Analysis and demonstration of phase modulation-based fiber-optic radio frequency transfer using dispersion shifting

This paper theoretically analyze signal and noise properties in phase modulation-based (PM-based) fiber-optic radio frequency (RF) transfer system, and experimentally demonstrate RF transfer using dispersion shifting. The dispersion-induced phase noise (DPN) and power spectral density (PSD) of the transferred RF signal are derived. The experimental results indicate that the DPN is highly dependent on phase noise characteristics of optical carrier for different categories of lasers, and the short-term frequency stability of transfer system cannot be predicted solely by linewidth. The distribution of optical carrier phase noise ought to be considered when using different categories of lasers. For eliminating dispersion-induced signal fading, chirped fiber Bragg grating (CFBG) and dispersion compensation fiber (DCF)-based dispersion shifting are employed, respectively, in the PM-based RF transfer system. CFBG-based dispersion shifting scheme exhibits stronger temperature and optical carrier linewidth-related timing fluctuation than DCF-based scheme. Based on the proposed signal fading elimination approach and active phase compensation technique, a 9 GHz RF signal is transferred over a single-span of 90 km fiber link, the measured frequency stabilities reach ${\bf 4.8 \times 10^{-14}}$ at 1 s and ${\bf 7.7 \times 10^{-17}}$ at 10,000 s, respectively. The demonstrated research provides valuable guidance for high-fidelity, long single-span and optical amplifier-free fiber-optic transfer of microwave atomic clocks.