Wave field reconstruction inversion （WRI） is an improved full waveform inversion theory that has been proposed in recent years. WRI method expands the searching space by introducing the wave equation into the object...Wave field reconstruction inversion （WRI） is an improved full waveform inversion theory that has been proposed in recent years. WRI method expands the searching space by introducing the wave equation into the objective function and reconstructing the wavefield to update model parameters, thereby improving the computing efficiency and mitigating the influence of the local minimum. However, frequency-domain WRI is difficult to apply to real seismic data because of the high computational memory demand and requirement of time-frequency transformation with additional computational costs. In this paper, wavefield reconstruction inversion theory is extended into the time domain, the augmented wave equation of WRI is derived in the time domain, and the model gradient is modified according to the numerical test with anomalies. The examples of synthetic data illustrate the accuracy of time-domain WRI and the low dependency of WRI on low-frequency information.展开更多
In order to obtain large broadband, a novel travelling-wave modulator with nonperiodic domain inversions and ridge structure is proposed. The composite structure is designed to achieve velocity matching between the op...In order to obtain large broadband, a novel travelling-wave modulator with nonperiodic domain inversions and ridge structure is proposed. The composite structure is designed to achieve velocity matching between the optical wave and the microwave, to get a 50 characteristic impedance and to reduce the loss of the microwave electrodes with finite element method (FEM). The calculation results show that the frequency response of the new device is flat up to 350 GHz with interaction length of 1 cm, characteristic impedance of 49 , and microwave refractive index of 2.5.展开更多
Investigating source parameters of small and moderate earthquakes plays an important role in seismology research. For small and moderate earthquakes, the mechanisms are usually obtained by first motion of P-Wave, surf...Investigating source parameters of small and moderate earthquakes plays an important role in seismology research. For small and moderate earthquakes, the mechanisms are usually obtained by first motion of P-Wave, surface wave spectra method in frequency-domain or the waveform inversion in time-domain, based on the regional waveform records. We applied the wavelet domain inversion method to determine mechanism of regional earthquake. Using the wavelet coefficients of different scales can give more information to constrain the inversion. We determined the mechanisms of three earthquakes occurred in California, the United States. They are consistent with the previous results (Harvard Centroid Moment Tensor and United States Geological Service). This proves that the wavelet domain inversion method is an efficient method to determine the source parameters of small and moderate earthquakes, especially the strong aftershocks after a large, disastrous earthquake.展开更多
In the contrast source inversion(CSI)method,the contrast sources(equiva-lent scattering sources)and the contrast(parameter perturbation)are iteratively recon-structed by an alternating optimization scheme.Traditionall...In the contrast source inversion(CSI)method,the contrast sources(equiva-lent scattering sources)and the contrast(parameter perturbation)are iteratively recon-structed by an alternating optimization scheme.Traditionally integral equation CSI method is formulated for transmission tomography using analytic Green’s function in homogeneous background.To extend the method to the case of reflection seismology,in this paper,we use WKBJ method to compute the Green’s function of depth dependent background media and the solving method of equations to initialize the contrast source of different frequencies,resulting in an efficient method to invert multi-frequency reflection seismic data–multi-frequency contrast source inversion method(MFCSI).Numerical results for the Marmousi model show that MFCSI method can obtain good results even when low frequency data are missing,in which case the conventional FWI fails.展开更多
Periodically poled lithium niobate on insulator(LNOI) ridge waveguides are desirable for high-efficiency nonlinear frequency conversions, and the fabrication process of such waveguides is crucial for device performanc...Periodically poled lithium niobate on insulator(LNOI) ridge waveguides are desirable for high-efficiency nonlinear frequency conversions, and the fabrication process of such waveguides is crucial for device performance. In this work, we report fabrication and characterization of locally periodically poled ridge waveguides. Ridge waveguides were fabricated by dry etching, and then the high-voltage pulses were applied to locally poled ridge waveguides. Second harmonic generation with normalized conversion efficiency of 435.5% W^(-1)·cm^(-2) was obtained in the periodically poled LNOI ridge waveguide,which was consistent with the triangular domain structure revealed by confocal microscopy.展开更多
基金supported by the National Natural Science Foundation of China(Nos.41374122 and 41504100)
文摘Wave field reconstruction inversion （WRI） is an improved full waveform inversion theory that has been proposed in recent years. WRI method expands the searching space by introducing the wave equation into the objective function and reconstructing the wavefield to update model parameters, thereby improving the computing efficiency and mitigating the influence of the local minimum. However, frequency-domain WRI is difficult to apply to real seismic data because of the high computational memory demand and requirement of time-frequency transformation with additional computational costs. In this paper, wavefield reconstruction inversion theory is extended into the time domain, the augmented wave equation of WRI is derived in the time domain, and the model gradient is modified according to the numerical test with anomalies. The examples of synthetic data illustrate the accuracy of time-domain WRI and the low dependency of WRI on low-frequency information.
基金This work was supported by the National Natural Science Foundation of China(No.60077030)
文摘In order to obtain large broadband, a novel travelling-wave modulator with nonperiodic domain inversions and ridge structure is proposed. The composite structure is designed to achieve velocity matching between the optical wave and the microwave, to get a 50 characteristic impedance and to reduce the loss of the microwave electrodes with finite element method (FEM). The calculation results show that the frequency response of the new device is flat up to 350 GHz with interaction length of 1 cm, characteristic impedance of 49 , and microwave refractive index of 2.5.
基金supported by National Natural Science Foundation of China (Grant Nos. 40974028 and 41030319)National Basic Research Program of China (Grant No. 2008CB425701)
文摘Investigating source parameters of small and moderate earthquakes plays an important role in seismology research. For small and moderate earthquakes, the mechanisms are usually obtained by first motion of P-Wave, surface wave spectra method in frequency-domain or the waveform inversion in time-domain, based on the regional waveform records. We applied the wavelet domain inversion method to determine mechanism of regional earthquake. Using the wavelet coefficients of different scales can give more information to constrain the inversion. We determined the mechanisms of three earthquakes occurred in California, the United States. They are consistent with the previous results (Harvard Centroid Moment Tensor and United States Geological Service). This proves that the wavelet domain inversion method is an efficient method to determine the source parameters of small and moderate earthquakes, especially the strong aftershocks after a large, disastrous earthquake.
基金supported by the National Science and Technology of Major Projects of China(grant no.2016ZX05024-001-004)the WTOPI Research Consortium of Modeling and Imaging Laboratory,University of California Santa Cruz,US。
文摘In the contrast source inversion(CSI)method,the contrast sources(equiva-lent scattering sources)and the contrast(parameter perturbation)are iteratively recon-structed by an alternating optimization scheme.Traditionally integral equation CSI method is formulated for transmission tomography using analytic Green’s function in homogeneous background.To extend the method to the case of reflection seismology,in this paper,we use WKBJ method to compute the Green’s function of depth dependent background media and the solving method of equations to initialize the contrast source of different frequencies,resulting in an efficient method to invert multi-frequency reflection seismic data–multi-frequency contrast source inversion method(MFCSI).Numerical results for the Marmousi model show that MFCSI method can obtain good results even when low frequency data are missing,in which case the conventional FWI fails.
基金supported by the National Key R&D Program of China(Nos.2019YFA0705000 and 2017YFA0303700)the National Natural Science Foundation of China(Nos.91950206,11627810,and 51890861)+2 种基金the Leading-edge Technology Program of Jiangsu Natural Science Foundation(No.BK20192001)the Key R&D Program of Guangdong Province(No.2018B030329001)the Fundamental Research Funds for the Central Universities(No.021314380177)。
文摘Periodically poled lithium niobate on insulator(LNOI) ridge waveguides are desirable for high-efficiency nonlinear frequency conversions, and the fabrication process of such waveguides is crucial for device performance. In this work, we report fabrication and characterization of locally periodically poled ridge waveguides. Ridge waveguides were fabricated by dry etching, and then the high-voltage pulses were applied to locally poled ridge waveguides. Second harmonic generation with normalized conversion efficiency of 435.5% W^(-1)·cm^(-2) was obtained in the periodically poled LNOI ridge waveguide,which was consistent with the triangular domain structure revealed by confocal microscopy.
