Coarse and fine bit synchronization for WDM interconnections using two subcarrier-multiplexed control pilot tones

We demonstrate the use of high- and low-frequency subcarrier-multiplexed pi lot tones as control signals to achieve both coarse and fine synchronizatio n in a bit-parallel wavelength-division-multiplexed optical interconnection . These control signals are located on each of the two outer wavelengths an d are combined with the baseband data before transmission, The phase differ ence of the tones enables: 1) fine synchronization to <1/8 of a bit time in the optical domain for ail wavelength channels simultaneously by comparing the high-frequency tones and using a discrete set of wavelength-dependent delays and 2) coarse synchronization over several bit times in the electric al domain by comparing the low-frequency tones and using shift registers.