The phase diversity wavefront sensor is one of the tools used to estimate wavefront aberration, and it is often used as a wavefront sensor in adaptive optics systems. However, the performance of the traditional phase ...The phase diversity wavefront sensor is one of the tools used to estimate wavefront aberration, and it is often used as a wavefront sensor in adaptive optics systems. However, the performance of the traditional phase diversity wavefront sensor is limited by the accuracy and dynamic ranges of the intensity distribution at the focus and defocus positions of the CCD camera. In this paper, a modified phase diversity wavefront sensor based on a diffraction grating is proposed to improve the ability to measure the wavefront aberration with larger amplitude and higher spatial frequency. The basic principle and the optics construction of the proposed method are also described in detail. The noise propagation property of the proposed method is also analysed by using the numerical simulation method, and comparison between the diffraction grating phase diversity wavefront sensor and the traditional phase diversity wavefront sensor is also made. The simulation results show that the diffraction grating phase diversity wavefront sensor can obviously improve the ability to measure the wavefront aberration, especially the wavefront aberration with larger amplitude and higher spatial frequency.展开更多
A method for extending dynamic range of phase diversity （PD） is proposed.The estimating of pupil phase is divided into two steps.Low-order Zernike coefficients of the phase are estimated firstly before all of the Ze...A method for extending dynamic range of phase diversity （PD） is proposed.The estimating of pupil phase is divided into two steps.Low-order Zernike coefficients of the phase are estimated firstly before all of the Zernike coefficients estimated.The method is based on the assumption that the aberrations of the system are dominated by low order Zernike modes,which is true to most practical situations.The algorithm of BroydenFletcher-Goldfarb-Shanno（BFGS） is used in the two steps for optimizing process.Computer simulations are conducted after the theoretical analysis.The result shows that this method can effectively avoid the trap in local minimum during iteration process,and the dynamic range that PD can detect extends from about 2λ to about 4λ.展开更多
Based on the analysis of the hydrocarbon geochemical characteristics in the Kuqa petroleum system of the Tarim Basin, this study discusses the causes and controlling factors of the phase diversities and their differen...Based on the analysis of the hydrocarbon geochemical characteristics in the Kuqa petroleum system of the Tarim Basin, this study discusses the causes and controlling factors of the phase diversities and their differences in geochemical features. According to the characteristics and differences in oil and gas phase, the petroleum system can be divided into five categories： oil reservoir, wet gas reservoir, condensate gas-rich reservoir, condensate gas-poor reservoir and dry gas reservoir. The causes for the diversities in oil and gas phases include diversities of the sources of parent material, maturity of natural gas and the process of hydrocarbon accumulation of different hydrocarbon phases. On the whole, the Jurassic and Triassic terrestrial source rocks are the main sources for the hydrocarbon in the Kuqa Depression. The small differences in parent material may cause diversities in oil and gas amount, but the impact is small. The differences in oil and gas phase are mainly affected by maturity and the accumulation process, which closely relates with each other. Oil and gas at different thermal evolution stage can be captured in different accumulation process.展开更多
The research in Coherent Optical Fiber Communication Systems (COFCS) using long waveband semiconductor laser diodes as transmitter and local oscillator has evolved gradually from an esteric subject studied in just a ...The research in Coherent Optical Fiber Communication Systems (COFCS) using long waveband semiconductor laser diodes as transmitter and local oscillator has evolved gradually from an esteric subject studied in just a few communication laboratories around the world to the field demonstration stage. This is mainly because of the possibility of receiver sensitivity improvement reaching 10～20 dB, that of frequency division multiplexing (FDM) with very fine frequency separation and the possibility of using electronic equalization network to compensate for the effect of optical pulse dispersion in the Single Mode Fiber (SMF). The author of the dissertation has engaged in the study on COFCSs since 1987. Undergoing 3 years of hard work, the finished research work includes two parts: Part I is the study on heterodyne COFCSs and their key components; Part II is the study on two branch phase diversity COFCS and its components. In the first part, using the Lamb′s semi classical theory and the model of vector field, the effects of various kinds of parameters, such as cavity detuning, cavity′s Q factor and the transverse magnetic field strength, on the intramode beat frequency tuning characteristics are analyzed. On the basis of the theoretical analysis, the equipment of 1 523 nm He Ne Stabilized Transverse Zeeman Lasee (STZL) with high frequency stability and certain continuous single frequency tuning range, has been established domestically for the first time. With the development of long waveband semi conductor laser diodes fabricated domestically, the author mainly deals with the long waveband COFCSs using semiconductor laser diodes as transmitter and local oscillator. To counter the poor spectrum characteristics of the conventional double heterojunction semi conductor laser diodes, the characteristics of 1.5 um InGaAsP GRINROD External Cavity Semi conductor Lasers (ECSL) in the case of strong and weak feedback conditions, is experimentally studied. Then the GRINROD Dissertation completed Apr.1991ECSLs with complete closed and compact structure are developed. Using this kind of lasers and other components made domestically, the long waveband large deviation FSK heterodyne single filter/ envelope detection systems and small deviation FSK heterodyne single filter/delay line frequency discriminator detection system are achieved for the first time. In those experiments, the frequency modulation characteristics, line width, single frequency continuous tuning range and frequency stability of the GRINROD ECSL are measured by means of IF spectrum. Meanwhile, the IF receiving circuits are optimized for obtaining stable transmission properties. The main research achievements in part II are the theoretical analysis of the diversity COFCSs. Firstly, the Bit Error Rate (BER) performance of two branch homodyne phase diversity ASK, DPSK and two branch homodyne phase polarization DPSK receivers are analyzed by means of characteristic function model. In the analysis, the effects of pre and post detection filters on the system performance are especially studied. Secondly, the impacts of the phase noise, shot noise, polarization mismatch and imbalance of branch circuits on the two branch homodyne phase diversity ASK receiver, and that of modulation frequency deviation on FSK receiver are analyzed in terms of Gaussian approximation. Lastly, an improved all fiber 90 degree optical hybrid is fabricated. Utilizing the hybrid and 1.5 um InGaAsP GRINROD and grating ECSLs, a low IF, two branch phase diversity FSK coherent optical fiber transmission system is experimented for the first time in China. Guan Kejian Born in Jan. 1963. He received his Ph. D degree in Apr. 1991, in Radio Engineering, Beijing Uni versity of Posts and Telecommunications.展开更多
The UWA channel is characterized as a time-dispersive rapidly fading channel, which in addition exhibits Doppler instabilities and limited bandwidth. To eliminate inter- symbol interference caused by multipath propaga...The UWA channel is characterized as a time-dispersive rapidly fading channel, which in addition exhibits Doppler instabilities and limited bandwidth. To eliminate inter- symbol interference caused by multipath propagation, spatial diversity equalization is the main technical means. The paper combines the passive phase conjugation and spatial processing to maximize the output array gain. It uses signal-to-noise-plus-interference to evaluate the quality of signals received at different channels. The amplitude of signal is weighted using Sigmoid function. Second order PLL can trace the phase variation caused by channel, so the signal can be accumulated in the same phase. The signals received at different channels need to be normal- ized. It adopts fractional-decision feedback diversity equalizer （FDFDE） and achieves diversity equalization by using different channel weighted coefficients. The simulation and lake trial data processing results show that, the optimized diversity receiving equalization algorithm can im- prove communication system＇s ability in tracking the change of underwater acoustic channel, offset the impact of multipath and noise and improve the performance of communication system. The performance of the communication receiving system is better than that of the equal gain combination. At the same time, the bit error rate （BER） reduces 1.8%.展开更多
文摘The phase diversity wavefront sensor is one of the tools used to estimate wavefront aberration, and it is often used as a wavefront sensor in adaptive optics systems. However, the performance of the traditional phase diversity wavefront sensor is limited by the accuracy and dynamic ranges of the intensity distribution at the focus and defocus positions of the CCD camera. In this paper, a modified phase diversity wavefront sensor based on a diffraction grating is proposed to improve the ability to measure the wavefront aberration with larger amplitude and higher spatial frequency. The basic principle and the optics construction of the proposed method are also described in detail. The noise propagation property of the proposed method is also analysed by using the numerical simulation method, and comparison between the diffraction grating phase diversity wavefront sensor and the traditional phase diversity wavefront sensor is also made. The simulation results show that the diffraction grating phase diversity wavefront sensor can obviously improve the ability to measure the wavefront aberration, especially the wavefront aberration with larger amplitude and higher spatial frequency.
基金Sponsored by the Ministerial Level Advanced Research Foundation (613290203)
文摘A method for extending dynamic range of phase diversity （PD） is proposed.The estimating of pupil phase is divided into two steps.Low-order Zernike coefficients of the phase are estimated firstly before all of the Zernike coefficients estimated.The method is based on the assumption that the aberrations of the system are dominated by low order Zernike modes,which is true to most practical situations.The algorithm of BroydenFletcher-Goldfarb-Shanno（BFGS） is used in the two steps for optimizing process.Computer simulations are conducted after the theoretical analysis.The result shows that this method can effectively avoid the trap in local minimum during iteration process,and the dynamic range that PD can detect extends from about 2λ to about 4λ.
基金supported by the Tarim Oil Field Research InstituteNational Natural Science Foundation (sanctified number:40602016)National Key Basic Research and Development Projects (Itemnumber:113404GJ0003)
文摘Based on the analysis of the hydrocarbon geochemical characteristics in the Kuqa petroleum system of the Tarim Basin, this study discusses the causes and controlling factors of the phase diversities and their differences in geochemical features. According to the characteristics and differences in oil and gas phase, the petroleum system can be divided into five categories： oil reservoir, wet gas reservoir, condensate gas-rich reservoir, condensate gas-poor reservoir and dry gas reservoir. The causes for the diversities in oil and gas phases include diversities of the sources of parent material, maturity of natural gas and the process of hydrocarbon accumulation of different hydrocarbon phases. On the whole, the Jurassic and Triassic terrestrial source rocks are the main sources for the hydrocarbon in the Kuqa Depression. The small differences in parent material may cause diversities in oil and gas amount, but the impact is small. The differences in oil and gas phase are mainly affected by maturity and the accumulation process, which closely relates with each other. Oil and gas at different thermal evolution stage can be captured in different accumulation process.
文摘The research in Coherent Optical Fiber Communication Systems (COFCS) using long waveband semiconductor laser diodes as transmitter and local oscillator has evolved gradually from an esteric subject studied in just a few communication laboratories around the world to the field demonstration stage. This is mainly because of the possibility of receiver sensitivity improvement reaching 10～20 dB, that of frequency division multiplexing (FDM) with very fine frequency separation and the possibility of using electronic equalization network to compensate for the effect of optical pulse dispersion in the Single Mode Fiber (SMF). The author of the dissertation has engaged in the study on COFCSs since 1987. Undergoing 3 years of hard work, the finished research work includes two parts: Part I is the study on heterodyne COFCSs and their key components; Part II is the study on two branch phase diversity COFCS and its components. In the first part, using the Lamb′s semi classical theory and the model of vector field, the effects of various kinds of parameters, such as cavity detuning, cavity′s Q factor and the transverse magnetic field strength, on the intramode beat frequency tuning characteristics are analyzed. On the basis of the theoretical analysis, the equipment of 1 523 nm He Ne Stabilized Transverse Zeeman Lasee (STZL) with high frequency stability and certain continuous single frequency tuning range, has been established domestically for the first time. With the development of long waveband semi conductor laser diodes fabricated domestically, the author mainly deals with the long waveband COFCSs using semiconductor laser diodes as transmitter and local oscillator. To counter the poor spectrum characteristics of the conventional double heterojunction semi conductor laser diodes, the characteristics of 1.5 um InGaAsP GRINROD External Cavity Semi conductor Lasers (ECSL) in the case of strong and weak feedback conditions, is experimentally studied. Then the GRINROD Dissertation completed Apr.1991ECSLs with complete closed and compact structure are developed. Using this kind of lasers and other components made domestically, the long waveband large deviation FSK heterodyne single filter/ envelope detection systems and small deviation FSK heterodyne single filter/delay line frequency discriminator detection system are achieved for the first time. In those experiments, the frequency modulation characteristics, line width, single frequency continuous tuning range and frequency stability of the GRINROD ECSL are measured by means of IF spectrum. Meanwhile, the IF receiving circuits are optimized for obtaining stable transmission properties. The main research achievements in part II are the theoretical analysis of the diversity COFCSs. Firstly, the Bit Error Rate (BER) performance of two branch homodyne phase diversity ASK, DPSK and two branch homodyne phase polarization DPSK receivers are analyzed by means of characteristic function model. In the analysis, the effects of pre and post detection filters on the system performance are especially studied. Secondly, the impacts of the phase noise, shot noise, polarization mismatch and imbalance of branch circuits on the two branch homodyne phase diversity ASK receiver, and that of modulation frequency deviation on FSK receiver are analyzed in terms of Gaussian approximation. Lastly, an improved all fiber 90 degree optical hybrid is fabricated. Utilizing the hybrid and 1.5 um InGaAsP GRINROD and grating ECSLs, a low IF, two branch phase diversity FSK coherent optical fiber transmission system is experimented for the first time in China. Guan Kejian Born in Jan. 1963. He received his Ph. D degree in Apr. 1991, in Radio Engineering, Beijing Uni versity of Posts and Telecommunications.
基金supported by National Natural Science Foundation of China(61531018)
文摘The UWA channel is characterized as a time-dispersive rapidly fading channel, which in addition exhibits Doppler instabilities and limited bandwidth. To eliminate inter- symbol interference caused by multipath propagation, spatial diversity equalization is the main technical means. The paper combines the passive phase conjugation and spatial processing to maximize the output array gain. It uses signal-to-noise-plus-interference to evaluate the quality of signals received at different channels. The amplitude of signal is weighted using Sigmoid function. Second order PLL can trace the phase variation caused by channel, so the signal can be accumulated in the same phase. The signals received at different channels need to be normal- ized. It adopts fractional-decision feedback diversity equalizer （FDFDE） and achieves diversity equalization by using different channel weighted coefficients. The simulation and lake trial data processing results show that, the optimized diversity receiving equalization algorithm can im- prove communication system＇s ability in tracking the change of underwater acoustic channel, offset the impact of multipath and noise and improve the performance of communication system. The performance of the communication receiving system is better than that of the equal gain combination. At the same time, the bit error rate （BER） reduces 1.8%.
