High-quality broad-band optical communication by time-division multiplexed pulse analog modulation: Nonlineary in diode lasers

Inter/cross modulation levels occurring in signals from stripe-geometry (GaAl)As double-heterostructure diode lasers are investigated by computer simulation for the case of time-division multiplexed (TDM) pulse-analog modulation (PAM). It is shown that pulse-position modulation (PPM) is the preferred modulation scheme for high pulse rates, and inter/cross modulation levels are evaluated for the format TDM-PPM. It is shown that the inter/cross modulation level is greatly improved when diode lasers are biased above threshold. Based on this evaluation, it is concluded that effectively inter/cross modulation-free optical transmission at a pulse rate up to
108 \times 10^{6}
pulses per second by TDM-PPM is feasible. This limiting rate permits the transmission of 12 color TV channels or 10800 telephony channels.