We investigate the electronic transport in a simple mesoscopic cross structure made of two wires(stubs)grafted at the same point along a quantum waveguide.We show that the structure may exhibit important phenomena suc...We investigate the electronic transport in a simple mesoscopic cross structure made of two wires(stubs)grafted at the same point along a quantum waveguide.We show that the structure may exhibit important phenomena such as bound in continuum(BIC)states.These states are transformed into electromagnetically induced transparency(EIT)resonance by detuning slightly the lengths of the stubs.The last phenomenon is used to propose and study a mesoscopic demultiplexer device with an input waveguide and two output waveguides.We give closed-form expressions of the geometrical parameters that allow a selective transfer of a given state in the first waveguide without perturbing the second waveguide.The effect of temperature on the transmission resonances is also examined by using Landauer-Büttiker formula.The analytical results of the dispersion relation and transmission and reflection coefficient are obtained using the Green's function method.展开更多
The advancement of terahertz technology in recent years and its applications in various fields lead to an urgent need for functional terahertz components,among which a terahertz switch is one example of the most impor...The advancement of terahertz technology in recent years and its applications in various fields lead to an urgent need for functional terahertz components,among which a terahertz switch is one example of the most importance because it provides an effective interface between terahertz signals and information in another physical quantity.To date many types of terahertz switches have been investigated mainly in the form of metamaterials made from metallic structures and optically-active medium.However,these reported terahertz switches usually suffer from an inferior performance,e.g.,requiring a high pump laser power density due to a low quality factor of the metallic metamaterial resonances.In this paper,we report and numerically investigate a symmetry-broken silicon disk based terahertz resonator array which exhibits one resonance with ultrahigh quality factor for normal incidence of the terahertz radiations.This resonance,which can never be excited for regular circular Si disks,can help to realize a superior terahertz switch with which only an ultra-low optical pump power density is required to modify the free carrier concentration in Si and its refractive index in the terahertz band.Our findings demonstrate that to realize a high terahertz transmittance change from 0 to above 50%,the required optical pump power density is more than 3 orders of magnitude smaller than that required for a split-ring resonator(SRR)based terahertz switch reported in the literature.展开更多
From detailed numerical calculations,we demonstrate that in simple photonic crystal structures,a discrete number of Bloch surface-localized eigenstates can exist inside the continuum of free-space modes.Coupling to th...From detailed numerical calculations,we demonstrate that in simple photonic crystal structures,a discrete number of Bloch surface-localized eigenstates can exist inside the continuum of free-space modes.Coupling to the free space causes the surface modes to leak,but the forward and back-reflected leakage may interfere destructively to create a perfectly bound surface state with zero leakage.We perform analytical temporal coupled-mode theory analysis to show the generality of such phenomenon and its robustness from variations of system parameters.Periodicity,time-reversal invariance,two-fold rotational symmetry and a perfectly reflecting boundary are necessary for these unique states.展开更多
文摘We investigate the electronic transport in a simple mesoscopic cross structure made of two wires(stubs)grafted at the same point along a quantum waveguide.We show that the structure may exhibit important phenomena such as bound in continuum(BIC)states.These states are transformed into electromagnetically induced transparency(EIT)resonance by detuning slightly the lengths of the stubs.The last phenomenon is used to propose and study a mesoscopic demultiplexer device with an input waveguide and two output waveguides.We give closed-form expressions of the geometrical parameters that allow a selective transfer of a given state in the first waveguide without perturbing the second waveguide.The effect of temperature on the transmission resonances is also examined by using Landauer-Büttiker formula.The analytical results of the dispersion relation and transmission and reflection coefficient are obtained using the Green's function method.
基金the National Key R&D Program of China(Grant No.2017YFA0701005)the National Natural Science Foundation of China(Grant Nos.11974221,91750201,61927813,and 61775229)+1 种基金Z.Han also acknowledges the support from the Taishan Scholar Program of Shandong Province,China(Grant No.tsqn201909079)Zhejiang Provincial Natural Science Foundation of China(Grant No.LY15F050008).
文摘The advancement of terahertz technology in recent years and its applications in various fields lead to an urgent need for functional terahertz components,among which a terahertz switch is one example of the most importance because it provides an effective interface between terahertz signals and information in another physical quantity.To date many types of terahertz switches have been investigated mainly in the form of metamaterials made from metallic structures and optically-active medium.However,these reported terahertz switches usually suffer from an inferior performance,e.g.,requiring a high pump laser power density due to a low quality factor of the metallic metamaterial resonances.In this paper,we report and numerically investigate a symmetry-broken silicon disk based terahertz resonator array which exhibits one resonance with ultrahigh quality factor for normal incidence of the terahertz radiations.This resonance,which can never be excited for regular circular Si disks,can help to realize a superior terahertz switch with which only an ultra-low optical pump power density is required to modify the free carrier concentration in Si and its refractive index in the terahertz band.Our findings demonstrate that to realize a high terahertz transmittance change from 0 to above 50%,the required optical pump power density is more than 3 orders of magnitude smaller than that required for a split-ring resonator(SRR)based terahertz switch reported in the literature.
基金BZ and MS were partially supported by the MIT S3TEC Energy Research Frontier Center of the Department of Energy under Grant No.DE-SC0001299SLC was partially supported by the MRSEC Program of the NSF under Award No.DMR-0819762This work was also partially supported by the Army Research Office through the Institute for Soldier Nanotechnologies under Contract No.W911NF-07-D0004.
文摘From detailed numerical calculations,we demonstrate that in simple photonic crystal structures,a discrete number of Bloch surface-localized eigenstates can exist inside the continuum of free-space modes.Coupling to the free space causes the surface modes to leak,but the forward and back-reflected leakage may interfere destructively to create a perfectly bound surface state with zero leakage.We perform analytical temporal coupled-mode theory analysis to show the generality of such phenomenon and its robustness from variations of system parameters.Periodicity,time-reversal invariance,two-fold rotational symmetry and a perfectly reflecting boundary are necessary for these unique states.
