Stabilized Modulated Photonic Signal Transfer Over 186 km of Aerial Fiber

Aerial suspended optical-fiber links are being considered as economical alternatives to buried links for long-distance transfer of coherent time and frequency signals. We present stability measurements of an actively stabilized 20 MHz photonic signal over aerial fiber links up to 186.2 km in length. Absolute frequency stabilities of 2.7x10^-3 Hz at 1 s of integration, and 2.5x10^-5 Hz at 8x10^3 s of integration are achieved over this longest link. This stability is compared to that achieved over buried links for both radio and microwave frequencies. The results show that aerial fiber links are a suitable alternative to buried links for a wide range of frequency transfer applications.