High-precision optical frequency transfer over a 96 km urban fiber link

We demonstrated the optical frequency transfer over a 96 km urban business network in Shanghai. The key factors affecting the optical frequency transmission system, such as fiber link quality, feedback compensation strength, and out-of-loop fiber temperature variation, are studied for the urban fiber link characteristics. The effective suppression technique of complex urban fiber link noise with different feedback compensation parameters is studied. With active phase noise suppression, the optical frequency stability can reach 1.9×10-16 at 1 s and 2.2×10-18 at 10,000 s over a 96 km urban fiber link. This work potentially plays an important role in optical clock frequency comparison, and it makes a good foundation for future research on long-distance optical frequency transfer over an urban business network.