Coherent optical BPSK detection

Summary form only given. A coherent phase-locked synchronous oscillator (CPSO) was created by adding a feedforward and a feedback loop to the SO. An optically excited CPSO network was formed using a 4.3-GHz AVANTEK oscillator. Before the CPSO loop was formed, the oscillator was tuned near the subcarrier frequency with the DC bias in the loop filter. When the oscillator was tuned to within +/-3 MHz, the loop could be closed and the CPSO phase locked to the subcarrier frequency. An extremely pure subcarrier signal was obtained. The recovered subcarrier and subcarrier+data (supplied from the transmitter in this case) are applied to the mixer to detect the data. In a proper coherent detection scheme the subcarrier+data are recovered at the output of the photodiode