Studying the Double Rayleigh Backscattering Noise Effect on Fiber-Optic Radio Frequency Transfer

Abstract

We report the effect of the double Rayleigh backscattering (DRB) noise, in which the interference of the signal light with the double Rayleigh backscattered light, on the fiber-optic radiofrequency (RF) transfer system. Here, we theoretically analyze and experimentally demonstrate that the DRB noise within the fiber link will become the dominative noise on the fiber-optic RF transfer system once narrow linewidth lasers are used. The strong DRB noise is experimentally confirmed through the measurement of the effect of the coherent interference term of the signal light and the double Rayleigh backscattered light on the 100 km RF transfer system. Our results provide evidence that the conventional RF transfer technique with the telecommunications-grade lasers, in which the chromatic dispersion effect in the single-mode fiber is compensated by dispersion compensation fibers (DCFs), could be the better choice for high-performance RF transfer.

Fiber Radio Frequency Transfer Using Bidirectional Frequency Division Multiplexing Dissemination

“…In the range of 0.002 − 0.1 Hz, the 120 km proposed compensated link is almost consistent with the system noise floor, which indicates that the phase noise in this low frequency range induced by the fiber-optic link can be effectively suppressed. Compared with the 120 km compensated scheme with the backscattering noise (about -116 dBc at 0.1 Hz, -121 dBc at 1 Hz), the phase noise of the 120 km proposed scheme is significantly lower within 0.1 − 100 Hz, demonstrating that the backscattering noise induced by the optical reflections including connectors and the Rayleigh backscattering has a significant effect on the system performance [19]. All the measurements have the sharp bump in the range of 0.001 − 0.003 Hz, which are mainly affected by the outside loop phase noise induced by the temperature fluctuations.…”

“…At the LS, the frequency standard (Rigol Inc., DSG 830) with ω r0 = 100 MHz is multiplied to ω r1 = 1 GHz and ω r2 = 200 MHz by the PDROs. The LS and the RS are connected by 120 km SMFs (consisting of 10, 30, 50, 30 km single-mode fiber spools), placed in a normal laboratory with the peak-to-peak temperature fluctuations about 3 • C [19], [20]. To suppress the impact of the chromatic dispersion, the proper dispersion compensating fibers (DCFs) are used [19], [20].…”

“…The LS and the RS are connected by 120 km SMFs (consisting of 10, 30, 50, 30 km single-mode fiber spools), placed in a normal laboratory with the peak-to-peak temperature fluctuations about 3 • C [19], [20]. To suppress the impact of the chromatic dispersion, the proper dispersion compensating fibers (DCFs) are used [19], [20]. We set the wavelengths of the CWLs with the 0.4 nm difference at the both sites around 1550 nm.…”

“…The phase noise of all compensated configurations has a bump observed at about 200 Hz. This part noise is mainly determined by the PLL parameters, the phase noise of the RF signal and the propagation delay from the fiber [19]. At the high frequency range (> 10 3 Hz), the ripples with the same period can be observed in different transfer configurations under the 120 km fiber link, which are mainly caused by delayed self-interferometry [22].…”

Synchronized Laser Modules With Frequency Offset up to 50 GHz for Ultra-Accurate Long-Distance Fiber Optic Time Transfer Links

“…Such small offsets are, however, useful only in case of short links, not exceeding some 40 to 50 kilometers [23], unless sophisticated laser switching techniques are involved [26]. This is because of Rayleigh backscattering, which causes a substantial level of intensity noise [31]. To mitigate this problem optical filters are necessary, which are in practice available at reasonable cost only for the frequencies defined by the International Telecommunications Union (ITU) in Recommendation G.694.1 for DWDM networks.…”