibre loop mirror is proposed and demonstrated. We simulate theoretically its output spectra and experimentally realize a flat-top output with a high extinction ratio. Compared to filters consisting of the conventional Panda polarization maintaining fibre, filters based on a high birefringence photonic crystal fibre loop mirror have better temperature stability. This kind of filter can be expected to be used widely in Wavelength-division-multiplexing(WDM) systems in the future.展开更多
Flat lenses are designed by means of graded negative refractive index-based photonic crystals （PCs） constructed using air-holes tuned with different shapes. By gradually modifying the filling factor along the transv...Flat lenses are designed by means of graded negative refractive index-based photonic crystals （PCs） constructed using air-holes tuned with different shapes. By gradually modifying the filling factor along the transverse direction, we obtain the graded negative index-based lenses for the purpose of focusing an incident plane wave. The finite-difference and timedomain （FDTD） algorithm is adopted for numerical calculation. Our calculation results indicate that these lenses can finely focus incident plane waves. Moreover, for the same size of air-holes, the focusing properties of the lens with rectangular air-holes are better than those with the other shaped air-holes. The graded negative index PCs lenses could possibly enable new applications in optoelectronic systems.展开更多
We demonstrate the hybrid focusing points of sonic crystals for a multi-source array applied to flat sonic crystal lenses. The contributions of different point source couples form hybrid focusing points. Ray-trace ana...We demonstrate the hybrid focusing points of sonic crystals for a multi-source array applied to flat sonic crystal lenses. The contributions of different point source couples form hybrid focusing points. Ray-trace analyses are conducted for acoustic flat lenses with multi-source configurations. The finite-difference time-domain （FDTD） simulation of flat lenses with multi-source configurations demonstrates the establishment of pure and hybrid focusing points in a pyramidal constellation. The number of focusing points in the pyramidal constellation depends on the number of point sources. We propose an acoustic device for fine-tuning the location of a far-field hybrid focusing point and discuss its benefits for acoustic energy focusing application.展开更多
The influence of silicon slice flatness on bonding technology and the relation between a foreign particle and resulting bubble are quantitatively presented by the elastic theory. It is demonstrated experimentally by X...The influence of silicon slice flatness on bonding technology and the relation between a foreign particle and resulting bubble are quantitatively presented by the elastic theory. It is demonstrated experimentally by X-ray double crystal diffractometry and infrared imager.展开更多
Surface-sensitive measurements are crucial to many types of researches in condensed matter physics.However,it is difficult to obtain atomically flat surfaces of many single crystals by the commonly used mechanical cle...Surface-sensitive measurements are crucial to many types of researches in condensed matter physics.However,it is difficult to obtain atomically flat surfaces of many single crystals by the commonly used mechanical cleavage.We demonstrate that the grind-polish-sputter-anneal method can be used to obtain atomically flat surfaces on topological materials.Three types of surface-sensitive measurements are performed on CoSi(001)surface with dramatically improved quality of data.This method extends the research area of surface-sensitive measurements to hard-to-cleave alloys,and can be applied to irregular single crystals with selective crystalline planes.It may become a routine process of preparing atomically flat surfaces for surface-sensitive technologies.展开更多
Graded negative refractive index-based photonic crystal （PC） lenses are designed by gradually modifying the sizes of air holes along the transverse direction for focusing the incident plane wave. To study the tunabi...Graded negative refractive index-based photonic crystal （PC） lenses are designed by gradually modifying the sizes of air holes along the transverse direction for focusing the incident plane wave. To study the tunability of the graded negative index-based PC, we introduce filling factor A, gradually tune the filling factor, and use the finite-difference and time-domain （FDTD） algorithm for numerical calculation. Our calculation results indicate that the focal length and the spot size increase with A increasing. For the same A value, the focal length of a PC with elliptical air holes is the longest, and those of PC with square and rectangular air holes are the shortest. Moreover, when the focal length is greater than 1 ~xm, the focal parameters of the PC are highly insensitive to the variation of A. When the focal length is less than 1 gm, the PC lenses have higher transmittances and all well focus with a beam spot size breaking the diffraction limit. This feature possibly makes the graded negative index-based PC lenses have some new applications in optoelectronic systems.展开更多
An improved plan-wave expansion method is adopted to theoretically study the photonic band diagrams of twodimensional（2D） metal/dielectric photonic crystals.Based on the photonic band structures,the dependence of fl...An improved plan-wave expansion method is adopted to theoretically study the photonic band diagrams of twodimensional（2D） metal/dielectric photonic crystals.Based on the photonic band structures,the dependence of flat bands and photonic bandgaps on two parameters（dielectric constant and filling factor） are investigated for two types of 2D metal/dielectric（M/D） photonic crystals,hole and cylinder photonic crystals.The simulation results show that band structures are affected greatly by these two parameters.Flat bands and bandgaps can be easily obtained by tuning these parameters and the bandgap width may reach to the maximum at certain parameters.It is worth noting that the hole-type photonic crystals show more bandgaps than the corresponding cylinder ones,and the frequency ranges of bandgaps also depend strongly on these parameters.Besides,the photonic crystals containing metallic medium can obtain more modulation of photonic bands,band gaps,and large effective refractive index,etc.than the dielectric/dielectric ones.According to the numerical results,the needs of optical devices for flat bands and bandgaps can be met by selecting the suitable geometry and material parameters.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No.10704006)
文摘We investigate in detail the influence of line defects on focusing of electromagnetic waves in a two-dimensional photonic-crystal flat lens. Through simulations, we find that a focusing can always be observed when a line defect in the lens is introduced along the light transmission direction and the width of the line defect is less than λ/2. However, there appear two focusings when the width of the line defect is more than λ/2. When the line defect is introduced along the direction perpendicular to the transmission, there is always one focusing.
基金Project supported by the National Natural Science Foundation of China(Grant No10704006)the Young Scholars Fund of Beijing University of Chemical Technology and the Supercomputing Centre,Computer Network Information centre,Chinese Academy of Sciences
文摘We have investigated in detail the influence of defect on the focusing of electromagnetic waves in a two-dimensional photonic-crystal flat lens by using the finite-difference time-domain method. The result shows that many focusings can be observed at the symmetrical positions when a defect is introduced into the lens. Furthermore, the wave-guides in the lens can confine the transmission wave effectively and improve the quality of the focusing.
基金supported by the"100 Projects"of Creative Research for the Undergraduates of Nankai University under Grant(BX6-224)
文摘A novel all-fibre flat-top comb filter based on a high birefringence photonic crystal fibre loop mirror is proposed and demonstrated. We simulate theoretically its output spectra and experimentally realize a flat-top output with a high extinction ratio. Compared to filters consisting of the conventional Panda polarization maintaining fibre, filters based on a high birefringence photonic crystal fibre loop mirror have better temperature stability. This kind of filter can be expected to be used widely in Wavelength-division-multiplexing(WDM) systems in the future.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.11079014,61077010,90923036,and 60977041)the 100-Talent Program of the Chinese Academy of Sciences
文摘Flat lenses are designed by means of graded negative refractive index-based photonic crystals （PCs） constructed using air-holes tuned with different shapes. By gradually modifying the filling factor along the transverse direction, we obtain the graded negative index-based lenses for the purpose of focusing an incident plane wave. The finite-difference and timedomain （FDTD） algorithm is adopted for numerical calculation. Our calculation results indicate that these lenses can finely focus incident plane waves. Moreover, for the same size of air-holes, the focusing properties of the lens with rectangular air-holes are better than those with the other shaped air-holes. The graded negative index PCs lenses could possibly enable new applications in optoelectronic systems.
文摘We demonstrate the hybrid focusing points of sonic crystals for a multi-source array applied to flat sonic crystal lenses. The contributions of different point source couples form hybrid focusing points. Ray-trace analyses are conducted for acoustic flat lenses with multi-source configurations. The finite-difference time-domain （FDTD） simulation of flat lenses with multi-source configurations demonstrates the establishment of pure and hybrid focusing points in a pyramidal constellation. The number of focusing points in the pyramidal constellation depends on the number of point sources. We propose an acoustic device for fine-tuning the location of a far-field hybrid focusing point and discuss its benefits for acoustic energy focusing application.
文摘The influence of silicon slice flatness on bonding technology and the relation between a foreign particle and resulting bubble are quantitatively presented by the elastic theory. It is demonstrated experimentally by X-ray double crystal diffractometry and infrared imager.
基金Project supported by the Science Fund from the Ministry of Science and Technology of China(Grant Nos.2016YFA0401000,2016YFA0300600,2016YFA0302400,2016YFA0300504,and 2017YFA0302901)the National Natural Science Foundation of China(Grant Nos.11622435,U1832202,11474340,11822412,11574371,11674369,11574394,11774423,and 11774399)+4 种基金the Fund from the Chinese Academy of Sciences(Grant Nos.QYZDB-SSW-SLH043,XDB07000000,and XDB28000000)the Science Challenge Project,China(Grant No.TZ2016004)the K C Wong Education Foundation,China(Grant No.GJTD-2018-01)the Beijing Natural Science Foundation,China(Grant No.Z180008),the Fund from the Beijing Municipal Science and Technology Commission,China(Grant Nos.Z171100002017018,Z181100004218005,and Z181100004218001)the Fundamental Research Funds for the Central Universities,China,and the Research Funds of Renmin University of China(Grant Nos.15XNLQ07,18XNLG14,and 19XNLG17).
文摘Surface-sensitive measurements are crucial to many types of researches in condensed matter physics.However,it is difficult to obtain atomically flat surfaces of many single crystals by the commonly used mechanical cleavage.We demonstrate that the grind-polish-sputter-anneal method can be used to obtain atomically flat surfaces on topological materials.Three types of surface-sensitive measurements are performed on CoSi(001)surface with dramatically improved quality of data.This method extends the research area of surface-sensitive measurements to hard-to-cleave alloys,and can be applied to irregular single crystals with selective crystalline planes.It may become a routine process of preparing atomically flat surfaces for surface-sensitive technologies.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11079014 and 61077010)
文摘Graded negative refractive index-based photonic crystal （PC） lenses are designed by gradually modifying the sizes of air holes along the transverse direction for focusing the incident plane wave. To study the tunability of the graded negative index-based PC, we introduce filling factor A, gradually tune the filling factor, and use the finite-difference and time-domain （FDTD） algorithm for numerical calculation. Our calculation results indicate that the focal length and the spot size increase with A increasing. For the same A value, the focal length of a PC with elliptical air holes is the longest, and those of PC with square and rectangular air holes are the shortest. Moreover, when the focal length is greater than 1 ~xm, the focal parameters of the PC are highly insensitive to the variation of A. When the focal length is less than 1 gm, the PC lenses have higher transmittances and all well focus with a beam spot size breaking the diffraction limit. This feature possibly makes the graded negative index-based PC lenses have some new applications in optoelectronic systems.
基金Project supported by the National Basic Research Program of China(Grant No.2011CB922200)the National Natural Science Foundation of China(Grant No.605210010)
文摘An improved plan-wave expansion method is adopted to theoretically study the photonic band diagrams of twodimensional（2D） metal/dielectric photonic crystals.Based on the photonic band structures,the dependence of flat bands and photonic bandgaps on two parameters（dielectric constant and filling factor） are investigated for two types of 2D metal/dielectric（M/D） photonic crystals,hole and cylinder photonic crystals.The simulation results show that band structures are affected greatly by these two parameters.Flat bands and bandgaps can be easily obtained by tuning these parameters and the bandgap width may reach to the maximum at certain parameters.It is worth noting that the hole-type photonic crystals show more bandgaps than the corresponding cylinder ones,and the frequency ranges of bandgaps also depend strongly on these parameters.Besides,the photonic crystals containing metallic medium can obtain more modulation of photonic bands,band gaps,and large effective refractive index,etc.than the dielectric/dielectric ones.According to the numerical results,the needs of optical devices for flat bands and bandgaps can be met by selecting the suitable geometry and material parameters.
