Intermodulation distortion for a hybrid AM-VSB/digital system using a 1.55-μm laser and an optical amplifier

The performance of a hybrid AM-VSB/BPSK optical fiber transmission system utilizing 1.55-μm distributed feedback (DFB) laser and Er doped optical amplifier is presented. A BPSK modulated 2-MHz pseudorandom digital channel is substituted for one of the AM channels in a 60-channel CATV system and optically transmitted using a directly modulated 1.55-μm DFB laser. The intermodulation distortion effects with and without optical amplification were studied. No degradation of the AM channels is observed unless the modulation depth of the BPSK channel is increased far beyond the level required for successful transmission to the point where laser clipping effects become significant.