Microwave frequency transfer over a 112-km urban fiber link based on electronic phase compensation*

Abstract

We demonstrate the transmission of a microwave frequency signal at 10 GHz over a 112-km urban fiber link based on a novel simple-architecture electronic phase compensation system. The key element of the system is the low noise frequency divider by 4 to differentiate the frequency of the forward signal from that of the backward one, thus suppressing the effect of Brillouin backscattering and parasitic reflection along the link. In terms of overlapping Allan deviation, the frequency transfer instability of 4.2 × 10−15 at 1-s integration time and 1.6 × 10−18 at one-day integration time was achieved. In addition, its sensitivity to the polarization mode dispersion in fiber is analyzed by comparing the results with and without laser polarization scrambling. Generally, with simplicity and robustness, the system can offer great potentials in constructing cascaded frequency transfer system and facilitate the building of fiber-based microwave transfer network.

Cascaded Microwave Frequency Transfer over 300-km Fiber Link with Instability at the 10−18 Level

“…Behind the DCF, a bidirectional erbium-doped fiber amplifier (Bi-EDFA) with a gain of about 10 dB was used to compensate the optical loss caused by the DCF and to improve the SNR at detection. As demonstrated previously [25], the PMD effect has a slight influence on the fiber-based microwave frequency transfer using the EPC approach. Therefore, there was no use of polarization scramblers to average out the PMD effect.…”

“…The performance of each single-span link was urement system prior to the cascaded frequency tran compensated single-span link in terms of overlappi from the propagation delay fluctuations of fiber, as sh compared with previous results over a 112-km urban of electronics package (violet trace) [25]. Figure 6a…”

“…Although the OPC approach can achieve better transfer instability, the compensation actuator, which consists of a piezo-electric fiber stretcher and thermally-controlled fiber spool [31,35], is complex and has small dynamic range, which is inconvenient for extensive applications. On the contrary, the EPC approach has strong adaptability and little PMD fluctuation effect due to the voltage-controlled oscillator (VCO) used as an actuator [25], except that the performance is slightly poorer than that of the OPC approach. Therefore, in order to broaden the application range of the fiber-based microwave frequency transfer system, we adopted the EPC scheme.…”

“…Consequently, frequency transfer over satellite links is insufficient for many application requirements. Fortunately, taking advantage of the low loss, high reliability and active phase stabilization potential of optical fiber, high stability has been demonstrated for direct optical frequency transfer [14][15][16][17] and radio-frequency (RF) transmission using the intensity modulation of an optical carrier [18][19][20][21][22][23][24][25] over fiber links. The instability of fiberbased optical frequency transfer reached the 10 −20 level at 10 4 s over an urban fiber of more than 100 km [16,17], while microwave frequency transfer has presented an instability of 10 −19 level at one day over an urban fiber of about 80 km [19,20].…”

“…The National Time Service Center (NTSC) of the Chinese Academy of Sciences (CAS) undertakes the task to generate, maintain, and transmit the national standard of time (Beijing Time), which has already demonstrated an ultra-stable microwave frequency transfer over a 112-km urban fiber link with an instability of 4.2 × 10 −15 at 1 s and 1.6 × 10 −18 at one day [25]. In this work, to achieve microwave frequency transfer with high precision over a thousand kilometers of fiber and construct fiber-based microwave transfer network, we first used fiber spools to perform a microwave frequency transfer experiment with a cascaded system.…”