The generation mechanism of the first arrivals in the cased boreholes for the poorly bonded conditions is investigated. Based on the analyses of the Riemann surface structure of the characteristic function, the disper...The generation mechanism of the first arrivals in the cased boreholes for the poorly bonded conditions is investigated. Based on the analyses of the Riemann surface structure of the characteristic function, the dispersion features, excitation spectra and contributions of modes excited in the cased boreholes with different cementing types are studied. The phase velocity dispersion studies of leaky modes show that high-order modes form "plateau" regions with one approximate velocity denoted by v separated by their cutoff frequencies, in which the phase velocity changes little with a considerable frequency range, while the group velocity keeps a relatively constant high value. Usually, the operation frequency range of a specific cementing evaluation acoustic logging tool is covered by such a "plateau" region. Mode excitation and contribution analyses show that the first arrivals in the cased boreholes for the poorly bonded conditions are the contributions from leaky modes, where the traveling velocity of the first arrivals processed by slowness time coherence(STC) method is equal to the approximated velocity v. Analyses on generation of leaky modes in the cased boreholes supplement the understanding of the generation mechanism of the first arrivals.展开更多
Based on digital signal processing theory,a novel method of designing optical notch filter is proposed for Mach-Zehnder interferometer with cascaded optical fiber rings coupled structure.The method is simple and effec...Based on digital signal processing theory,a novel method of designing optical notch filter is proposed for Mach-Zehnder interferometer with cascaded optical fiber rings coupled structure.The method is simple and effective,and it can be used to implement the designing of the optical notch filter which has arbitrary number of notch points in one free spectrum range(FSR).A design example of notch filter based on cascaded single-fiber-rings is given.On this basis,an improved cascaded double-fiber-rings structure is presented to eliminate the effect of phase shift caused by the single-fiber-ring structure.This new structure can improve the stability and applicability of system.The change of output intensity spectrum is finally investigated for each design parameter and the tuning characteristics of the notch filter are also discussed.展开更多
A microwave photonic link （MPL） with high spurious-free dynamic range （SFDR） is proposed and analyzed. The optical carrier is divided equally into two paths. The path I is modulated by radio frequency （RF） signa...A microwave photonic link （MPL） with high spurious-free dynamic range （SFDR） is proposed and analyzed. The optical carrier is divided equally into two paths. The path I is modulated by radio frequency （RF） signals in a Mach-Zehnder modulator （MZM）, and the phase of path 2 is controlled before the combination with path 1. By properly adjusting the phase difference of the two paths with the optical phase shifter, the third-order intermodulation distortion （IMD3） can be significantly suppressed. A proof-of-concept simulation is carried out. The results show that a reduction of 40 dB in the IMD3 and an improvement of 21.1 dB in the SFDR are achieved as compared with the conventional MZM-based MPL. The proposed MPL shows the advantages of simple structure, low cost and high efficiency.展开更多
基金the National Natural Science Foundation of China(Grant Nos.11134011 and 41274134)
文摘The generation mechanism of the first arrivals in the cased boreholes for the poorly bonded conditions is investigated. Based on the analyses of the Riemann surface structure of the characteristic function, the dispersion features, excitation spectra and contributions of modes excited in the cased boreholes with different cementing types are studied. The phase velocity dispersion studies of leaky modes show that high-order modes form "plateau" regions with one approximate velocity denoted by v separated by their cutoff frequencies, in which the phase velocity changes little with a considerable frequency range, while the group velocity keeps a relatively constant high value. Usually, the operation frequency range of a specific cementing evaluation acoustic logging tool is covered by such a "plateau" region. Mode excitation and contribution analyses show that the first arrivals in the cased boreholes for the poorly bonded conditions are the contributions from leaky modes, where the traveling velocity of the first arrivals processed by slowness time coherence(STC) method is equal to the approximated velocity v. Analyses on generation of leaky modes in the cased boreholes supplement the understanding of the generation mechanism of the first arrivals.
基金supported by the National Natural Science Foundation of China (No.10804070)the Innovation Program of Shanghai Municipal Education Commission (No.09YZ06)Shanghai Leading Academic Discipline Project (No.S30108)
文摘Based on digital signal processing theory,a novel method of designing optical notch filter is proposed for Mach-Zehnder interferometer with cascaded optical fiber rings coupled structure.The method is simple and effective,and it can be used to implement the designing of the optical notch filter which has arbitrary number of notch points in one free spectrum range(FSR).A design example of notch filter based on cascaded single-fiber-rings is given.On this basis,an improved cascaded double-fiber-rings structure is presented to eliminate the effect of phase shift caused by the single-fiber-ring structure.This new structure can improve the stability and applicability of system.The change of output intensity spectrum is finally investigated for each design parameter and the tuning characteristics of the notch filter are also discussed.
基金supported by the Fundamental Research Funds for the Central Universities(No.JB142001-9)the Programme of Introducing Talents of Discipline to Universities China 111 Project(No.B08038)
文摘A microwave photonic link （MPL） with high spurious-free dynamic range （SFDR） is proposed and analyzed. The optical carrier is divided equally into two paths. The path I is modulated by radio frequency （RF） signals in a Mach-Zehnder modulator （MZM）, and the phase of path 2 is controlled before the combination with path 1. By properly adjusting the phase difference of the two paths with the optical phase shifter, the third-order intermodulation distortion （IMD3） can be significantly suppressed. A proof-of-concept simulation is carried out. The results show that a reduction of 40 dB in the IMD3 and an improvement of 21.1 dB in the SFDR are achieved as compared with the conventional MZM-based MPL. The proposed MPL shows the advantages of simple structure, low cost and high efficiency.
