We demonstrate an atmospheric transfer of microwave signal over a 120 m outdoor free-space link using a compact diode laser with a timing fluctuation suppression technique.Timing fluctuation and Allan Deviation are bo...We demonstrate an atmospheric transfer of microwave signal over a 120 m outdoor free-space link using a compact diode laser with a timing fluctuation suppression technique.Timing fluctuation and Allan Deviation are both measured to characterize the instability of transferred frequency incurred during the transfer process.By transferring a 100 MHz microwave signal within 4500 s,the total root-mean-square(RMS)timing fluctuation was measured to be about 6 ps,with a fractional frequency instability on the order of 1×10-12 at 1 s,and order of 7×10-15 at 1000 s.This portable atmospheric frequency transfer scheme with timing fluctuation suppression can be used to distribute an atomic clock-based frequency over a free-space link.展开更多
Studying orbital angular momentum（OAM） spectra is important for analyzing crosstalk in free-space optical（FSO）communication systems. This work offers a new method of simplifying the expressions for the OAM spectra...Studying orbital angular momentum（OAM） spectra is important for analyzing crosstalk in free-space optical（FSO）communication systems. This work offers a new method of simplifying the expressions for the OAM spectra of Laguerre-Gaussian（LG） beams under both weak/medium and strong atmospheric turbulences. We propose fixing the radius to the extreme point of the intensity distribution, review the expression for the OAM spectrum under weak/medium turbulence,derive the OAM spectrum expression for an LG beam under strong turbulence, and simplify both of them to concise forms.Then, we investigate the accuracy of the simplified expressions through simulations. We find that the simplified expressions permit accurate calculation of the OAM spectrum for large transmitted OAM numbers under any type of turbulence. Finally,we use the simplified expressions to analytically address the broadening of the OAM spectrum caused by atmospheric turbulence. This work should contribute to the concise theoretical derivation of analytical expressions for OAM channel matrices for FSO-OAM communications and the analytical study of the laws governing OAM spectra.展开更多
Comparing the traditional teaching methods with the modem communicative teaching methods in language theory and also in teaching practice, students can learn much better in an encouraging communicative class atmospher...Comparing the traditional teaching methods with the modem communicative teaching methods in language theory and also in teaching practice, students can learn much better in an encouraging communicative class atmosphere. The article analyzes the characteristics of an encouraging communicative class atmosphere and provides some practical methods to achieve it.展开更多
基金supported by ZTE Industry-Academia-Research Cooperation Funds,the National Natural Science Foundation of China under Grant Nos.61871084 and 61601084the National Key Research and Development Program of China under Grant No.2016YFB0502003the State Key Laboratory of Advanced Optical Communication Systems and Networks,China
文摘We demonstrate an atmospheric transfer of microwave signal over a 120 m outdoor free-space link using a compact diode laser with a timing fluctuation suppression technique.Timing fluctuation and Allan Deviation are both measured to characterize the instability of transferred frequency incurred during the transfer process.By transferring a 100 MHz microwave signal within 4500 s,the total root-mean-square(RMS)timing fluctuation was measured to be about 6 ps,with a fractional frequency instability on the order of 1×10-12 at 1 s,and order of 7×10-15 at 1000 s.This portable atmospheric frequency transfer scheme with timing fluctuation suppression can be used to distribute an atomic clock-based frequency over a free-space link.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61575027 and 61471051)
文摘Studying orbital angular momentum（OAM） spectra is important for analyzing crosstalk in free-space optical（FSO）communication systems. This work offers a new method of simplifying the expressions for the OAM spectra of Laguerre-Gaussian（LG） beams under both weak/medium and strong atmospheric turbulences. We propose fixing the radius to the extreme point of the intensity distribution, review the expression for the OAM spectrum under weak/medium turbulence,derive the OAM spectrum expression for an LG beam under strong turbulence, and simplify both of them to concise forms.Then, we investigate the accuracy of the simplified expressions through simulations. We find that the simplified expressions permit accurate calculation of the OAM spectrum for large transmitted OAM numbers under any type of turbulence. Finally,we use the simplified expressions to analytically address the broadening of the OAM spectrum caused by atmospheric turbulence. This work should contribute to the concise theoretical derivation of analytical expressions for OAM channel matrices for FSO-OAM communications and the analytical study of the laws governing OAM spectra.
文摘Comparing the traditional teaching methods with the modem communicative teaching methods in language theory and also in teaching practice, students can learn much better in an encouraging communicative class atmosphere. The article analyzes the characteristics of an encouraging communicative class atmosphere and provides some practical methods to achieve it.
