Approaching 1 bit/s/Hz spectral efficiency

Summary form only given. The possibility of achieving ultrahigh spectral efficiency of over 1 bit/s/Hz was investigated. By using optical duobinary signals which have a narrower spectrum than conventional IM signals, the spectral efficiency was improved to 0.6 bit/s/Hz. Through the use of polarization interleave multiplexing, spectral efficiency of over 1 bit/s/Hz was achieved. A 1.28 Terabit/s WDM signal has been packed into a bandwidth of only 1.28 THz (10.2 nm), i.e., the flat gain region of conventional EDFAs.