Linewidth-tolerant QPSK homodyne transmission using a polarization-multiplexed pilot carrier

Quadrature phase-shift keying homodyne transmission has been demonstrated using a polarization-multiplexed pilot carrier generated in a transmitter and a LiNbO/sub 3/-based hybrid module in a receiver for self-homodyne detection at 20 Gb/s. No degradation in receiver sensitivity was observed up to a linewidth of 30 MHz. Furthermore, we obtained error-free operation with a bit-error rate of less than 10/sup -11/. The proposed scheme can provide stable real-time multilevel modulation/demodulation formats, free from linewidth requirements, to enhance spectral efficiency.