PLL-free synchronous QPSK polarization multiplex/diversity receiver concept with digital I&Q baseband processing

This synchronous quadrature-phase-shift keying (QPSK) receiver concept allows us to process signals in parallel after electronic demultiplexing. An automatic electronic polarization control with a control time constant in the low microsecond range is provided. It is followed by a phase-locked loop free carrier recovery. An intermediate frequency linewidth tolerance of up to 10(-3) times the QPSK symbol rate is expected. Commercially available distributed feedback lasers shall, therefore, suffice.