Long-term ultrastable frequency dissemination via a 50-km spooled fiber link using a two-section DFB laser

Abstract

The stable long-distance transmission of radio-frequency (RF) signals holds significant importance from various aspects, including the comparison of optical frequency standards, remote monitoring and control, scientific research and experiments, and RF spectrum management. We demonstrate a scheme where an ultrastable frequency signal was transmitted over a 50 km coiled fiber. The optical RF signal is generated using a two-section distributed feedback (DFB) laser for direct modulation based on the reconstruction equivalent chirp (REC) technique. The 3-dB modulation bandwidth of the two-section DFB laser is 18 GHz and the residual phase noise of −122.87 dBc=Hz is achieved at 10-Hz offset frequency. We report a short-term stability of 1.62 × 10 −14 at an average time of 1 s and a long-term stability of 6.55 × 10 −18 at the measurement time of 62,000 s when applying current to the front section of the DFB laser. By applying power to both sections, the stability of the system improves to 4.42 × 10 −18 within a testing period of 56,737 s. Despite applying temperature variations to the transmission link, long-term stability of 8.63 × 10 −18 at 23.9 h can still be achieved.

Stability-enhanced RF signal transmission over long fiber-optic links

“…Figure 3(a) illustrates the phase fluctuations of the transmission system under different conditions. The method for calculating phase fluctuations has been extensively described in previous articles [19] . The black line represents the signal's phase fluctuation during free transmission over a 50 km link, exhibiting a delay variation of about 280 ps over a testing time of 60,000 s. In contrast, the red line indicates the phase jitter of the signal after compensation by the system, with a delay variation of only 0.97 ps over the same 60,000 s testing time.…”

“…As shown in Fig. 1(a), the schematic diagram of the phase stability transmission system is nearly identical to the previous transmission system in terms of instrument arrangement [19] . In this paper, two modifications and optimizations were primarily carried out to reduce the optical power loss in the link and the effects of Brillouin scattering and backward Rayleigh scattering on system stability.…”