Researchers complete high-precision time-frequency scattering

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Professor PAN Jianwei and colleagues at the China University of Science and Technology of the Chinese Academy of Sciences studied the high-precision time-frequency scattering experiment in high-loss free space between remote sites, simulating the high precision time-frequency. – satellite-ground links in orbit in the effects of channel loss, atmospheric noise and transmission delay.

This link experiment shows that the instability of time-to-frequency transfer via a satellite in medium-high Earth orbits could reach E-18 at 10,000 s, allowing the potential performance of optical atomic clocks and intercontinental comparison of clocks on the ground. The study was published in the journal Optica.

High precision diffusion and time-frequency comparison techniques apply to all types of large-scale precision measuring systems. Currently, the systems of international metrology standards are at the stage of quantification. The frequency standard is at the heart of precision measurement systems and international metrology. Other basic physical quantities, with the exception of the amount of matter (mol), are directly or indirectly related to frequency. On the other hand, new optical frequency standard technologies are developing rapidly, the accuracy of which is two orders of magnitude better than that of the original “second” definition frequency standard.

The most important part of the technical roadmap for changing the “second” definition is to fix the intercontinental time-frequency comparison with the optical frequency standard at the E-18 level. Having high precision ultra-long distance time-to-frequency comparison or broadcast is an unresolved problem, while satellite-to-ground linkage is recognized as the most feasible solution.

In this study, the researchers used a double-comb linear optical sampling time measurement method. Compared with continuous wave or single photon binding method, this complex binding has the advantage of high temporal resolution and large ambiguous range.

The researchers first comprehensively analyzed parameters such as loss of satellite-to-ground link, Doppler effect, link-time asymmetry and atmospheric noise, and found that high-orbit links allow comparison or a more stable time-frequency scattering by taking advantage of the long duration, a wide range of common view, and the lower relativistic effects.

Next, they performed a high orbit satellite-to-ground time-frequency transmission experiment to simulate links with the effects of link loss, atmospheric noise, and delay.

Using low noise optical comb amplification, low loss and high stability double comb interference optical path, and high precision high sensitivity linear sampling, the researchers built a horizontal atmospheric free space. of 16 kilometers and a high precision double comb time. -Frequency transmission link in Shanghai. The frequency transmission link achieved an instability of 4E-18 at 3000 s with an average loss of 72 dB and a link delay of 1 s.

Based on these results, they expected the instability of time-to-frequency transfer over a high-orbit satellite-to-ground link to reach 10-18 at 10,000 s.

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