OPTICAL-DATA SYNCHRONIZATION USING TUNABLE TRANSMITTERS AND NONZERO DISPERSION LINKS

A new digital feedback loop for synchronizing optical data with a cloc k at an arbitrary point in a fiber-optic link has been experimentally demonstrated and its physical limitations have been analyzed. The feed back loop consists of a tunable transmitter, a nonzero dispersion link , and standard microwave and digital electronics. The feedback loop wa s able to suppress thermal fluctuations with an accuracy better than 1 ps using either a temperature tuned DFB laser diode or a current tune d DBR laser diode. No bit-error rate penalty was measured during close d loop operation compared to back-to-back transmission. The physical l imitations of the loop stem from noise in the receiver and the actuato r increment. Thermally induced phase fluctuations in the fiber at freq uencies above the loop bandwidth were found negligible. The maximum ex perimental delay time for stable operation was 0.86 s, indicating the possibility of closed loop operation for very long fiber links. The fe asibility of packet synchronization is discussed. Moreover, a new sche me is proposed to circumvent wavelength reset when the system approach es the operating boundaries.