The analytical expression for the transmission spectra of coupled cavity waveguides （CCWs） in photonic crystals （PCs） is derived based on the coupled-mode theory （CMT）. Parameters in the analytical expression ca...The analytical expression for the transmission spectra of coupled cavity waveguides （CCWs） in photonic crystals （PCs） is derived based on the coupled-mode theory （CMT）. Parameters in the analytical expression can be extracted by simple numerical simulations. We reveal that it is the phase shift between the two adjacent PC defects that uniquely determines the flatness of the impurity bands of CCWs. In addition, it is found that the phase shift also greatly affects the bandwidth of CCWs. Thus, the engineering of the impurity bands of CCWs can be realized through the adjustment of the phase shift. Based on the theoretical results, an interesting phenomenon in which a CCW acts as a single PC defect and its impurity band possesses a Lorentz lineshape is predicted. Very good agreement between the analytical results and the numerical simulations based on transfer matrix method has been achieved.展开更多
This paper theoretically investigates the dependence of leaky mode coupling between inner core fundamental mode and outer core defect mode on phase and loss matching in pure silica dual-core photonic crystal fibres wi...This paper theoretically investigates the dependence of leaky mode coupling between inner core fundamental mode and outer core defect mode on phase and loss matching in pure silica dual-core photonic crystal fibres with the multi-pole method. The complete mode coupling can take place when both the phase and loss matching conditions are satisfied at the avoided anti-crossing wavelength. It shows the influences of cladding structure parameters including the diameters of cladding air holes d1, diameters of outer core holes d2 and hole to hole pitch A on the characteristics of leaky modes coupling. The coupled-mode theory is used to analyse the mode transition characteristics and the complete coupling can be clearly indicated by comparing the real and imaginary parts of propagation constant of the leaky modes.展开更多
In this paper,a stepwise coupled-mode model with the use of the direct global matrix approach is proposed.This method is capable of handling two-dimensional problems with either a point source in cylindrical geometry ...In this paper,a stepwise coupled-mode model with the use of the direct global matrix approach is proposed.This method is capable of handling two-dimensional problems with either a point source in cylindrical geometry or a line source in plane geometry.With the use of the direct global matrix approach,this method is numerically stable.In addition,by introducing appropriately normalized range solutions,this model is free from the numerical overflow problem.Furthermore,we put forward source conditions appropriate for the line-source problem in plane geometry.As a result,this method is capable of addressing the scenario with a line source on top of a sloping bottom.Closed-form expressions for coupling matrices are derived and applied in this paper for handling problems with pressure-release boundaries and a homogeneous water column.The numerical simulations indicate that the proposed model is accurate,efficient,and numerically stable.Consequently,this model can serve as a benchmark model in range-dependent propagation modeling.Although this method is verified by an ideal wedge problem in this paper,the formulation applies to realistic problems as well.展开更多
Sound propagation in a wedge-shaped waveguide with perfectly reflecting boundaries is one of the few range- dependent problems with an analytical solution, and hence provides an ideal benchmark for a full two-way solu...Sound propagation in a wedge-shaped waveguide with perfectly reflecting boundaries is one of the few range- dependent problems with an analytical solution, and hence provides an ideal benchmark for a full two-way solution to the wave equation. An analytical solution for the sound propagation in an ideal wedge with a pressure-release bottom was presented by Buckingham and Tolstoy [Buckingham and Tolstoy 1990 J. Acoust. Soc. Am. 87 1511]. The ideal wedge problem with a rigid bottom is also of great importance in underwater acoustics. We present an analytical solution to the ideal wedge problem with a perfectly reflecting bottom, either rigid or pressure-release, which may be used to provide a means for investigating the sound field in depth-varying channels, and to establish the accuracy of numerical propagation models. Closed-form expressions for coupling matrices are also provided for the ideal waveguides characterized by a ho- mogeneous water column bounded by perfectly reflecting boundaries. A comparison between the analytical solution and the numerical solution recently proposed by Luo et al. [Luo W Y, Yang C M and Zhang R H 2012 Chin. Phys. Lett. 29 014302] is also presented, through which the accuracy of this numerical model is illustrated.展开更多
This paper introduces the design and applications of integrated As2S3 sidewall Bragg gratings on LiNbO3 substrate. The grating reflectance and bandwidth are analyzed with coupled-mode theory. Coupling coefficients are...This paper introduces the design and applications of integrated As2S3 sidewall Bragg gratings on LiNbO3 substrate. The grating reflectance and bandwidth are analyzed with coupled-mode theory. Coupling coefficients are computed by taking overlap integration. Numerical results for uniform gratings, phase-shifted gratings and grating cavities as well as electro-optic tunable gratings are presented. These integrated As2S3 sidewall gratings on LiNbO3 substrate provide an approach to the design of a wide range of integrated optical devices including switches, laser cavities, modulators, sensors and tunable filters.展开更多
Topological photonics have led to robust optical behavior of optical devices, which has alleviated the influence of manufacturing defects and perturbations on the device performance. Meanwhile, temporal coupled-mode t...Topological photonics have led to robust optical behavior of optical devices, which has alleviated the influence of manufacturing defects and perturbations on the device performance. Meanwhile, temporal coupled-mode theory(t-CMT) has been developed and applied widely. However, the t-CMT of cascaded coupled cavities(CCC) system and its corresponding high-order filter has yet to be established. Here, the t-CMT of CCC system is established based on the existing t-CMT. By combining the CCC with topological waveguides, a versatile design scheme of high-order nonreciprocal add-drop filter(HONAF) is proposed. The relationship between the coupling effect of cavities and transmission and the filtering performance of HONAF is analyzed quantitatively. Then, a method to improve the transmission efficiency and quality factor of the filter is given. The proposed HONAF is based on the combination of gyromagnetic photonic crystals and decagonal Penrose-type photonic quasicrystals. The transmission and filtering performance of the HONAF are numerically analyzed, which verifies the consistency between theoretical prediction and numerical simulation. The established t-CMT of CCC system can be widely used in coupled resonator optical waveguides and their related systems. The proposed HONAF with excellent performance can also be applied to wavelength division multiplexing/demultiplexing systems.展开更多
A 2-mm-long silicon-on-insulator grating emitter with a narrow angular full width at half-maximum(FWHM)and a high sideband suppression ratio(SSR)is proposed and designed.It consists of a Si_(3)N_(4)/Si grating with an...A 2-mm-long silicon-on-insulator grating emitter with a narrow angular full width at half-maximum(FWHM)and a high sideband suppression ratio(SSR)is proposed and designed.It consists of a Si_(3)N_(4)/Si grating with an approximate Gaussian emission profile along the grating length,which aims to reduce the sidelobe intensity of the scanning light in the far-field,thereby improving the resolution of the longitudinal steering resolution of the light detection and ranging(lidar).Numerical analysis shows that the angular FWHM of the emitted beam could be as low as 0.026°for a grating length of 2.247 mm and the input TE-like waveguide mode at 1550 nm,and the SSR could be more than 32.622 dB.Moreover,this Si_(3)N_(4)/Si grating exhibits a favorable fabrication error tolerance when considering the width and length variation of the Si_(3)N_(4)overlayer in practice.Our design offers a promising platform for realizing integrated optical phased arrays for the long-distance solid-state lidar.展开更多
The temporal coupled-mode theory(TCMT)has made significant progress in recent years,and is widely applied in explaining a variety of optical phenomena.In this paper,the optical characteristics of the metasurface compo...The temporal coupled-mode theory(TCMT)has made significant progress in recent years,and is widely applied in explaining a variety of optical phenomena.In this paper,the optical characteristics of the metasurface composed of nano-bars and nano-rings are simulated.The simulation results are well explained by TCMT under the coupled basis vector.However,when the structural asymmetry is large,the fitting of results shows that the total radiation loss is not conservative,in contradiction to the requirement of traditional TCMT.We solved this inconsistency by introducing the propagation phase into the near-field coupling term of TCMT.The studies show that,unlike the local mode near the exceptional point which corresponds to the radiation loss of the bright mode,the global mode near the diabolic point is closely related to the propagation phase.Furthermore,the structure near the diabolic point shows characteristic cross-coupling with the change of period.This study proposes a new theoretical framework for comprehending the interaction of light and matter and offers some guiding implications for the application of TCMT to a variety of related domains.展开更多
We use the nonlinear coupled-mode theory to theoretically investigate second-harmonic generation(SHG) in subwavelength x-cut and z-cut lithium niobate(LN) thin-film waveguides and derive the analytical formula to calc...We use the nonlinear coupled-mode theory to theoretically investigate second-harmonic generation(SHG) in subwavelength x-cut and z-cut lithium niobate(LN) thin-film waveguides and derive the analytical formula to calculate SHG efficiency in x-cut and z-cut LN thin-film waveguides explicitly.Under the scheme of optimal modal phase matching(MPM), two types of LN thin films can achieve highly efficient frequency doubling of a 1064 nm laser with a comparable conversion efficiency due to very consistent modal field distribution of the fundamental wave and second-harmonic wave with efficient overlap between them.Such a robust MPM for high-efficiency SHG in both the subwavelength x-cut and z-cut LN thin-film waveguides is further confirmed in a broad wavelength range, which might facilitate design and application of micro–nano nonlinear optical devices based on the subwavelength LN thin film.展开更多
基金Project supported by the National Natural Science Foundation of China （Grant No 10374065）, the Natural Science Foundation of Guangdong Province of China （Grant No 32050）, the Ministry of Education of China （Grant No 204107）, and the Department of Education of Guangdong Province of China （Grant No Z03033）.
文摘The analytical expression for the transmission spectra of coupled cavity waveguides （CCWs） in photonic crystals （PCs） is derived based on the coupled-mode theory （CMT）. Parameters in the analytical expression can be extracted by simple numerical simulations. We reveal that it is the phase shift between the two adjacent PC defects that uniquely determines the flatness of the impurity bands of CCWs. In addition, it is found that the phase shift also greatly affects the bandwidth of CCWs. Thus, the engineering of the impurity bands of CCWs can be realized through the adjustment of the phase shift. Based on the theoretical results, an interesting phenomenon in which a CCW acts as a single PC defect and its impurity band possesses a Lorentz lineshape is predicted. Very good agreement between the analytical results and the numerical simulations based on transfer matrix method has been achieved.
基金Project supported by the National Key Basic Research Special Foundation of China (Grant No. 2010CB327605)the National High-Technology Research and Development Program of China (Grant No. 2009AA01Z220)+2 种基金the Key Grant of the Chinese Ministry of Education (Grant No. 109015)the Discipline Co-construction Project of Beijing Municipal Commission of Education (Grant No. YB20081001301)the Open Fund of Key Laboratory of Information Photonics and Optical Communications (Beijing University of Posts and Telecommunications), Ministry of Education,and the Specialized Research Fund for the Doctoral Program of Beijing University of Posts and Telecommunications (Grant No. CX201023)
文摘This paper theoretically investigates the dependence of leaky mode coupling between inner core fundamental mode and outer core defect mode on phase and loss matching in pure silica dual-core photonic crystal fibres with the multi-pole method. The complete mode coupling can take place when both the phase and loss matching conditions are satisfied at the avoided anti-crossing wavelength. It shows the influences of cladding structure parameters including the diameters of cladding air holes d1, diameters of outer core holes d2 and hole to hole pitch A on the characteristics of leaky modes coupling. The coupled-mode theory is used to analyse the mode transition characteristics and the complete coupling can be clearly indicated by comparing the real and imaginary parts of propagation constant of the leaky modes.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10734100 and 11125420)the Knowledge Innovation Program of Chinese Academy of Sciences
文摘In this paper,a stepwise coupled-mode model with the use of the direct global matrix approach is proposed.This method is capable of handling two-dimensional problems with either a point source in cylindrical geometry or a line source in plane geometry.With the use of the direct global matrix approach,this method is numerically stable.In addition,by introducing appropriately normalized range solutions,this model is free from the numerical overflow problem.Furthermore,we put forward source conditions appropriate for the line-source problem in plane geometry.As a result,this method is capable of addressing the scenario with a line source on top of a sloping bottom.Closed-form expressions for coupling matrices are derived and applied in this paper for handling problems with pressure-release boundaries and a homogeneous water column.The numerical simulations indicate that the proposed model is accurate,efficient,and numerically stable.Consequently,this model can serve as a benchmark model in range-dependent propagation modeling.Although this method is verified by an ideal wedge problem in this paper,the formulation applies to realistic problems as well.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11125420 and 10734100)the Knowledge Innovation Program of the Chinese Academy of Sciences
文摘Sound propagation in a wedge-shaped waveguide with perfectly reflecting boundaries is one of the few range- dependent problems with an analytical solution, and hence provides an ideal benchmark for a full two-way solution to the wave equation. An analytical solution for the sound propagation in an ideal wedge with a pressure-release bottom was presented by Buckingham and Tolstoy [Buckingham and Tolstoy 1990 J. Acoust. Soc. Am. 87 1511]. The ideal wedge problem with a rigid bottom is also of great importance in underwater acoustics. We present an analytical solution to the ideal wedge problem with a perfectly reflecting bottom, either rigid or pressure-release, which may be used to provide a means for investigating the sound field in depth-varying channels, and to establish the accuracy of numerical propagation models. Closed-form expressions for coupling matrices are also provided for the ideal waveguides characterized by a ho- mogeneous water column bounded by perfectly reflecting boundaries. A comparison between the analytical solution and the numerical solution recently proposed by Luo et al. [Luo W Y, Yang C M and Zhang R H 2012 Chin. Phys. Lett. 29 014302] is also presented, through which the accuracy of this numerical model is illustrated.
文摘This paper introduces the design and applications of integrated As2S3 sidewall Bragg gratings on LiNbO3 substrate. The grating reflectance and bandwidth are analyzed with coupled-mode theory. Coupling coefficients are computed by taking overlap integration. Numerical results for uniform gratings, phase-shifted gratings and grating cavities as well as electro-optic tunable gratings are presented. These integrated As2S3 sidewall gratings on LiNbO3 substrate provide an approach to the design of a wide range of integrated optical devices including switches, laser cavities, modulators, sensors and tunable filters.
基金supported by the National Natural Science Foundation of China(Grant Nos.61405058,and 62075059)the Natural Science Foundation of Hunan Province(Grant Nos.2017JJ2048,and 2020JJ4161)the Fundamental Research Funds for the Central Universities(Grant No.531118040112)。
文摘Topological photonics have led to robust optical behavior of optical devices, which has alleviated the influence of manufacturing defects and perturbations on the device performance. Meanwhile, temporal coupled-mode theory(t-CMT) has been developed and applied widely. However, the t-CMT of cascaded coupled cavities(CCC) system and its corresponding high-order filter has yet to be established. Here, the t-CMT of CCC system is established based on the existing t-CMT. By combining the CCC with topological waveguides, a versatile design scheme of high-order nonreciprocal add-drop filter(HONAF) is proposed. The relationship between the coupling effect of cavities and transmission and the filtering performance of HONAF is analyzed quantitatively. Then, a method to improve the transmission efficiency and quality factor of the filter is given. The proposed HONAF is based on the combination of gyromagnetic photonic crystals and decagonal Penrose-type photonic quasicrystals. The transmission and filtering performance of the HONAF are numerically analyzed, which verifies the consistency between theoretical prediction and numerical simulation. The established t-CMT of CCC system can be widely used in coupled resonator optical waveguides and their related systems. The proposed HONAF with excellent performance can also be applied to wavelength division multiplexing/demultiplexing systems.
基金supported by the Shanghai Municipal Science and Technology Major Project(No.2017SHZDZX03)。
文摘A 2-mm-long silicon-on-insulator grating emitter with a narrow angular full width at half-maximum(FWHM)and a high sideband suppression ratio(SSR)is proposed and designed.It consists of a Si_(3)N_(4)/Si grating with an approximate Gaussian emission profile along the grating length,which aims to reduce the sidelobe intensity of the scanning light in the far-field,thereby improving the resolution of the longitudinal steering resolution of the light detection and ranging(lidar).Numerical analysis shows that the angular FWHM of the emitted beam could be as low as 0.026°for a grating length of 2.247 mm and the input TE-like waveguide mode at 1550 nm,and the SSR could be more than 32.622 dB.Moreover,this Si_(3)N_(4)/Si grating exhibits a favorable fabrication error tolerance when considering the width and length variation of the Si_(3)N_(4)overlayer in practice.Our design offers a promising platform for realizing integrated optical phased arrays for the long-distance solid-state lidar.
基金supported by the National Natural Science Foundation of China(NSFC)(Nos.21873004 and 11304002)the Natural Science Foundation of Anhui Province(Nos.2108085MA23 and 1208085MA07)the Anhui Provincial Quality Project for Higher Education Institutions(No.2019mooc066).
文摘The temporal coupled-mode theory(TCMT)has made significant progress in recent years,and is widely applied in explaining a variety of optical phenomena.In this paper,the optical characteristics of the metasurface composed of nano-bars and nano-rings are simulated.The simulation results are well explained by TCMT under the coupled basis vector.However,when the structural asymmetry is large,the fitting of results shows that the total radiation loss is not conservative,in contradiction to the requirement of traditional TCMT.We solved this inconsistency by introducing the propagation phase into the near-field coupling term of TCMT.The studies show that,unlike the local mode near the exceptional point which corresponds to the radiation loss of the bright mode,the global mode near the diabolic point is closely related to the propagation phase.Furthermore,the structure near the diabolic point shows characteristic cross-coupling with the change of period.This study proposes a new theoretical framework for comprehending the interaction of light and matter and offers some guiding implications for the application of TCMT to a variety of related domains.
基金supported by the National Natural Science Foundation of China (No.11974119)Guangdong Innovative and Entrepreneurial Research Team Program(No.2016ZT06C594)+1 种基金National Key R&D Program of China(No.2018YFA0306200)Dongguan Introduction Program of Leading Innovative and Entrepreneurial Talents,Guangdong Science and Technology Innovation Strategy Special Foundation (No.2019B090904007)。
文摘We use the nonlinear coupled-mode theory to theoretically investigate second-harmonic generation(SHG) in subwavelength x-cut and z-cut lithium niobate(LN) thin-film waveguides and derive the analytical formula to calculate SHG efficiency in x-cut and z-cut LN thin-film waveguides explicitly.Under the scheme of optimal modal phase matching(MPM), two types of LN thin films can achieve highly efficient frequency doubling of a 1064 nm laser with a comparable conversion efficiency due to very consistent modal field distribution of the fundamental wave and second-harmonic wave with efficient overlap between them.Such a robust MPM for high-efficiency SHG in both the subwavelength x-cut and z-cut LN thin-film waveguides is further confirmed in a broad wavelength range, which might facilitate design and application of micro–nano nonlinear optical devices based on the subwavelength LN thin film.
