In this paper, we present a simple theoretical approach to calculate the multiple ionization of big atoms and molecules induced by very high-q fast projectiles in a strong coupling regime （q/v 〉 1）. The results obt...In this paper, we present a simple theoretical approach to calculate the multiple ionization of big atoms and molecules induced by very high-q fast projectiles in a strong coupling regime （q/v 〉 1）. The results obtained from this approach are in excellent agreement with the available experimental data. A probable scenario of molecular multiple ionization by fast and very high-q projectiles is discussed. The very small computational time required here and the good agreement with the existing experimental data make it a good candidate for studying the multiple ionization of complex molecules under high linear energy transfers.展开更多
A high quality-factor （Q） cavity based on a one-dimensional （1D） photonic crystal with gradated elliptical holes was designed using FDTD simulation. Different gradient profiles of the mirror holes were found to co...A high quality-factor （Q） cavity based on a one-dimensional （1D） photonic crystal with gradated elliptical holes was designed using FDTD simulation. Different gradient profiles of the mirror holes were found to correspond to different Q- values of the cavities. A simple strategy is proposed to construct high-Q cavities by using an S-shaped gradient profile for the elliptical holes＇ minor axes, such as a cosine function or Gaussian function. Using such a strategy, a Q value exceeding two million is obtained with only ten mirror holes in a cavity.展开更多
Space–time metasurfaces are promising candidates for breaking Lorentz reciprocity,which constrains light propagation in numerous practical applications.There is a substantial difference between carrier and modulation...Space–time metasurfaces are promising candidates for breaking Lorentz reciprocity,which constrains light propagation in numerous practical applications.There is a substantial difference between carrier and modulation frequencies in space–time photonic metasurfaces that leads to negligible spatial pathway variation of light and weak nonreciprocal response.To surmount this obstacle,herein,the design principle of a high-quality-factor space–time gradient metasurface is demonstrated at the near-infrared regime that increases the lifetime of photons and allows for strong power isolation by lifting the adiabaticity of modulation.The all-dielectric metasurface consists of an array of silicon subwavelength gratings(SWGs)that are separated from distributed Bragg reflectors by a silica buffer.The resonant mode with ultrahigh quality-factor exceeding 10^(4)is excited within the SWG,which is characterized as magnetic octupole and features strong field localization.The SWGs are configured as multijunction p–n layers,whose multigate biasing with time-varying waveforms enables modulation of carriers in space and time.The proposed nonreciprocal metasurface is exploited for free-space optical power isolation by virtue of modulationinduced phase shift.It is shown that under time reversal and by interchanging the directions of incident and observation ports,power isolation of≈35 dB can be maintained between the two ports in free space.展开更多
The method of terahertz(THz)resonance with a high-quality(high-Q)factor offers a vital physical mechanism for metasurface sensors and other high-Q factor applications.However,it is challenging to excite the resonance ...The method of terahertz(THz)resonance with a high-quality(high-Q)factor offers a vital physical mechanism for metasurface sensors and other high-Q factor applications.However,it is challenging to excite the resonance with a high-Q factor in metasurfaces with proper sensitivity as well as figure of merit(FOM)values.Here,an all-dielectric metasurface composed of two asymmetrical rectangular blocks is suggested.Quartz and silicon are the materials applied for the substrate and cuboids respectively.The distinct resonance governed by bound states in the continuum(BIC)is excited by forming an asymmetric cluster by a novel hybrid method of cutting and moving the cuboids.The investigation focuses on analyzing the transmission spectra of the metasurface under different variations in structural parameters and the loss of silicon refractive index.When the proposed defective metasurface serves as a transmittance sensor,it shows a Q factor of 1.08×10^(4)and achieves an FOM up to 4.8×10^(6),which is obtained under the asymmetric parameter equalling 1μm.Simultaneously,the proposed defective metasurface is sensitive to small changes in refractive index.When the thickness of the analyte is 180μm,the sensitivity reaches a maximum value of 578 GHz/RIU.Hence,the proposed defective metasurface exhibits an extensive number of possible applications in the filters,biomedical diagnosis,security screening,and so on.展开更多
This paper describes the specially designed geometry of a dry-etched large-wedge-angle silica microdisk resonator that enables anomalous dispersion in the 780 nm wavelength regime. This anomalous dispersion occurs nat...This paper describes the specially designed geometry of a dry-etched large-wedge-angle silica microdisk resonator that enables anomalous dispersion in the 780 nm wavelength regime. This anomalous dispersion occurs naturally without the use of a mode-hybridization technique to control the geometrical dispersion. By fabricating a1-μm-thick silica microdisk with a wedge angle as large as 56° and an optical Q-factor larger than 107, we achieve a visible Kerr comb that covers the wavelength interval of 700–897 nm. The wide optical frequency range and the closeness to the clock transition at 698 nm of 87 Sr atoms make our visible comb a potentially useful tool in optical atomic clock applications.展开更多
An efficient method to mount a coupled silica microsphere and tapered fiber system is proposed and demonstrated experimentally. For the purpose of optomechanical studies, high-quality-factor optical(Q_o～ 10~8) and me...An efficient method to mount a coupled silica microsphere and tapered fiber system is proposed and demonstrated experimentally. For the purpose of optomechanical studies, high-quality-factor optical(Q_o～ 10~8) and mechanical modes(Q_m～ 0.87 × 10~4) are maintained after the mounting process. For the mounted microsphere, the coupling system is more stable and compact and, thus, is beneficial for future studies and applications based on optomechanical interactions. Especially, the packaged optomechanical system, which is tested in a vacuum chamber,paves the way toward quantum optomechanics research in cryostat.展开更多
We investigate the diffraction of the guided modes of a dielectric slab waveguide on a simple integrated structure consisting of a single dielectric ridge on the surface of the waveguide. Numerical simulations based o...We investigate the diffraction of the guided modes of a dielectric slab waveguide on a simple integrated structure consisting of a single dielectric ridge on the surface of the waveguide. Numerical simulations based on aperiodic rigorous coupled-wave analysis demonstrate the existence of sharp resonant features and bound states in the continuum(BICs) in the reflectance and transmittance spectra occurring at the oblique incidence of a transverseelectric(TE)-polarized guided mode on the ridge. Using the effective index method, we explain the resonances by the excitation of cross-polarized modes of the ridge. Formation of the BICs are confirmed using a theoretical model based on coupled-wave theory. The model suggests that the BICs occur due to the coupling of quasi-TE and quasi-transverse-magnetic modes of the structure. Simple analytical expressions for the angle of incidence and the ridge width predicting the location of the BICs are obtained. The existence of high-Q resonances and BICs enables using the considered integrated structure for sensing, transformation of optical signals, and enhancing nonlinear light–matter interactions. Due to the Lorentzian line shape of the resonances near the BICs, the structure is also promising for filtering applications.展开更多
Ultra-high quality(Q) whispering gallery mode(WGM) microtoroid optical resonators have demonstrated highly sensitive biomolecular detection down to the single molecule limit;however, the lack of a robust coupling meth...Ultra-high quality(Q) whispering gallery mode(WGM) microtoroid optical resonators have demonstrated highly sensitive biomolecular detection down to the single molecule limit;however, the lack of a robust coupling method has prevented their widespread adoption outside the laboratory. We demonstrate through simulation that a phased array of nanorods can enable free-space coupling of light both into and out of a microtoroid while maintaining a high Q. To simulate large nanostructured WGM resonators, we developed a new approach known as FloWBEM,which is an efficient and compact 3D wedge model with custom boundary conditions that accurately simulate the resonant Fano interference between the traveling WGM waves and a nanorod array. Depending on the excitation conditions, we find loaded Q factors of the driven system as high as 2.1 × 10~7 and signal-to-background ratios as high as 3.86%, greater than the noise levels of many commercial detectors. These results can drive future experimental implementation.展开更多
Planar ring resonator waveguides are fabricated in thin films of As2S3 chalcogenide glass,deposited on silicaon-silicon substrates.Waveguide cores are directly written by scanning the focused illumination of a femtose...Planar ring resonator waveguides are fabricated in thin films of As2S3 chalcogenide glass,deposited on silicaon-silicon substrates.Waveguide cores are directly written by scanning the focused illumination of a femtosecond Ti:sapphire laser at a central wavelength of 810 nm,through a two-photon photo-darkening process.A large photoinduced index change of 0.3–0.4 refractive index units is obtained.The radius of the ring resonator is 1.9 mm,corresponding to a transmission free spectral range of 9.1 GHz.A high loaded（intrinsic） Q value of 110,000（180,000） is achieved.The thermal dependence of the resonator transfer function is characterized.The results provide the first report,to the best of our knowledge,of directly written high-Q ring resonators in chalcogenide glass films,and demonstrate the potential of this simple technique towards the fabrication of planar lightguide circuits in these materials.展开更多
We experimentally demonstrate high optical quality factor silica microdisk resonators on a silicon chip with large wedge angles by reactive ion etching. For 2-μm-thick microresonators, we have achieved wedge angles o...We experimentally demonstrate high optical quality factor silica microdisk resonators on a silicon chip with large wedge angles by reactive ion etching. For 2-μm-thick microresonators, we have achieved wedge angles of 59°, 63°,70°, and 79° with optical quality factors of 2.4 × 10~7, 8.1 × 10~6, 5.9 × 10~6, and 7.4 × 10~6, respectively, from ～80 μm diameter microresonators in the 1550 nm wavelength band. Also, for 1-μm-thick microresonators, we have obtained an optical quality factor of 7.3 × 10~6 with a wedge angle of 74°.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11174116 and 11175075)
文摘In this paper, we present a simple theoretical approach to calculate the multiple ionization of big atoms and molecules induced by very high-q fast projectiles in a strong coupling regime （q/v 〉 1）. The results obtained from this approach are in excellent agreement with the available experimental data. A probable scenario of molecular multiple ionization by fast and very high-q projectiles is discussed. The very small computational time required here and the good agreement with the existing experimental data make it a good candidate for studying the multiple ionization of complex molecules under high linear energy transfers.
基金supported by the National Natural Science Foundation of China(Grant Nos.61275045,91121019,and 61021003)the National Basic Research Program of China(Grant No.2013CB632105)
文摘A high quality-factor （Q） cavity based on a one-dimensional （1D） photonic crystal with gradated elliptical holes was designed using FDTD simulation. Different gradient profiles of the mirror holes were found to correspond to different Q- values of the cavities. A simple strategy is proposed to construct high-Q cavities by using an S-shaped gradient profile for the elliptical holes＇ minor axes, such as a cosine function or Gaussian function. Using such a strategy, a Q value exceeding two million is obtained with only ten mirror holes in a cavity.
基金supported in part by Air Force Office of Scientific Research(Grant No.FA9550-18-1-0354).
文摘Space–time metasurfaces are promising candidates for breaking Lorentz reciprocity,which constrains light propagation in numerous practical applications.There is a substantial difference between carrier and modulation frequencies in space–time photonic metasurfaces that leads to negligible spatial pathway variation of light and weak nonreciprocal response.To surmount this obstacle,herein,the design principle of a high-quality-factor space–time gradient metasurface is demonstrated at the near-infrared regime that increases the lifetime of photons and allows for strong power isolation by lifting the adiabaticity of modulation.The all-dielectric metasurface consists of an array of silicon subwavelength gratings(SWGs)that are separated from distributed Bragg reflectors by a silica buffer.The resonant mode with ultrahigh quality-factor exceeding 10^(4)is excited within the SWG,which is characterized as magnetic octupole and features strong field localization.The SWGs are configured as multijunction p–n layers,whose multigate biasing with time-varying waveforms enables modulation of carriers in space and time.The proposed nonreciprocal metasurface is exploited for free-space optical power isolation by virtue of modulationinduced phase shift.It is shown that under time reversal and by interchanging the directions of incident and observation ports,power isolation of≈35 dB can be maintained between the two ports in free space.
基金the Key Research and Development Program of Ningxia Province,China(2021BEB04068)。
文摘The method of terahertz(THz)resonance with a high-quality(high-Q)factor offers a vital physical mechanism for metasurface sensors and other high-Q factor applications.However,it is challenging to excite the resonance with a high-Q factor in metasurfaces with proper sensitivity as well as figure of merit(FOM)values.Here,an all-dielectric metasurface composed of two asymmetrical rectangular blocks is suggested.Quartz and silicon are the materials applied for the substrate and cuboids respectively.The distinct resonance governed by bound states in the continuum(BIC)is excited by forming an asymmetric cluster by a novel hybrid method of cutting and moving the cuboids.The investigation focuses on analyzing the transmission spectra of the metasurface under different variations in structural parameters and the loss of silicon refractive index.When the proposed defective metasurface serves as a transmittance sensor,it shows a Q factor of 1.08×10^(4)and achieves an FOM up to 4.8×10^(6),which is obtained under the asymmetric parameter equalling 1μm.Simultaneously,the proposed defective metasurface is sensitive to small changes in refractive index.When the thickness of the analyte is 180μm,the sensitivity reaches a maximum value of 578 GHz/RIU.Hence,the proposed defective metasurface exhibits an extensive number of possible applications in the filters,biomedical diagnosis,security screening,and so on.
基金National Key R&D Program of China(2016YFA0302500,2017YFA0303703)National Natural Science Foundation of China(NSFC)(61435007,11574144,11621091,61475099)
文摘This paper describes the specially designed geometry of a dry-etched large-wedge-angle silica microdisk resonator that enables anomalous dispersion in the 780 nm wavelength regime. This anomalous dispersion occurs naturally without the use of a mode-hybridization technique to control the geometrical dispersion. By fabricating a1-μm-thick silica microdisk with a wedge angle as large as 56° and an optical Q-factor larger than 107, we achieve a visible Kerr comb that covers the wavelength interval of 700–897 nm. The wide optical frequency range and the closeness to the clock transition at 698 nm of 87 Sr atoms make our visible comb a potentially useful tool in optical atomic clock applications.
基金supported by the Strategic Priority Research Program(B) of the Chinese Academy of Sciences (grant no. XDB01030200)National Basic Research Program of China (grant nos. 2011CB921200 and 2011CBA00200)+2 种基金the National Natural Science Foundation of China (grant no. 61308079)Anhui Provincial Natural Science Foundation (grant no. 1508085QA08)the Fundamental Research Funds for the Central Universities
文摘An efficient method to mount a coupled silica microsphere and tapered fiber system is proposed and demonstrated experimentally. For the purpose of optomechanical studies, high-quality-factor optical(Q_o～ 10~8) and mechanical modes(Q_m～ 0.87 × 10~4) are maintained after the mounting process. For the mounted microsphere, the coupling system is more stable and compact and, thus, is beneficial for future studies and applications based on optomechanical interactions. Especially, the packaged optomechanical system, which is tested in a vacuum chamber,paves the way toward quantum optomechanics research in cryostat.
基金Russian Foundation for Basic Research(RFBR)(16-29-11683,17-47-630323)Ministry of Science and Higher Education of the Russian Federation(State assignment to the FSRC “Crystallography and Photonics” RAS)
文摘We investigate the diffraction of the guided modes of a dielectric slab waveguide on a simple integrated structure consisting of a single dielectric ridge on the surface of the waveguide. Numerical simulations based on aperiodic rigorous coupled-wave analysis demonstrate the existence of sharp resonant features and bound states in the continuum(BICs) in the reflectance and transmittance spectra occurring at the oblique incidence of a transverseelectric(TE)-polarized guided mode on the ridge. Using the effective index method, we explain the resonances by the excitation of cross-polarized modes of the ridge. Formation of the BICs are confirmed using a theoretical model based on coupled-wave theory. The model suggests that the BICs occur due to the coupling of quasi-TE and quasi-transverse-magnetic modes of the structure. Simple analytical expressions for the angle of incidence and the ridge width predicting the location of the BICs are obtained. The existence of high-Q resonances and BICs enables using the considered integrated structure for sensing, transformation of optical signals, and enhancing nonlinear light–matter interactions. Due to the Lorentzian line shape of the resonances near the BICs, the structure is also promising for filtering applications.
基金National Key R&D Program of China(2016YFA0301300)National Natural Science Foundation of China(NSFC)(61671090,61875021)+4 种基金Natural Science Foundation of Beijing Municipality(2192036)China Scholarship Council(CSC)(201706470049)Beijing University of Posts and Telecommunications Excellent Ph.D.Students Foundation(CX2017302)DeMund Foundation Graduate Student Endowed Scholarship in Optical and Medical Sciences Friends of Tucson Optics(FOTO)ScholarshipDefense Threat Reduction Agency(DTRA)(HDTRA1-18-1-0044)
文摘Ultra-high quality(Q) whispering gallery mode(WGM) microtoroid optical resonators have demonstrated highly sensitive biomolecular detection down to the single molecule limit;however, the lack of a robust coupling method has prevented their widespread adoption outside the laboratory. We demonstrate through simulation that a phased array of nanorods can enable free-space coupling of light both into and out of a microtoroid while maintaining a high Q. To simulate large nanostructured WGM resonators, we developed a new approach known as FloWBEM,which is an efficient and compact 3D wedge model with custom boundary conditions that accurately simulate the resonant Fano interference between the traveling WGM waves and a nanorod array. Depending on the excitation conditions, we find loaded Q factors of the driven system as high as 2.1 × 10~7 and signal-to-background ratios as high as 3.86%, greater than the noise levels of many commercial detectors. These results can drive future experimental implementation.
基金the support of the Israeli Science Foundation (ISF),under grant 635/10
文摘Planar ring resonator waveguides are fabricated in thin films of As2S3 chalcogenide glass,deposited on silicaon-silicon substrates.Waveguide cores are directly written by scanning the focused illumination of a femtosecond Ti:sapphire laser at a central wavelength of 810 nm,through a two-photon photo-darkening process.A large photoinduced index change of 0.3–0.4 refractive index units is obtained.The radius of the ring resonator is 1.9 mm,corresponding to a transmission free spectral range of 9.1 GHz.A high loaded（intrinsic） Q value of 110,000（180,000） is achieved.The thermal dependence of the resonator transfer function is characterized.The results provide the first report,to the best of our knowledge,of directly written high-Q ring resonators in chalcogenide glass films,and demonstrate the potential of this simple technique towards the fabrication of planar lightguide circuits in these materials.
基金supported by the National Basic Research Program of China (Nos. 2012CB921804 and 2011CBA00205)the National Natural Science Foundation of China (Nos. 61435007 and 11321063)
文摘We experimentally demonstrate high optical quality factor silica microdisk resonators on a silicon chip with large wedge angles by reactive ion etching. For 2-μm-thick microresonators, we have achieved wedge angles of 59°, 63°,70°, and 79° with optical quality factors of 2.4 × 10~7, 8.1 × 10~6, 5.9 × 10~6, and 7.4 × 10~6, respectively, from ～80 μm diameter microresonators in the 1550 nm wavelength band. Also, for 1-μm-thick microresonators, we have obtained an optical quality factor of 7.3 × 10~6 with a wedge angle of 74°.
