Experimental study on optical frequency transfer via communication fibers

Along with the rapid development of the optical clocks, optical frequency transfer via communication fibers has shown much higher precision than the conventional methods. In this paper, we report the progress on the optical frequency transfer via communication fibers at NTSC. Over a 71-km spooled fiber, the optical frequency transfer with a residual instability (Allan deviation) of 5.4E-15 at 1s and 5.6E-18 at 10⁴s is demonstrated. Furthermore, for a measurement bandwidth of 100 Hz, the instability is 1.2E-15 at one second and 1.4E-18 at 10⁴ s. This transfer instability is fundamentally limited by the fiber length. The Allan deviation curves fall as τ^-1 for short times, which is consistent with the fact that the transferred signal is dominated by white phase noise. This experimental achievement provides the foundation for the upcoming optical transfer experiment over a 300-km urban communication fiber link.