RESUMO
The Sagnac effect is an important factor that leads to nonreciprocity in long-haul fiber-optic time and a frequency transfer system. For high-precision time transfer, correction must be performed to eliminate the time difference based on the trajectory of the path. However, the routing information may be not detailed enough to guarantee sufficient precision for Sagnac correction. Thus, nodes along the path must be surveyed with a certain sparsity. We provide a practical method for estimating the average distance of these nodes. Six simulated paths are generated to validate the method for different uncertainties.
RESUMO
In this paper we experimentally demonstrate a transmission delay compensation scheme for precise fiber-optic time transfer. The scheme is based on a clock counter and an electronic variable delay line, which theoretically can provide unlimited compensation range. We perform successive tests in three optical fiber links of different lengths in which both continuous drifts and abrupt hop of the transmission delay are effectively compensated. The total transmission delay variation induced in the experiments is much larger than most of the reported cases. This large-dynamic compensation scheme is quite suitable for time transfer links whose transmission delay varies a lot.
RESUMO
In this paper, we propose and demonstrate a scheme to achieve point-to-multipoint dissemination of radio frequency (RF) signals in a local area fiber optic network with tree topology based on wavelength-division multiplexing (WDM) technique. The phase changes caused by the fluctuations of the transfer links are passively canceled at remote end instead of at local end, which makes it feasible to flexibly build a tree-topology local area dissemination network with great cost-effectiveness. For the first time, we study the limit of long-term performance which is caused by temperature-induced variation of group velocity dispersion (TIVGVD) in dissemination networks using WDM techniques. In the proof-of-concept experiments, 38.5 km and 50 km fiber links are established to disseminate a 1 GHz frequency signal with fractional instability of 10(-17) order after 10(4) s averaging time. Then 17.4 nm wavelength spacing is introduced between local carrier and user carrier to verify the theoretical analysis. Under a controlled fiber temperature variation of about 21 °C, the obtained overlapping Allan deviation (ADEV) agrees well with the simulation results after 10(4) s time scales, which proves the validity of our theory. The theory has practical values in predicting and optimizing the capacity and performance of a WDM-based local area RF dissemination network.
RESUMO
In this Letter, we propose a fiber-based stable radio frequency transfer system by a hybrid frequency modulation scheme. Creatively, two radio frequency signals are combined and simultaneously transferred by only one laser diode. One frequency component is used to detect the phase fluctuation, and the other one is the derivative compensated signal providing a stable frequency for the remote end. A proper ratio of the frequencies of the components is well maintained by parameter m to avoid interference between them. Experimentally, a stable 200 MHz signal is transferred over 100 km optical fiber with the help of a 1 GHz detecting signal, and fractional instability of 2×10(-17) at 10(5) s is achieved.