Bit synchronization using subcarriers for control signaling

We demonstrate bit synchronization of two 1-Gb/s nonreturn-to-zero input signals to within 125 ps (1/8 of a bit time) using a subcarrier as the control signal for determining the time delay between the two baseband channels. The 1-GHz subcarrier for each channel is superimposed onto the baseband data at the transmitter, then recovered and mixed in real time with a local clock at the switching node to generate a signal proportional to the relative phase differential. This phase differential signal is used to dynamically set optical space switches thereby controlling the path through a matrix of delay lines. Each channel is independently synchronized to the local clock, resulting in the synchronization of the two output streams to within a fraction of a bit time.