We present a fully stabilized Yb-fiber frequency comb locked to a microwave standard and an optical reference separately. The carrier-envelope offset frequency is generated by a standard f–2f interferometer with 40 d...We present a fully stabilized Yb-fiber frequency comb locked to a microwave standard and an optical reference separately. The carrier-envelope offset frequency is generated by a standard f–2f interferometer with 40 dB signal-tonoise ratio. The offset frequency and the repetition rate are stabilized simultaneously to the radio frequency reference for more than 30 hours, and the fractional Allan deviation of the comb is the same as the microwave standard of 10^(-12) at 1 s.Alternatively, the comb is locked to an ultra-stable optical reference at 972 nm using an intracavity electro-optic modulator,exhibiting a residual integrated phase noise of 458 mrad(1 Hz–10 MHz) and an in-loop tracking stability of 1.77× 10^(-18) at 1 s, which is significantly raised by six orders comparing to the case locked to the microwave frequency standard.展开更多
光纤通信具有容量大、距离远、抗干扰能力强等优点,是实现高速率、大容量信息传输的技术。低密度奇偶校验(Low Density Parity Check,LDPC)码由于具有良好的纠错性能,可以有效提升光纤通信系统的传输可靠性。为进一步提升该方法的健壮性...光纤通信具有容量大、距离远、抗干扰能力强等优点,是实现高速率、大容量信息传输的技术。低密度奇偶校验(Low Density Parity Check,LDPC)码由于具有良好的纠错性能,可以有效提升光纤通信系统的传输可靠性。为进一步提升该方法的健壮性,文章研究LDPC码的优化设计方法。先深入探讨LDPC码的基本原理及其在光纤通信中的应用,接着提出一种基于密度进化和有限字长效应分析的LDPC码优化方法,并通过光学特性仿真OptSim工具进行了验证。实验结果表明,优化后的LDPC码在不同码长下的误码率均取得了显著降低,特别是在长码字情况下,其纠错性能显著提升。展开更多
Deep rock mass has the unique ＂self-stressed＂ block-hierarchical structure, anomalous low friction （ALF） was one of the typical nonlinear get-mechanical and dynamic responses in deep block rock mass, which occurre...Deep rock mass has the unique ＂self-stressed＂ block-hierarchical structure, anomalous low friction （ALF） was one of the typical nonlinear get-mechanical and dynamic responses in deep block rock mass, which occurred as the result of movements of large-scale get-blocks under the impact of external pulses （such as a deep confined explosion, earthquakes, rock bursts and etc.）. ALF phenomenon obtained its name to describe the curious phenomenon that the friction between interacting get-blocks qua- si-periodically disappears at some discrete points in time along the direction orthogonal to the direction of the external pulse. With the objective to confirm the existence of the ALF phenomenon and study the get-mechanical conditions for its occurrence experi- mentally and theoretically, laboratory tests on granite and cement mortar block models were carried out on a multipurpose testing system developed independently. The ALF phenomenon was realized under two loading schemes, i.e., blocks model and a working block were acted upon jointly by the action of a vertical impact and a horizontal static force, as well as the joint action of both ver- tical and horizontal impacts with differently delayed time intervals. We obtained the rules on variation of horizontal displacements of working blocks when the ALF phenomenon was realized in two tests. The discrete time delay intervals, corresponding to local maxima and minima of the horizontal displacement amplitudes and residual horizontal displacements of the working block, satis- fied canonical sequences multiplied by （√2）＇. Some of these time intervals satisfied the quantitative expression （√2）＇ ,alva. At last, 1D dynamic theoretical model was established, the analytical results agreed better with the test data, while the quantitative expression drawn from test data was not validated well in theoretical analyses.展开更多
The creep properties of optical fiber used in fiber optical sensors were studied in this paper. A low co- herent white light double interferometer system was designed and calibrated and the creep deforma- tions of opt...The creep properties of optical fiber used in fiber optical sensors were studied in this paper. A low co- herent white light double interferometer system was designed and calibrated and the creep deforma- tions of optical fibers under static and cyclic loadings were measured with this device. The research results showed that polymer coated optical fibers crept at the beginning when they were under static or cyclic load. As the number of the cyclic loading or the static loading times increased the creep tended to stop. Thus to ensure that the optical fiber keeps pre-stress for long time in pressure transducer, it is recommended that the optical fiber should be tensioned cyclically before being fixed into the sensor device.展开更多
基金Project supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDA1502040404 and XDB21010400)the National Natural Science Foundation of China(Grant Nos.91850209 and 11774234)。
文摘We present a fully stabilized Yb-fiber frequency comb locked to a microwave standard and an optical reference separately. The carrier-envelope offset frequency is generated by a standard f–2f interferometer with 40 dB signal-tonoise ratio. The offset frequency and the repetition rate are stabilized simultaneously to the radio frequency reference for more than 30 hours, and the fractional Allan deviation of the comb is the same as the microwave standard of 10^(-12) at 1 s.Alternatively, the comb is locked to an ultra-stable optical reference at 972 nm using an intracavity electro-optic modulator,exhibiting a residual integrated phase noise of 458 mrad(1 Hz–10 MHz) and an in-loop tracking stability of 1.77× 10^(-18) at 1 s, which is significantly raised by six orders comparing to the case locked to the microwave frequency standard.
文摘光纤通信具有容量大、距离远、抗干扰能力强等优点,是实现高速率、大容量信息传输的技术。低密度奇偶校验(Low Density Parity Check,LDPC)码由于具有良好的纠错性能,可以有效提升光纤通信系统的传输可靠性。为进一步提升该方法的健壮性,文章研究LDPC码的优化设计方法。先深入探讨LDPC码的基本原理及其在光纤通信中的应用,接着提出一种基于密度进化和有限字长效应分析的LDPC码优化方法,并通过光学特性仿真OptSim工具进行了验证。实验结果表明,优化后的LDPC码在不同码长下的误码率均取得了显著降低,特别是在长码字情况下,其纠错性能显著提升。
基金Projects 50525825 and 90815010 supported by the National Natural Science Foundation of China2009CB724608 by the National Basic Research Program of ChinaBK2008002 by the Natural Science Foundation of Jiangsu Province
文摘Deep rock mass has the unique ＂self-stressed＂ block-hierarchical structure, anomalous low friction （ALF） was one of the typical nonlinear get-mechanical and dynamic responses in deep block rock mass, which occurred as the result of movements of large-scale get-blocks under the impact of external pulses （such as a deep confined explosion, earthquakes, rock bursts and etc.）. ALF phenomenon obtained its name to describe the curious phenomenon that the friction between interacting get-blocks qua- si-periodically disappears at some discrete points in time along the direction orthogonal to the direction of the external pulse. With the objective to confirm the existence of the ALF phenomenon and study the get-mechanical conditions for its occurrence experi- mentally and theoretically, laboratory tests on granite and cement mortar block models were carried out on a multipurpose testing system developed independently. The ALF phenomenon was realized under two loading schemes, i.e., blocks model and a working block were acted upon jointly by the action of a vertical impact and a horizontal static force, as well as the joint action of both ver- tical and horizontal impacts with differently delayed time intervals. We obtained the rules on variation of horizontal displacements of working blocks when the ALF phenomenon was realized in two tests. The discrete time delay intervals, corresponding to local maxima and minima of the horizontal displacement amplitudes and residual horizontal displacements of the working block, satis- fied canonical sequences multiplied by （√2）＇. Some of these time intervals satisfied the quantitative expression （√2）＇ ,alva. At last, 1D dynamic theoretical model was established, the analytical results agreed better with the test data, while the quantitative expression drawn from test data was not validated well in theoretical analyses.
文摘The creep properties of optical fiber used in fiber optical sensors were studied in this paper. A low co- herent white light double interferometer system was designed and calibrated and the creep deforma- tions of optical fibers under static and cyclic loadings were measured with this device. The research results showed that polymer coated optical fibers crept at the beginning when they were under static or cyclic load. As the number of the cyclic loading or the static loading times increased the creep tended to stop. Thus to ensure that the optical fiber keeps pre-stress for long time in pressure transducer, it is recommended that the optical fiber should be tensioned cyclically before being fixed into the sensor device.
