Synchronization Monitoring of I/Q Data and Pulse Carving Misalignment for a Parallel-Type RZ-DQPSK Transmitter by Measuring RF Clock Tone/Low Frequency Power

We experimentally demonstrate a technique for monitoring the time misalignment of in-phase/quadrature (I/Q) data streams and pulse carver/data in a 20-Gb/s return-to-zero differential quadrature phase-shift-keying (RZ-DQPSK) transmitter. By measuring the radio-frequency clock-tone power at 10 GHz and low frequency power at 600 MHz, a monitoring power dynamic range of 18 dB is obtained for I/Q data misalignment and 6 dB is shown for carver/data misalignment. With the monitor information, a simple feedback loop is proposed to automatically align the RZ-DQPSK transmitter.