Alignment monitoring technique for pulse carver and data modulator in RZ-DPSK systems using an optical frequency discriminator

A technique for monitoring the timing alignment between a pulse carver and a phase modulator in return-to-zero differential phase-shift keying systems is proposed. An optical frequency discriminator and a microwave detector centered at a half of the phase modulation data rate are used to monitor the spectrum broadening caused by timing misalignment. The proposed method has a large detection dynamic range and is polarization-independent.