8 Gb/s subcarrier multiplexed coherent lightwave system

The authors describe the first wideband coherent detection optical communications systems using two microwave subcarriers to transmit 8 Gb/s with an RF bandwidth efficiency of 1 b/s/Hz. It is demonstrated that two subcarriers each carrying 4 Gb/s QPSK (quadrature phase shift keying), compactly spaced at just twice the data rate, can achieve a receiver sensitivity ( eta P) of -26.5 dBm with as little as 0.5 dB crosstalk between subcarriers. The results are within 11 dB of the shot noise limit.>