J. Miao

Fiber-based multiple-access ultrastable frequency dissemination

We demonstrate a fiber-based multiple-access ultrastable frequency dissemination scheme over an 83 km fiber link. As a performance test, we reproduce the disseminated 9.1 GHz radio-frequency modulation signal at an arbitrary point in the dissemination channel. Relative frequency stability of 7×10(-14)/s and 5×10(-18)/day is obtained. Highly synchronized frequency signals can be regenerated along the entire fiber pathway and its applications are discussed.

Fiber-based multiple-access optical frequency dissemination.

We demonstrate a fiber-based, multiple-access optical frequency dissemination scheme. Without using any additional laser sources, we reproduce the stable disseminated frequency at an arbitrary point along the fiber link. Relative frequency stabilities of 3×10(-16)/s and 4×10(-18)/10(4) s are obtained. A branching fiber network for high-precision synchronization of optical frequency is made possible by this method, and its applications are discussed.

Ultra-stable radio frequency dissemination in free space

We demonstrate an ultra-stable radio frequency (RF) dissemination scheme over 80 m free space. The frequency dissemination stability is 3.2 × 10(-13)/s and 4.4 × 10(-17)/day, which can be applied to transfer frequency signal without compromising its stability in a global navigation satellite system (GNSS) or radio astronomy.

Fiber-based time and frequency dissemination between THU and NIM

We build up a time and frequency dissemination system via the 80 km urban telecommunication fiber network between Tsinghua university (THU) and the National Institute of Metrology (NIM). A 9.1 GHz microwave frequency is disseminated on this link. Using the proposed phase noise compensation method, the frequency dissemination stability on the order of 7 × 10-15/s and 4.5 × 10-19/105 s has been demonstrated. In addition, we also disseminate the timing signal between THU and NIM. Using the delay time compensation method, transfer delay stability within 50 ps at measurement periods from 1s to 1000s has been demonstrated.

The three corner hat measurement of three hydrogen masers in remote locations via fiber based frequency synchronization network

As the first step of Beijing regional time and frequency network, Currently, Tsinghua University (THU) and the Changping site of National Institute of Metrology (NIM-Changping) have been linked and synchronized via the fiber network. The frequency stability of the hydrogen maser in NIM and the ultra-stable crystal oscillator steered by a cesium atomic clock in THU was measured. More atomic clocks from the Beijing Institute of Radio Metrology and Measurements, Hepingli site of NIM and Peking University (PKU) will join the synchronization network soon, with these clocks we can get the stability of each clock though three-corner-hat method.

Portable microwave frequency dissemination in free space and implications on ground-to-satellite synchronization

Frequency dissemination and synchronization in free space play an important role in global navigation satellite system, radio astronomy, and synthetic aperture radar. In this paper, we demonstrated a portable radio frequency dissemination scheme via free space using microwave antennas. The setup has a good environment adaptability and high dissemination stability. The frequency signal was disseminated at different distances ranging from 10 to 640 m with a fixed 10 Hz locking bandwidth, and the scaling law of dissemination stability on distance and averaging time was discussed. The preliminary extrapolation shows that the dissemination stability may reach 1 × 10(-12)/s in ground-to-satellite synchronization, which far exceeds all present methods, and is worthy for further study.

Fiber-based multiple-access ultrastable radio and optical frequency dissemination

We demonstrate a fiber-based multiple-access ultrastable frequency dissemination scheme for both radio frequency modulated on the optical carrier and optical frequency. Relative frequency stabilities of 7 × 10^-14/s and 5 × 10^-18/day for radio frequency, 3 × 10^-16/s and 4 × 10^-18/10⁴s for optical frequency have been obtained, respectively. Using this method, highly synchronized radio-frequency modulation signal or the optical signal itself can be regenerated along the entire fiber link and it is expected to have potential applications.

Progress of the Beijing regional time and frequency network

We report progress of the Beijing regional time and frequency network and a series of innovations used for it, including the fiber based multiple-access RF dissemation system, phase-locked free space RF dissemination system.

Fiber Based Time and Frequency Synchronization System

We build up a time and frequency synchronization system via the 80 km urban fiber link between Tsinghua University and the National Institute of Metrology in Changping city. Using the system, we demonstrate simultaneous time and RF signal distribution via optical fibers. The measured frequency dissemination stability of a 9.1 GHz RF signal is 7 × 10−15/s, 5 × 10−19/day, and the measured time synchronization accuracy is 50 ps. Relevant results were published on the Scientific Reports of Nature Publishing Group. To further build up a regional time and frequency network, integrated-designed modules are needed. Its long term continuous running stability and commonality should be tested. In this paper, we introduce the design of the frequency dissemination modules. After 135 days’ continuously running, we get the million-second frequency dissemination stability of 8 × 10−19/106 s. We also introduce our multiple-access download module, which improves the frequency dissemination scheme from the traditional point to point protocol to be a tree structure protocol, and greatly improves its applicability. Using it, the stability of the receiving frequency signal at arbitrary accessing point is almost 4 orders of magnitude better than that using directly accessing method. All of these modules will be applied to build up the regional time and frequency network.

Progress of ultra-stable frequency dissemination and synchronization in free space

We demonstrate a new ultra-stable frequency dissemination scheme on L band over 100m atmosphere. By compensating phase noise actively and a series of frequency conversions, the phase fluctuation is well compensated. Two links disseminate different frequency signals phase locked to a common reference simultaneously, and recover the disseminated frequency respectively at remote site. The stability of dissemination with phase compensation in free space is 3×10-13/s and 4×10-17/day. The relationship between dissemination stability and propagating distance is also discussed.