4-Gb/s heterodyne transmission experiments using ASK, FSK and DPSK modulation

An experimental heterodyne lightwave transmission system operating at 4 Gb/s is described. The optical sources were 1.5- mu m-wavelength DFB (distributed feedback) and DBR (distributed Bragg reflector) semiconductor lasers. ASK, FSK, and DPSK modulation formats were investigated; baseline receiver sensitivities of 175, 191, and 209 photons/bit, respectively, were achieved. Transmission experiments through up to 160 km of conventional single-mode fiber and up to 175 km of dispersion-shifted fiber are also reported.<
>