Frequency stability characterization: DFB laser and Raman pump performance on a distributed clock signal over...

Distribution of timing and frequency signals in a fast-changing world requires unprecedented levels of stability for characterization. Transfer of frequency references over long distance without introducing any additional instability is of urgent concern for optical clock development. Choice of optical transmitter is critical to achieving accurate and stable RF clocks for end users. In this paper, we report the stability performance of the distributed feedback (DFB) laser and the Raman pump for transmitted clock signals. The DFB laser and the Raman pump were modulated with 2, 4, and 6 GHz RF clock signals from a signal generator and transmitted over 24.69 km SMF-Reach fiber. At 10 kHz offset frequency, we measured lowest phase noise of -121.22dBc/Hz and highest spectra power of -5.38dBm at 2 GHz for the DFB laser. Transfer stabilities of 1.366×10^-12 and 1.626×10^-12 for 2 and 4 GHz, respectively, at 1000 s averaging time were achieved. This technique does not require additional amplifiers for long-distance frequency distribution, making it simple and economical, and hence satisfying the requirements for next-generation optical fiber networks.