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

We propose a method for optimizing the phase stability of microwave signal transmission over long distances.First,the design of the photon link was modified to reduce the radio frequency （RF） signal's baseline noise and increase power.Second,a low-noise driver circuit was developed for a two-section distributed feedback （DFB） laser designed using reconstruction equivalent chirp （REC） technology to create an ultra-stable laser,and its performance was characterized through linewidth data.Test results indicate that the DFB laser achieved narrower linewidth,improving system phase stability.When an injection current （30 mA） is applied to the reflection section of the two-section DFB laser,the laser linewidth will be narrower （1.38 MHz）,further enhancing the system's phase transmission stability.At a 1 Hz offset frequency,a residual phase noise of -88.65 dBc/Hz is obtained.The short-term stability with an averaging time of 1s is 1.60×10-14,and the long-term stability over a testing time of 60,000s is 3.41×10-18.Even after incorporating temperature variations,the long-term stability reaches 8.37×10-18 at 22 h.