80ch AM-FDM signals optical transmission

The authors investigate the laser diode (LD) over-modulation which causes composite second-order (CSO) distortion and limits the maximum number of loading channels, even if a perfectly linear LD is used. Measured results of CSO are presented as a function of modulation depth for various numbers of channels. The maximum number of channels is found for an ideal LD which has no distortion except the over-modulation area. Using newly developed distributed-feedback (DFB)-LDs for analog transmission, the authors have achieved 64-channel AM-FDM signal transmission of over 8-dB loss, with a fiber launching power of 3 mW, CNR of 51 dB, CSO of less than -60 dBc, and a CTB of less than -65 dBc. >