Patent ID: 7609974

Claim:
A data transmission method comprising: generating a transmission optical signal having a frame, the frame including n symbols and containing a pilot signal with fixed amplitude and phase in one of the symbols and a data signal in two or more of the symbols, where n is an integer of 3 or more; outputting the transmission optical signal to a transmission line; generating a frame-timing signal from the transmission optical signal received from the transmission line; and separating the data signal from the transmission optical signal received from the transmission line according to the frame-timing signal, wherein the separating step comprises: splitting the transmission optical signal into a plurality of split optical signals; delaying one of the plurality of split optical signals with a first delay time corresponding to an integral multiple of a single symbol period; coupling a second one of the plurality of split optical signals with the delayed split optical signal to generate a first coupled split signal; photoelectrically converting the fist coupled split optical signal into an electrical signal; and extracting the data signal in a symbol corresponding to the delay time from the electrical signal according to the frame-timing signal.