Long-Haul High Precision Frequency Dissemination Based on Dispersion Correction

Long-distance and high-precision fiber microwave frequency transmission

“…In the optical fiber microwave transmission system of several hundred kilometers to one thousand kilometers, the main limitation is the loss of the optical fiber link, the optical fiber dispersion and the loop lock bandwidth. Therefore, in the study of long-distance fiber microwave frequency transmission scheme, there are mainly three methods: First, multiple optical amplifiers are used to amplify the optical signal to increase the transmission distance [7][8][9] . In order to further reduce the optical power loss, Tsinghua University [9] uses Bragg grating instead of negative dispersion compensation fiber, which reduces the power loss caused by dispersion compensation fiber, but increases the optical path asymmetry.…”

“…Therefore, in the study of long-distance fiber microwave frequency transmission scheme, there are mainly three methods: First, multiple optical amplifiers are used to amplify the optical signal to increase the transmission distance [7][8][9] . In order to further reduce the optical power loss, Tsinghua University [9] uses Bragg grating instead of negative dispersion compensation fiber, which reduces the power loss caused by dispersion compensation fiber, but increases the optical path asymmetry. The second is to realize long-distance transmission of optical fiber microwave frequency by cascading single-stage devices, such as cascade transmission of the National timing Center at 212km [10] .…”

Microwave Frequency Dissemination over a 250 km Fiber Link with Stability at the 10−18 Level

“…In 2021, the Beijing University of Posts and Telecommunications conducted a 1007 km microwave phase compensation experiment, achieving transmission stability of 8.2 × 10 −14 at 1 s and 7.78 × 10 −17 at 10,000 s [16]. In 2022, Tsinghua University performed on-site fiber optic link experiments over a distance of 300 km, with transmission stabilities of 2.2 × 10 −14 at 1 s and 2.6 × 10 −17 at one day, and laboratory fiber optic reel experiments over a distance of 500 km, with transfer stabilities of 1.7 × 10 −14 at 1 s and 6.7 × 10 −18 at 100,000 s [17]. In 2022, the National Time Service Center (NTSC) achieved 212 km optical fiber microwave frequency transmission by cascading method and achieved a microwave frequency transmission stability of 6.2 × 10 −15 at 1 s and 6.4 × 10 −18 at 40,000 s through the on-site link from Lintong site and Chang'an site (both in Xi'an) [18].…”

“…There are three main methods to study the scheme of long-distance optical fiber microwave frequency transmission: first, multiple optical amplifiers are used to amplify the optical signal to increase the transmission distance, such as Beijing University of Posts and Telecommunications [16] and Tsinghua University [17]. In order to further reduce the loss of optical power, Tsinghua University uses Bragg grating instead of negative dispersion compensation fiber to reduce the power loss caused by dispersion compensation fiber.…”

Remote Residual Instability Evaluation of Comb-Based Precise Frequency Transmission for Optical Clock

“…Conventional proposals to assess instability loss often use the local oscillator as the reference to compare with the recovered frequency signal directly at the remote site. This scheme, shown in Figure 1a, is only applicable to transmission demonstrations where the local end and remote end are located at the same place in the laboratory [10][11][12][13][14]. It is not feasible for an actual transfer system, because the local site and the remote site are usually in different locations, even hundreds of kilometers apart.…”