Optical homodyne receiver based on an improved balance phase-locked loop with the date-to-phaselock crosstalk suppression

An improved balanced phase-locked loop (PLL) with postdetection processing is proposed to eliminate the data-to-phaselock crosstalk which potentially limits the usable ratio of laser linewidth to bit rate in pilot-carrier phase-shift keying (PSK) optical homodyne systems. The phase-lock current is first subtracted from the output signal of the data receiver before input to the loop filter. An attenuator is used to ensure the equilibrium of the feedback output signal and data-to-phaselock crosstalk. A shaping filter is introduced to simulate the distortion of data signals at the output of the preamplifier. The homodyne receivers based on this kind of PLL have the advantage of a large tolerance for the laser linewidth compared with the conventional balanced PLL receivers.<>