Precision Optical Carrier Transmission Over 110km Through Urban Fiber Network

Optical carrier frequency at 1.5ìm was transmitted over 110km through round-trip fiber network (JGNII) between Tsukuba and Kashiwa, in which all the delivering fibers were installed in urban environment. Additional phase noise of the optical carrier caused by the fiber length fluctuations was detected by using phase-frequency discriminator (PFD), and was suppressed by controlling fiber stretcher and Acousto-Optic Modulator (AOM). The residual frequency instability due to the fiber length fluctuation was reduced down to 1.5x10-15 at the averaging time of 1s.