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 pilot tones as control signals to achieve both coarse and fine synchronization in a bit-parallel wavelength-division-multiplexed optical interconnection. These control signals are located on each of the two outer wavelengths and are combined with the baseband data before transmission. The phase difference of the tones enables: (1) fine synchronization to <1/8 of a bit time in the optical domain for all 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 electrical domain by comparing the low-frequency tones and using shift registers.