Multichannel coherent FSK experiments using subcarrier multiplexing techniques

The results for coherent digital subcarrier multiplexed (SCM) lightwave system experiments are described. A total of 20 frequency-shift-keyed (FSK) channels at 100 Mb/s each were transmitted on one optical carrier using microwave subcarriers in a multioctave configuration. A complete description of the system performance, including carrier-to-noise ratio, crosstalk, intermodulation distortion, and receiver sensitivity, is given. With a phase modulation index of β=0.13, a receiver sensitivity of -27 dBm was obtained, representing a 14-dB improvement over a 20-channel direct detection SCM system. Crosstalk due to adjacent channels is negligible with a channel spacing of twice the data rate (200 MHz). Theoretical and experimental results are compared, and conditions for optimal performance as a function of channel number and phase modulation index are discussed